dark frame library settings?

[iwols]

hi just going to start a dark frame library ,all to be taken with ccd set at -15 deg,as this seems to be the setting i use,put some figures into sgp,do these look ok,and what is a good suffix for darks,thanks

presume it doesnt matter what the filter wheel is set to.

 

[andrew s]

If you take offset/bias frame you only need take dark frames for the longest exposure you use as they can then be scaled (after dark subtraction) to any lower exposure.

I would, for a library ,do a lot more than 15 frames as this only reduces the noise by sqrt(15) about a factor of 4.

It is worth looking at the statistics of darks compared to offset/bias to see if you need use them at all.

Regards Andrew

[iwols]

25?  50?

[andrew s]

64 always seems about right as it reduces noise by a factor of 8 but it depends on what you are doing. As long as it does not introduce noise in your images,  spectra or photometry you can get away with less.

I look at the statistics and use that to decide.

Regards Andrew