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INDI Library v2.0.7 is Released (01 Apr 2024)

Bi-monthly release with minor bug fixes and improvements

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Bias frames - No data/empty?

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Replied by Anders Misfeldt on topic Re:Bias frames - No data/empty?

Actually, Ekos selects that exposure time for me. I (by accident) sat the time to 3.725 seconds last time, but Ekos just exposed the bias frames as the lowest possible (the 0.00003 s that’s written in the header). The file was named with the 3.725 label though.
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4 years 3 months ago #47330

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Replied by Jose Corazon on topic Re:Bias frames - No data/empty?

Have you tried shooting them as light frames and progressively setting a shorter exposure time? Then you find out when your camera hardware becomes limiting.
4 years 3 months ago #47331

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Replied by Anders Misfeldt on topic Re:Bias frames - No data/empty?

No, but I don’t think that’ll help since Ekos automatically sets the bias exposure time to 3.2E-5 s, no matter what I enter as exposure time.
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4 years 3 months ago #47334

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Replied by Jose Corazon on topic Re:Bias frames - No data/empty?

I understand.

That's when you set the tab for 'Bias'.

What I meant was that you should set the tab for 'Light' frames, then take images at the shortest exposure your camera will allow (Probably 1/1000s). Then use those as bias frames.
4 years 3 months ago #47335

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Replied by Chris Rowland on topic Re:Bias frames - No data/empty?

Let's try Science.
There's a hypothesis that the camera collects no data if the exposure is too short.
Try taking dark frames at shorter times until you see that the data goes to all zeroes.
Or try lights with the camera covered, it's the same thing.

Maybe there's a point where if the exposure is too short the camera does nothing.
4 years 3 months ago #47336

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Replied by Thomas Stibor on topic Re:Bias frames - No data/empty?

There is an excellent book/tutorial CCD Data Reduction Guide
that explains in very great detail with Python (astropy) code how actually an astronomical CCD image is formed.
In chapter Understanding an astronomical CCD image
is written:

In sub chapter Construction of an artificial (but realistic) image
is explained in detail how a offset (bias) image is formed.
4 years 3 months ago #47337

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Replied by Alfred on topic Re:Bias frames - No data/empty?

My bias frame was (automatically) taken with 3.200000E-05 exposure time (pulldown menu set to BIAS in Ekos) too and it is NOT empty. So something different is not right with andefeldt's setup.

Last edit: 4 years 3 months ago by Alfred.
4 years 3 months ago #47351
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Replied by Wouter van Reeven on topic Re:Bias frames - No data/empty?

It is possible that nothing is wrong with the Bias subs but rather with the way they are processed with PixInsight. Perhaps this should be asked in the PixInsight forum first? Either this leads to a correct way of processing them or to the conclusion that indeed the bias subs are wrong. In my experience it is best to start debugging at the end of the chain rather than at the start.


Wouter
4 years 3 months ago #47352

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Replied by Jose Corazon on topic Re:Bias frames - No data/empty?

This may be a stupid question, but how can the value for image resolution (arcsec/pixel) be negative in the FITS header?

SCALE = -9.551690E+02 / arcsecs per pixel
4 years 3 months ago #47353

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Replied by Jasem Mutlaq on topic Re:Bias frames - No data/empty?

So I'm not sure about the bias frame values, but the scale could be to missing focal length value. I just added more checks in INDI::CCD to prevent against generating bogus scale values.
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4 years 3 months ago #47363

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Replied by Anders Misfeldt on topic Re:Bias frames - No data/empty?

Wouter, all my Bias frames are produced in Kstars/Ekos and they show up as emtpy in all fits viewers. Values are 0 for min, max, std dev, median etc. Loading the fits files in KStars/Ekos doesn't give me a view as "Herrhausen" produces. My view is just completely white i Kstars (completely black in all other fits viewer programs) even after I've auto-stretched them. So I really don't think the problem is with PixInsight?
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4 years 3 months ago #47364

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Replied by Anders Misfeldt on topic Re:Bias frames - No data/empty?

@knro, my focal length are written in Ekos, but maybe it's not transfered to the Bias info?
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4 years 3 months ago #47365

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