View Full Version : re-mounting lenses in new shutters, new apeture scales ?

20-Jan-2008, 15:33

I have just re-mounted my 355/9 G-claron in an Copal 3 shutter with a aputure scale of a lens with 5.6 as the largest F no.:confused:

OK now.. would it be approx. right to convert,
5.6 8 11 16 22 32 45 64 to
9 11 16 22 32 45 64 90 ??

and my G-Claron 240/9 remounted into a copal polaroid 4.5 and converting
4.5 5.6 8 11 16 22 32
9 11 16 22 32 45 90

And if NOT (which most probably is the case:rolleyes: ) how far off would I be??
Corrections are appriciated!!:p

Best regards

Peter K
20-Jan-2008, 15:57
Hi Morten,

when you mount a lens to a different shutter, you need a new aperture scale. The largest aperture for the 355mm lens is 39,44mm and for the 240mm lens is 26,66mm so you cannot convert the f-stops. It's easy to make new scales on cardboard. Put the lens on your camera and focus on an even illumitated surface. With a TTL-lightmeter like a Sinarsix or Profisix close the diaphragm step by step and mark the f-stops on the new scale.

Peter K

Dan Fromm
20-Jan-2008, 16:08
Peter, for some of my lenses I use a simpler procedure that doesn't rely on metering.

I put the "new" cells in the "old" shutter whose scale is wrong for them. Then I open the shutter, close the diaphragm as far as it will go, look through the lens from the front and slowly open the diaphragm until its leaves just disappear. Where the pointer points is wide open for the "new" lens. One stop down is one stop down ...

This works fairly well as long as the new shutter will open wide enough to get the lens to full aperture. This doesn't work at all if the new shutter has no aperture scale.

Peter K
20-Jan-2008, 16:32
Dan, with your procedure you will only get the geometrically f-stop, but different transmission of the lens isn't taken in consideration. In the worst case, one lens with a high transmission changes the shutter with a lens with low transmission, you get a faulty aperture scale up to more than one f-stop.

Peter K

Dan Fromm
20-Jan-2008, 17:49
But Peter, the lenses we buy have geometrical f/stops, not photometrically determined t/stops. If the OP were, say, to have SKGrimes engrave an aperture scale on the "new" shutter, it would be geometric. That's how it is done. Your objection is valid but irrelevant for most LF lenses.

Zoom lenses are another matter entirely. I remember the Angenieux 8x8B that came with my 4008ZM. F/1.9, T/3.3 wide open based on tests with film. I ran a Nikon R8 through acceptance testing, got much the same result. It had the slowest f/1.4 lens in the known universe. But, e.g., the 6-70/1.4 Schneider as fitted to the 5008S-MultiSpeed, is engraved f/1.4 and seems to t-stop 1.4 as well, based on tests with film.



Peter K
21-Jan-2008, 02:28
that's the difference between a mechanical shop and the factory: the lens isn't only screwd in a new shutter but the distances are aligned to get the best performance and the transmission is taken into account. You have mentioned the Schneider lens. It isn't so funny to use a correction factor for every lens.

To avoid this there is an ISO Norm "Photography - Apertures and related properties pertaining to photographic lenses - Designations and measurements (ISO 517:1996)"

Peter K

Dan Fromm
21-Jan-2008, 06:10
Peter, thanks for the reply and for the reference to that ISO standard. I'm sorry, but learning what the standard says isn't worth CHF 56 to me.

I can't agree with you that LF lenses' apertures are scaled in t/stops rather than f/stops. Some cine lenses, yes. Lenses for LF cameras in particular and still cameras in general, no. Please give a reference to actual practice.

I also find it hard to believe that lens manufacturers fettle lenses for best performance before shipping. This for several reasons. I've removed a fair number of lenses' cells from barrels or shutters and have never found shims, even though many posts here warn that we should take care not to lose shims, if any are present, when doing that. There are substantial variations in performance between lenses of the same make, model, and vintage (if not batch); see the Perez/Thalmann lens tests. I've seen no evidence on the cells of "touch-ups." It is possible that shutters and barrels are lightly machined -- the mechanical shop (in idiomatic US English, machine shop) you dismissed has, however, machined shutters for me to get the correct cell spacing -- but I haven't seen signs of the work.

