Polaroid MP4 Shutter

I picked up a Tominon 75mm macro lens with a Polaroid MP4 Shutter. The shutter operation seems strange to me. It seems to cock and fire in one stroke. Is that what self cocking shutters do? The problem is if you hold the shutter release down the shutter stays open like you were using bulb. It's only when you release the shutter that the time you set starts. I'm wondering if it has a problem or if I'm operating it correctly.

Thanks
Chris

Yes, one stroke cocks the shutter and releases it. That's what self-cocking shutters do.

On B, it should open when the release lever is at the end of its stroke and close when the lever is released. At all other speeds it should fire when the release lever is at the end of its stroke.

Sounds like yours has a problem.

Cocking and firing in one stroke is indeed what self cocking shutters do, but they should also complete the shot (close) without you having to let go of the release. I would exercise it a lot, and if that doesn't work, maybe a CLA, if the cost is not prohibitive. You could only use it for relatively long exposures, since you probably can't push and release much faster than about 1/50 of a second. With large format this is not an unreasonable suggestion -- many of my shots are between 1/10 of a second and several seconds.

The whole thing only cost $30. I may try tinkering with it my self. With bellows extension I may well be using bulb anyway.

On the shutters that I own there are 2 cable release posts, one opens the shutter and aperture blades for focusing and the other one is for taking the photo. There were several brands of shutters for the MP-3/4 system, Prontor, Copal, etc. Some were marked with the f/stops and some had no f markings depending on the end use. RandyB