Display Collimator

To display the collimator, you must set the display option on "Collimator"

The view port is empty if there is no defocused star analyzed.

The main goal of this view port is to provide a quantitative feedback during the alignment (collimation) process of your telescope.

The file name of the currently loaded raw image is displayed on top.

Three check box allows to individually select which optical aberration you want to measure and you can even combine them together.

Playing with optical analysis does not require a new frame analysis because all aberrations are calculated together in a single pass. The target is hidden when only the spherical aberration is selected. Since the spherical aberration is axisymmetric there is no directional information related to such aberration, unlike for coma or astigmatism.

The star center offset Y and X bars shows the distance in pixels of the selected defocused star from the camera frame center.

The defocus error bar shows the difference between the defocused expected for the analysis and the defocus measured by the wavefront analyzer.

A tooltip displays the values of each bar cursors (gray triangle). The defocus error tooltip shows also the defocus tolerance.

As collimation actions (tighten or releasing collimation knobs) slightly push the telescope out of the defocus tolerance. After each move of the collimation knobs you must check the defocus error and if the bar become orange or red you must move the focuser in the opposite direction to restore the expected defocus. Most likely the star may need to be re-centered as well.

The distance R of the selected defocused star from the center of the image is displayed on the upper right corner in pixel.

R = 6 px means that the selected defocused star is located at a distance of 6 pixels from the image center.

The current defocus travel in microns from circle of least confusion is displayed on the upper left corner.

The saturation gauge display the strength of the selected star and if it saturated or not. If there is any saturation the wavefront analysis may be inaccurate.

A red cross is displayed over the viewport when the star is saturated does not provide accurate wavefront.

The score of the selected optical analysis, is displayed by a rotating cursor hovering the target. You can also read the score below the target and look if the score is poor, marginal, fair or good.

The score is a value between 0 and 10. Zero being the worst, 10 the best. The goal is to bring the score at 8 or above, in the green zone.

The score is computed for the aberration selected only (coma, astigmatism and spherical).

The score is computed relative to the local seeing entered by the user. Since most telescopes in most locations are seeing limited the alignment of the telescope optics (collimation) is good enough when the score is at or above 8. This is the point of diminishing return, there is no added value to continue the collimation process beyond this point.

Blue dots scatter over the target shows the score of the previous analysis. They are showing the trend of the collimation process. To read the score of each dot you can hover the dot with the mouse cursor and read the tooltip.

To disable the scatter plot, uncheck the scatter plot check box bellow :

To clear the scatter plot, click on button

To change the scatter plot history (the maximum number of blue dot visible on the target). By default 50, you must disconnect SKW change the value and connect.

To help knowing which collimation screw must be tighten or loosen, SKW is able to superimpose the position of the three screws on top of the collimator target.

Collimation screws are displayed when the check box is checked, otherwise the screws are hidden.

The angle of the collimation screws must be defined for each mirror.

To select the mirror, just select the mirror number. The number can be entered by pressing the key 1 or 2 or by acting on the spinner on the right side.

The angle can be adjusted by entering a value in degrees between -360 and +360 or by acting on the spinner on the right side.

Both angles are stored inside the selected instrument and save in the workspace.

Prior starting collimation we recommend to follow our procedure to make a proper setup for telescope alignment

To achieve a proper collimation we recommend the following procedure :

To learn more about alignment procedure, you can watch the various documentation, tutorials and videos available on our Web site

If you telescope has at least one spherical mirror (SCT, CDK, iDK, ...)

1. Start by minimize the coma therefore tick the coma check box only.

2. Center a suitable defocused star on the center of your camera sensor.

3. Take a first frame..

4. Load and analyze the first frame

5. Adjust the collimation screws of the secondary (most likely) or primary mirror to minimizing the coma, increasing the score (seeing Innovations Foresight tutorials for further inside).

6. Capture a new frame

7. Load and analyze the new frame.

8. Look at the score and repeat this procedure until the coma score is at or above 8 for your local seeing.

9. Select spherical one (tick the spherical box only)

10. Take a new frame, load and analyze.
11. If the score is below 8 adjust the mirror spacing accordingly (seeing Innovations Foresight tutorials for further inside) and repeat if necessary

When the spherical aberration is caused by an incorrect distance between mirrors, you can try to push/pull one mirror (e.g. primary) and measure after each move of the spherical aberration is reducing. As spherical aberration is symmetrical, the result on your image will be bloated stars. If you can not minimize spherical aberration by changing the two mirror spacing by a reasonable amount (few millimeters) chance is that the spherical aberration is coming from the optics itself (mirror figures), collimation will not be able to remove it.

If you telescope has both aspherical mirrors (RCT, ...)

1. Start by minimize the coma therefore tick the coma check box only.

2. Center a suitable defocused star on the center of your camera sensor.

3. Take a first frame..

4. Load and analyze the first frame

5. Adjust the collimation screws of the primary mirror ONLY to minimizing the coma, increasing the score (seeing Innovations Foresight tutorials for further inside).

6. Capture a new frame

7. Load and analyze the new frame.

8. Look at the score and repeat this procedure until the coma score is as high as possible (no coma).

It is paramount to adjust the primary for minimizing coma, never use the secondary. Although both can minimize coma using the primary insures that the collimation process will eventually converge in few iterations. Otherwise the astigmatism, especially off axis will only increase become less and less balanced (identical in magnitude and symmetrical in direction in the four corners of the chip). Even no coma on axis or even across the all field (on and off axis) does NOT mean that the telescope is aligned (collimated). It only means that the secondary mirror optical axis crosses the primary optical axis at the coma free point. It is very likely that both optical axes are still tilted leading to astigmatism. This problem doe snot exist if one, or both, telescope mirrors are spherical.

9. When coma is minimize on axis tick the astigmatism ONLY check box (deselect the coma).

10. Place a suitable defocused star on the one corner of the chip, but stay away from vignetting, the star needs to be off axis but it does not need to be too close to the camera chip edge.

11. Take a frame.

12. Load and analyze the frame, record the score and the direction of the astigmatism.

13. Repeat this operation for the 3 left corners, if possible place the stars always close the same off axis distance form the chip sensor. Again be sure that you do not go too far off axis leading to vignetting.

14. Compare the 4 analysis and scores, the score magnitudes should be close to each other (off axis score may be below 8) and the directions should balanced, hence symmetrical. In the context of astigmatism the directionality is symmetrical along any diagonal therefore having two score marks 180 degrees from each others relates to the same directionality (seeing Innovations Foresight tutorials for further inside).

15. Adjust the secondary mirror ONLY to make off axis astigmatism balanced (same score magnitude symmetrical directionality). Most likley this will increase coma therfore you should repeat the procedure from the step 1 to 14 until the off axis astigmatism is balanced and the on axis coma is minimized.

16. Select spherical one (tick the spherical box only)

17. Take a new frame, load and analyze.
18. If the score is below 8 adjust the mirror spacing accordingly (seeing Innovations Foresight tutorials for further inside) and repeat if necessary

When the above procedure is followed the alignment of a telescope with aspherical mirrors (RCT, ...) converge in few iterations (typically 3), Otherwise collimation will ONLY diverge (even if one can keep the coma very low) until one hits the mechanical limits of the collimation screws.