Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

stargazine_ep28_banner.thumb.jpg.b94278254f44dd38f3f7ee896fe45525.jpg

Avocette

So are Darks a waste of time?

Recommended Posts

A new YouTube video from Peter Zelinka, who seems to make sense in his typical videos, appears to be saying that with DSLRs, Dark frames can't correct the inherent streaks and colour casts of the Lights. I'm sure his heart is in the right place (avoiding unnecessary time wasting) but is his head making the wrong conclusions?

 

Edited by Avocette

Share this post


Link to post
Share on other sites

I think ive heard others say the same thing.  Also that dithering is the way to go with DSLRs

Edited by CraigT82
  • Like 2

Share this post


Link to post
Share on other sites

I found that with a DSLR the temp would change so much that the darks would not match and therefore not help. Once I stared Dithering, I found this helped a lot more than darks. With. Cooled camera darks help a lot more as temp is constant and darks can be matched a lot easier. 

  • Like 1

Share this post


Link to post
Share on other sites

Depends also on whether you want to do accurate photometry.  If so, take a dark just before (or after) each science shot to be certain that the temperature has not changed significantly.  If the temperature is fairly constant over a significant period the darks can be taken less often.

  • Like 1

Share this post


Link to post
Share on other sites

Tony Hallas says the same thing and his DSLR images are very good indeed. Use a 12 pixel dither. Even with set point cooled CCD I'm not always convinced by darks, just convinced sometimes. Surprisingly it's with my noisy Kodak 11 meg chip, which gives darks like a snowstorm, that I find that the subtraction of a bias and the use of a bad pixel map gives the best results. It's an easy experiment to make, in any event.

Olly

  • Like 2

Share this post


Link to post
Share on other sites

Craig Stark alluded to this in a presentation about image processing (https://stark-labs.com/craig/resources/Articles-&-Reviews/RTMC_2015.pdf), page 64! He states that a BPM is 'Useful on DSLRs where pixel model doesn’t entirely hold.' 

I had assumed this was a general rule for DLSRs and always used a BPM instead of darks as it meant I only needed to take lights/flats each session.

However, I realise he might not have meant it as applying to all DSLRs...🙄

John

Share this post


Link to post
Share on other sites
3 hours ago, Jokehoba said:

he might not have meant it as applying to all DSLRs.

If you've a modern DSLR, I think darks are a waste of time. If you've an older DSLR, then dark frames maybe the only way to correct banding. We've an eos450d which falls into the latter category. We have master darks corresponding to the common light frame exposures we use. They are all taken around 20°. Using dark optimization (we use iris/siril) with the master bias subtracted dark frame applied to each of the light frames before stacking effectively removes the banding; forget about matching temperature.

Just our €0.02 'works for us' take on it:)

Cheers and clear skies.

Edited by alacant
  • Like 2

Share this post


Link to post
Share on other sites

I happen to have access to unmodified EOS 450D and EOS 600D cameras plus a recently modified EOS 550D so I’m very interested in all evidence about these models. And of course I’d love to save unnecessary time if shooting lots of darks at various ambient temperatures isn’t really helpful.

Share this post


Link to post
Share on other sites
17 hours ago, Avocette said:

unnecessary time if shooting lots of darks

Hi

We have 3 master dark frames, 3, 4 and 5 minutes for our 450d. 15 frames each. They only took around 2 hours to produce and using dark frame optimisation obviates the need for temperature matching. Simply reuse the master dark frames choosing according to exposure time rather than temperature.

If you're thinking of dark frames to reduce noise on a 450d, then I'd say use one of your other cameras. If OTOH, you want to remove streaking and banding and in so doing make a dated camera produce acceptable results, then I'd say go for it.

Cheers and HTH.

Edited by alacant
  • Thanks 1

Share this post


Link to post
Share on other sites

Here is the same 450d sequence processed with and without dark frame subtraction.

However, any modern eos with the 18Mp sensor or better, shouldn't need dark frames e.g. our 700d is completely clean; use dither instead.

Cheers and HTH

s3.thumb.jpg.9c80aed5cc70f23402824f36676b002d.jpg

 

Edited by alacant
  • Like 1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.