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Bias frames - reusing


m37
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Hi guys

From what I've read in MEPC and elsewhere I can re-use Bias frames from a DSLR for all images taken with the same DSLR.

Is this right? And also will it change over time e.g. in a year will there be any change to the bias signal? I would guess not but just checking.

Not much hassle to shoot them every time, usually use 1/4000 as it's the shortest exposure time I have.

cheers

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Hi guys

From what I've read in MEPC and elsewhere I can re-use Bias frames from a DSLR for all images taken with the same DSLR.

Is this right? And also will it change over time e.g. in a year will there be any change to the bias signal? I would guess not but just checking.

Not much hassle to shoot them every time, usually use 1/4000 as it's the shortest exposure time I have.

cheers

Yes at a push, but they must be all at the same ISO setting and at the fastest shutter speed of the camera. I am not quite sure if the bias taken at the height of the summer heat is the same as the one taken in the middle of the winter, in any case bias is the easiest of all the calibration frames, the darks and the flats are your problem.

A.G

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Here's a thread dealing with a similar question:

http://stargazerslounge.com/topic/92031-how-to-take-bias-frames-on-a-dslr/

Darks are probably more valuable for DSLR imaging, and they contain the bias info already. You can create a library for different temperatures and save these for later.

So yes you can save calibration frames for sure, but over time your CCD/CMOS will degrade and I can't tell you how often to redo these frames. Six months as a ball park figure?

/Jesper

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Bias frames remain usable for quite some time but I tend to refresh both my Bias and Dark frames every 6 months or so to allow for sensor 'ageing' - more critical for Darks than for Bias though. However, I don't lose sleep over this if I forget to do it!

That said, taking BIas frames is so quick that it would be a trivial task to take them each session if you were worried about them..

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I was told in a thread a while back that using a Canon means you do not need to shoot bias frames, as you add darks to the image.

Is that correct? Not done any imaging in a long while :/

My understandng is that if you are not going to use flats then bias is not necessary as bias is already in the dark frames and it will be subtracted from the lights, but if you use flats then bias is needed as it needs to be subtracted from the flats before a master flat is prepared, but I am sure that other more knowledgable members will shed a light on this.

Regards,

A.G

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