Whats going on here?

[Earl]

Any idea what is causing the big circles?

[Ant]

Is it there on all frames?

Maybe an internal reflection?

The screen grab says 1:3 - is this an RGB image combined into one? maybe a dew spot on the red filter?

Nice FOV, going to be a nice image!

Ant

[RobH]

It does rather look like an internal reflection.

What did the imaging train comprise of?

Rob

[Ben Ritchie]

Would appear to be internal reflections of some sort, what do you have in the optical path?

[Earl]

Cheers for the input.

This is a OSC image with a Skywatcher Flattener and Astronimik 2" CLS filter.

I have a feeling my Flats are just not working in PI

[Ben Ritchie]

I'm guessing the filter is attached to the flattener, then 55mm or so spacing to the CCD? That would seem roughly right I think for such a broad internal reflection, the old halo-prone Astronomik LRGB filters would give much smaller halos as the filterwheel was closer to the CCD.

edit: here's a good analysis http://www.astrodon.com/articles_faq/articles_faq/press_release:391,355,49

[Earl]

This is a single sub

[Earl]

I'm guessing the filter is attached to the flattener, then 55mm or so spacing to the CCD? .

Yep right on the button

[Earl]

All my problems seem to occur as soon as I add flats in to the equation.

[Ben Ritchie]

You can figure out exactly which surface is the culprit by following the analysis in the Astrodon article, but I'd suspect it's a reflection off the CCD window and back off the inner surface of the CLS.

You can check this by removing the filter and seeing if the halo goes away. If it doesn't, then maybe it's a reflection off an element in the flattener, but i'd bet on the filter.

All my problems seem to occur as soon as I add flats in to the equation.

What happens if you stretch an image hard without applying flats first? Forget about trying to keep the image pretty, can you still see the halo?

[Earl]

Ah

that last image is not a pure sub, it is a calibrated sub. this is a true sub, and there does not appear to be any reflections that i can see....

[Ben Ritchie]

*deleted, stupid suggestion*

The fact that the halo is coincident with a bright star means that it must be present in the light frames, flats are field illumination from an even source, not discrete point sources

[Earl]

humm im not so sure now am i imagining a circle in there or not

[Earl]

*deleted, stupid suggestion*

damn i missed it

[Ben Ritchie]

damn i missed it

Phew! Fingers worked faster than brain that time

Dunno if it's my monitor and/or imagination, but think I can see the halo in that single frame, stacking and calibrating probably just makes it more visible?

[Earl]

Im just integrating all my lights but without any calibration.

[Earl]

Here are all my subs integrated and the halo is there on the one star.

So presume.

a) obviously its in the lights so it has to be optical train so its the reflection.

Calibration cannot be working as there are more circles which do not exist in the lights appearing

Just a side note... this is a 23 sub stack without any star alignment been used.... wt?

[Earl]

Well now I am totally puzzled.

This image is 23 subs calibrated only with the Bias Master

Not aligned...does PI cache alignment?

The reflection is there but only in the one place.

What on earth is going on during calibration then?