Rodenstock 135mm, f-stop jammed

[Rich Ullsmith]

I've gently tried to manipulate the only two parts of this thing that can be manipulated: the barrel to change the f-stop, and a two-position gnurl that releases the lens from the f-stop detentes. Both are locked, with the f-stop at 5.6.

I cannot recall any untoward events that would cause this. The blades are intact and symmetrical, stuck at f5.6.

Any suggestions?

 

[Michael W]

I've seen it happen where oil between the blades gets frozen in cold weather. That mechanism had to be disassembled and cleaned.

 

[MattKing]

Is that the widest aperture on the lens?

If so, I think you have inadvertently set the function that permits you to move quickly from the working aperture to the focusing aperture, to that focusing aperture.

Pull down on the gnurl and wiggle to see if you can release it.

 

[Rich Ullsmith]

Nope. I store it in its original plastic cannister in a room with less than 60% humidity, and never below 60f. Weird. It feels like a mechanical catch, so perhaps it does have to be disassembled.

Again, the f-stop detente will not slide to release (it's a two position switch . . .one position engages the f-stop detentes, and the other allows you to select any f-stop in between) and regardless of its position, the barrel will not twist to change aperture.

I'll play with it some more before I get the screwdriver out.

 

[Rich Ullsmith]

Matt, if I had to guess, it's that gnurl that is the problem. I'll play with it again tonight. I discovered this while setting up to print, and instead of blowing a valuable printing session on troubleshooting, I just adjust the cold lamp with the intensity knob.

 

[Rich Ullsmith]

I will look at it again tonight, but I do not believe the blades are a problem. I have already applied some moderate amount of force, and am certain that the force is not being transmitted to the blades.

 

[Steve Goldstein]

Bob Salomon from HP Marketing (the Rodenstock rep) is active on the Large Format Photography Forum. You might try dropping him a PM there. His user name is "Bob Salomon - HP Marketing".

 

[Rich Ullsmith]

Bob Saloman, wilco.

 

[georg16nik]

On the Rodenstock Rodagon f/5,6 135mm, the front rim holding the group unscrew and you have the diaphragm innards accessible.
There is a plastic rim that holds the blades. Could be that your lens was dropped or the lubrication dried out.
I've had dry lubrication on my 50mm Rodagon but the 135mm I use is still kicking without maintenance.
I am talking about the “zebra” Rodagons.

 

[Rich Ullsmith]

I'm at work or I would do that right now. I really think it's something with the f-stop detente on/off, because it won't slide. Even if the blades were welded together, why would a selector switch not work? I'll take it apart tonight and report back.

 

[Newt_on_Swings]

I think some of the rodagons were push and pull on the barrel to release click stops or for smooth aperture changes. Maybe something got jammed up in that. Enlarger lenses are not too complicated to take apart. Once you open it up it should be apparent what is wrong with it. Good luck!

 

[Rich Ullsmith]

And apparently it was luck that was required. Took it out of the cannister this morning, perhaps it sensed my ill intent of disassembly, with full knowledge that most darkroom crap I take apart takes a long time to put back together and maybe this scared it straight, because it works perfectly. There is something to be learned here, just not sure what . . .

 

[John Koehrer]

Karma. Ya musta been a good boy.

 

[Rick A]

Danged dark room gremlins, that's what.