Screw to M adaptor: Follow up questions

[existrandom]

hello all,

in a previous thread some memeber talked about the machining tolerance of these adaptors

i just bought an 50mm japanese made, un-branded adaptor from a local store; i mounted a Canon LTM 50/1.8 on my M4, and the lens locked into place securely but there seems to be a bit of play;

if i turn it far clockwise (facing the camera front) then i can see the 90 framelines appear within the 50 framelines, if i turn a bit anti-clockwise, the 90 framlines disappear but a trace of its top frame appearing inside the 50 frameline;

i tried to clean the gruds in the lens mount thread and the problem is still there

does that mean the adaptor is poorly machined?
will that affect focus accuracy?

thanks for your comment in advance

lee

 

[hth]

Since it is a screw adaptor, you can always turn the lens on the thread while the adaptor is locked into the bayonet mount. But, what you describe sounds as if the whole adaptor moves since it affects the framelines, it should not do that. I think you should take it back to the store and try other adaptors.

Regarding focus accuracy...
There are manufacturing tolerances on these adaptors, but also on camera bodies and lenses too. You will never know without measuring if the tolerances takes each other out or work together to throw things too far off. (You can always measure how far it moves when you turn the locked lens, find the thread pitch and calculate how far the lens actually moves.)

On the other hand, many people just take photos and if the results are good (sharp enough compared to other lenses for example), do not bother too much. While other people have to test and test, measure and send all the stuff off for proper alignment. I am in the first group, but I think anyone should do whatever they need to do, to sleep well.

/Håkan

 

[former member]

I have the set of three Leitz adapters. None of them do this, all lock into place and bring up only the intended framelines.

 

[jlw]

There are two different key dimensions on these adapters:

-- The frameline that gets indexed is determined by a little tab inside the body mount. When you attach a lens, one of its bayonet lugs pushes this tab upward as you turn the lens into place. How far it gets pushed determines what frameline you'll see.

The locking position of the lens is determined by the locking catch in the camera body and the little matching slot machined into the back of the lens mount (or adapter.) It sounds as if you've got an adapter in which this slot was machined a bit too wide. That means that even after the catch has locked into it, there's enough slop to let you twist the lens back and forth slightly in the mount. That pushes the frameline-selecting tab up and down, causing different framelines to display.

This is annoying, but shouldn't affect focusing accuracy. What you've got to watch is that if the notch is TOO badly machined, the catch may not lock into it at all. If that happens, the lens could fall out if you twist it too vigorously!

-- The thickness of the adapter also can vary. Just yesterday at a camera show, I bought a genuine Leitz screw-to-bayonet adapter, and measured its thickness with a digital caliper -- it was 0.97mm to 0.98mm thick all the way around. On the other hand, the "Kenko" brand adapter I bought from B&H last week measured anything from 1.01mm to 1.05mm in thickness at various points around the rim. A few hundredths of a millimeter may not sound like much -- but it was enough to make sure that any lens mounted on the Kenko adapter would not line up the rangefinder at infinity! (That adapter is on its way back to B&H for an exchange.)

An odd thing about Leica-mount cameras is that this thickness difference will NOT cause inaccurate focusing, as long as you're using a 50mm lens. The reason is that the movement of the rangefinder arm is designed to follow the natural movement of a 50mm lens as it focuses in and out. That means that if your adapter is a bit too thick, it won't throw the lens and rangefinder out of sync: the rangefinder will just "think" that you've focused a bit closer, and will continue to synchronize correctly.

However, the extra thickness CAN keep the lens from reaching infinity focus, which can cause poor sharpness at long distances. The rangefinder will indicate this (as it did with my Kenko adapter above) -- if your other lenses line up OK at infinity, but the lens in the adapter does not, you know that the adapter's thickness is not accurate.

 

[Steve Hoffman]

Get a real Leitz adapter. They are on eBay all the time, constantly.

 

[jlw]

Get a real Leitz adapter. They are on eBay all the time, constantly.

Also, some photo stores have them -- I know there are several in the used department of B&H at any given time. Sometimes their prices are lower than eBay final prices!

I'd have to say, though, that some of the independent adapters are just as accurately machined as the Leitz ones. The trick is knowing which are which. I spent $15 on a digital caliper, which tells me instantly if one is made correctly. If not, it goes back to the vendor.

 

[peter_n]

Get a real Leitz adapter. They are on eBay all the time, constantly.

But they are also expensive and as jlw says above, some of the independents are good too. I have one Leitz adapter that cost $75 and I only bought it because I was desperate at the time. It does work OK. My others are either Marumi or Voigtlander, they all work OK too. The Marumis cost $30, almost 1/3 of the price of a Leitz piece.

 

[existrandom]

hello,

i think my un-branded adaptor is like what jlw described, it seems focusing OK, a test roll shall confirm this, will report when i have the film D/P later today

cheers!

lee

 

[existrandom]

hello all,

from the test roll, there seems to be no problem focusing near objects; have not tried something at infinity albeit long DOF though

i tried to file the mount's protrusion against the framline hatch, seems working better although the play of the mount is still there...

any further comment?

cheers!

lee