Adding apetures to a barrel lens

[David Martin]

I picked up a couple of process lenses and am keen to try them out. One of them (Zeiss S-Tessar 300mm/f5.6) has no iris so is wide open. Focussing the room light (strip light) on my desk I can see that the circle of sharp coverage might not be quite big enough for 5x4. So I'd like to stop it down a bit. I tried cutting holes in paper and holding those over the back (there is no place for an iris inside the lens) and this seemed to improve the image. Hard to tell really as the image gets darker and holding such a large lump of glass still is not easy. I really want to get the image as sharp as possible on 5x4 without loosing too much light.

I have to add a shutter to the other (though I might be tempted to just do the hat trick on a long exposure).

Any suggestions? Preferably cheap ones.

..d

[William Mortensen]

If you don't mind cutting a slot in the barrel, you could use Waterhouse Stops. You'd be guessing at where the nodal point is, but you'd be much, much closer than putting the aperture behind the lens.

[Donald Qualls]

I'd suggest it's worth reevaluating the coverage on that S-Tessar after you get it mounted in something; it's hard to imagine a 300 mm lens of any sort, much less a Tessar derivative, not covering 4x5 (I've got a 13.5 cm Tessar from the 1920s that does it, just). The idea of Waterhouse type stops is sound, though you might want to unscrew the front or rear groups from the barrel and measure stuff to at least ensure you cut the slot between the cemented doublet group (rear group in a common Tessar, but might be front in a process version) and middle element. Anywhere in that void space should be close enough. Also, if the doublet is in front, you might find the lens performs better at distances beyond about 1:2 image size if you reverse it...

[Struan Gray]

Somewhere in the archives of the usenet group rec.photo.equipment.large-format is a post by Steve Grimes himself saying that the 300 mm f5.6 S-Tessars are impractically expensive to mount in a shutter or a barrel with an iris. That's why I didn't bid :-)

A slot for Waterhouse stops might well work. My first move would be to see if either of the lens groups will unscrew so that you can get a cardboard stop in between the elements. On some industrial optics they are glued into place, or the outer element has a metal rim rolled over it, in which case you're stuffed.

If you won the auction I think you won, the other lens was a single-coated 240 mm APO-Ronar. A similar lens has been my mainstay slightly long optic for a while now. Although I have a Sinar Copal shutter to fit behind my barrel lenses in UK weather I was always able to get by with the hat trick at f22.

[David Martin]

>If you won the auction I think you won, the other lens was a single-coated 240 mm APO-Ronar. A similar lens has been my mainstay >slightly long optic for a while now. Although I have a Sinar Copal shutter to fit behind my barrel lenses in UK weather I was always able >to get by with the hat trick at f22.

I did win that auction. Having done a bit of browsing it seems I got a good deal even if I never use the 300.

Does the 240 mount in a copal 1 shutter? I have noticed that the lens is symmetrical in that the barrel can be inverted by swapping the elements at each end. This may help with manufacturing a suitable mount for it as there is a spare (ie not used for anything) ring on the front that will fit the back..

The 300 is quite a heavy beast. I'm primarily interested n using it for astronomy so could well play with it wide open. Just have to find a suitable mounting board for it. The lens is at work right now (I brought the smaller one home with me tonight). I'll take a closer look tomorrow.

..d

[Struan Gray]

A modern 240 mm APO-Ronar comes in a Copal 1, but the cells on mine have the wrong threads and spacing. A Copal 1 has different threads front and rear, and my lens looks exactly like the one in the auction listing, so I'd guess you are out of luck.

I have seen 240 mm APO-Ronars of this vintage mounted in shutters, but they have been in Copal 2 or 3 sized shutters with adaptor rings to couple the lens cells to the shutter body. That kind of machining will be expensive compared to what you just paid, even if you can find a cheap shutter.

Front mounting ahead of a cheapie shutter, or making a shutter lenscap is probably your best bet if you don't want to spend much. Look for dumped Tektronik oscilloscope cameras: they often have an Oscillo-Paragon lens that is fairly useless in itself, but which comes in an Ilex 3 shutter that has a fair-sized opening - larger than the cells on my 240 mm APO-Ronar.

The lens is excellent - assuming yours hasn't been banged about. I use mine for infinity landscapes and close ups and it is sharp and contrasty for both. I have just replaced mine with a 240 Germinar-W, but that is because I want a lens that easily goes into a shutter, not because I am unhappy with the Ronar's performance.

The S-Tessar would probably make a good objective lens for a homemade low-magnification wide-field telescope.

