Mounting "DB" lenses in Copal shutters

[Cletus]

Does anyone know if it's possible to take a lens mounted in a Sinar DB mount and screw it directly into a Copal shutter? For instance, could one take an APO Sironar-S 240/5.6 in DB mount, unscrew the element groups and screw them right into into a Copal 3 shutter? Any special considerations for other size shutters?

I am aware there is an aperture scale correction to consider and there could be some mismatch there, but how likely is it that lens element spacing between the front and rear would be maintained in the switch? I would think the spacing would need to be the same in a DB mount as in a shutter, just because of the way the lens works optically, no?

I've never even personally seen, or held a DB mount lens, so I'm just assuming the front and rear groups can simply be unscrewed, as with a Copal mounted lens...is there any more to it than that? I keep seeng some fairly nice lenses (Sironar-S 240 for instance) selling for much less than Copal mounted in DBs and I was just thinking.....

[Richard Wasserman]

I just did this with a 210mm Apo Sironar S into a Copal 1 shutter. The DB lens elements screwed directly into the new shutter with no issues. Be sure to use any spacers that might be on the DB board and I think you'll be fine.

[Cletus]

Thanks Richard! Really encouraging to hear it worked out as easily as I hoped it would. Now to keep my eagle eyes open for a gem lens going cheap in a DB mount!

[Ken Lee]

The other trick is determining the aperture scale on the newly-shutter-mounted lens, and writing it on the side of the shutter.

For example, my 150mm f/5.6 lens fits in a Copal 0 shutter, and does my 240mm f/9 lens. One aperture scale can't work for both lenses. When I purchased each shutter-mounted lens, they came with proper aperture scales already in place.

When someone like SK Grimes mounts a lens for you into a shutter, that's one of the services they provide: engraving the aperture scale into the shutter, based precisely on the lens in question.

Conversely, when we mount a previously shutter-mounted lens on a Sinar DB lens board, there's a cam on the board which controls aperture, according to the focal length and aperture of the lens. It needs to be set precisely.

It's not "plug and play" as they say.

[Bob Salomon]

Cletus,
Both the Sinar Copal shutter and the Copal that you are screwing the groups into are both mechanical objects that have tolerances. So do lenses. It is not at all impossible that one shutter needs shims and another doesn't. Or might need thicker or thinner shimming.

All you can do is try it. But to really see you should try to compare some critical work in each shutter with the same subject, lighting, film, processing, etc. If one is better at the edges or corners or the center at f22 you have your answer.

When we have lenses that need re-shuttering we send them back to the factory so they can do it to original factory specs. Anyway else is really a guess.

[Cletus]

Ken - yep, I understand there's some further work to do once the lens is in the shutter. I figured if I managed to get that far, I'd either figure it out, or depending on how good the deal, pay SKG to do the new scale.

I was more just wondering if it was as simple as it seemed to just unscrew and screw in the elements. Thanks for your comments!

[Paul Ewins]

One thing you could do is get a digital vernier caliper and measure the overall length of the lens when mounted in the DB/DBM board and then check it again when remounted in the shutter. If it is identical (or close to) then there shouldn't be a major problem. I once tried remounting the cells from a Konica process lens into a Copal 3. The cells screwed right in but the overall length in the shutter was 4mm longer than in the barrel so I gave up.

[Richard Wasserman]

My sample is pretty small only having done this once. In my case everything was a direct fit. I tested the corners, using the maximum rise and fall on my Norma, and see no softness. I scanned the negatives on an Imacon and looked at them large. I for one am very happy, and I saved a LOT of money.

I believe that Rodenstock sells the aperture scales—B&H has them on their website as a special order item.

[Bob Salomon]

My sample is pretty small only having done this once. In my case everything was a direct fit. I tested the corners, using the maximum rise and fall on my Norma, and see no softness. I scanned the negatives on an Imacon and looked at them large. I for one am very happy, and I saved a LOT of money.

