1. Features
2. Requirements
3. Overview
4. User Interface
5. Camera
6. Long Exposure
7. Image Review
8. Zones
9. Integration
10. Levels
11. Darks
12. Flats
13. Reticle
14. Telescope Control
15. Tracking/Autoguiding
16. Measurements
17. Declination of a Star
18. Focus
19. Image Selection
20. Camera Angle
21. Alignment
22. Determination of periodic error
23. Saving Images
24. Hot Keys
25. Preferences:
AstroSnap is video capture software specially created for acquiring astronomical images with a Web cam.
Features of the software:
Since Version 1.2
Since Version 1.3
WARNING, VERY IMPORTANT!!
Operating systems:
Windows 95, Windows 98, Windows ME
Windows 2000 and Windows XP (except for making long exposures (see special notes).
Does not work with Windows NT 4.0
Hardware: PC Pentium II 233 minimum, (recommended PIII 500) with 32 Mb of memory (128 Mb recommended).
Needed disk space: 2 Mb (program and help file together)
Conditions of use:
You can contact me at this address to ask questions or make suggestions:
All ideas will be carefully considered for improving this software. Obviously, remember that I do this as a hobby. So don't become impatient if you don't get an answer from me the same day!! Like all of you, I am also afflicted with the "Subway-work-family-sleep" syndrome, and sometimes by distractions of indefinite duration!!
For taking long exposure with modified Philips webcams, Astro-Snap directly accesses the computers parallel port. Under Windows 95, 98, and ME (Millenium) this posed no problem. However that is not the case under Windows 2000 and XP. These two operating systems do not allow hardware to be directly used by the software. Instead, it must be accessed via a "service". This service is called "Porttalk" and is downloadable from the following address (only 25 Kb):
1 - unzip the file
2 - only these files are used: allowio.exe porttalk.sys porttalk.reg
3 - execute porttalk.reg (which will update the registry); you only need to do this once
4 - copy porttalk.sys into the folder C:\WINDOWS\system32\drivers (you only need to do this once)
5 - copy allowio.exe into the folder where you installed Astro-Snap (you only need to do this once)
6 - In Notepad, create a small batch file with these two lines:
CD C:\Documents and Settings\AstroSnap
ALLOWIO astrosnap.exe 0x387
(explanations) The first line tells the computer the location of the folder where you installed Astro-Snap The second line executes ALLOWIO and instructs it to authorize Astro-Snap to access port 0x378 (LPT1).
Save this file with a *.bat extension; for example, "ASTROSNAP.BAT"
Astro-Snap is constructed from independent, yet interactive modules.
The images can be furnished from a video camera or from a sequence of bitmaps provided from any media. These images are sent to the main window of the software, which I have titled the 'video window', to be displayed.
The information contained in these images can be processed simultaneously by different functions:
After these operations, the image may be:
Finally, the image can be saved manually or automatically according to programmable 'timer'.
This structure allows some freedom in the operations you may want to perform with the images. It means, for example, that you can use the software to do only guiding, or for performing alignment, or to follow an object like the moon, or make more elaborate images and save the result for later processing.
When you click on the "Start" button, the "Integration" window appears. The image is also displayed in the video window, with the regions of display and detection marked and centered, as described below. FIXME
The "Stream" button allows faster acquisition of images. In this mode, the camera can reach 30 images per second, depending on the power of your computer.
When you click on the "Stream" button, its label will chage to "Frame". When you click again on the button, the camera returns to single-image mode.
Be careful - while the camera is in streaming mode you won't have access to the dialog boxes for configuring the camera (Source, Format). The camera is in an exclusive mode, where the driver is dedicated exclusively to the rapid capture of images. To regain access to driver parameters, you need to go back to "Frame" mode.
This program has worked, since version 1.2, with the Philips Vesta and ToUcam cameras modified using the Steve Chambers method which enables making exposure, of unlimiated duration. The "Long Exposure" button opens a dialog which allows you to start taking long exposures.
The starting window for long exposures is accessed by clicking the button "Long Exposure" in the function "Camera".
In this window you can configure your long exposures. The parameters are only used of you use a Philips Vesta or Toucam camera, modified by the Steve Chambers method, which is described on the internet at this site:
Astro-Snap works with long exposures as if it were controlling a standard CCD camera.
Astro-snap gives you the ability to reload images that you have previously saved and review them at your leisure. To do this, click in the "File" menu on "Open" and choose "Image" or "Dark" or "Flat".
Windows will open a dialog box in which you can chose the file or files to open. You can choose a single file or several files simultaneously (up to 400).
The reason for opening several simultaneously is, for example, to be able to review the bitmaps as if reviewing a film.
After having clicked on the "Open" button, Astro-Snap will load the name and position of each file chosen into a list sorted by sequence number.
Be aware, if you open several files it is IMPERATIVE that ALL the files have the same dimensions!
Once the files are loaded, a window titled "Review Control" will appear, as shown above. You can then display the files one-by-one, or display them rapidly (like a film), both forward and in reverse. You can move to the first file or the last file. And finally you can review th efiles in a loop. If you have loaded 200 files, then it will review all the files in sequence and then restart, infinitely.
To see the function of each button in the window, hover the mouse over it for a second. A tooltip will popup in ywllow font describing its function.
The most interesting aspect of this function is that absolutely ALL the functions available from Astro-Snap while the camera is active can be used with the image review. In effect, the images reviewed are displayed in the video window.
You can, for example, use the tracking function to align the images. You can add the images with the integration function, or apply a dark or a flat. And finally, you can save the result of all these operations into new files.
This function allows you to set the sizes and locations of the zones of detection and display. You can define the location of each zone in the video window.
The zone of detection is represented by crosshairs:
You can set the size of the zone of detection by moving the Detection slider.
To position the zone of detection, just click in the video window at the desired place.
To center the zone of detection in the video window, press on the "Shift" key and then click anywhere in the video window.
The zone of display is defined in the video window by a blue frame in dotted lines. It is limited to a frame of size 800 x 600 pixels.
You can set the size of the zone of display by moving the Display slider.
To position the zone of display, just click in the video window with the right button of the mouse at the desired place.