[Dan Fromm]

Um, Struan, I'm not as sure as you that the 300/5.6 S-Tessar will work well at distance. I once asked Charlie Barringer about 'em. He told me that they're copy machine lenses. So they're optimized for near distances. And he told me that Zeiss used the "S-" prefix, as in S-Biogon, S-Planar, S-Distagon, S-Tessar , to indicate that the lens was special purpose. He thought the special purpose almost always involved working at near distances.

Also, about ex-Tektronix oscilloscope camera Ilex Universal #3s. I'm confident that not all are like the two I've had, but mine had no external threading at the rear. I once discussed how to put one on board with Steve Grimes. He suggested using an externally-threaded flange that screwed into the back of the shutter and clamped the board between itself and the rear of the shutter body. More expense, since standard flanges are threaded internally. I gave up on mine, sold 'em via eBay, and got a couple of ex-MP-4 Copal #1 press shutters. The MP-4 Copals are big enough for my purposes. I've even hung a 260/10 Process Nikkor in front of one to use on a 2x3 Speed Graphic.

Cheers,

[Struan Gray]

Dan, you could well be right. Other 'S' lenses I have come across have as you say been optimised for low-distortion closeups or repro work, and a Tessar, being unsymmetrical, won't preserve its corrections at other subject distances as gracefully as the plasmats and dialytes. Still, it's easy enough to hold an eyepiece (aka a CCTV lens) up behind it at see how good or bad the image is. A plywood lensboard and a sheet of film won't hurt either.

The Oscillo-paragon I have here on my desk has the mounting flange on the outside rim of the rear element. As you say, there is no external threadng on the shutter body. For skinflint use it would be perfectly possible to glue either the front or rear of the shutter to a lensboard You could also use a reversing/stepper ring with male threads on each side, but the oddball 45 mm thread for the lens cells isn't a stock item.

My preferred method would be to mount the shutter in a lenscap and just pop it onto the front of the lens when needed. You don't need to worry about alignment or good mechanical stability: just keep it light tight. I have done this with polaroid Copal 1's on longer homebrew lenses, but I suspect they will vignette the 240 mm APO-Ronar on 4x5. I can have a play at home tonight if anyone is interested.

[Ernest Purdum]

If anybody cares, a lens mounting which has neither a shutter or provisions for changing the aperture is called a "sleeve" mount. It is rather common for the elements or groups to be "spun" into place in the metal tube, so that there is no feasible way of re-mounting them. Slotting the tube for Waterhouse diaphragms would probably result in a lot of metal fragments inside the tube. As a result, sleeve mounted lenses are difficult to do anything useful for general photography with unless they have threaded cells. Even should that be the case, mounting the cells in a shutter would probably be expensive. I see sleeve mounted Clarons (not G-Clarons) on sale rather frequently and doubt if anything much can be done with them.

Regasrding the Apo-Ronar, I don't have one to take measurements from, but I would guess that it would take a larger shutter than an Ilex or Wollensak #3 to be completely free of vignetting when front-mounted. Even though an Apo-Ronar has quite a narrow angle of view, it should benefit by being mounted back in as close to the diaphragm as possible.

[Struan Gray]

I just tried my Ilex Oscillo-Paragon No. 3 shutter in front of my APO-Ronar. It vignettes wide open, but not at f22. That is with the rear of the shutter in contact with the front of the lens body (the glass is quite deeply recessed, so no danger of scratches).

On my APO-Ronar the filter thread is 48 mm, not 49: a 49 mm filter does not fit, and my Vernier caliper measures just over 47 mm across the inside surface of the threads. If you were to mount the Ilex via a male-male thread adaptor you would need a 48 mm to 45 mm step down ring, which is a custom item and probably will cost more than the lens did. (I should add that I have only measured the Ilex thread size with a caliper: it may be some oddball imperial thread).

The good news is that the projecting lip on the back of the shutter into which the rear cell screws is almost exactly the right size to have a 48 mm male thread cut onto the outside. Were it me, and were I inclined to pay for custom work, I would get a machinist to do this rather than pfaff about with adaptors. This will also help with some of the vignetting at larger apertures than f22.

On the other hand, the barrels of the APO-Ronar and the shutter are close enough in outside diameter that creative use of gaffers tape would probably do the job well enough for government work.

[David Martin]

That sounds interesting. The APO-Ronar I have looks like it has two identical elements on either side of the barrel, plus a non-lens glass panel that screws in to the front part of the lens. This is then covered by a ounting ring which screws onto the barrel.

I would glue the shutter to the ring with the clear glass using an appropriate adhesive (time to talk to a materials scientist) and keep a roll of gaffer tape for emergencies ;-)

..d

[Dan Fromm]

Struan, www.skgrimes.com gives dimensions for Ilex shutters. IIRC, the #3 is threaded 44 TPI. Not like a filter, alas.

I don't use gaffer tape, I use the black masking tape sold as darkroom tape. It leaves no residue when removed.