Shutter speeds

[flatulent1]

I come relatively new to the world of folders, having shot SLRs most of my life, so I have no practical experience to draw on. My Perkeo II, for example, has a Prontor-S shutter, with speeds listed as B, 1, 2, 5, 10, 25, 50, 100, and 300. Is it fair to assume that the shutter speed is actually infinitely variable between 1 second and 1/300th of a second, and the markings are there as a guide? Say, if I set the dial between 100 and 300 would I get a shutter speed reasonably close to 1/200th of a second?

Not that any of this matters, since I shoot b&w print film and attempt to process my own, but one day I'd like to load some Velvia in my 6x9 Ikonta, just for the thrill of seeing those really really big slides, fully aware that exposure latitude is a bit tighter with chromes.

 

[flatulent1]

...

<sound of crickets chirping>

 

[B&Jdude]

flatulent1: I am not familiar with the inner workings of a Prontor shutter, but the answer to your question would be found in the shape of the speed control cam.

A typical mechanical shutter has a cam of some sort that acts like a wedge to move a lever or pin which controls the length of time that the shutter is open.

Some shutters, like a dial-set Compur, have a cam with a continuously increasing radius, and as you turn the speed setting dial, the cam steadily varies the shutter speed. With such a shutter you have a continuum of speeds between fast and slow, and can set approximate intermediate speeds.

Other types of shutters have a cam that changes shutter speeds in a "stair-step" fashion . . . between each speed setting, there is a point where the cam suddenly jumps to the next speed. These types are not designed to be continuously variable between speed settings.

Maybe someone here knows which type cam is used in your Prontor.

 

[B&Jdude]

P.S. You can generally feel the step up between speeds on a shutter with the "stair-step" cam, as it will have a distinct resistance when moving the pin/lever at each "step" where the speed changes.

 

[flatulent1]

You sound as though you've had a few of these apart. I have three folders and an Argus C3; shutter speed settings on all of these feel 'stepless'. And I was wondering about the difference between the Prontur and Compur shutters, the Compur seemingly having a longer 'throw' (from the pictures I've seen) than the Prontur, and therefore more accuracy in setting speeds in between, I assume. Ah well, I should just take pictures with them and be happy.

 

[Ian Grant]

I have a few Ibsor & Prontor shutters and they seem to be variable between most of the marked shutter speeds, however not between a 1/100th & 1/300th on the Prontor-S as that appears to use a different cam to get the highest shutter speed, a "stair-step cam" as B J Dude puts it.

Ian

 

[Ian Grant]

I have a few Ibsor & Prontor shutters and they seem to be variable between most of the marked shutter speeds, however not between a 1/100th & 1/300th on the Prontor-S as that appears to use a different cam to get the highest shutter speed, a "stair-step cam" as B J Dude puts it.

Ian

 

[B&Jdude]

Many of the shutters are continuously variable on their lower speeds as they use the same spring to operate them and the cam varies the length of time that a gear train and/or "wiggler" pendulum operates. They have stronger springs which come into play when you set the higher speeds. At their fastest settings, they don't use the gears for timing, and are therefore not continuously variable between those speeds.

Some of those shutters with speeds like 1/400 or 1/500 are so tough to set on the high speed that you almost wish you had a monkey wrench handy. When setting the fastest speeds, you have to hold the shutter with your other hand to keep it from unscrewing from the retaining ring. A Supermatic comes to mind here.

 

[flatulent1]

Ooo, ouch, I know the feeling; I have one like that. I'm afraid I'm going to break it if I try to force it to its highest setting.

 

[Greg Heath]

I have a prontor s downstairs on the workbench. I will take it apart and post some pics

greg