Will LTM > M adapter upset lens register?

[Bluesman]

Hi guys -

Just for fun, I toyed around with my M2 body and some lenses, just to see how well the RF was adjusted. In the process, I noticed something not-so-funny: my lenses do not seem to focus correctly. The pictures I shot so far are OK, but none of them are real closeup + wide open stuff.

After establishing that RF settings matched the lens scale settings pretty well, I tried the frosted-tape-in-the-film-plane ploy at 1,5m distance....and this is where the "fun" starts.

None of the lenses give best focus on the film plane tape at the matching RF/scale setting!

The true distance between object and film plane is 1.5m (measured).

So:
a) The 35mm/2.5 Voigtländer is almost 50cm off (sharp in film plane when scale on 1m!),

b) the 90/3.5 VL is about 10-15cm off (sharp with scale on 1,35m) and

c) the Jupiter 12 is also off by a huge 40cm (sharp at 1,1m on scale).

I also tried getting an old junker Jupiter 8 to a) match the scale to the RF and b) be sharp at the correct setting. I almost nailed it (the scale is about 2mm off, compared to the RF, but I have good focus on the tape.), but it required adding about 1mm of paper shims to the J8. (Is this normal?)

This led me to think that maybe the LTM-M adapters I use upset the lens register. After all, the adapter builds a mm or so on the distance between film and back of lens. Could this be true, or do I have a totally misaligned M2 body or RF or am I just doing something wrong here??

I don´t have a M bayonet lens, just LTM + adapters, so I can´t verify it the other way around. I have a LTM body, but it´s a bottom loaded Zorki..

Any comments? I hate not being able to shoot wide open and close up.

Edit: I also have a Bessa R2A, but that one is loaded and busy elsewhere at the time, no chance to test the same on it just now.

Cheers /Richard, Sweden

 

[ferider]

If the RF for all lenses aligns well at infinity, and the focus scale on
the CV lenses (not the Jupiters) matches real distance measured with
a tape measure at 1m or so, you most likely are doing a mistake with
the frosted tape in the focal plane check. If the tape is only a little
bit off the focal plane, you will see exactly the errors you are
describing.

Best is to take actual glass or plexi glass and put it on the film rails to make
sure it is flat and parallel to the rails. I usually use an old Olympus
matte focusing screen. Nothing beats a test film instead, of course.

With the Jupiters at close up it's another story. Because most likely
they are calibrated towards the Contax standard, the focusing
scale will be off at close distance. Still, with the J12 and even the J8
you will get sharp pictures because the DOF covers the focusing
error.

Normal quality adapters (like CV, Leitz and Marumi) might cause
very small difference in registry noticable with very long throw lenses
only, but not with the lenses you are looking at though.

Best,

Roland.

 

[jlw]

An LTM>M adapter definitely will affect focusing accuracy of non-50mm lenses at all distances, if the adapter is of the wrong thickness. And surprisingly often, this is the case!

We've had several longish threads about this on the R-D 1 forum (I suspect the issue showed up there first because it's so easy to do quick test shots with the R-D 1.)

My own experience has been that the genuine, no-longer-in-production, Leica-brand adapters are never "off." But more than half of the other adapters I've bought have been too thick -- some only a few hundredths of a mm, others by a more significant amount.

The ones that are only slightly off, I've thinned down with abrasive paper and continued to use. The ones that were drastically too thick had to be retired.


Now, why did I say that an out-of-tolerance adapter will affect focusing accuracy only on non-50mm lenses? It's because your camera's rangefinder is set up for the focusing movements of a 50mm lens. If you have a 50 on the adapter and the adapter positions the lens slightly too far from the camera, the rangefinder simply will interpret this as the lens being focused a bit closer and still will couple correctly. (This does mean the lens won't focus all the way to infinity, but there's enough DOF at infinity that you might not notice.)

But non-50mm lenses require different amounts of extension: wider lenses require less and longer lenses require more. As you've probably noticed, these lenses require a cam mechanism to "translate" the movements of their focus couplers to match the movements of a 50mm lens. So for example, if you've got a wide-angle lens on the adapter, and the adapter is too thick, the extra thickness changes the lens' focusing point by much more than it would a 50mm lens... while the rangefinder coupler applies only a 50mm lens' worth of "translation." The result is that your true focusing point is closer than the rangefinder indicates.

If you've got a micrometer, you can quickly determine whether or not your adapters are OK. The thickness between the front and rear mounting surfaces should be 0.98 - 0.99 mm. (The nominal differences between body flange thickness for a screwmount and M mount camera is supposedly exactly 1.00mm, but apparently Leitz left an 0.01-0.02mm tolerance on its adapters to provide a bit of clearance for easier mounting and dismounting.)

If you don't have a micrometer, one way to test whether or not this is the source of your problems is to buy or borrow a genuine Leitz adapter, and repeat the tests you've done. When shopping for Leitz adapters, though, beware of fakes! I've seen a few suspicious ones lately appearing on eBay. Genuine ones will say "Leica" and "E. Leitz Wetzlar" in nicely engraved styled letters; I've seen ones that simply are engraved "LEICA" in plain block letters, and I suspect these are not genuine. (Considering the price difference between Leica and non-Leica adapters, you can see why a disreputable machinist might be tempted to boost the price of his adapter by engraving these five letters on it!)

There could be other issues causing this type of problem as well (such as the rangefinder on your M2 being miscalibrated) but if you are using adapters on all your lenses, this is certainly the first thing to check! Good luck...

 

[ferider]

Jlw,

you know we share the adapter experience, we talked about this before.

But no way a normal adapter will cause 50cm fault at 1m focus for a (new) 35mm lens !

Roland.

 

[Bluesman]

Thanks for the replies & tips, folks -

hmm...I admit I am not using glass for the film plane, just what I thought was well-stretched frosted tape. Could the difference be that drastic, really? The adapters are 2 x CV, 1 x Leitz original, BTW.

<<red-faced..looking up some clear & stiff plastic to use with the tape...

/R

 

[ferider]

I am really puzzled about your 35/2.5 observation.

I were you, I would run a test film and be done with it.

Best,

Roland.

 

[artur5]

Jlw,

you know we share the adapter experience, we talked about this before.

But no way a normal adapter will cause 50cm fault at 1m focus for a (new) 35mm lens !

Roland.

Yes, I don't believe it either. Misfocusing from 1,5 to 1 mtr. with a 35mm lens implies that the adapter should be only 0.63mm. thick.
Much more likely the culprit is the frosted tape -not flat enough and/or out of the exact focal plane.

 

[Bluesman]

So here we go again - the film plane now being a strip of clear stiff plastic (from a CD box), things look a lot better, and I look a lot more stupid. Everything checks out better now - thanks for your concern/tips/replies 🙂

Cheers from Sweden /Richard, noob