To center the zone of display in the video window, press on the "Shift" key and then click anywhere in the video window with the right button of the mouse.
Caution: The zone of display is linked to the zone of detection. If the zone of detection is moved (manually or by the "Tracking" function), then the zone of display will be moved along with the zone of detection.
New!
Starting with version 1.3, you can unlink the zone of display from the zone of detection. To do this, click the checkbox "The zones are linked".
This is the principal capability of the software.
When you check the "Integration" checkbox, the integration window displays the result of processing carried out on the images sent by the camera to the software.
To make an integration, first choose the desired type of integration you want to perform. This choice is made depending on the type of object concerned.
Single Mode:
This mode is intended to be used if you want to obtain an image of a deep sky object, for example a globular cluster like M13.
After you click on the "Start" button, all the images acquired by the camera are added in real time in the integration window until you stop the capture by clicking on "Stop". You can then reinitialize the integration window to start over by clicking on the "Reset" button, or then click again on "Start" to continue again later!
You can observe the process of integration in real time. The image in the integration window becomes increasingly brilliant as images are added.
You can set the levels of visualization during integration. This modifies the exposure and contrast, and allows you to better distinguish the object which you capture.
You can also apply a dark frame that you recorded previously (see below). You can set the weighting of the dark frame to be applied to the image by moving the vertical cursor (see Dark function) located on the left in the video window.
The size of the images can be up to 800x600 pixels.
Dark Mode:
This mode is intended for acquiring a dark frame, which will be applied later during the acquisition of deep sky images. The Dark frame is stored in a buffer. It is then usable at any time, as long as the program runs.
Start the acquisition of the dark frame, and wait until a sufficient number of dark images have been integrated. In general I recommend to make a dark frame with a number of images significantly higher than that of the integrations that you will make later.
See the Dark Function.
Flat mode (since V1.1):
This mode is intended for acquiring a flat frame (uniformly-lighted frame), which will be applied later, like a dark frame, during the acquisition of deep sky images. The flat frame, like the dark frame, is stored in a buffer. It is usable then at any time, as long as the program runs.
The flat is created by aiming at a uniformly lighted surface, like a smooth wall in indirect light, or better still, a part of the sky with no stars at twilight.
See the Flat Function.
Loop Mode:
This mode is to be used if you want to observe a planet, which is much more brilliant.
First set the number of images which will make up the resulting integration. Same as for the "Single" mode, start the integration by clicking on the "Start" button.
This method works in the following way:
The images arriving at the camera are added one by one. As soon as the number of images integrated reaches the number set previously, then the images which had been added at the beginning are withdrawn from the end.
This makes it possible to have an live composite "image". You can observe the planet moving slowly across the field. With this mode of integration, images are limited to a size of 320x240 pixels. You can then save the image in progress by clicking on the "Save" button. You can also use automatic saving.
This function allows you to approximately set the contrast and the exposure of the resulting image.
Each pixel of the image can have a value (for each color) ranging between 0 and 65535. Value 0 corresponds to absolute black, and value 65535 corresponds to the most brilliant hue which a pixel can hold. This value thus corresponds to the intensity of the pixel.
The pixel values in the image thus lie between two limits, called levels.
The Low level slider sets the minimal value of the pixel in the display. You define, in effect, the default value of "black". For example, if you set the cursor on 20000, then "black" will have value 20000. The pixels with value under 20000 are all black and those above are gradually brighter.
The High level slider sets the maximum value of the pixel in the display. You define, in effect, the default value of "white". For example, if you set the cursor on 30000, then "white" will have value 30000. The pixels with value over 30000 are all white and those below are gradually darker.
The values "Min" and "Max" located at each end of each slider define the operating range of the slider. If for example in the "Min" region you enter the value 5000, and in the "Max" region you enter 10000, then the slider will be able to vary between these two values. This allows you to set the precision with which you want set the levels.
The "Current" fields, located to the right of each slider, indicate the current minimal and maximum values of the image during the course of integration.
The field "Nb. Images" indicates the number of integrated images.
The radio buttons "B/W" and "Color" make it possible to display the image in grayscale or colors.
The three checkboxes, for red, green and blue, individually allow you select the components of color to be taken into account for the display of the image during integration.
Dark frames can be applied in two ways.
The first way uses the usual method of subtracting the dark image from the acquired images. This method is easy and quick, but inconvenient because it leaves dark pixels inside the objects being imaged. To have a bright nebula like M42 dotted with tiny black holes isn"t the best image. You can use the vertical slider to regulate the "force" with which the dark frame is applied to the image currently being integrated.
The second method is a bit more advanced. In place of subtraction of the image, each pixel over a certain threshold is replaced by the average of the values of the pixel around it. So a bright pixel in the dark frame is "softened" rather than being eliminated.
Note:The dark frame will only be correctly applied if "Tracking" mode is disabled. But if you use autoguiding, there is no such limitation.
Here is an example of using dark frames.
Imagine that it"s 8 PM, and you"ve just set up your telescope.
Start Astro-Snap.
Start your camera.
Click on the menu item "Video" and then "Source"
Choose 5 images/second.
Set the gain to approximately 75%
Click on close.
Dark Frame Acquisition
Put a cover over the telescope, or over the camera.
Click on the button "Long Exposure".
Go to the levels, and set the "Low" level to 0 and the "High" level to 255.
Click the "Integration" checkbox in the main window.
Click on the radio button labelled "Dark".
Click on the "Reset" button to empty the darks buffer from any possible image.
Click on the "Start" button.
Go to the "Long Exposure" window.
Choose the length of exposure for the Dark frame which you would like to make. Normally it"s the same duration is the images you will later make.
Enter "1" for the number of exposures. Qhen the exposure is done, it will autmatically stop.
Click on "Run" and wait for the exposure to be made.
Click on "Stop" in the "Integration" window on top of the main window.
The Dark frame will appear in the integration window.
If you want to save the dark image, do it now. Choose a name in the "Prefix" field, put the sequence counter to "1", choose the tab "Manual Save", then click on the "Save" button. If you name your image "dark" then it will be saved using the filename "dark1.bmp".
