Problem with flat frames? Advice please

[Herrman]

Hi,

First light with my new Atik 383L couple of nights ago.

After taking the light frames, I left the rig assembled and took the flat frames indoors last night, having cooled the camera first. I'd expected an even illumination, but the image shows this is not the case. I use an Earlsman light panel, which was flush against the dew shield. The telescope is an EQ80 with TS focal reducer 2" fitting. I've used this combination many times with my 40D DSLR and have always achieved evenly illuminated flats.

My question is; is the flat frame taken with the Atik normal, or is there a problem.

Any help, comments, advice offered will be gratefully received.

All the best Herrman

[Jessun]

Herrman, I don't use either this particular light panel or your camera, but you should get a clue from looking at your lights after stacking without using these flats. If the same gradient with accompanied other errors then appears then I'd suspect some optical misalignment in the imaging train.

It the lights don't reproduce this then I'd take a closer look at the panel again.

Just an idea.

Good luck

[Herrman]

Hi Jesper,

Many thanks for your response.

I did stack the lights prior to taking the flats- and here it is. There are a number of unwanted arifacts present that need to be removed, and I was hoping the the flats would go someway towards sorting the out. The image itself is not great- it was my first time with a CCD and I was just keen to try it and the Artemis software out. I've used autolevels in PS7 to bring out some structure, but that's about it. If you have any thought on the image I'd be very interested to hear them.

Thanks again, all the best, Herrman

[Jessun]

Herrman, congratulations to your first light!

I wonder, is this a brand new camera? The reason I ask is that the artefacts are likely to be dust or tiny stains on the CCD and lots of it too. If you shine a torch to the CCD then at some angles you often see it yourself. Try using one of those rubber blower things, and gently blow it clean. Careful no to blow hard or touch it at all.

Flats will 'cure' this to some extent but in my personal opinion you it's worth having a somewhat cleaner CCD.

You see a few of these 'dust bunnies' in your flat, but the top left corner only vaguely corresponds between the flat and the lights. It's a start though. The camera is the new addition so probably the culprit.

Again, just my opinion.

[Shibby]

Hmm the illumination doesn't seem to match your flats. Could something have dewed up when you brought your kit inside?

[Jessun]

Just adding a few stretches of the flat. Not sure what to make of it though to be quite honest...

[samir_ansari]

I think I know what this might be - Does the Atik 383 have a mechanical shutter?

If your flat exposures are too short you will end up catching the shutter as it's closing. Try and take a flat of about 2-3 seconds and the problem should be gone.

Hope this helps.

[Herrman]

Hi Jesper,

Many thanks for your encouragement and advice.

It's a humble start, but I'm quite pleased with the results for a first night out. I'm not too keen on the Artemis software, but hopefully I'll get to grips with it. It's a new camera, and I think the dust has accumulated on the other optical surfaces- once back indoors I don't like putting covers on equipment until it's fully dried, and I think this is when the dust gets in. I've got some of that Baader wonder cleaner stuff, so I'll try and clean the optics with this. Still, I've now subtracted the flats and lights, and here's the result; much better, but still room for plenty of improvement- I'd be happy to receive advice from anyone on how to do better. What perplexes me most is the illuminated corner of the image, I'd say it was moon-glow, but the moon was to the other side of the frame and the artefact also appeared in the flat frames. I think the next step is to change the optical configuration and see if the problem.

All the best, Herrman

PS SGL won't let me upload images at present- I'll try again later

[Herrman]

Hi Lewis,

Many thanks for your reply.

The flats were taken indoors the next day, I'd left the objective cover off for a couple of hours the night before, so condensation shouldn't have been a problem, although could it have formed on the sensor when the camera cooled to the previous night's setting? This is a technique that I've used when working with my DSLR, and I've never had this problem before:icon_scratch:.

Thanks again, all the best Herrman

[Herrman]

Hi Samir,

Many thanks for your reply- I think you may have sussed it!

I wasn't sure what exposure to use for the flats, so I went for 0.01 sec, I'm used to working with traditional cameras, so perhaps this is too short for the Atik. I'll try a range of longer exposures, and let you know how I get on.

All the best, Herrman

[Herrman]

Here's the flat & dark adjusted image

Herrman

[Earl]

CAn you upload the fit file to a dropbox account and link it?

[kookoo_gr]

I also have an atik 383L+ and i can confirm that it is smear from the shutter if you use exposures to take flats or images lower than 0.2sec (it mentions it at the manual) the best exposures to take flats are from 2 sec and above.

[Herrman]

Hi Kookoo,

Thanks for the information; I think that's solved this little mystery! I did read the manual, but missed the piece on flat frame exposures.

Thanks again to you all for your help.

Regards, Herrman

[Herrman]

Hi Earl,

I'm not sure how to do that, but I'll see if I can find out and give it a try. Regards, Herrman

[Catanonia]

Yes the flat exposure is too short. You need to reduce the light and take 3 - 4 second flats to stop shutter interaction. I get the same with the QHY9