Yes, I've seen pictures of test charts supposedly used by lens makers and by manufacturers of cine cameras. I find it hard to believe that they're used for more than pass/fail testing, especially in the case of mass produced items like S8 cameras. Again, reported variations in performance between even "elite" lenses for S8 cameras, e.g., the 6-80/1.2 Angenieux fitted to some Beaulieus, casts doubt on the manufacturers' propaganda.



Peter K
21-Jan-2008, 10:49

the Apo-Ronar made by Rodenstock is a process lens for 1:1 work, but when this lens is mounted in a leaf-shutter it is optimized for long distances. For this the distance between the cell and the diaphragm will be aligned carefuly. The same was done with one of my enlarging lenses, an Apo-Rodagon. And lenses are marked with the exact focal length. Of course not all lenses for cheap still cameras are treated in this way.

There was no particular machine shop in my mind as I mentioned that alignment of a lens isn't a marginal task.

Peter K

David Lindquist
21-Jan-2008, 10:52
I too had never encountered shims in lens shutter combinations until I unscrewed the front component of my 120mm Super Symmar HM some years ago and a very thin and fragile shim fell off. I gingerly replaced it and never unscrewed the front again. I wonder if that particular design was extra finicky about spacing to the point that final assembly involved shimming as necessary?

Information on the Schneider website about the Aspheric Super Symmar XL indicates the spacing of that design is very critical and that pains are taken to get it right, though the actual means (e.g. shimming) is not described. Quoting from the website: "The lens, which at great expense was
adjusted at the factory during its installa-
tion in the shutter, should never be un-
screwed and taken apart unnecessarily,
in order not to change the very precise
distance between the front and rear com-
ponent which must be maintained, and in
order to prevent its being screwed on
crooked if both parts are not put back
together properly.
2. If, for some reason, the shutter has to be
replaced, this must be done only at the
factory, because the tolerances which the
shutter has must be replaced by a new
precise calibration. For just as a Formula-¡
race car tuned for the highest perform-
ance responds more sensitively to “sand in
the gears” than a tractor, so does the
Super-Symmar XL Aspheric react more
sensitively to deficient adjustment in con-
nection with installation in the shutter
than a more simply constructed lens."

I carefully unscrewed the front component of my 110mm Super Symmar XL and there was no shim. Of course it could very well be that some component/shutter combinations go together "right" without shimming while others do need to be shimmed.
David Lindquist

Dan Fromm
21-Jan-2008, 13:47
And lenses are marked with the exact focal length. Of course not all lenses for cheap still cameras are treated in this way.
<snip>Peter, I'm afraid we're going to continue to disagree. Perhaps over the appropriate, um, frame of reference, perhaps over lens manufacturers' practice.

I've had a number of process lenses. Apo Ronars, G-Clarons, Apo Saphirs, Apo Nikkors, Process Nikkors, Apo Gerogons, variously badged Staeble lenses, Apotals, Apo Lustrar, RF-5. I know with certainty that the Apo Saphirs and Nikkors were shipped with quality control slips that indicated actual focal length and separation of nodes to within a few tenths of a mm. The Staeble lenses had actual focal length and nodal separation indicated on a slip of paper glued to the barrel. I expect that the others were shipped with similarly exact information to allow them to be focused precisely by tape measure or cam; that the QC slips were not with the lenses when I bought them is an accident of their history. So we agree that some lenses for specialized purposes were shipped with actual as well as nominal focal length marked on them.

I've had a number of general purpose taking lenses, some very expensive. The only ones that had measured as well as nominal focal length indicated on them were the 20 38/4.5 Biogons that I extracted from aerial cameras; these also had exact flange-to-film distance at infinity marked to allow shims for collimating them to the camera to be made. Each lens had its own little shim, thickness specifed to +/- 0.01 mm, and engraved with the lens' serial number. Oh, yes, the 38 Biogon's nominal focal length is 38.5 mm; my lenses' measured focal lengths ranged from 38.3 mm to 38.8 mm.

