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Archive 2012 · Question about 5D III's HDR mode auto ISO behaviour in co...
  
 
MayaTlab
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p.1 #1 · p.1 #1 · Question about 5D III's HDR mode auto ISO behaviour in comparison with bracketing.


Hi,

I've noticed a difference in behaviour when using HDR or bracketing on the 5DIII when used with auto ISO and I'd like to know if there is a way to make the HDR mode works like the bracketing mode in that regard.

Here it is :

When ISO is set to auto, and let's say, for example, with a minimum shutter speed of 1/60th second, in HDR mode the camera will pick the lowest ISO it can use for the overexposed shot, and use it for all the others. The result is that both the underexposed and normally exposed shots are shot with a higher shutter speed than necessary, adding noise in the process.

If I use the regular bracketing option, the camera will adjust ISO for each shot so that the shutter speed stays as close as possible to the minimum shutter speed set in auto ISO, which optimises noise performance.

Now, I really like to use the HDR mode instead of bracketing, for three reasons : 1) even if set in silent mode, it will fire at 6 fps, lessening the chance of blurring the subject, 2) it automatically calculates the necessary bracketing, and 3) even if I don't use it, the final jpeg helps to know if the three shots are properly aligned.

But unfortunately, because I can't find a way to curb its auto ISO behaviour to work like the regular bracketing mode, I limit it to well-lit scenes.

Am I right to say that there currently is no way to change this behaviour ?



Dec 18, 2012 at 10:25 AM
3iron
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p.1 #2 · p.1 #2 · Question about 5D III's HDR mode auto ISO behaviour in comparison with bracketing.


I would think that you should use M to control the ISO when shooting HDR. If you all ISO to shift when you change apeture adjustment, the camera will adjust ISO to attempt to keep everything as it was.
To really capture as much as possible in the photo, you want to control what apeture and ISO as well as shutter speed are.
You may be getting by with auto, but you will get better results if you take control of the camera.



Dec 18, 2012 at 08:15 PM
MayaTlab
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p.1 #3 · p.1 #3 · Question about 5D III's HDR mode auto ISO behaviour in comparison with bracketing.


In fact, no, I won't get better results if I "take control of the camera". My point is that I'd like the ISO to float so that every shot in the bracketing sequence remains above the minimum shutter speed, so that for each and every shot the ISO is as low as possible, hence minimising noise.

If I were to manually select ISO, it means that I'd either have to raise it to a level that would uselessly increase noise for the underexposed and normally exposed shots in order to retain that minimum shutter speed for the overexposed shot, or set it to a more reasonable level for the normally exposed shot, which means the underexposed one would still be using a higher than necessary ISO setting, and the overexposed one a longer than desired shutter speed. This obviously is for time-critical situations (I do lock the ISO at 100 when I can use longer shutter speeds).

Now, the normal bracketing sequence on the 5DIII works just like I want it to, but for some reason the HDR mode does not follow the same behaviour.

Just an illustration, for the same hypothetical scene :

Normal bracketting, 3 ev spread, auto ISO minimum shutter speed set to 1/60th second :

Normal exposure : f2.8, 1/60th, ISO 400

Underexposed shot : f2.8, 1/60th, ISO 100

Overexposed shot : f2.8, 1/60th, ISO 3200

HDR mode, same spread, same minimum shutter speed :

Normal exposure : f2.8, 1/500th, ISO 3200 = useless noise increase.

Underexposed shot : f2.8, 1/4000th, ISO 3200 = useless noise increase.

Overexposed shot : f2.8, 1/60th, ISO 3200

Basically, it picks the necessary ISO for the overexposed shot, and keeps it for the others, for absolutely no obvious reason. The result is that the HDR mode gives me a noisier image after PP (let me re-precise that I'm working in raws here, but that I find the HDR mode to provide three very useful benefits over the normal bracketing that I'd like to use, see the first post).

I'm pretty sure there is no way to make the HDR mode behave like the normal bracketing mode, but I was wondering if somehow someone found one setting that did the trick.



Dec 18, 2012 at 08:53 PM





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