DSLR Imaging and Darks

[Startrek (Martin)]

For those who use DSLRs for imaging at prime focus has anyone done a comparison between using the cameras internal long exposure noise reduction and conventional dark frames
When I first started AP 3 years ago that’s how I use to image it but added double the capture time , so decided to capture conventional darks with advice from members
I would assume that the internal darks are matched more closely to the subs characteristics and therefore reduce noise and improve SNR to that of conventional dark calibration frames
I welcome and comments or advice on the above topic

[John W (John Wilkinson)]

I use the cameras internal long exposure noise reduction system all the time - works for me. I use exposures up to 90 sec. using a Canon camera. You can adjust the darkness of the pic during post processing.

[Startrek (Martin)]

Thanks for replying John
I should have (added) mentioned exposures typically from say 2 minutes to 5 minutes plus where dark current , read noise and shot noise is a real big problem for DSLR’s
At relatively short exposures noise is fairly easy to control with conventional darks, dithering and multiple exposures

[sil (Steve)]

I did compare both but found little difference but I had low hot pixels and noise so processing differences is negligible. However in preprocessing your subs you do use darks in combination with other steps so pre-dark removal on the lights using in-camera darks reduces calibration accuracy overall. plus in-camera reduction is per light frame and when you're taking hundreds of lights it adds up, whereas taking darks properly you dont take the same amount. so overall your session time captures more light. plus dont forget flats and bias too.

[leon]

Hi martin, when i was still imaging with a set up like yours I would always use the Camera noise reduction, yes it made the exposure twice as long however i found the time spent well worth it.

Leon

[CalvinKlein (Kelvin)]

I've been led to believe from expert commentators that LENR was a huge waste of time and that taking darks afterwards was the better option.

However where I can see a benefit is over a long imaging session, particularly in summer, where the temperature could drop several degrees from the start of the evening. (though to offset that the sensor temperature gradually increases to a certain point every time an image is taken)

I wonder if a better solution would be to somehow manually take a few dark frames, say every hour, and apply those darks to the previous hour's worth of light frames..

I've just bought myself a CentralDS cooled / modded Canon 6D to try to minimise the problem of dark noise.

[RyanJones]

Hi Martin,

I don’t/haven’t used in camera noise reduction but what I will say from my experience is that if you keep your sub length down slightly, at least to the point where you’re not getting amplifier noise etc and just take more subs, the noise level becomes much more manageable. If you considered the amount of extra time it would take to use in camera noise reduction and applied that to your capture tine, you’d find you’d be much less aggressive with your stretching and subsequently not amplifying the noise in post processing. I know every camera/setup/sky is different so I’m not telling you what will work but for me I found that 3min subs with a total of roughly 10hrs integration works pretty well for my images. That’s not to say my images are great or even noiseless but I will say that noise leveles aren’t concerning me in my current images. Bare in mind I use a dual NB filter so my integration time is significantly longer but I’m just using it as an example. I have taken up to 10min and more often 5 min subs with the same setup but I’ve found that the camera just doesn’t seem to like it and produces much better subs at 3mins.

I hope this helps

Cheers
Ryan

[Startrek (Martin)]

Thanks all for your comments
Appreciate it

Ryan
I started using the internal long exposure noise reduction function and the high ISO noise reduction function on my 600D when I first started AP standing next to my scope with a remote shutter hand controller 3 years ago before I learnt how to take darks. Unfortunately those images were lost when my old PC died so I have nothing to compare with today’s images taking conventional darks
Yes I agree limiting your exposure time does mitigate some of your noise but also reduces your good signal as well especially on the dimmer objects like mag 8 to 10 galaxies , so I suppose there is a juggling act between sub exposure time and number of exposures on various magnitude objects and of course your location ( I image in Sydney at Bortle 8 and at my weekender south coast NSW at Bortle 3 )
Im always guilty of pushing my DSLR to hard thinking long exposures and plenty of them will give me good data and then I can always process the noise out of the image later, but as we all know that’s just dreaming
My little home made cooling fan has helped a bit though
I might experiment this summer on one object like M42 with say a 2 , 3 and 4 minute exposure and use 3 options , internal noise reduction , conventional darks and a combination of both and see how well the noise is reduced after stacking and processing
Thanks again for your input , well received

[raymo]

Martin,If it is of any interest in light of the recent posts of some of my images that you requested, all my images were done with long exposure NR enabled,
and high ISO NR on strong. I've never used separate darks, flats etc: so can't
comment on the subject of this thread.
raymo

[Startrek (Martin)]

Raymo
Thanks for letting me know
Your images were extremely good with little or no noise evident
I’m keen to experiment this summer with the cameras internal noise reduction to see if it helps
Cheers