How long the F3 would do an exposure on A varying between cameras and I would not use it that way, not pass the 8 sec. With such low light level the meter doesn't have enough light to make a good reading any way. Unlike the Oly the F3 is a sample and hold camera that is it would take the light measurement and use that value for the exposure. If you don't think so, with the camera on A, release the shutter with the lens cap on, open the lens cap and shine bright light thru it. The shutter won't close. But if you do this on the Olympus OM-2 the shutter would close right away.
Originally Posted by okto
I have to check the F5, although you can manually set the shutter speed to 30 minutes, I think the F5 would simply quit working on A if the light level is too low.