Finally, uncheck the "Integration" checkbox.
Remember that you don"t need to save the dark frame. It is in memory and can be used from there.
"Live" application of a dark frame
Go to "Long Exposure" mode if you aren"t already there.
Choose the duration of the exposure.
Enter "0" in "Number of exposures" (indicating unlimited exposures).
Click on the button "Run" in the "Long Exposure" window.
The exposures will expose as they are made, and will appear in the video window AND in the integration window.
Now, verify that you have set the lower level to "0" and the higher level to"255".
Move the vertical slider on the "Dark" tab. The values are in percentages, from 0 (no dark) to 100 (maximal dark). As you move the slider you will see that the images appearing the integration window have more or fewer dark pixels removed, depending on the position of the slider.
Keep in mind that there are two methods of applying the dark frame (controlled by the radio buttons "Subtract" and "Intel" on the "Dark" tab). The default method is "Subtract" which simply subtracts the pixels of the dark image from the actual image. The other method is more forgiving. The method "Intel" (intelligent) will replace a hot pixel with an average of the values of the pixels around its position in the actual image. This avoids the unattractive "black holes" appearing after a subtraction.
To use this method, choose the radio button "Intel" and then use the vertical slider as for the previous method. You can change the value in the field using the two small arrows. The field indicates the distance from the hot pixel from which to use average pixel values to replace it. If you choose 1, it will use the pixels immediately around the hot pixel. If you choose 2 or 3 then it will take pixels positioned in an area of 2 or 3 pixels around the dark pixel for this operation.
Once you have found a good setting, you can let the images arrive. If you want to save the automatically as they are created, then choose the tag "Auto Save" in the "Integration" window, choose "One Time" and then "Save an image as 1 image" "Until Stop" and click on the "Run" button.
When you have taken enough exposures, perform the operayion in reverse:
Click on "Stop" in the "Integration" window.
Click on "Stop" in the "Long Exposure" window.
Put the dark cursor to "0". If you don"t do that, it will continue to apply dark frames when you return to video mode, which will take a long time. You will see a mostly black image and will wonder what has happened ...
Close the "Long Exposure" window.
Question:
I see a black image in the integration window.
Answer:
When you use Dark frames at a value greater than 0%, Astro-Snap changes its mode of functioning with respect to the levels of visualization (high and low level). The pixels of the images coming from the camera have a maximum value of 255. If your lower level is higher than 255 or your high level is at 2000 or more, then you image will be black.
For this reason, when you have your black images, the first thing to verify is the levels. Be sure that the high level has a value lower than 255 (normally it will be at 255) and the high level also (value will normally be 0).
If you previously recorded a flat frame, you can apply it to the image present in the window of integration, by checking the "Active" box.
Note: The flat frame will be applied correctly only if "Tracking" mode is inactive.
The Astro-Snap software is equipped with a graduated reticle which is constructed according to the size of the pixels of your camera and the focal distance of your instrument. It is displayable at will, and is superimposed on the video window. It is composed of concentric circles and a cross graduated in degrees, minutes, or seconds of arc, according to the parameters set previously.
Check the "Reticle" checkbox to display the reticle.
Orient.::
Use the slider to modify the orientation of the reticle. Be careful - if you change this after having used the automatic function to determine the camera angle, you will have to repeat that operation to again coordinate the reticle with the camera angle.
"Circles":
Check this box so that the concentric circles are displayed.
"Cross":
Check this box so that the graduated cross is displayed.
Position of the reticle:
You can center the reticle where you want on the video window by pressing the "Ctrl" key and clicking in the video window at the desired place. You can also put the reticle at the center of the video screen, by clicking on the "C/Scr" button. If you want to place the center of the reticle at the center of the tracking crosshairs, then click on the "C/Mire" ("C/Cros") button.
If your telescope is motorized and you have an interface that lets you control it from your computer, then this functionality will allow you to do so easily.
Mode:
This mode is reserved for users of telescopes with a type LX200 interface.
You can use it to set the speed of displacement among the four available on the telescope.
Direction buttons:
These buttons allow you to control the movement of your mount. There are are nine:
Important: You can also cause movement of the mount by doing "Ctrl-Shift-click" in the video window. The mount will move itself to center the video at the point where you have clicked.
M.A.P.:
This mode is reserved for users of motorized focusers.
It allows control of focusing by the software. The two buttons "IN" and "OUT" allow varying of focus.
The Autofocus mode allows automatic focusing on a star.
Just click the "Run" button to activate this function, and on "Stop" to disable it.
See the tab "Telescope Control" on the "Preferences" menu to configure autofocus.
Current position:
Functionality reserved for LX200 interfaces.
Clicking on this button, the interface returns the actual position of the instrument in RA/Dec.
Go to ...:
This function is usable for telescopes having an LX200 interface.
It allows using the internal catalog of the interface to automatically point the telescope towards an object.
To use this function:
This function makes it possible to stabilize the image on the selected object.
Assuming that you already have an object in the video window of the software, click on the "Track" check box , then in the video window on the object of interest.
Crosshairs will appear on the object:
They will remain centered on the object, even if the object moves in the window.
Depending on the object, (star or planet), go to the "Zones" function, described previously and set the size of the "Detection" cursor so that the crosshair is a little larger than the object in question.
Then return to the "Tracking" function, and choose the type of tracking.
For a weak star, choose "Bright Pixel".
This first method of detection locates the crosshairs on the brightest pixel in the region of interest.
For a brilliant star or a planet, choose "Axis Sum". This method sums all the pixels of each column and each row of the region, and centers the view on the intersection between the most brilliant line, and the most brilliant column. So this takes into account the exposure and the surface of the object. The object must be of spherical shape for this method tracing to be effective. For this second method, it is essential that the region of detection is larger than the object itself.
A third method is implemented in version 1.1. It is a method of tracking by programmed drift. It is particularly useful for non- motorized mountings, with objective from 300mm focal length to the maximum.
First of all it is necessary to program the drift by clicking on the "Def" (Define) button. Choose a star located as close as possible (maximum 2 degrees) to the field where the object which you want to image is located. Click on the star, and then on the "Execute" button. The crosshairs will follow star until it disappears from the field while recording very precisely the direction and the speed of its movement.
