Long Exposure Noise Problems

I am venturing into new waters with long exposures in the 4 and 5 minute range using stacked ND filters. Problem is, the images are so noisy, that any post processing work makes them very grainy, and very un-usable. I am shooting in RAW, at ISO 100, on a Canon 7D with a 24-70L lens. Attached is a 100% crop of an area that shows the problem. Not a great image, but a learning image to get used to the exposures before I go on a trip in a couple weeks.

Any ideas on why this is happening, and what can be done about it. I am going to run a test later today to see if turning on LE NR will help at all, but since this is shot mid day, I did not know if that would have any effect.

TIA for any advice.

I've found that if you want great long exposures and do not want to be hassled by digital artefacts, then it's good to shoot BW film.

I know this might not help as your equipment is digital though, just saying...

I might assume that your canon has a long exposure noise reduction or something like that. Problem with using those is that exposures times double and your image might soften a bit.

Can you post the image to see where this crop comes from?

another thing, you might emulate grain into your digital image to mask the digital-ness of your file.

If you are thinking LE NR, that's going to double your exposure time for each shot. I would suggest you look into image averaging. If you take only 2 shots using that you won't be spending any more time than with LE NR. And it doesn't take much time at all in post.

i just got a Powershot SX260 and it has a "Handheld NightScene" setting where it takes 3 shots (rapid fire) and combines them in-camera. I think you will start to see this on more cameras and I think it is using image averaging in-camera. Someone can correct me if I'm wrong. I do know that the shots turn out pretty noise free, at least with a quick zoomed in look on the LCD.

On my site, there are some night time long exposures using the 7D with a 24LII.

Images 19, 20, 21. Click and view the "O" size: http://www.nathantpham​.com …t#!i=1703307988​&k=bvw28pG

I didn't really notice much of a noise issue. There is some, but not bothersome to me. If you don't nail exposure and end up underexposing, then you will get noisier images. I didn't even bother reducing noise in Lightroom on these images.

Bob - I think you're probably on the right track. Those cameras are probably aligning and averaging the 3 shots. That method would be less useful for long exposures, unless everything in the image is more or less still.