Old ICA lens question

[Dan Fromm]

OP, dagor types have symmetrical, often identical, front and rear cells that are cemented triplets. If you shine a single light on a cell (in shutter with the shutter closed or out of the shutter), if the cell is a cemented triplet you should see two bright reflections from the two air-glass interfaces and two faint reflections from the two glass-cement-glass interfaces. The faint reflections can be very hard to see.

The air spaces Steven referred to are gaps between elements. For example, the cells of plasmat type lenses (sometimes called air-spaced dagors) have an outer element that's a cemented doublet and an inner element that's a singlet. There is a gap, called air space, between the outer doublet and the inner singlet. Plasmat types will show four bright reflections from the four air-glass interfaces and one faint reflection from the one glass-cement-glass interface.

Steven, I looked in P-H Pont's handy table of diaphragm scales. If I read the table correctly, Stolze 5.4 corresponds to f/7.7. I think f/5.4 is correct. If so, the likely double anastigmat is a dialyte. OP, a dialyte cell contains two singlets, will show four bright reflections and no faint ones.

Further on the ease of confusing unlabeled Dagors and dialytes, Goerz made f/6.8 Dagors and f/6.8 dialyte type double anastigmats. The more expensive dialyte types had names, the cheapies were engraved doppel anastigmat. Year ago a very sincere but not very competent person rooked me, sold me an f/6.8 Goerz doppelanastigmat as a Dagor.

[grat]

OP, dagor types have symmetrical, often identical, front and rear cells that are cemented triplets. If you shine a single light on a cell (in shutter with the shutter closed or out of the shutter), if the cell is a cemented triplet you should see two bright reflections from the two air-glass interfaces and two faint reflections from the two glass-cement-glass interfaces. The faint reflections can be very hard to see.

I removed the front element, shone a fairly bright LED into it at an angle, and see 2 bright reflections, each with a small ghost reflection "above" it.

Rear element (Finally used some closed-cell foam and a pair of vice-grips to gently, but firmly, remove the rear element) shows the same pattern.

Also, measuring the focal length by measuring the distance from lens to film plane while focused 40 feet away comes out very close to 120mm. Side note: It appears to cover 4x5 pretty well. There may be some slight vignetting, but the lens board I was using has... "issues".

Measuring the diameter of the exposed lens gives me around 21.5mm (the calipers are accurate, it's my measuring which is questionable). That gives me f/5.6, or something very close to it. There's enough room for error it could be 5.6, or 5.4. I don't see how it could be f/6.8.

Looking at the threads, I see the threads for the front cell are much, much finer than the threads for the retaining ring-- Should a dial-set compur have .5mm thread pitch?

The air spaces Steven referred to are gaps between elements. For example, the cells of plasmat type lenses (sometimes called air-spaced dagors) have an outer element that's a cemented doublet and an inner element that's a singlet. There is a gap, called air space, between the outer doublet and the inner singlet. Plasmat types will show four bright reflections from the four air-glass interfaces and one faint reflection from the one glass-cement-glass interface.

Right.

[David Lindquist]

For the lens cells, dial-set Compurs were threaded 40 threads per inch rather than a metric pitch. The reason why Deckel did not use a metric pitch is, as far as I know, lost to antiquity. If you do the arithmetic 40 threads per inch would be a pitch of 0.635mm. The pitch of the flange/retaining ring thread is 29 1/13 threads per inch on most/all dial set Compurs. I'd really like to know who came up with that. Again if you do the arithmetic here you get a metric equivalent of 0.874mm. SK Grimes shows the flange thread on these shutters have a pitch of 0.9mm. Clearly that's close enough; their flanges fit my dial set Compurs.

David

[grat]

I looked at those, but the listings for the dial-set Compurs are all way too big for this one.

This is a tiny little shutter, with a 32-ish mm flange diameter. skgrimes has a 32.34 with a .7mm thread that we're going to try-- the thread pitch seems very close to 0.7, but I'm not an expert on measuring such small amounts, even with a pair of calipers.

The face on the shutter is only 2.25" across-- The Compurs that skgrimes list for the 0.9mm pitch thread are all 3" faces.

Otherwise, I fire up my 3D printer and see if I can make a nylon retaining ring for it.

[David Lindquist]

Maybe you can determine if it fits one of the dial-set Compur sizes here: https://www.largeformatphotography.i...+Jena+15cm+3.5

See post number 7. Unfortunately this doesn't give the face diameter but only the inside diameter of the thread for the cell mounting. I have several dial-set Compurs, they are all about 3" in diameter.

David

[grat]

Mine doesn't match any of those.

The serial number (275516) places it somewhere between 1914 (250,000) and 1920 (450,000).

In the 1919 ICA catalog, it's listed as a "Kompur" Nr. 0.

[grat]

As a follow-up, skgrimes suggested a 32.5/0.7 retaining ring usually used on compound (very small) shutters.

Turns out to be a perfect fit.

I did notice when stopping down, the iris opening takes on a teardrop shape-- is this an indicator of a problem? It seems to operate smoothly, and the shutter works well in all other ways, so I'm a little reluctant to open it.

[J. Patric Dahlen]

I did notice when stopping down, the iris opening takes on a teardrop shape-- is this an indicator of a problem?

Yes, it's a problem. The pivot pin of one of the aperture blades had become dislodged from its hole. The aperture blades in this shutter are made of treated paper and are easily damaged.

[grat]

Yes, it's a problem. The pivot pin of one of the aperture blades had become dislodged from its hole. The aperture blades in this shutter are made of treated paper and are easily damaged.

*sigh*. I was so hoping someone would say "no, it's fine!".

I'm also guessing this isn't something an amateur should try to fix-- Anyone still repairing these things, or should I look for a new shutter?

[J. Patric Dahlen]

It should be an easy fix for a repariman. It's a good idea to tell that person that this version of Compur has the delicate paper aperture blades so he doesn't try to dip the whole shutter in a liquid to clean it. Of course, some of them work with these shutters all the time, but some maybe haven't seen one in ten years and maybe the last one he worked on had metal aperture blades.


Maybe you should try the lens before spending money on it? The Maximar was ICA's top of the line in-house six element lens, so you might like it, but perhaps not.