Once this operation carried out, you can aim the camera at the field where the object of interest is located and then click on the radio button "Drift". From then on, the program will repeat the movement recorded beforehand, but in the field where the camera is now aimed, and thus will follow the object automatically.
Since version 1.2, a fourth method, called limit detection, allows rapid registration of planetary images. The program first determines the top, bottom, left, and right edges of the object being imaged, relative to a level determined automatically. It then centers the image using these limits.
Since version 1.3, the tracking function can also be used for autoguiding. In this case, the frame stays fixed and commands sent to the telescope cause the object to be recentered in the tracking frame.
To activate autoguiding, check the checkbox. The autoguiding parameters can be set by clicing on the "Def" button or by choosing the "Autoguiding" tab in the Preferences dialog.
"Decal.+1"> Button
If you use Astro-Snap with a webcam used only for guiding, with image acquisition made separately by a CCD camera, then you might find this useful for getting better resolution on your CCD image by moving each image by one or more pixels.
Depending on a parameter specified on the "Autoguiding" tab in the preferences, the fact of clicking on this button will cause the repositioning of the guide star following a sequence previously defined in a repositioning file.
The software enables you to measure angles in the video window.
Just press the "Alt" key, then click on the first point in the window, then press the "Alt" key again, then click on the second point. Measurement in minutes, degrees and seconds of arc is displayed in the field entitled "Calculated Angle", located in bottom left of the video window.
If you want also the linear distance corresponding to the angular measurement, then enter the distance which separates you from the object concerned, in the same units of measurement, in the "Earth-Object Distance" field. Corresponding distance is then displayed in the "Calculated Distance" field.
For example, if you want to determine the diameter in kilometers of a crater on the Moon, enter 384000 (km) (distance from the Earth to the Moon) in the "Earth-Object Distance" field. Then click successively on two diametrically opposed points of the crater in question. You will have the angular distance, and its corresponding linear distance in km!
If you want to obtain linear distance separating the two components of a double star, then if you know the distance which separates you from the stars you proceed in the same way except you will enter the distance in light-years. The result will be also returned to you in light-years. (1 LY corresponds roughly to 10 000 000 000 000 km). Obviously, the measurement will be correct only if the two stars are both approximately the same distance away, which is seldom the case.
Caution: measurements are correct only if you have already correctly entered the optical characteristics of your telescope as well as of your camera.
AQUI
The software can determine the approximate declination of a star. To perform this function, see the description of "Camera Angle".
The software determines the declination of star by calculating its speed of drift when your mount tracking motor is turned off. It is known that the angular velocity of drift of a star is 15,04 seconds of arc per second when it is located at the celestial equator (Declination = 0°), and 0 seconds of arc per second at the poles (Declination = 90°).
The software thus can determine a star"s "absolute" declination, but cannot distinguish whether the star is in North or the South.
Remember: So that calculations will be correct, you must have entered all the fields concerning optical characteristics (seePreferences/Optics) and those of the camera which you use (seePreferences/Camera).
This function helps you focus by measuring in real time the FWHM of a star on the screen.
The FWHM (Full Width Half Maximum) is the measurement of the diameter of the image of star, consisting of the pixels whose intensity is at least equal to half of the intensity of the most brilliant pixel of this star.
When focus is bad the image is fuzzy, the star appears smeared, broad and low-contrast compared to its background, and the FWHM will be large. When focus is good the image is clear, the star appears small, brilliant and very high-contrast (pin-prick) compared to its background, and the FWHM will be much smaller.
Therefore the smaller the FWHM the better the focus.
To guarantee the effectiveness of measurement, it is necessary to choose a star which does not saturate the sensor. As a general rule, use a star of approximately magnitude 6.
To activate the Focus aid , choose the tab "Focus", then check the "Active" box.
Automatically, the software will also activate the tracking function.
Click on the star which you will use to focus . The "tracking" crosshairs will follow the star. Then in each image sent by the camera the FWHM of the star will be calculated and will be displayed in the "FWHM" field.
For better visibility when your eyepiece is far from your microcomputer, check the "BIG" box. This will reveal a small window, where the measurement of the FWHM will appear in larger characters. The characters are sufficiently large to be visible from a distance of 2 meters approximately.
The level used for FWHM (Full Width Half Maximum) is calculated automatically. In certain cases, if you want to manually set the level of FWHM (which I do not recommend), you can uncheck the "Auto" box. In this case you can define the intensity of the pixels which will be taken into account for the calculation of the image diameter of the star used.
If your microcomputer is equipped with a sound card, then you will be able to benefit from "sound messages". See the description of "Image Selection" for more details on this option.
New!
Starting with version 1.3, focusing can be controlled from your computer if you have a motorized focuster that uses an LX200 interface or a Bonduelle (parallel port) interface. See the description of Focus.
This function makes it possible to do two things:
1 - Quantification of the quality of an image.
It allows, by a method which I have just discovered, to quantify the quality of an image (clearness, contrast).
Once activated it selects in real time the best images among all those provided to the camera, this according to a level which you can set in the "Preferences" Image Selection window.
Only the video images whose quality is higher than the level you set are passed to the integration window. This is particularly useful for planetary images, where turbulence plays a preponderant role.
If in addition you back up the images in groups on your hard disk, only the "good" images will be backed up. This reduces the space used on your disk, as well as time spent to choose the images to integrate for your composition.
On right-hand side of the level slider is a small "led" square. If it is red, the images are not passing to the integration window since they do not have required quality. As soon as it turns to green, that means that image was selected, and is transferred to the integration window.
Using the controls:
DCT:
This checkbox enables image selection.
Snd:
This checkbox enables sound cues. Useful to help in focusing on complex objects.
BIG:
This checkbox displays a small window containing the value (in "real-time") of the quality of the current image. This value is displayed in large numbers so that it will be visible from a distance from your monitor.
Reset button:
2 - Assistance with focusing on complex objects.
It helps you to focus on, in particular the Moon and on planets of a significant relative diameter (Mars, Jupiter, Saturn).
