Darks and Dark Library Software

[johnb]

Hi

I use Dark Library software and it seems quite useful, When I add Listed Darks to the DSS file it works fine but there seems to be no way to select the ones i want so if it finds say 25 darks to add but I only have say 10 lights I then have to edit the DSS file manually so I have an appropriate number of darks for the number of lights

Anyone else do this ?

John B

[roundycat]

Forgive me but what you are saying does not make any sense. There is not really any relationship between the number of lights you take and the number of darks used to calibrate them. There is no reason under the sky why you should not use 25 darks assembled as a master dark to calibrate each of ten lights, or twenty lights or one or two thousand.

If the software says different it is wrong.

Dennis

[johnb]

That's ok I often dont. If I build up the library and for say 25 lights and the lib finds 40 matching darks then use all 40. If I understand correctly ?

John b

[roundycat]

The simplest way to approach image calibration is to ensure you have light frames that are all the same exposure and temperature. Making a matching set of Darks then becomes a lot easier.

When you have shot a set of Darks the obvious thing to do with them is to combine them into a master dark. The individual darks are not then actually much use, making the master means they have done their job.

You should be able to include the master in your calibration routine and forget the individual darks - even delete them. There is very little point in having to re-combine all your darks every time you want to dark subtract a light frame.

Dennis

[afm038]

Dennis,

I'm also in the process of creating a CCD dark library for different exposure times, different temperatures and binning.

I have most of the exposures done (10 in each series) so what software should I be looking to use to make a master dark out of each series ?

Should the exposures be averaged or median combined to form the master or does it not matter and the software takes care of it ?

Thanks, Andy

[adamsp123]

As Dennis says once you have generated a master dark, say during a DSS run ie running a new set of lights and darks, DSS will save the master dark then in future stacks, if appropriate, you can just select the master dark that was generated, no need to reload all the original darks.

Andy I still use DSS for both my DSLR and CCD, just change the DSS from Debayer to mono.

[roundycat]

I think you have your answer!

Ten darks is a bit miserly. Bearing in mind you take them on a cloudy night go for twenty to thirty to keep the added noise to a minimum. Same goes for Bias. I usually go for about twenty Flats and subtract Bias from each one before combining rather than use flat darks.

I always use a Median combine for calibration frames but if it gives you trouble with your flats over or under correcting then try Average for the Flats. Stay with Median for darks and bias.

Dennis

[afm038]

Thanks guys.

I'll take some more exposures, as you say they can be taken anytime. Not so sure about the bias, how do I take a zero length exposure or do I just take the fastest exposure the camera can take whilst capped (as for darks) ?

I assume Pete that you mean in DSS the raw/fits DDPS window - fits files tab - you just uncheck the monochrome etc. box and the camera select then becomes not available ?

Andy

[adamsp123]

Thanks guys.

I'll take some more exposures, as you say they can be taken anytime. Not so sure about the bias, how do I take a zero length exposure or do I just take the fastest exposure the camera can take whilst capped (as for darks) ?

I assume Pete that you mean in DSS the raw/fits DDPS window - fits files tab - you just uncheck the monochrome etc. box and the camera select then becomes not available ?

Andy

Bias=fastest

In DSS - yes the raw/fits window

[afm038]

Thanks guys for the further information.

I'll take some bias frames for calibrating the flat frames as you suggest.

Andy