A few words on Equivalence and comparing systems

Started Apr 2, 2013 | Discussions thread
richarddd
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Re: The role of ISO
In reply to Great Bustard, Apr 3, 2013

Great Bustard wrote:

Dr_Jon wrote:

The only issue I have with all the equivalence talk, other than that it is the the topic that "keeps on giving" is that when I put a 70-200 f.28 lens on my FF camera my first thought isn't "Ah, the sensor is twice the area of my GH3 so I should immediately crank up the ISO two stops".

Although it is fair to say GH3 ISO is really equivalent to a bigger number than FF ISO in some ways (i.e. noise) and just reflects the smaller sensor needs more "gain" to get the exposure and so the ISO is just what makes the maths work. (People do seem to see ISO as some thing that is equivalent between systems, rather than being implemented as a fudge-factor to make exposure maths work).

First of all, please take a read of gollywop's outstanding post on exposure to see what ISO is all about:

http://www.dpreview.com/forums/post/51136862

Secondly, if "when I put a 70-200 f.28 lens on my FF camera my first thought isn't 'Ah, the sensor is twice the area of my GH3 so I should immediately crank up the ISO two stops'." then you are thinking wrong.

Instead, you should be thinking that FF will use two stops higher ISO than mFT for the same DOF and shutter speed as mFT.  But often, when there is ample light, FF will be able to shoot whatever DOF they want and use a lower shutter speed than mFT.

For example, while the FF photographer might shoot 200mm f/5.6 1/400 ISO 1600 as opposed to 100mm f/2.8 1/400 ISO 400 on mFT, they might also shoot at 200mm f/5.6 1/400 ISO 100 as opposed to 100mm f/2.8 1/1600 ISO 100 on mFT, light permitting.

In any camera, you should be setting exposure to maximize light on the sensor consistent with desired DOF and motion blur, but without clipping highlights in which you wish to preserve detail and, depending on your sensor characteristics, should be considering raising ISO to lower noise (again, without undesirable highlight clipping).

Thinking about the settings a photographer with another camera would use doesn't seem very productive.

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