For that, you need only aim your camera at the object concerned, check the "Active" box, then follow the evolution of the quality of the image in the "Current" field. The higher the figure in this field, the better the focus. The maximum value fields ("Best" and "Worse") are updated continually. The ideal situation is that the value in the "Current" field is as close as possible to that of the "Best" field.
If your microcomputer is equipped with a sound card, then you can benefit from sound message on the evolution of your focus, by checking the "Soun" checkbox. You will then be able to move away from the microcomputer to concentrate on the eyepiece.
Example:
In summary, if you have heard, in this order:
If you do not hear the "Stop!" in the fourth step, then click on the "Reset" button, and start over.
You can also set the sensitivity of detection in the "Preferences" Focus window.
One of the questions which generally arise during an evening"s observation, when your camera is in the visual back, is how to aim it.
The task is particularly difficult if you have a Newtonian telescope on a German equatorial mounting.
Astro-Snap makes it possible to calculate the angle of the camera, and orient the software reticle, which will be displayed with your image in the video window to the same angle.
To launch the function, click in the menu bar on "Operations", then "Camera Angle". Follow the instructions indicated by the following message:
First aim at a star.
Then click on the star in the video window, so that the tracking crosshairs
pick up the star.
Turn off the tracking motor of the telescope, so that the star drifts freely in the field.
Immediately after having turned off the engine, click on the "Run" button which appears to the left of the video window.
The crosshairs will follow the drift of the star to the edge of the field. At this time, calculation will be finished and the program informing you of the end of the processing. The angle will be indicated in the "Orient." field located to the left of the video window.
The camera does not need to be physically aimed an a particular way, rather the function "camera angle" is used to "tell" the software how the camera is aimed. It "sees" a star drift through the field (when the tracking motor is stopped), and it can determine the 4 cardinal points. As the star always drifts towards the west, it "learns" which direction is west and therefore knows the other three directions.
The software reticle will angle itself along the East-West axis. When you display the reticle you will then always know the direction where the camera is aimed.
Note: This function must be used prior to using the alignment help.
Who never heard of hours spent doing polar alignment to make only one photograph or CCD image?
One of the most precise methods of performing polar alignment, but also longest and stressing, is the method of Bigourdan.
Without going in the details of this method, which is already described in many works and on many sites dedicated to astronomy, it is a method of aligning the mount by successive approximations.
According to the direction and amplitude of the drift of a star in the field of a reticulated eyepiece, one corrects the mount in azimuth and altitude repeatedly while making increasingly fine corrections. Initially you correct the azimuth mounting while following the drift of a star located it the South, then then you correct altitude while following a star located close to the horizon in the East or the West.
This program makes it possible to precisely quantify the corrections to be carried out at various stages of this method.
This thus makes it possible to significantly reduce the time spent to perform polar alignment
The software is based on the images returned by the camera, calculating the angle corresponding to the error of orientation of the mount compared to the polar axis.
According to the various parameters of your telescope (and especially of mounting) that you provided beforehand, it indicates to you, in millimeters and turns of screw or crank (if your mount is equipped with it), the exact value of the correction to be made in the orientation of your mounting.
Important: So that the calculations carried out during this operation are correct, you must have provided information in all the fields concerning the optical characteristics (see Preferences/Optics), and those of the camera that you use (see Preferences/Camera), as well as characteristics of your telescope mount (see Preferences/Mount).
To launch the function, click in the menu on "Operations" and then "Drift Polar Align". The following window appears.
Before launching the function, the software reminds you that you absolutely must have entered the camera angle with the function "Operations/Camera Angle". Just click on the "Determine the camera"s heading" button to launch that function automatically.
Once this is done, choose the stage that you will be performing, in the section "Guidestar Position". In the "Guidestar Declination" field enter the approximate declination, in degrees, of star pointed for each of the two stages of the method of Bigourdan.
Note: Since V1.1, the software can calculate the declination of any star, see the "Decl. " tab, in the group of tabs located in bottom on the left of the video window. See "Declination of a star".
For the first stage (Azimuth setting), this value will be probably 0.
For the second stage (East/West), since you will not be able to probably use a star being located at the horizon, it will be a value close to 20° or 30°. If you have a graduated dial on the axis of declination of your mount, then note the value it indicates.
To start processing of stage chosen, click on the button "Start the procedure".
Follow then the instructions indicated by the following message:
First aim at a star.
Then click on the star, which appears in the field of the camera, so that the tracking cross-hairs
pick up the star.
Verify that your mount is tracking, then click on the "Run" button, which appears to the left of the video window.
The cross-hairs will follow star to the edge of the field or until you stop the function by clicking on the "Stop" button. At this time, calculation will be finished and the program will inform you of the end of processing.
While processing, the software will inform you of the evolution of the calculations of the alignment in the following window:
Note: You should know that the precision of the provided figures is proportional to time that you allow the software to make calculations.
Carry out the correction indicated by the software, and redo the operation. To do that, in the "Drift Polar Aligning" window click on the "Settings" tab, then restart the procedure.
Once you have carried out the correction indicated by the software (after some experience you will need only 3 iterations to achieve polar alignment within 5 minutes of arc) you can carry out the operation on a star located at the East or the West, by taking care to specify it by checking the corresponding radio button.
Let us imagine for example that your mount is on a tripod which you adjust to correct the alignment.
Start with one tripod leg pointed due South.
If the software tells you to move the polar axis 15mm towards the west, then you need to move your Southern foot 15mm towards the east, since it is directly opposite the pole.
On the other hand, if you start with a foot pointed due North, then you need to move the foot in the same direction that the software indicates.
To be able to use this method it is necessary that one of the three feet (East or West) is well planted in the ground, since it will be used as a pivot.
Set the two other feet (as described elsewhere) on a piece of plastic or wood or other smooth material so they can slide without too much resistance.
The advantage is to draw a grid (spacing = cm) on the plate on which you will set the foot that you will move physically. This grid will have to be directed towards the foot which is used as pivot. Then you will be able to easily measure the displacement which you will have to make with respect to the southern (or northern) foot.