I believe that Rodenstock sells the aperture scales—B&H has them on their website as a special order item.

B&H gets the scales from us. So does any other dealer who needs scales for their customers.

[EdSawyer]

I just did this moving an apo sironar s from a DB mount into a copal 0. Worked perfectly (had to pop out the trim ring on the copal 0, thanks SK grimes for the advice!). Measured the same overall length to within the limits of my caliper (1/1000 of an inch).

[Sal Santamaura]

I just did this moving an apo sironar s from a DB mount into a copal 0. Worked perfectly (had to pop out the trim ring on the copal 0, thanks SK grimes for the advice!...So you didn't take my word for it and wanted to confirm with Adam, eh?


http://www.largeformatphotography.info/forum/showthread.php?98583-Apo-Sironar-S-DB-Question&p=978412&viewfull=1#post978412

:D:D

[EdSawyer]

hi Sal -
Sorry, never saw that reply! Yes, that was indeed the case. Thanks for the correct info too, sorry I didn't look there until just now.

-Ed

[Sal Santamaura]

...Sorry, never saw that reply!...Don't apologize! In your shoes, even if I had seen it, I'd have looked for corroboration elsewhere rather than just trust somebody posting on the Internet. Thus my two "grin" emoticons in post #11. :)

[rdenney]

Rodenstock lenses often include a shim, but I've never seen a shim with Schneider lenses. Maybe the optical design of the Rodie Sironar is a little pickier about spacing than the equivalent Symmar, even though they are both plasmats.

My assumption would be that the variation that requires such shimming would be in the optics, and not in the shutter. Yes, shutters are mechanical and have tolerances, but those tolerances will be down in the small fractions of a millimeter, and probably a good bit less than the thickness of the shim in my Rodie 210/5.6, for example. If the machining of the shutter parts is no better than that, then I'd be surprised if the shutters even worked.

I'd be surprised if the Sinar DB mounts weren't just Copal shutters stripped of the actual shutter part and leaving the internal frame and aperture. I'd bet Sinar bought them from Copal that way, sorta like how they buy the Auto-Aperture Shutter, which is made by Copal. It's also consistent with the way the Swiss have traditionally done things, using horizontal supply structures. The shape of the smooth enclosure on a DB mount does not refute that assumption, but I've never seen the insides.

Assuming that is the case, and with all due respect to Bob, the shims could probably stay with the lens cells with a low risk of harm to the performance from moving to a different shutter. The results can be confirmed with testing, which I'm sure the factory does when it remounts a lens in a new shutter.

Rick "making an educated guess, but still a guess" Denney

[EdSawyer]

Rick, good thoughts. This lens did have a single shim, and I moved it from the DB mount to the copal 0 shutter.

the DB mounts may share some parts with a shutter but they seem rather different. the aperture is spring-loaded and uses a different type of actuation for example. A nicely made mount, no doubt.

[Ken Lee]

I'd be surprised if the Sinar DB mounts weren't just Copal shutters stripped of the actual shutter part and leaving the internal frame and aperture. I'd bet Sinar bought them from Copal that way, sorta like how they buy the Auto-Aperture Shutter, which is made by Copal. It's also consistent with the way the Swiss have traditionally done things, using horizontal supply structures. The shape of the smooth enclosure on a DB mount does not refute that assumption, but I've never seen the insides.

The apertures are different: not only a different number of blades, but different shapes when partially closed. I will post a photo later if someone else doesn't.

The mechanism which changes aperture on a DB Shutter mounted lens is more like what we see with SLR cameras: a spring keeps the lens wide open, but a lever gets pulled to narrow the aperture at the right moment. This allows gradual depth-of-field preview by squeezing the cable release, either partially or fully.

Unlike shutter-mounted view camera lenses, those mounted in DB boards remain wide open until the shutter is tripped - at which point they are closed-down to the preselected aperture - and then open again.

For that reason, I like to use them in the field whenever possible, not just in the "studio". With a P or P2 at least, the camera can be operated entirely from the rear.