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Old 29-03-2013, 10:12 AM
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Ryderscope (Rodney)
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Ryderscope is offline
Join Date: May 2006
Location: Glanmire, NSW
Posts: 1,718
Meade ED80 - Spherical Aberration??

This post is a follow on from the flat field problem that I am having with my Meade Series 5000 ED80. It was recommended that I do a star test on the scope which I have done and it seems that the OTA may have some spherical aberration.

I tried the star test visually using an 8mm Ethos and Televue 2x barlow (had to also use a 50mm extension to get sufficient back focus). This showed a definite difference between the forward and back focus. I then hooked up the camera with the 2x barlow and took the attached images. The images were 1/5 second, ISO 800, zoomed to 100% and then cropped from the screen image. I made sure to centre the image in the field of view when taking the photos.

I was wondering if I could garner the views of those more informed than I am on these matters to see if this test is showing spherical aberration and if this is the case what, if anything, can be done about it.
Attached Thumbnails
Click for full-size image (Back Focus.JPG)
11.3 KB65 views
Click for full-size image (Forward focus.JPG)
10.9 KB70 views
Click for full-size image (In Focus.JPG)
10.2 KB62 views
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