I think you're defending an ideal against the real. Nominal focal length isn't always actual, that's why Graflex made so many distance scales for lenses of the same nominal focal length.

David thanks for the information about your 120 SS HM. Its good to know I really haven't seen everything yet.



21-Jan-2008, 13:52
I've removed a fair number of lenses' cells from barrels or shutters and have never found shims, even though many posts here warn that we should take care not to lose shims, if any are present, when doing that.

Thanks for saying this, Dan. I've had the same observation - not once have I seen shims to "correct" lens spacing. The only shims I've ever seen were on rangefinder camera, like the Kodak Retina, where it actually makes sense from a focus perspective.

Peter K
21-Jan-2008, 14:23
I know the difference between nominal and actual focal lenght. E.g. my Rodagon 1:5,6/150mm is marked with 149,7 on the back flange and the Apo Rodagon has three shims, 2 with 0.1mm and 1 with 0,3mm. Both lenses where no special order.

Peter K

David Millard
21-Jan-2008, 14:56
Thanks for saying this, Dan. I've had the same observation - not once have I seen shims to "correct" lens spacing. The only shims I've ever seen were on rangefinder camera, like the Kodak Retina, where it actually makes sense from a focus perspective.

I recently purchased three 240mm Apo-Ronars, latest blue-ring version, that had been placed in barrel mounts for use in an optical inspection machine. Each of the three had a thin shim behind the front lens assembly, which I assumed, based on reading other forum postings here and elsewhere, were for correcting optical performance at distances nearer infinity. I placed one of these lenses in a Copal 1 shutter, and tested it (using Fuji 64T with a 69cm rollfilm back on my Technikardan) against a 240mm Fuji A at .1X at several apertures. The results between the lenses were indistinguishable to me. I realized after the fact that this test would have provided an additional comparison if it had also been performed without the shim in place, but that wasn't my goal at the time. My 90mm f/8 Nikkor also has a shim behind the front assembly, and there was an insert in the Nikon literature in the box stressing its importance.

Incidentally, I determined the aperture scale using a back that I have built that accepts a Nikon D70 and other F-mount cameras. Maximum aperture is easily found using the histogram, and 1 stop increments can be subsequently located by changing the ISO or the shutter speed on the camera. I printed an aperture scale in a single-celled table in Microsoft Word, then went to Kinkos and printed this on cardstock with the color inverted, so that it has white numerals on a black background. I applied cellophane tape to the surface for additional protection, and the result looks indistinguishable from an original aperture scale. I'll be happy to post a picture of the lens in shutter tomorrow, when I have time to take it :rolleyes:

Dan Fromm
21-Jan-2008, 15:34
To sum up part of the discussion, the position of some, not all, fairly modern lenses' cells in the shutter/barrel is tweaked by the maker by shimming. Whether this is the case for older lenses is unclear, but it certainly is possible. That said, many lenses, especially older ones, have no shims.

From which I conclude two things. When taking cells out of a shutter/barrel, one should be alert for the presence of shims but not be surprised if none are there. And broad generalizations aren't safe.

David, thank you very much for presenting more examples of lenses with shims and for giving a photometric procedure for scaling an aperture.

There's still one question on which Peter and I disagree that's wide open. Are LF lenses' aperture scales geometric (f/stops) or photometric (t/stops)? Secondary question, not asked clearly yet. With relatively modern coated lenses, does the difference between the two matter?



Ole Tjugen
21-Jan-2008, 16:07
Repro lenses may be shimmed, because optical precision is (was) vital for that kind of work. Wide-angle lenses are more sensitive to cell spacing than most other lenses, so WA lenses are more likely to be shimmed (but don't have to be).

to the best of my knowledge, LF lenses are marked in F-stops - if it were T-stops that would have been marked. With most lenses or fairly recent vintage it makes practically no difference. Even my aging and visibly yellowed Apo-Lanthar has only lost about 1/4 stop. An uncoated dialyte loses about 2/3 of a stop, and that's just about the worst case scenario in LF lenses (8 air/glass surfaces).

David Millard
22-Jan-2008, 16:26
My home-made cardstock aperture scales: