40mm lens and framelines

[warren_williams]

<p>I recently purchased a M2 and a 40mm Voigtlander Nokton. I am trying to decde if I am happier using the 50mm framelines or the 35mm lines. Fefore I file anything, I exparimented and have found that by not mounting the lens fully, the 35mm lines engage. The lens is about 1/16"-1/8" away from engaging the release button. Will this alter the focusing accuracy of the rangefnder or have some other adverse affect on operations. The mount is stiff enough that I don't believe it will turn while I focus or fall off by accident.</p>

[Troll]

<p>The 35mm framelines of my M6 exactly match the field of view of a 40mm Summicron at distances over 15'. I don't know how the cam follower surface of a Nokton is cut -- just see if the ragefinder is properly aligned for some distant object, if so you're in business.</p>

[james mitchell dc]

<p>When using a 40mm lens, I always found the 35 lines more comfortable on an M2. You will see a bit more than you'll get, but it's easier that a slight obstruction using the 50 lines. Bill is right. The 35 framelines of the M6 and, from my experience, the RD-1(s) is almost exact for a 40mm lens.</p>

[james mitchell dc]

<p>Also, I would always mount the lens fully, locked into place. If for no other reason, I had a 50 'cron rigid fall off an M3 once when it was not quite locked into place. There's no reason to take the chance.</p>

[Rob F.]

<p>"Also, I would always mount the lens fully, locked into place."</p>

<p>Yes, for the reason stated. While you are making up your mind, you can flick the frameline lever with you rleft hand while composing. Now for the technical analysis: 50mm - 40mm =10mm error. 10mm/50mm = 0.2, or a 20% error. 40mm - 35mm = 5mm error. 5mm/35mm = 14.3% error. 35mm frameline wins.</p>

<p>Additionally, the Leica M framelines, even on the M2, are a little undersized, so at distances longer than close up, the error is small. With an M6, MP, or M7, the frames are right on at other than close distance, exactly as Bill Mitchell said.</p>

<p>With my M2, I actually use my 35mm lenses. With my M6 & MP, I use the CV 40mm. But I would have no problem using the 40 on my M2 with the 35mm framelines. I would just "shoot tight," by imagining the picture to be a little smaller than the frameline shows.</p>

[Gus Lazzari]

<p>Warren, to answer your question about it altering <em>"the focusing accuracy of the rangefnder"</em> <strong>no</strong>, it doesn't change the cam or film plane distance.<br>

Just do it a little bit at a time and have a steady hand. Check then re-check, over & over.</p>

<p>There's a saying in construction:<strong> "Measure three times, cut once"</strong></p>

[mpo]

<p>Gus:"Warren, to answer your question about it altering 'the focusing accuracy of the rangefinder' no, it doesn't change the cam or film plane distance".<br>

You're wrong Gus, not mounting the lens fully<strong> will </strong>cause a focus error if you use the camera rangefinder. It will happen so because the camera will "read" the lens cam in the wrong spot, thus fooling the rangefinder.<br>

OTOH, as you said, the lens to film distance doesn't change, so you can always focus correctly by using the lens scale.</p>

[Rob F.]

<p>I'm sure Gus meant that filing the cam to bring up the 35mm framelines won't alter the focus. I doubt he was referring to not rotating the lens fully into place.</p>

<p>While on the subject of filing: it's important to be sure we are filing the right surface! It's the leading edge of the bayonet lug that gets filed, not the end of it. The length of the lug remains unchanged. about 1/2 millimeter off the leading edge should do it. I cut out pieces of masking tape to protect the glass and the helicoid. (making sure, of course, that the tape can't stick to the glass!)</p>

[mpo]

<p>Rob, maybe you are right, only Gus can tell, but if I read correctly, Warren makes only one question and it clearly refers to the dangers of not mounting the lens fully: <em>"The lens is about 1/16"-1/8" away from engaging the release button. Will this alter the focusing accuracy of the rangefnder or have some other adverse affect on operations? The mount is stiff enough that I don't believe it will turn while I focus or fall off by accident." </em></p>

[Gus Lazzari]

<p>Thanks Rob I did mean it that way. I was addressing the <strong>"Before I file anything"</strong> portion of Warren's question.</p>

<p>But after re-reading Warren's question, I understand how it can be taken Marcelo's way too.</p>