Durst Automatica

[johnnyrod]

I recently picked up one of these unusual cameras:
Rare, but not working by John Rodriguez, on Flickr
There is an interesting back story to the automatic exposure mechanism:
http://camerapedia.wikia.com/wiki/Durst_Automatica
which involves pneumatics. The camera itself is a 35mm scale-focus with 50mm f2.8 Durst Radionar lens. Mine arrived fairly grubby and seeming not to respond. There is precious little around on repair notes, but I had read about perished rubber tubing for the pneumatics, so opened it up to see what supplies might be required. It turned out to be a much simpler affair than I'd embarked on (notes to follow on Flickr some day), but soon after the main front plate was off, which holds the guts of it in one place:
Untitled by John Rodriguez, on Flickr
As you can see, no tubing at all. It is both simple and complex, innovative and half baked, viz...
The shutter is a Prontor an has mechanically-controlled speeds from 1 second to 1/300th. In manual mode, these work like any other, and you choose the aperture. In auto mode, the selenium meter (mine is nearly dead) controls the shutter speed, which is indicated on the top plate by a needle. You select the aperture that corresponds to the film ISO - they are not linked so if you change the aperture, you will under- or over-expose (a bit like a thyristor auto flash, if you like) - this lack of linkage is the half-baked part.
See the silver piston with the lever attached - this connects to the shutter cocking shaft (the black gear just above the lens). When the shutter is cocked, the piston is pushed up into the meter body, when the shutter is fired, it descends, and its speed is where the pneumatic control comes in.

• In manual mode the piston is uncontrolled, so the Prontor escapement measures the time.
• In auto mode (Prontor set to 1/300 i.e. as fast as possible) the air is admitted to the piston depending on the meter reading, slowing its fall and braking the shutter cocking shaft, which when fired will rotate back to its start position - this braking is the shutter speed control.

I have yet to determine how it relates to the time readings on the top plate (or to accuracy of exposure itself!), but it does work to some extent. In auto, the auto shutter is quite quiet as the main clockworks of the shutter are out of use, and the cocking shaft is rotating slower than normal - manual is pretty familiar though!
It's larger than it looks and fairly well made, plus the styling at the time is more 1970s so must have looked pretty whizzy at the time (1961 or so I think?)

 

[johnnyrod]

Minor update: there meter is actually almost fine. It read about a stop overexposed. The automatic speeds are more or less right, tending to too fast towards the top end. The manual speeds are reasonable but around half a stop or more too fast i.e. underexposing - balances out the meter, more by luck than design. I'm not sure how useful the auto mode is, as ISO100 has to be used at f11, ISO200 at f16, meaning that a lot of the time the speeds required are quite slow.

 

[Muggins]

Well, that was a new one to me - never heard of it!

Always good to see someone prepared to fix these old beasties.

Adrian

 

[Luddite Frank]

What's old is (was?) new again...

The Bausch & Lomb "Unicum" shutters from the "brass-bound" plate camera eras employed pneumatic "escapement" to control shutter speeds: depending on where speed selector was positioned, determined the stroke on the escapement piston: slower shutter speed = longer piston stroke.

Don't know how accurate they were... settings ranged from 1/100 down to 1/8 second on the couple that I have.

When they're cleaned-up, they seem to work.

This is a fascinating bit of technology... thanks for sharing !

LF

 

[johnnyrod]

Interesting, Frank! I happened across one of these a while back and read the story, then ended up picking up a bargain - some of them seem to go for a lot of money. Well, a lot for what on paper isn't the world's biggest deal. I'm not sure what is inside the pneumatic module, I presume a trap-needle arrangement as I have seen before with auto cameras with selenium cells.

I forgot to say, ISO200 equates to f16 (ISO100 to f11 etc.) so the automatic speeds tend to be quite slow as without bright sun, you would need a few stops more light than f16 and 1/200.

 

[Luddite Frank]

I have always been a little suspicious of early auto-exposure cameras... they all seem to have the automatics control the shutter speed, which can make for some dicey shooting if there's any movement / wind / camera shake.

I have a Rollei-Magic TLR that seems to still be in working order... haven't actually run any film through it yet.

I suspect your Durst system uses the Meter to vary the bleed-opening on the pneumatic, as this would probably move the least amount of machinery / require the least force to manipulate.