Now THATS some vigenetting!!!

[UlteriorModem]

The story is this is the first set of data collected with the new ASI071mc-pro.

I did have bias and dark calibration frames, but no flats. But I wanted to put the data together to get a feel for what I had.

What I found was a surprise! Holy vigenetting! The dark curve at the bottom of the frame is the pick off prisim getting in the way. But I cant really account for that level of well defined vigenetting. Did I get the focal reducer too close? Too far? The star shapes don't look too bad.

18 x 300 sec frames at -15C gain:90 offset:20. 10" RC at a focal length somewhere around 1400mm.

Vigenetting by Tom Whit, on Flickr

[yobbo89]

Is the bottom of the frame from an oag mirror?

[UlteriorModem]

Yea the pick off prisim. I have fixed that

[UlteriorModem]

Aha! I found the culprit!

Went and looked up the CCTD67 focal reducer and it states "a fully illuminated circle of 29mm @ .67X" That is at a spacing of 101mm.

The cameras sensor is 28.4mm diagonal. So it should be fine. But I measured the spacing and it was out to 108.

According to their formulas that puts it at .6459X which results in a fully illuminated circle of 28.4mm that's cutting it a little close!

TLDR: Focal reducer spaced too far to fully illuminate the sensor!

Thanks for bearing with me

[JayTee]

Thanks for the info, I'm very interested in purchasing this FR with my Christmas money.

Thanks,
JT

[UlteriorModem]

Your welcome! That is why I posted the findings it to help folks out

I probably never noticed it so much with the ASI1600mc which has a smaller sensor at 21.9 vs 28.4 on the 071.

I moved the spacing in about 7 or 8mm but wont have a chance to check it out for some time. Maybe do some flats or something but weather is not good for almost a week.

Almost forgot.. here is the tech paper on the CCTD67. Its a little tough to read as 2 different FRs are discussed.

https://www.astro-physics.info/tech_sup ... chdata.pdf