Quote:
Originally Posted by Peter.M
The first thing I would make sure of is that the collimator is at the focal point of the telescope. If that is not the case it does not matter what you do, the hotspots will never look right in the central and offset pupils.
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Spot on...
Here is more technical details:
When the autocollimator mirror is at the focal plane, reflection 2 image is located on the primary mirror surface -- same level as reflection P. Therefore, both will have the same apparent size and there will be no parallax as you view them from both pupils.
When the autocollimator mirror starts to move below the focal plane, reflection 2 will start to rise above the mirror surface. Not only it will appear larger but parallax will be introduced. The opposite is true.
If you look at the last photo of the first post, you will see the following:
1- Reflection 2 is larger than reflection P
2- You will also see reflection 6 which can only be seen when the autocollimator mirror is below the focal plane.
One more observation. Center spot reflection will appear slightly larger when the Blackcat is below the focal plane.
How critical is it to get the autocollimator mirror precisely at the focal plane?
NOT THAT CRTITICAL. As long as reflection 2 size appears about the same size as reflection P then the location of the autocollimator is good. I found that as long the the autocollimator mirror is within 1% of the scope's focal length from the focal plane, both reflections will appear about the same size. So, for a scope with 1000mm focal length, the autocollimator mirror location is OK if it stays within 10mm from the focal plane.
To be fair to Catseye instructions, it does state at the top:
"*Equal-sized images as illustrated & best results are achieved with the focuser/autocollimator racked in/out appropriately to place the autocollimator mirror at or very near the focal plane."
Jason