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A common complaint about the OM-D E-M5 BIOS version 1.5 and earlier is that “there is no exposure compensation when using Auto-ISO in Manual mode.” It took me a while to get my head around this, so I thought an explanation would help new owners. Warning – I’m going to start with the basics here, for those who need it!
First let’s look at “iAuto” mode. Here Auto-ISO is always in use, and the exposure calculation is done for us by varying aperture, shutter time and ISO according to a programmed algorithm. (We may each have our opinions of this algorithm, but that is not the subject here!) Because we have no control whatever over the exposure, this mode is probably seldom used by most FM members, but it is there if you are in a rush.
To gain some control over exposure, we go first to “P” mode. Here the exposure is also calculated for us (again let’s leave out opinions on how it is done, and whether it is done in the same way as in iAuto mode!) But now we can optionally (1) turn auto ISO on and off and/or (2) bias or “compensate” the exposure calculation up or down, using the sub (front) dial, to better suit our intentions. Remember that the algorithm is controlling all three exposure elements: aperture, shutter speed, and (optionally) ISO.
“A” mode allows us to assume control over aperture: we set aperture using the main dial and let the algorithm control shutter speed and (optionally) ISO. And the sub dial still allows us to “compensate.” The “S” mode works exactly the same way, except that the main dial controls shutter speed.
It seems reasonable to assume that if we now go to “M” mode, we should be able to set both aperture and shutter speed, and still “compensate.” But now we set aperture with the sub dial and shutter speed with the main dial – and there is no third dial to “compensate” with! Of course, that doesn’t matter, because we can simply change either shutter speed or aperture with the dials and get a new exposure.
But if we chose to also use Auto-ISO in manual mode (and remember that use of Auto-ISO in manual mode is optional, and we must enable it by setting “All” under “ISO-Auto” in custom menu E) then everything changes. Let’s call the aperture and shutter speed settings at the time Auto-ISO is turned on the “base exposure.” With Auto-ISO on, if we turn either wheel then Auto-ISO changes the ISO to maintain the base exposure! This is counter-intuitive because it is essentially the opposite of what exposure compensation does in the other three modes! To change the base exposure, you must turn off Auto-ISO, make the desired dial changes, turn Auto-ISO back on, and now the new setting is the base exposure.
Clearly, Auto-ISO is essentially useless in manual mode. If anyone has a useful work-around, PLEASE post it! Otherwise, add your voice to the outcry.
Come on, Olympus – set Auto-ISO free in manual mode!
(Thanks to FM member 1customjeweler for twisting my head and leading me to post this.)