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Still learning (after 10 years!)


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Well I'm still learning after 10 years!  Read an article about long exposures with a 183c CMos camera and the emphasis was on the Dark frames taken.

So last night (in a brief clear sky!) I did some 300s Darks with everything covered then tried 10 x 300s exposures at Unity gain and 24 Offset on M13.

Also got 2 x 300s on M27 before the clouds rolled in! I processed them this morning and was surprised at the result for a fan cooled cam! No sensor

glow at all and the Darks x 10 worked really well. What I did notice is that I need to do some more longer exposure Flats and Dark Flats as there

is a bit of vignetting. I will try to do them before Saturday nights forecast clear sky's! Comments welcome please..

 

large.M13100621_300FinishSmall.jpg.6ef2af13827f397dd71a77448cdd65fa.jpg

 

large.M27100521_300FinishSmall.jpg.fd519c5110c85131af221f499ceae071.jpg 

 

Edited by RonC
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Like my 294, the 183 definitely needs matching darks to ameliorate the starburst amp glow.

 

Dark scaling/no darks doesn't work for these sensors.

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If the vignetting is dark around the edges, does that mean the Flats need to be a longer exposure or a shorter exposure?

I'm getting stuck with this!!

 

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24 minutes ago, RonC said:

If the vignetting is dark around the edges, does that mean the Flats need to be a longer exposure or a shorter exposure?

I'm getting stuck with this!!

 

 

What acquisition software are you using?

Generally, I tend to go for about ⅓ total sensor saturation (so about 20500 ADU) in APT.

 

I am not familiar with any other software, but I'd be surprised if the same numbers don't still apply.

 

It's so much easier with DSLRs!

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Ah, there's your problem then. That's far too low.

 

Try using the CCD Flats Aid to take the guesswork out of it. Leave the settings at default, but I personally like to shoot a minimum 30 flats. Up to you, really.

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Depends on the bit depth.

IIRC Ron is running at 8 bit ( and binning?) so max ADU is about 4000 and a 1/3 to 1/2 of that is what to aim at.

 

 

Not sure about gain as when I do flats for my solar you can up the gain to get a decent flat.

 

After 16 flats I think they say satistically there is little difference , saying that I do 31 as they don't take that long to do.

 

Darks should match your imaging run settings as near as you can with cams with no set point cooling.

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I've gone back and forth with the creator of APT previously on this very subject and sorry to say, I don't recall what the definitive answer was. I'll see if I can dig it out.

 

What I do recall, in my camera's extended pixel mode (what I shoot with most), it drops from 14 to 12 bits. In the early days i shot my flats with the assumption the ideal ADU values were similar to what you were using and as a result, I also had terrible vignetting.

 

In this mode, the 294 has vaguely similar characteristics to the 183, albeit in a larger sensor.

 

Yes, you are right about the bit depth of the camera's ADC, but if APT is measuring from the output FITS file, i.e. post-ADC, aren't these by definition 16bit (0-65536)?

 

I'm by no means an expert at this, so I'm genuinely curious.

 

Kev

 

 

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We sorted this out about a month ago, well just about as I suspect there is still a slight light light leak or un equal illumination but it was minimal.

 

The higher ADU flats were overcorecting Rons images.

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This happened because I tried using 300s at 1x1 Binning, I got the darks sorted but had to re-do the Flats to match.

The resulting images were no better (in my opinion) than those I take at 120 - 180s but the 1x1 looks to have more

definition. The ongoing saga continues.....

 

Thanks both for your valuable input..

Ron

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So 1x1 binning could be running at 16 bit or 12 bit

 

 

if 16 bit you want to aim for 21000/ 30000 ish as Kev states

if 12 bit 1400 to 2000 which I think you have been running at (I was wrong when I said 8 bit)

 

 

Edited by Ibbo
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