Old 30-08-2008, 07:18 PM
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Analyze This Vigneting

Hey all,

Pic below is a Flat through the scope, I,m assuming this to be vigneting, is there anything I can do about this?.

Details are 8" F4 newt taken with a 400d and Baader mpcc, I had to move the primary mirror up the tube by about 16mm and use a low profile focuser to achieve focus with the camera. any ideas or help would be nice.
The image has been stretched a far bit to make it more apparent.
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Last edited by PeterO; 30-08-2008 at 09:52 PM. Reason: more info
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Old 30-08-2008, 09:01 PM
Ian Robinson
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Get a lower profile focusor and a bigger diagonal ?

The draw tube is too long.
The draw tube is so long it is stopping some of the light from the secondary from reaching the focus plane of the camera.
A bigger diagonal will ensure full illuminations of the fov (no drop off).

You should have moved the primary rather than secondary.

Last edited by Ian Robinson; 30-08-2008 at 09:15 PM.
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Old 30-08-2008, 10:12 PM
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Moving the main mirror up the tube would increase the size of the light cone at the secondary. The secondary may be too small to illuminate the entire field. The 400d sensor is quite large.
Also the illumnation does not seem to be centered. Is the scope precisely collimated? I read somewhere that these f4 newts are very fussy about collimation.


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