In case you have not or cannot correctly provide the radius of the altitude and azimuth settings of your mount, a tab has been added to the software which permits correcting the values entered, comparing the value of the correction which you have indicated, and that which you have effectively applied to achieve polar alignment (in the corresponding axis). It is the tab "Corrections for mount settings".
For example, the software tells you to make a correction of 15mm towards the East.
You then carry out a correction of 15mm towards the East.
You restart the operation.
It now tells you to make a correction of 30mm, still in the same direction.
This means two things:
- either you performed the correction, but in the wrong direction
- or you performed the correction, but the optics of your instrument show you a reversed image.
In this case, go to "Preferences/Polar Align" and check the "Invert azimuth corrections" box for corrections in azimuth.
From there it will provide you the corrections in the same direction.
The first time that you use this function, I strongly advise you to note all the corrections on a paper. You will see why later.
Now, let us set out again of the beginning. It tells you to make a correction 15mm towards the East.
You carry out this correction.
Click on the button "First correction". It will record the figure that it provided you.
Restart the operation.
Now it still asks you to make a correction of 10mm towards the East.
You carry out this correction.
As long as the corrections are in the same direction, the value will be positive, if one is in the different direction (towards the west for example) the value will be negative.
You still start again X times, until you have a correction of approximately 1mm, which means that you are relatively well aligned compared to the polar axis.
Now add all the corrections which you have carried out to lead to this result (the values that you noted on your paper.
That makes 15mm + 10mm + X mm = (27mm for this example).
In the tab "Correction for mount settings" of the Drift Polar Aligning window,check the mount axis to be corrected, then in the field "First correction proposed by Astro-Snap" you would enter "15" (in the case of our example).
Then in the field "Total applied necessary correction" field, you would enter "27".
Then click on "Calculate".
It will modify the value of the radius for setting the corresponding axis, so next time you perform polar alignment it will give you a good value the first time. To save the modification, click the "Apply changes" button.
Periodic error is the bane of astrophotographers.
Once you have performed an irreproachable alignment, you can launch this function to determine the precision of tracking of your mount.
Click in the menu on "Operations", then "Periodic Error Calculation".
The following window appears:
As expected, you must first have defined the camera angle.
The procedure is quite simple. Just click on the "Demarrer" ("Start the procedure"). Follow the instructions in the popup window:
You just need to aim at a star, click on the star after having activated tracking, then click on the "Run" button which appears to the left of the video window.
The result is obvious. The graph of the tracking errors appears gradually, relentless, and without appeal. Absolutely all the tics of your equipment are recorded and shown!
This should obviously be launched on a day without too much turbulence or wind!
You can move the graph by dragging with the right mouse-button.
You can zoom on a region by framing it by dragging towards the upper right with the left mouse-button. To un-zoom, drag towards the lower left.
Manual Recording:
This function makes it possible to save the "current" image appearing in the integration window to a Bitmap file, which you can then process with image processing software .
You enter the name of the file to save (with the complete path) in the "Prefix" field, or click the "Search" button. In the "Size" field appears the size (in bytes) of the file which you will save.
The file names have a suffix which is a sequence number, of which you can define the starting number in the field "Current Number".
You can define the length of the strings containing this number by checking the checkbox "Fixed Length" and entering a value in the field to the right of it. The suggested value is 4.
Since version 1.1, you can save all the acquisition parameters of the bitmap for each bitmap. These parameters are recorded in a text file whose name is identical to the image filename, but whose extension is ".par". To activate the recording of the parameters with the bitmaps, check the box "Save parameters".
Example of the contents of a .par file
Date/time: 02/08/01 18:34:59
Video resolution: 320 X 240 pixels
Dimensions of the image: 320 X 240 pixels
A number of images indiv.: 81
Mode Loops: 80 images
Minimal Intensity: 9585
Maximum Intensity: 43511
Low Level: 12027
High Level: 16230
Dark applied (Nb Img): 72/350
Flat applied (O/N): N
Black and White (O/N): O
Red (O/n): O
Green (O/n): O
Blue (O/n): N
Type of follow-up: None
Cut region of detect°: N/A
Inversion video/tracking: N
Quality of the image: N/A
Better image: N/A
Worse image: N/A
Level of selection: N/A
Automatic saving:
With version 1.1 arrives the capability to automatically save bitmaps. The rate of saving is completely configurable via window shown below.
Examples:
1 - I want to save all the images arriving at the camera, at the maximum rate, during 1 minute:
2 - I want to create a sequence of images of Jupiter to highlight its rotation. Each sequence will be a composition of images recorded during 30 seconds at the rate of 1 image a second. The sequences will be recorded at 15 minute intervals.
3 - I want to create a time-lapse sequence (with simple images) to highlight the run of the clouds. The images will be spaced 10 seconds. The whole will last 45 minutes.
You will have in all 6x45=270 images.
You will be able to use your bitmaps, which are numbered, to make for example a AVI using an AVI tool editor.
Here is the list of different actions possible in the video and display (or integration) windows:
Astro-Snap is now multi-lingual.
Choose, in the dropbox, the list you want to ouse with the program.
All the parameters of the language are included in a file called "Language.ini", located in the folder where Astro-Snap was installed. This file is created to be "open". That is, you can translate for yourself the terms used in Astro-Snap into whatever language you wish. Just create a new header at the end of the file, using one of the following examples:
[Italiano]
[Deutsch]
etc.
Once you have created this header, just copy/paste all the elements from the first language defined in the folder to the end of it, and replace the terms by those in the new langauge.
Now you can translate into your maternal tongue!
And if you would send me your language file, it will be my pleasure to include it in all subsequent versions of the software!!
In this tab you can define the default folder where your images will be stored.
As its name indicates it contains the information relating to the optics of your telescope or objective.
Primary focal distance (mm): The focal length of the optics of the telescope.
Barlow: If you use a Barlow, then check the box fill in its magnification.
F.Reducer: If you use a focal reducer, then check the corresponding checkbox and fill in the reduction ratio.
Total Focal length: This information is automatically calculated from the information that you entered in the preceding fields.
