Flat frame artefacts showing in final integrated image

[carl]

Hi,

I'm having a particular challenge where the artefacts from my flat frame are showing up in my final integrated image. Have taken my images using iTelescope.net. Their own Master Flat looks pretty much identical to the one I'm creating so the issue is coming up after that point.

Processed the Flats using the Master Bias with "Calibrate" unchecked. Lights were processed using Master Dark and Master Flat. I would expect the artefacts in the Flat to be removed from the Light files, but it's appearing.

Don't worry about the star blooming, etc. as this isn't for pretty picture purposes.

.xisf files

• Flats settings
• Lights settings
• Master bias
• Master dark
• Master flat
• Final image

Any ideas on what I may be doing wrong here?

Master flat


Integrated image



Thanks,
C.

[sharkmelley]

Try calibrating a single light frame.  What happens?  Maybe you could provide a light frame so we can try.

It's pretty difficult to work out what's going on from your integration.  Did a meridian flip take place during the session? I notice that the dark areas appear in the same place in the rotated integration.  That rotation might also provide a clue.

In any case, either the filter or the sensor looks really filthy.  Maybe a slug has been crawling over it, leaving a slimey trail   I certainly wouldn't want to pay money to use equipment in that condition.

Mark

[carl]

Thanks for the response Mark.

I just tried calibrating a single light frame and I see the same issue. Imaging was done over a number of nights and there definitely was a meridian flip. I've linked two light frames (one E one W) for people to have a play with.

I agree, the filters are filthy and it's something I've spoken to them about. Unfortunately I've already done 10hrs of imaging on this project so I need a way to get this to work with the current files - short of starting over

Light frame 1
Light frame 2

[sharkmelley]

It's pretty clear that the pattern of "dark tracks" in the light frames does not match the pattern in the master flat.

That's why the flats don't work.  I've attached a side by side comparison.

Maybe if you take a new set of flats they will match the lights.  Who knows.  It depends on the cause of the issue.

Mark

[ngc1535]

That sure looks like frost (which would change, and not flat out).
Either that... or something is growing on the CCD window.
I would think getting an understanding of what that stuff is in the flats should be the priority.
-adam

[pfile]

2nd time in a week ive seen lousy data from itelescope, and the 3rd or 4th overall. id ask for my money back and also ask them to fix their camera.

i agree with adam that this seems like frost.

also if im not mistaken, they provide calibration masters produced with maxim, which can be a real pain to make work in a different processing program due to 32b fits incompatibilities.

rob

[carl]

Thanks for the info everyone. Glad it's not something I'm doing specifically here to cause this. They're going to check the scope for me and take new flats.

I agree that it's disappointing for a service that you pay for. Their own master flats have this artefact on them and I would've thought they'd have checked. However I do have to say that Christian in particular has been incredibly responsive and helpful along the way.

also if im not mistaken, they provide calibration masters produced with maxim, which can be a real pain to make work in a different processing program due to 32b fits incompatibilities.

You're correct. Although I'm not using their masters and have taken my own darks and bias frames. Unfortunately I need to use their flat subs (not master) as it's more difficult to do this remotely.

Thanks again everyone. I'll send through an update when I know more.

Cheers,
C.

[carl]

Brief update for the spectators.

I ran another quick session and got the iTelescope system to provide calibrated lights as well as the raw frames. They use MaximDL I believe. The artefact is still there (although not as strong) in their calibrated file. So it's most likely at issue with the flats at their end and not a processing thing I'm doing.

Calibrated light example

I've asked them to check the luminance filter for smile and run another set of flats for me. Let's see what comes of it.

[carl]

Looks like an issue with the CCD itself. Scope is going to go offline and I'll be asking for a refund. Such a shame

[pfile]

i hope they get it sorted... my feeling is they have a lot of nice stuff in some really dark/great locations, but it all only kind of works.

rob