Originally posted by ManuH Actually the K-m has a DOF preview that you can assign to the 'help' button but it's only a digital preview, not optical. No deal breaker for me as the optical one is not that easy to see, and below f/2.8 is not working anyway.
If I understand well you're using the optical DOF preview as a live meter? Why not use the aperture ring with M lenses to achieve the same?
I think you might be misunderstanding. With M lenses, normally, the meter doesn't display at all. You can press the appropriate button (Green, AE-L, whatever) to set a shutter speed that results in a zero meter reading, but the meter does not continue to display. So you cannot then see how changes in lighting or composition affect the exposure. By doing an optical DOF preview, the meter actually displays for as long as you keep holding the switch, enabling you to see how the exposure will vary between shadows and lights, for instance. This allows me to decide if I need to adjust the suggestion given by the Green button, and to see in advance how I'll need to adjust exposure for other shots in the same setting.
Seeing the meter display is absolutely fundamental to how I use M mode, and the optical DOF preview is the only way to get this with M lenses. So a camera with no DOF preview is severely crippled for me - it limits me to the "Green button" method only. That's fine to get a quick starting point, but it's no substitute for actually seeing the meter display for as long as I want.
So I'm not actually talking about using the DOF preview to gauge DOF - I normally couldn't care less about that. I'm talking about using the DOF preview as a means of seeing the meter reading while I scan about the scene. No DOF preview, no meter reading.
Not sure what your pont is about the aperture ring. Of coruse you need to use the aperture ring to select an aperture, but that doesn't cause the meter to display - it display only while doing a DOF preview.