Do I need dark flats?

[ZiHao]

I am using a DSLR and only takes bias frames and flat frames but no darks as the temperature I believe doesn't match. I heard that if you already have bias frames or when the flats are of short exposures, you don't need dark flats. But IMO, usually dark flats aren't necessary. What do you think?

[wxsatuser]

A second or two for flats most likely ok with out darks, use a low ISO and a bright source.

[bottletopburly]

I believe if you use bias then don’t use dark flats or vice versa , It would be better to dither using a dslr if possible as that will get rid of walking noise and the need for darks .

[ollypenrice]

The situation regarding dark flats is different in the case of CCD chips and CMOS chips. A CCD camera can have its flats accurately calibrated by subtracting a master bias because this will, to all intents and purposes, be the same as a short dark exposure to match the flats exposure. WIth CMOS chips a flat dark must be shot at the same settings as the flats in question.

With regard to an uncooled DSLR camera (especially in warm Malaysia!) I really don't know what you should do. Personally I would experiment. Try making a stack of flats uncalibrated and then use the same set with dark flats and see if there is any difference in the final deep sky image when you try one then the other.

Sometimes I find dark flats necessary to avoid over-correction and sometimes I find I can't tell the difference. In theory you should certainly take them but when you have no control over chip temperature I think only experiment will find the best answer.

Olly

 

[wxsatuser]

Agree, experiment and see if there is a difference

[rickwayne]

Only way to be sure. With a DSLR, and the short exposures one would use for flats, there shouldn't be enough dark current to matter -- bias should be all you need. But reality trumps pontification any day.

[happy-kat]

With the 1100d I find dark flats do help and they are so easy to take it's no trouble

[alacant]

Hi

Only have experience of 2 DSLRs.

450d: master dark frame applied to each light frame with a proper dark optimisation algorithm is the only way to eliminate banding. Dark flat frame: no difference.

700d: dark frames of any type introduce more noise.

Bias and dither essential for both cameras.

Flat frames help with vignetting in both cases but if you have a clean sensor, try without and correct in software. 

HTH