Can Flat Files be reused in DSS ?

[Newforestgimp]

Hi All,

I've recently started a first foray into Deep Sky Tracker and something puzzles me, the creation of FLAT FILES. Why can you not create a base level set of Flat files that can be re-used for various projects ? Same question applies to the BIAS Offset files although these are much easier to generate at the time of each shoot.

Andy H

[teoria_del_big_bang]

Someone with more experience will probably be able to answer better than myself but from my understanding basically it is because the flat images will change slightly over a fairly short period of time even if the camera orientation does not change.

With flats you are trying to remove things like dist bunnies, general blemishes on optical surfaces.

As you can imagine dust and blemishes will accumulate over time and so what is in the optical path one day will be different several days, or maybe weeks later.

I believe some do use the same flats for several weeks or months and to a large extent they probably work fine until there is a significant change in the build up of dust and other blemishes, so if time is short and you cannot get the time to take more flats then using a recent set would be acceptable, so long as something has not been removed and rotated such as camera or filters. But obviously if you are able to take flats at in the same session then that is ultimately the best option.

Bias again will change with time and temperature so as long as they are taken all at same temperature as the lights and other calibration frames and are recent then using the same bias frames would be acceptable but as they take such a short time to obtain it is not a bad idea to take a new set at least every few months.

That's my understanding anyway, as I say somebody I am sure will have a better insight into the whys and wherefores and you will find many do use a library of these short term, whilst others will always use new frames, I am sure.

Steve

Edited November 27, 2020 by teoria_del_big_bang

[Newforestgimp]

29 minutes ago, teoria_del_big_bang said:

Someone with more experience will probably be able to answer better than myself but from my understanding basically it is because the flat images will change slightly over a fairly short period of time even if the camera orientation does not change.

With flats you are trying to remove things like dist bunnies, general blemishes on optical surfaces.

As you can imagine dust and blemishes will accumulate over time and so what is in the optical path one day will be different several days, or maybe weeks later.

I believe some do use the same flats for several weeks or months and to a large extent they probably work fine until there is a significant change in the build up of dust and other blemishes, so if time is short and you cannot get the time to take more flats then using a recent set would be acceptable, so long as something has not been removed and rotated such as camera or filters. But obviously if you are able to take flats at in the same session then that is ultimately the best option.

Bias again will change with time and temperature so as long as they are taken all at same temperature as the lights and other calibration frames and are recent then using the same bias frames would be acceptable but as they take such a short time to obtain it is not a bad idea to take a new set at least every few months.

That's my understanding anyway, as I say somebody I am sure will have a better insight into the whys and wherefores and you will find many do use a library of these short term, whilst others will always use new frames, I am sure.

Steve

Thanks Steve,

That makes sense, but taking flats on a camera lens I invariably change the blinking focus by mistake.