The precise collimation
When we have a new newton telescope we shroud avoid touch the collimation of the secondary mirror as we may get into troubles.
Good collimation is very important if we would like to have perfect high resolution images. But sometimes brand new telescopes may come misaligned.
So this is a short guide how to do a precise collimation. Unfortunately the best way to collimate is to disassemble the whole telescope.
You best do this when cleaning up the mirrors. Use optical collimator eyepiece. Laser collimator is not enough to ensure correct collimation as there is a
position in witch the secondary can be tilted and still beam compensated by the primary return back at the centre. You will best find that, when observe a
diffraction image of a bright star with high magnification 200x+ and it will show a bit comma. You can use laser in addition for more precise alignment after
using a collimator eyepiece. Best way to check if the telescope is collimated is to observe a star just in-front and after the focus with high magnification.
You should see good ring under good atmospheric seeing. But if you have a secondary mirror tilt, you will see it only into the diffraction image of a star.
So here is the procedure. Consider you had removed the primary mirror for washing.
1. Print a sheet with concentric circles and put the tube vertically on it so you can precise align the secondary first.
2. Check for secondary axis rotation with the collimator eyepiece! You should see the secondary mirror well concentric to the focuser tube and the printed circles.
This is the key for the alignment as if there any rotation or tilt, you will not able to correct it after putting back the primary mirror.
If you need to do correction first loosen the rest of the screws then do rotate the centre bolt. Be careful with the alignment screws do not over tighten them,
as they are getting easily cracked. To tighten one you need to loose a bit the rest 2.
3. Make sure that the the collimator eyepiece cross or the laser beam hits the centre of the sheet with the concentric circles.
4. Put the primary mirror. Look again trough the collimator eyepiece. You have again 3 screws that define the position of the mirror and 3 that tighten it.
5. Make sure that the centre of the primary mirror, the cross of the collimator eyepiece and the shadow of the hole you look trough, exactly match. Do not
touch the secondary mirror as we had already verified in step 3 that it is well aligned.
6. Now you can put the laser collimator to adjust this even more accurate and make yourself more conformable as for the larger newtons you are not able to look and reach the screws of the primary at the same time.
Laser complicators do not work with cassegrain telescopes, because of the hole in the centre :) The beam never touch the primary. Put a flash light into the eyepiece holder and project the light. By mesaringsaring the shadow you can do the collimation. Then you can use a real star for more precise adjustment.
Moon at 45% illumination and 70x magnification. With aperture of 200mm,14,1 stops dynamic range, color depth of 23.7 bits at this image there are slight color variation on the moon surface that reveals it’s structure.
This is the beginning of my research on how dark the sky could be and what is benefit of a dark sky for astrophotography. I was inspired from those 2 sites. First one presents mathematical model of how dark the sky is.
You can find my last DSLR Astrophotography article in Bulgarian at page 76. I am sharing my last findings for this publication, Specially written for the Institute of Astronomy.
> NOWADAYS IS HARDER TO SHOOT LONG INTEGRATION TIMES WITHOUT GETTING ANY SATELLITE PASSING TROUGH THE FRAME
Satellites, cosmic trash or UFOs, the moving spots are everywhere on the sky. Typical satellite behavior is to reflect sun light. It should be yellow or white and could fade and shine due to its rotation.
If you have used DeepSky stacker to stack RAW files, maybe you have notice that the resulting image is poor of color saturation. This is because it has a higher number of bits then the display could show.