Differnt types of shots?

[keef_uk]

Hello,

Can someone please put into laymens terms a breif description of what and how to create Flat, Bias, Dark & Lights frames? And what ratio they should be used

Cheers

Keith

[kookoo_gr]

Light frames are the photos you take.

Dark frames are frames of the same time duration as the light frames but are taken with the lens cap on. you have no light, you only capture black.

Bias frames are dark frames but their duration is the shortest exposure your camera can take.

Flat frames. you need to cover your lens with an evenly illuminated white light that will show imperfections of your optics like dust particles and vignetting and you must not change the focus or remove the camera. the duration of the flat frames is about 2/3 of the full well capacity of your camera (it is the number where the camera chip is saturated). their common duration is about 1 sec but the difficult task to obtain the white light. at the diy section there are a lot diy flatboxes

the number of the calibration frames except the light frames is about 15-30 frames each

[ollypenrice]

Electro uminescent panels probably provide the easiest way to create flats. If all were perfect your flats would just be even, white, featureless images but they won't be. The lens will be brighter in the middle and specs of dust near the chip will create big soft shadows. In processing your lights, any areas too bright or too dark will be adjusted on the basis of the flat which is there to identify the errors.

The point about darks is that they contain most the noise inherent in your image because they were taken in the same circumstances minus the light. Any signal they contain is false (ie noise) so you simply subtract this to correct your light frame.

Bewae of double subtracting bias. The bias signal is in the dark so don't subtract it twice.

The only reason to take bias frames is to stack them into a master bias and use this as if it were a dark frame for your flats whan you stack those into a master flat. There is no need to take any other kind of dark for your flats, the master bias is fine and makes life easier.

Olly

[keef_uk]

thanks kookoo