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View Full Version : Another thing to worry about: Bad screw/bayo adapters!


jlw
04-09-2005, 21:09
This isn't really R-D 1 specific, but I'm posting it here because there isn't a general "technical" forum...

...Even though I had thought my R-D 1's RF alignment was fine, after reading the thread about adjusting it I decided to check again and decided I should do a little more tweaking of the vertical alignment to try to get it "perfect." Reaching that gray screw was a bit scary because of the angle involved, but I did get it and was pleased to see the difference when I had the vertical bang-on rather than just "close."

Having done this, I immediately started checking all my lenses for infinity focus, using a distant but contrasty TV antenna tower, to make sure the vertical adjustment hadn't disturbed that (I know, it shouldn't, but when you're poking around with screwdrivers you never know...)

The first lens I checked was my Canon 50/1.4, and it lined up perfectly at infinity. Then I tried my 35/1.7 Ultron, and was annoyed to find that it did NOT quite reach infinity. I bought this lens new and have never messed with its innards, so I didn't see why it should be "off."

Then, on a whim, I switched the two lenses' screw-to-bayo adapters. Sure enough, now the Ultron focused to infinity and the Canon would not -- it HAD to be the adapter!

They were having a sale on them at the local Harbor Freight Tool store last week, so I had bought a digital caliper with an LCD readout switchable for inches or millimeters. I put this on mm and measured the thickness of each adapter at several points around its rim.

The "good" adapter measured 0.98 or 0.99 mm all the way around. Makes sense: I knew that the flange-to-film distance of an M body is exactly 1mm less than a screwmount body, so making the adapter slightly thinner than that would allow 0.01mm margin at both the body-to-adapter surface and the adapter-to-lens surface to allow clearance for removal.

Then I measured the "suspect" adapter. Its thickness was 0.98mm about halfway around -- but on the other half, it measured as much as 1.02 to 1.03mm thick! Obviously either it hadn't been machined perfectly flat, or had been warped slightly during the subsequent finishing... and apparently, this slight additional thickness is enough to keep the RF from reaching infinity.

Now not being able to reach infinity is annoying enough -- but going from theory (and some theorist correct me if I'm wrong) I am guessing that this extra thickness would also throw off focusing for non-50mm lenses only.

I say that because this type of rangefinder is calibrated so the follower arm moves in and out by the same distance a 50mm lens moves in and out when focused; because of this, a 50mm lens doesn't need a differential cam to compensate for its focusing. So, even if the adapter is too thick, it will move BOTH the lens and the cam out by the same amount -- so correct focus will be maintained even though the lens won't reach infinity.

But a shorter lens requires less extension to focus at a given close distance than a 50mm lens requires -- so a too-thick adapter would move the lens disproportionately vs. the RF cam, causing the lens to "front-focus" (focus on a plane closer than the one intended.)

I hadn't noticed this behavior with the Ultron, possibly because of its relatively generous DOF and/or because the disparity isn't too great.

But a lens with a shorter focal length would have a greater disparity, and of course a longer-focal-length lens would be "off" in the opposite direction (back-focus rather than front-focus) because the too-thick adapter would be providing proportionately LESS extension than indicated by the RF cam.

Sorry if that's too complicated, but the moral of the story is that non-spec screw-to-bayo adapters apparently ARE out there, and they can affect both infinity focus (of all lenses) and RF accuracy (of non-50mm lenses.)

I'm now trying to decide whether I should try to lap 0.05mm off the too-thick area of the adapter, or just say the heck with it and try my luck with a new one.

If anyone else has a metric caliper, it might be interesting to measure your adapters and report if you've got any "deviants"...

denishr
04-09-2005, 23:12
Hm, I had a generic German LTM adapter that's gone bad - I found about it when some of my shots came out focused wrong - after some fiddling, just like you did, I tracked it down to the adapter. I don't have very precise caliper like yours, but I could see that it's the adapter, since I also had trouble screwing it onto a body. I tried warping it a bit - bad idea - broke off one of the tabs...
Anyway, it's retired now, and I got a new one from Merkle Camera in Canada - which works great.
On a sidenote, anyone have any technical info about these LTM-M adapters, like the exact measures for the framelines tabs, etc...?

BTW, the Merkle adapter seems to screw on my M bodies with less effort than Voightlander one...

Denis

mtokue
04-09-2005, 23:55
Semi interesting thread over at Pnet with regards to an LTM-M adapter
Thread Here (http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=0074lT)
Recomending Bower adapters. I've just checked mine
I have one original Leitz one and a Non Branded one.
Both seem to work fine, Now to try and find my Calipers......

