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Help with Testing and Evaluating Newtonian F4 Optics & Performance

Collimation Equipment Imaging Optics Reflector
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#1 GaryShaw



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Posted 10 April 2021 - 11:50 AM

Hi All:


I'm hesitant to open up a can of worms regarding improving the performance of my optics. I'm just a 3 year veteran of EAA observing and only know enough to get myself in trouble jumping down the rabbit hole of my optics - which seem to be serving me fairly enough for what I do. .I am, however, bugged by egg-shaped stars and generally prefer to do the best I can with what I have. So, I'm hoping to investigate and test my gear and see what's working well and what's not - and, with help from you folks along the way, decide which improvements to tackle and which to live with. Two questions for now:


Question 1:

Recently I learned of CCD Inspector and downloaded it - thinking it could play a role in analyzing my optics and helping me decide what, if anything, needed to be adjusted. I sensed from a quick look at it, that this app can become a major learning task by itself so, before I undertake that path, I'd appreciate comments or insights from those of you who've used it, about the good features that will 'matter' and other types of testing features to ignore. It would be great to hear from you on this.


Question 2:

While investigating optics testing forum topics, I came across someone who had done an initial test based on assessing the appearance of Bahtinov mask spikes. The test starts with a well-focused Bahtinov pattern in the image center. Without further adjustments to focus, the star and it's mask pattern are moved successively to each corner. Differences in how the center 'spike' moves when the star goes to each of the corners, is, I assume, indicative of some aspect of optical performance...tilt?, collimation?, coma? (corrector in place) or some other optical indicator.


So, below I have attached 5 Bahtinov patterns taken first from the center and then moved to each of the corners as described above. The differences between them are not dramatic (I hope this is a good thing) but there are slight differences and they tell a story of my optics that I hope you can explain to me. You may want to zoom a bit to see the different locations more clearly.


many thanks for any insights on the above questions and opinions on any aspect of optical performance testing.




Attached Thumbnails

  • Center but towards LR.jpg
  • upper Right.jpg
  • Lower Right.jpg
  • Upper Left.jpg
  • Lower Left.jpg

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