Ever since I moved over to Canon Digital SLR’s I have noticed that the lightmeter seems to want to underexpose my images by about 1/3rd of a stop. So I generally completely ignore the lightmeter and only shoot on the histogram presented by the camera. Because of this I have always shot about 1/3 to 2/3 of a stop overexposed (according to the information the camera gives me) If I shoot JPG, I shoot 1/3rd if RAW 2/3rd over.

Why the difference?

When I shoot RAW, I will reduce my exposure in my RAW converter to the correct exposure. This will recover my highlights and recover some Dynamic Range and Contrast for me. On a JPG setting, the camera will do the post processing and there is no option to reduce the exposure and recover the highlights, so the exposure needs to be closer to correct from the get go.

Back to the High ISO and Noise… what does this do for me?

Look at these two images. The first is the original shot as measured by the camera, shot at ISO4000, f/4 with a Canon 5DmkII and a 17-40 f/4L (RAW shots, no noise reduction)

ISO4000_f4_no-NR_metered

The next is the same image, just over exposed by about 1 stop in total

ISO4000_f4_no-NR-over-exposed

The shots are very noisy, but already you can see the overexposed shot has a much neater noise pattern.

The next two shots shows the same image adjusted in RAW for exposure. The original image needed to be lifted a bit to get the correct exposure.

ISO4000_f4_no-NR

The overexposed image needs to be reduced to get to the exact exposure.

ISO4000_f4_no-NR_exposure_reduced

Right away you can see a massive improvement in the visual noise of the image, without any direct noise reduction software influence.

Lastly I will use my RAW converter’s built in Noise Reduction features to smooth out the image as best we can. Again, the original metered and adjusted image:

ISO4000_f4_NR

To get any kind of usable image, you have to be quite heavy handed to get rid of especially the chromatic (colour) noise. However, on the overexposed image, I can use a lot less noise reduction which results in much sharper and more accurate images concerning dynamic range, contrast and overall exposure.

ISO4000_f4_NR_exposre_reduced

Now all I need to do is to reduce the physical size of the image from a 21mp to something like a 16mp or 12mp image, and I end up with a quite clean and commercially usable image.

Please note that the higher your ISO, the less DR (Dynamic Range) you have so you will have to compensate for that in post production. Also note that having a very sharp lens really helps when you have to shoot at high ISO. The higher your ISO noise levels, the less contrast and sharpness due to the lack of edge definitinion. If your image lack edge definition because your lens isn’t sharp, then the whole process becomes even more dificult!

by Sean Nel

sean_nel

 

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