Mike

Sean Reid
04-10-2005, 04:26
jlw,

This is a good thing to point out. I've been using the CameraQuest adaptors and they seem fine. Who made your bad adapter?

Sean

peter_n
04-10-2005, 06:12
Semi interesting thread (http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=0074lT) over at Pnet with regards to an LTM-M adapter
Mike I remember that thread. The Bower adapters that Roger talked about are now branded as Adorama and they are made by Marumi. They are identical to the Marumis with the exception of the branding and the box. The adapter that Denis got from Merkle Camera in Canada is also a Marumi. Both Remy (RML) on this forum and I have several of these adapters and they are a quality item. Also they only cost $29.95 from Merkle.

jlw
04-10-2005, 06:36
The bad adapter was one of the generic ones from CameraQuest. I had bought a set of three: two are fine and the other is too thick (or warped; effect is the same.) My "reference" adapter, the one I had on the 50mm lens, was a Bower. I ordered it from B&H; it says "Bower" on the box, and comes with a metal "skate key" for installing/removing it.

There are physical differences in the adapters -- for example, the CameraQuest generics have chrome plating on the mounting surface that meets the camera body, while it's unplated on the Bower, and the lettering for the focal lengths are different styles -- so it seems that the different brands really do come from different OEMs.

The two "good" CameraQuest adapters measure slightly thicker than the Bower adapter (they average 1.00 mm rather than 0.98-0.99 -- the thickness of the chrome plating could account for this) but still are within the range for infinity focus.

I wish I still had a gen-yoo-wine Leitz screw-to-bayo adapter to measure as a "gold standard," but I swapped away the one I used to own. Anybody got a set of Leitz adapters AND a metric caliper?

peter_n
04-10-2005, 06:53
Does the metal "skate key" have "Mount Adapter Japan" in all capitals inscribed on one side?

jlw
04-10-2005, 07:02
Nope, mine has no markings. It does have a small hole in one 'ear,' which I would guess is so you could hang it from a cord, but there's no lettering on it. Maybe Bower uses different OEMs, too...

peter_n
04-10-2005, 07:06
It sounds like they do. That's the lettering that is on both on my Adorama and Marumi adapters. BTW although the Marumi adapters are very nicely finished, they are not chrome plated.

David Kieltyka
04-10-2005, 09:06
Hmmm, my Kobalux 21mm front-focuses on my R-D1 but this seems to be the case regardless of the adapter I use. Curiously the same lens works fine on my M2. Most of my adapters are Voigtländer branded. I imagine Cosina contracts them out but I don't know. I do have a Leitz adapter but haven't yet tried it with the 21mm. Guess I should.

-Dave-

kabkos
04-10-2005, 09:10
I measured a couple of my Leitz adapters and the measurements were 0.99mm to 1.00mm.

karl

Doug
04-10-2005, 11:20
I would tend to trust more an adaptor without chrome plating on one side, just showing brass. I think this indicates it's been finish-machined to precise thickness after plating.

kbg32
04-12-2005, 06:14
It is also a good idea to make sure that the lens is screwed snug into the adapter. When I didn't have enough adapters to go around, I always unscrewed the lens from the adapter while it was still attached to the camera. When mounting a different lens, I usually the gave the lens a "little extra" turn to make sure it is mounted flush. Tight, but not too tight.

jlw
04-17-2005, 13:13
Epilogue: Today I got a file out of the garage and worked my way around the back side of my 'bad' adapter, filing it down to a uniform 0.99mm thickness. In most cases, filing just enough to remove the chrome plating was enough. With the file I was using (fairly coarse) about five strokes with moderate pressure would remove about 0.01mm of thickness -- so don't overdo!

Now my lenses focus to infinity when using this adapter, hurray!

Notes: If you need to do the same, I suggest you use a small, fine flat or triangular file. I used a large, fairly coarse flat file because it was all I had, and it was fairly difficult to control. In addition to filing the target area (the stepped area on the inner edge of the mounting flange) I found it impossible to avoid nicking the side wall with the edge of the file, and as a result, the finished job looks somewhat scabby. Also, make sure you keep the file parallel to the flange, so you don't file a bevel into it, and check frequently with your caliper so you remove only enough material.

If you want to get serious about this, it might be safer to do it by fabricating some kind of ring-shaped tool that just matches the diameter of the stepped area, then use grinding paste to remove the material, applying the paste only in the areas that need to be reduced.