Azimuth setting radius:
For a German type mount, it"s the distance between the azimuth setting axis and the push/pull screws" rotation axis. For a telescope like the C8 or equatorial platforms, for which you turn the tripod itself, it"s different. Assuming you pivot your tripod keeping one foot on the ground (which serves as an axis of rotation) it"s the distance between this foot and one of the others.
Altitude setting radius:
Here also it depends on the setting possibilities of the telescope (and also the way you usually do things).
It may be the distance between the elevation axis of the equatorial wedge and push/pull screws.
If you control the height of your mount from the feet (telescopic tubes, cales, vis sans fin), then it"s the height "H" of the triangle formed by the three legs of the tripod and the ground.
Screw thread pitch
If you use a tripod whose height is variable, or if the azimuth setting mechanism is made with a push screw, then you should give, for each axis, the right thread pitch. It is the distance between two threads.
This last case gives the most precise results, because the program uses the number of turns to apply tothese screws in order to correct the direction of the mount.
Here is a fork mount which corresponds to each of these elements:
Translation of terms used in this image:
Altitude Axis : Axe d"altitude
alt setting radius : Rayon de reglage en altitude
Azimuth axis: Axe azimuth
azimuth setting radius : Rayon de reglage en azimuth
Knob Axis : Axe de la molette de reglage
Interface Type frame:
Astro-Snap can control a telescope using one of several interfaces:
Here are the various parameters.
Frame "Control of the interface":
Depending on the type of interface selected, the choice of the type of port is done automatically.
The default values which you will find are the standard values, used in the grand majority of situations. You can modify these parameters in the improbable case where your interface is paraameterized differently.
For a serial interface:
Guiding:
Focusing:
"Autofocus" frame:
In Astro-Snap, the autofocus functions in the following way:
The software will proceed by using an algorithm to find the best FWHM possible for the guide star.
It repeats steps 3 to 5 until the FWHM value attains the "FWHM Stop Value" or until the user decides to stop the procedure.
Initial time of function of the motor (ms):
This is the initial time of motor function.
"FWHM Stop" value (pixels):
This is the best FWHM one estimates to be able to obtain on the chosen star.
Achay interface for the serial port
Web site of Achay Doan:
http://members.aol.com/achay2
Site of Frédéric Guinepain:
http://www.astrosurf.com/fguinepain lien interface pour autoguidage
Suivre le lien "interface pour autoguidage"
Site of Sylvain Weiller:
http://astrosurf.com/sweiller/autoguidage/AutoG.html
Site of Pierre et Florent Dubreuil:
http://perso.wanadoo.fr/florent.dubreuil/audine/
Suivre le lien "Guidage webcam"
Etienne Bonduelle interface for the parallel port
Site of etienne bonduelle:
http://www.astrosurf.com/astrobond
or more directly:
http://www.astrosurf.com/astrobond/eblxingf.htm
http://www.astrosurf.com/astrobond/eblxinge.htm
Here are the various parameters:
Neutral zone:
This field contains the diameter (in pixels) of a zone in which the center of the guide star can move without causing a correction reaction from the mount.
Pulses (only Achay):
The Achay interface is functionally characterised by pulses limited in time. This pulses can vary from 15 ms to 945 ms.
This field allows specifying the duration of impulses required when one presses on the direction buttons North, South, East, and West.
Inverse in Dec:
This checkbox enables inverting the direction of the commands sent to the declination motors.
Inverse in A/D: This check box enables inverting the direction of the commands sent to the Right Ascension motors.
Displacement files are simply text files containing a sequence of movements to apply to the tracking frame. The following example moves the tracking frame in the form of a square of 4 pixes per side, starting at the top and towards the right, clockwise. At the end of the sequence, it restarts automatically.
The format is:
Displacement in X, displacement in Y
One line per long exposure
1,0
1,0
1,0
1,0
0,1
0,1
0,1
0,1
-1,0
-1,0
-1,0
-1,0
0,-1
0,-1
0,-1
0,-1
If the checkbox "Use a deplacement file" is checked, then at each long exposure the frame will be displaced according to the line in the displacement file where the cursor has "exposed".
One can also manually run displacements. To do this the checkbox "Use a displacement file" should be cleared, and click each time on the button "Decal.+1" located in the "Autoguiding" frame in the tracking function.
Frame "Motor speed":
The speed of the motors in each direction is represented by the four fields arranged in a square. Clockwise, the fields contain the speed (in seconds of arc per second) for the directions:
The checkboxes associated with each field indicate whether the direction has been activated or not. If a checkbox is cleared, then all impulse commands in this direction are disabled.
Backlash Time (ms):
This value can be given in milliseconds or in the percentage of the time of functioning of the motor.
For example:
1 - If you know that the motor takes 100 milliseconds to stop, and you want at instant T that it turn for 1 second (1000 milliseconds), then put the value 100 into the field "ms". That way, the impulse given will be 1000 - 100 = 900 ms.
2 - You could instead enter 10%. This way, if you want it to turn for 1000 milliseconds, then chooses the corresponding radio button, and you choose "10"%.
So, the duration of the impulse will be from [ (100 - 10) / 100 ] x 1000 = 900 ms.
Similarly, for a desired duration of 2500 ms with 15% backlash time. You would in that case have [ (100 - 15) / 100 ] x 2500 = 2125 ms.
Frame "Learning:"
Astro-Snap is capable of learning the speed at which the motors move in each direction. For that, it needs to query the motor. It will move the motors in Right Ascension and in Declination in one direction at a time, and calculate the speed for each direction. The circuit is West ->North ->East ->South.
Important: The program is based on the orientation of the reticle to determine the direction for corrections. Therefore, before using "autoguiding", determine the orientation of the camera.
Enter in the field "Duration for each direction" the duration of movement in each of the 4 directions. The duration of displacement should be long enough that the calculated speed will be significant. If one enters 4000 milliseconds, the motors will move for 4 seconds in each durection. The total duration of the operation will then be 16 seconds.
Then click on the button "Learn".
If you don"t use the learning function, you can enter approximate values in each of the four fields described above.
