I hope someone with some knowledge of the above can help. Reading the manual, I understand that setting the camera to automatic, whatever lens is mounted on the camera should be set to the smallest aperture on that lens and the camera will choose the shutter speed, regardless what the shutter is dialled manually. Is that correct?

There two auto modes with the OM-40 (OM-PC in the USA). You can shoot in aperture priority, program, or full manual.

Aperture Priority is when you set the aperture to whatever f-stop you want to use, and the camera then chooses the correct shutter speed to give correct exposure. The shutter speed you have set on the camera doesn't matter, since the camera sets it automatically, ignoring the manual speed ring.

Program is when the camera chooses both the aperture and shutter speed. For this, the aperture must be set to the smallest aperture the lens offers (for example f16 on the 50mm f1.8). Doesn't matter where you have the shutter speed set.

Full manual, you set aperture and shutter speed yourself.

Thanks Chris, that makes sense, but I'd used an OM1 originally 30 odd years ago. As you know it is a totally manual camera and I can't get used to an Olympus that thinks for you, though I can see the advantages in certain circumstances!

derek andrews said:

Thanks Chris, that makes sense, but I'd used an OM1 originally 30 odd years ago. As you know it is a totally manual camera and I can't get used to an Olympus that thinks for you, though I can see the advantages in certain circumstances!

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You can use the OM-40 in full manual, but its not as well implemented as on the "Pro" model OM bodies (OM-1, 2, 2sp, 3, 3Ti, 4, 4Ti). On the OM-40, the viewfinder tells you what shutter speed to set in manual after you set the aperture you want. This is crude because it only shows the speeds in one-stop increments, so accuracy is low compared to the pro bodies that have a moving needle or moving bar graph to center, which allows much finer accuracy.

You don't have to set the aperture to it's smallest, you can use a larger one if you want to (to bias it towards a higher shutter speed?). Page 48 in the manual.