Canon EOS 6D LENR useful quirks

If you're using LENR (Long Exposure Noise Reduction) on a Canon EOS 6D or 5D to shoot in-camera darks, you can shoot several lights in a row until the camera forces a dark frame that it subtracts from the previous shots. I described this in an earlier post, where I noted that you could shoot three light frames in a row before the camera would pause and create its dark frame of the same duration.

 

I just read, in Alan Dyer's iBook "How to Photograph and Process Nightscapes and Timelapses," that you can extend this to four light frames for the 6D and 5D Mark III, and five for the 5D Mark II. Oddly enough, you gain one light frame by shooting Raw + JPEG.

 

Apparently the way The EOS nD (single digit) cameras do this is by storing the frames in the buffer, then subtracting the dark from them in one batch and spitting them all out to the memory card. I can't understand how also shooting JPEGs in this process buys you one more light frame. (I would think it would be the opposite, that there'd be even less buffer memory available. But for some reason, if you shoot only JPEG, you get one fewer light frame.   ) Nonetheless, I just verified this with my 6D.

 

I have no use for the JPEGs alongside the Raws, but they take up so little space that I'll just shoot that way, and increase my percentage of exposures that are light frames from 75% to 80%.

Great info Ralph, thanks for sharing. I have not tested 7D II yet; does it work the same way? Regards

Unless you are shooting single frames on a fixed tripod for a nightscape, or going to re-sample down in resolution for a video, shooting LENR is a very bad way to shoot dark frames for long exposure deep-sky images.

 

Using the same single dark for multiple lights is even worse than using a single dark in-camera dark for single lights.

 

The dark noise associated with the thermal signal for a signle dark will then be added to each frame and it will make the overall noise much worse in the final stack.

 

If you are shooting multiple lights for deep-sky, shoot separate darks and create a good master dark for subtraction from each light frame. This introduces the least amount of calibration noise.

 

Jerry

aorion314 here, as a somewhat newbie to AP it is always appreciated when Jerry make a clear statement on the various aspects of AP. I have learned much from his books and his posted comments over the years thanks for your excellent skill set, you a highly valued member of CN IMHO. Respectfully submitted.

Edited by aorion314, 21 December 2014 - 01:27 PM.

Or, you could dither and not use any darks?

 

My last imaging session, I dithered fairly agressively as well as taking darks.  I processed the stack both with and without darks and couldn't tell the difference with or without.

 

There's no free lunch (it takes time for the mount to settle after dithering), but if your exposures are longer than your mount's settle time (or I guess 3 times your settle time for LENR), then it might make sense to dither instead of shooting darks. Then you only have to shoot lights, flats and bias.

aorion314 here, as a somewhat newbie to AP it is always appreciated when Jerry make a clear statement on the various aspects of AP. I have learned much from his books and his posted comments over the years thanks for your excellent skill set, you a highly valued member of CN IMHO. Respectfully submitted.

 

Hi aorion314,

 

Thank you very much for your very kind words, I do appreciate them!

 

Jerry

When I read this, I wrongly though it was a good idea. But as Jerry says, it is not.

 

It should have been better to Canon to shot several darks (min 5), combine them to a master dark and then substract this master dark to each light, using the sensor's temperature to align the master dark to each light's temperature.

In the winter I just shoot darks. In the summer I use lenr on the first 5-10 images everytime I turn on the camera screen and take darks at the end of the session. Dslr sensor temps are not regulated and change throughout the night. Powering up live view spikes the temps. For me this creates difficulty getting good calibration. When you have good darks you can stretch a thoroughly integrated image very deep before you start to have noise issues.