Issue with imaging train, overexposed middle?

[skiap]

Hi guys,
I have issue with my imaging train and can't figure it out what's wrong with it.
It's skywatcher ed80 doublet with 0.85 orion reducer/flattener and zwo asi533mc pro.
I thought it's my optolong filter - it's not, got same result without the filter
I thoroughly cleaned the optics both the reducer and the scope - that didn't help as well

Can it be the camera sensor itself?

Any suggestions?

Thanks

[BigNoel]

Is the arrangement and spacing OK?
I can't comment specifically on your rig as I've only seen a Canon DSLR in use with that reducer on an ED80. On that rig, the corrector was mounted to the DSLR's T-ring. This would have given around 55mm backfocus from corrector to the sensor.
You might already have the ~48.5mm needed (if my thinking is correct) but if you don't it might be something to look at.

If you're concerned it might be the sensor - take the reducer out of the equation and see if you get a field with different illumination (though it wont be flat).

[jahnpahwa]

Heya Filip,

Have you taken some darks with the setup? This might also quickly help to narrow things down.

I asked someone the other day about the 533MC, whether they still used darks given the super low noise of the sensor. They said most certainly yes.

(Also, I used to live in SoHo, and sometimes wish that I still did! What a spot :) )

JP

PS - nice colour choice on the focuser... rig is looking so nice!

[The_bluester]

Are you imaging with lights on that might impact the scope? Particularly via any sort of light leaks in the image train? A more brightly illuminated center is not unusual and should be fixed with flats, but the hot center and cross shape looks a bit unusual to me. Flats would still be the first place I would start though.

And yes to dark frames, every time. Low dark current is not no dark current and there will still be some hot or cold pixels which darks will help you calibrate out. I invest a day or two every few months to shoot a new set of darks. I usually take 100 of each exposure time I use, with the senor cooled to my normal temperature and generate master darks for each exposure time that I use and I then use master darks for the following couple of months, archiving the old ones to go with the data shot while they were the current set.

[skiap]

I finally took my rig outside and now the issue is gone. How? I have no clue but its definitely gone. I haven't done anything except cleaning the lens, the camera sensor and the reducer.

Anyway, now my small stars have tiny rings inside, what the hell is happening every time i go outside there is a brand new problem to solve :( Please see attached pictures, they haven't been modified just autostretch in pi. Everything else looks in focus, can this be collimation issue? I was using optolong l-enhance if it makes any diff.

[The_bluester]

It looks just to be out of focus there.

What capture software are you using? While your Moonlite is not motorised (That I can see) software like Sequence Generator can provide feedback on the average HFR of the stars in a frame that you can use to dial the focus in. Lowest HFR=best focus.

[skiap]

It was the Detect and Clean hot and cold pixels setting in dss
Unchecked both and voila, another problem solved :)

[The_bluester]

Well that is a really strange effect, it really looks like it is just out of focus!

I have not used DSS in a long time, I found stretching and colour management to be so much easier in APP that I never looked back.