I have a question and need your imaging knowledge: I am using a Newt 800, 8 inch, F/3.9 Camera is an ASI1600MM-C Mono camera I am using a 7 pos filter wheel and the donut shows up on...

nikonshooter Loc: Spartanburg, South Carolina

I am using a Newt 800, 8 inch, F/3.9

Camera is an ASI1600MM-C Mono camera

I am using a 7 pos filter wheel and the donut shows up on all filters so I can rule that out.

I have used the camera with filter wheel on a Vixen refractor Ed81s and no donut so I am doubtful it is the sensor (refractor is 625mm F/7)

So I have examined the Newt's mirrors and see nothing.

It is easily removed with flats so I really don't care.....crap, yep I care - I am dying to know WTF is going on.

The donut sure looks like an out-of-focus star but the stars are in focus.

So - heap on the knowledge I am at a loss.

(Download)

SonnyE Loc: Communist California, USA

My best guess would be a ghost reflection of the secondary at the front of the tube.

No reason, just what my eyes are telling my gut impression.

Is it just with that camera?

nikonshooter Loc: Spartanburg, South Carolina

There is no donut when I use a DSLR or CCD camera.....just with this ASI1600 cmos. I sent an email to ZWO Optical - they make the camera with the picture and they think it is crap on my sensor. So here I go taking the camera apart to clean. I have no problem cleaning my DLSR sensors - but unscrewing stuff makes me crazy.

JimH123 Loc: Morgan Hill, CA

nikonshooter wrote:

There is no donut when I use a DSLR or CCD camera.....just with this ASI1600 cmos. I sent an email to ZWO Optical - they make the camera with the picture and they think it is crap on my sensor. So here I go taking the camera apart to clean. I have no problem cleaning my DLSR sensors - but unscrewing stuff makes me crazy.

This is a reflection. There is nothing on the sensor. Does it go away if you have no filter?

You can also rotate the camera. If it were on the sensor, the donut would rotate too. But a reflection would not.

Another thought is if the scope is pointed somewhere else, does the donut remain?

Is there a light leak that is allowing the strong light from the moon to get in? If you cover the camera, does the donut go away?

nikonshooter Loc: Spartanburg, South Carolina

BINGO - Jim when you stressed reflection over sensor crud....I was with you. I tried rotating the camera - same results - I removed the filter wheel - same result .....then like a great big ole slap in the freak'n face I took the coma corrector off - BINGO. So checked the corrector in the light and could see an ever so slight smudge. I cleaned that and BINGO.

Whooo ahhh!

Thanks for your insight....I used your suggestions that helped me rule out the cameras' sensor and EFW - I examined the mirrors on the scope and couldn't see anything there either.

Tis fixed!!

SonnyE Loc: Communist California, USA

We will be expecting film at 11....

JimH123 Loc: Morgan Hill, CA

nikonshooter wrote:

BINGO - Jim when you stressed reflection over sens... (show quote)

Great! I forgot to suspect the coma corrector! Its such a perfect donut, I wonder what left the smudge???

Europa Loc: West Hills, CA

I have a dozen of these in mine, I suspect it's on my camera lenses cause they are always in the same position, no matter how I turn the camera. They do come out with flats, but like you said...irritating, would rather they go away...glad you found the issue.

CraigFair Loc: Santa Maria, CA.

nikonshooter wrote:

I am using a Newt 800, 8 inch, F/3.9 br br Camera... (show quote)

I think it is something on the scope glass. I had the same thing happen when I had a spot on my Mirror.
That's my best guess.
Craig

CraigFair Loc: Santa Maria, CA.

Europa wrote:

I have a dozen of these in mine, I suspect it's on my camera lenses cause they are always in the same position, no matter how I turn the camera. They do come out with flats, but like you said...irritating, would rather they go away...glad you found the issue.

What Brian is saying about rotating the camera and see where it goes.
Craig