As a general rule, on your telescope you will have two speeds or more:
As soon as this information is saved, the pulses will be exactly the duration needed to center the guide star. The appropriate motor will then stop, even if the guiding image hasn"t yet arrived.
Then, it"s simple - just activate the "Tracking" function, then click the checkbox "Autoguiding".
Pixel size (hxw):
This tab is for the size (height and width) of one pixel of the camera sensor. This value is in µm (microns).
If you know the pixel size for your camera (manufacturer specifications), then enter it.
If you do not know it, the software can calculate it automatically, with the assistance of your equipment. (Caution! this function works only if the pixels of the camera are square!).
This is the procedure:
First aim at a star located exactly on the celestial equator (Declination = 0°), preferably in the South.
Click then on the star which appears in the field of the camera, so that the tracking crosshairs
pick up the star.
Turn off the tracking motor of the telescope, so that the star drifts freely in the field.
Immediately after turning off the tracking motor, click on the "Run" button, which appears to the left of the Video window.
The crosshairs will follow the drift of the star to the edge of the field. At this time, calculation will be performed and the program will inform when processing ends.
The calculated size of the pixels will be indicated in the appropriate fields, as though you had entered them.
Set with a resolution of:
In this field enter the screen resolution which corresponds to the size of the pixels of the camera. In general it is the screen resolution that corresponds best to the number of physical pixels of the camera.
For example, a Philips Vesta, or Vesta Pro camera, sensor ICX09AK, has a size of 659 X 494 pixels.
In the list of resolutions which this camera can display, there are (among others) 320x240, 640x480 and 800x600. It cannot be 800x600, because this resolution is higher than the number of pixels in the sensor. It is thus about 640x480.
If you use the function that automatically calculates the size of the pixels, you must first choose the appropriate resolution (usually 640x480) using the menu item "Video/Format". The procedure for calculating the size of the pixels will anyway fill this field for you at the end of the calculation.
Here are the different parameters:
Control port:
This is the address of the parallel port to which the camera is attached. This information generally needs to be entered only one time. Choose the corresponding address from the dropbox.
Interval between exposures (ms):
Enter the time interval between two long exposures (rest time).
The modifications developed by Steve Chambers use certain of the data pins in the paralle port. The basic modifications only uses one pin, pin number 2, and only controls the start of the long exposure. Modification #2 described at Steve Chambers" web site includes using 4 of the 8 data pins of the parallel port to control new functions of the camera. Normally a "standard" has been adopted, so the usave of each pin is pre-determined and pre-programmed within Astro-Snap. However, to allow greater flexibility, the choice of pin and value at the start of each function remain variable, in case additional variations are developed. For each function, you can specify the pin to be used.
Even and Odd Lines:
It is these two pins which control the start itself of the long exposure.
Amplifier:
This pin controls the activation/de-activation of the pre-amplifier contained in the CCD sensor of the camera. Deactivation of the pre-amplifier greatly reduces thermal noise in the camera, and allows longer exposures.
Advance:
This is the advance (in milliseconds) with which the pre-amplifier is "re-lit" at the end of the long exposure. When the exposure is ended and the image has been sent to the PC, the pre-amplifier must be activated for a minimum duration.
Imagine that you make an exposure of 30 seconds. In theory, the pre-amp must be "re-lit" approximately 1 second before the end of the exposure. To do this, one would enter 1000 in the field (1000 ms).
Long Exposure Mode:
This function allows replacing the manual switch proposed in the first version of the modification. The software automatically switches to long-exposure mode for the exposures.
If the values which the program provides you during the process of alignment are obviously incorrect (for example, it provides figures of increasingly large displacement when you carry out the adjustments in the opposite way), then click on the check box corresponding to the axis on which you note these incorrect values.
When the "Image Selection" mode is activated, the program determines the quality of the images by converting each one to JPEG format and considering the size of the compressed image.
In this tab you can specify the compression ratio which the program will apply to each image. The lower the compression ratio, the slower and more demanding the image will be to generate. The higher the compression ratio, the faster the image will be to generate.
However keep in mind that the more you compress the image, the less precise the image selection will be. It"s a trade-off. It"s up to you to choose the setting.
I advise a compression ratio of 30. That setting worked best for me, without being too demanding on computer performance.
Be aware that the resulting image will not be compressed! Only the size of the compressed image is retained, in order to sort the images themselves by quality! The quality of the final images is absolutely not affected by the operation of selection.
This tab allows configuration of the focusing aid.
The changes of focus detected in the image are calculated from the average of a certain number of images (from 2 to 50). This is configurable in the "Mean for X measurements" field. This allows, among other things, to lessen random variations due to the noise of the camera.
The slider called "Variation Sensitivity", allows setting the threshold from which this variation "is announced". This variation is displayed in "per mille " (1/1000) of the interval between the minimal value and the maximum value of the FWHM recorded from the sequence of images sent by the camera. The allowed values go from 900 to 1000.
For example if the FWHM oscillates between 2 and 3.5 pixels, and the selected sensitivity is 980, then the limiting variation of detection is equal to:
Therefore any change of the FWHM of more than 0.03 pixels between two measurements is announced. If you checked the box "Soun" on the "Focus" tab, then the software will tell you "Yes!", if this change is an improvement or "No!" if you turn the focus knob in the wrong direction.
The slider called "Final Precision", allows setting the threshold of final precision of the focus.
Throughout focusing, the software will calculate the maximum and minimum FWHM values. As soon as the current value is closest to the minimum value (ideal setting for a best focus), the software will announce that the focus is the best.
The threshold of "proximity" to this ideal value is thus configurable. The allowed values go from 900 to 1000. This threshold, as the threshold of variation previously described is "per thousand" of the smallest value of FWHM obtained at the time of the focus.
For example if the ideal FWHM is 2 pixels, and the selected final precision is 970, then the real final precision will be:
Therefore if your focus reaches the ideal FWHM within less than 0.06 pixels, then the software will announce it to you. If you checked the box "Soun" on the "Focus" tab, then the software will tell you "Stop!".
New!
Starting with version 1.3, if you have a motorized focuser of type LX200 or Bonduelle (via parallel part) the software can control the focus. See Function - Telescope Control.