Can anybody recognize this artifact?

[RideDucati]

I just took a few shots of Sirius for focusing reasons and playing with ISO and exsposure lengths looking for noise and just playing around some. I was getting this artifact. Now I am assuming the round part is because of it's brightness because it is definitely too long of an exposure but the off-shoot to the side has made me wonder what could be causing it. I am using a Nikon D5500 that has a CMOS sensor without the antialiasing low-pass filter mounted directly to the rear of the Meade LX90-ACF using a t-ring to SCT adaptor.

Really I am even wondering on why the round artifact was happening but also the part off to the side. Is the side part caused by mirror slap or some other kind of shaking or from a long exposure since it is in close to the same direction of the star elongation. The photos were not even meant to be kept because I was just working on focus and noise but they made me wonder.

Any guesses, answers , tips would help. Thanks in advance.

[jambouk]

No idea, but it is very pretty, like some mysterious underwater primitive life form.

The main round one you could sort of think might be due to something refracting the light into a larger disc, but the other one to the side looks like the main one but just folded and taken at 90 degrees from the side. Have you examined all the optical surfaces carefully - looked at everything the light travels through or reflects off?

Do you get this sort of artefact when doing flats? Taking an image using the whole set up with a diffuse white light? Do you have a different camera to see if it is something trapped in the optical path within the scope, or to test the camera away from the scope to see if it something within the camera on the sensor?

Sometimes movement artefact results in odd shapes, but I think these shapes are too uniform and not random enough for that.

It will be interesting to see what it turns out to be.

James

[andrew s]

I would guess that it is light reflected from the micro lenses on the detector back to the secondary center and then back to the detector. The other artifact looks like a segment of an off axis reflection.

I would not worry about it as oit ois only by sible as the star is so bright.

Regards Andrew

[RideDucati]

All equipment is brand new including the telescope and camera. I dont have this issue shooting rugularly. But this extended length shot that overexposed the bright star is I'm pretty sure what created it. Intresting I didn't think about that it could be a reflection back and forth from the secondary and the sensor. And it is pretty, especially in RAW at full resolution. You are right it does look like a deep water organism. There is nothing wrong with any of the equipment separately. Camera is great normally and during regular photography. The telescope doesn't create that artifact during visual. I did notice that the color is exactly the same color as the UHTC coating on the ACF lens.

[STARDUSTPETE]

This may be caused by internal reflections on a part of your scope where the black paint has flaked off and the result is magnified on the camera chip. always seems to happen on very bright objects. Makes an interesting shot though.

[andrew s]

If it has an acf lens then it is probably a reflection of that rather than the secondary.

Regards Andrew

[RideDucati]

This may be caused by internal reflections on a part of your scope where the black paint has flaked off and the result is magnified on the camera chip. always seems to happen on very bright objects. Makes an interesting shot though.

I doubt there is any paint flaking off already, at least I hope not. Considering it's just a couple months old and kept inside under controlled temp and humidity conditions.

[gooselk]

You captured a supa nova in the making

Jokes aside: I think it's a back reflection of light onto other surfaces in the optical train and that's so prominent because of sirius being so bright.

Clear skies ... Lars

[glowingturnip]

reflection would make sense - i was thinking that that cusp at the top right looked like a lissajous-type squiggle, which would be consistent with light reflecting off a curved surface.

Either that or it's a Halloween spook.

[RideDucati]

Sounds reasonable to me. Thanks for the help everyone.

No idea, but it is very pretty, like some mysterious underwater primitive life form.

Do you get this sort of artefact when doing flats?

Sometimes movement artefact results in odd shapes, but I think these shapes are too unif 

It will be interesting to see what it turns out to be.

James

I don't get them during flats though. Thankfully.