50 and 75mm framelines

[Perceval]

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Some testing suggest to me that the 50mm frame lines in my Leica M6ttl actually give the coverage of a 75mm lens (tried with a Voigtlander 75mm f2.5 Color-Heliar).  I wonder if anyone has similar experiences that can corroborate this; or otherwise?

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[BradS]

You know that the 50mm and 75mm frame lines are displayed simultaneously - right?

So, whether you mount a 50mm lens or a 75mm lens...when you look through the view finder you see the frame lines for both focal lengths at the same time.

Do you see both? Maybe your camera has the 50mm framelines masked out or something weird?

Edited October 8, 2021 by BradS

[adan]

There are a lot of moving parts to that question (in some cases literally).

But it is the case that the M framelines usually show a bit less than what will appear in the final picture. Especially using the film M framelines (e.g. M6ttl), and at longer distances.

1) Parallax leeway: Since rangefinders (except the live-view digitals) do not view through the lens, the optical viewfinder sees the world from a point up and to the left from what the lens actually sees. It is about a 5cm/2-inch error from the center of the lens to the center of the viewfinder.

This makes it possible to accidentally cut off things at the top of the picture (i.e. people's heads). The M framelines do have some parallax correction (they move down and to the right as one focuses closer.) But they do not account for an additional error.....

2) Lens extension factor: Any lens without full internal focusing increases its distance from the image plane (film or sensor) when focused closer - in video parlance, it "breathes". When the lens moves away from the film/sensor, it projects a larger image. Its effective or apparent magnification increases and crops the scene even more.

Anyone who has ever used any kind of projector (movie, video, slide) has seen this effect - move the projector away from the screen or wall, and the image projected gets bigger and bigger (sometimes running right off the edge of a fixed-sized screen). So a 50mm lens focused right down to 0.7 meters will "frame" like, perhaps, a 56mm lens.

Leica corrects for THAT by sizing the framelines for the worst-case scenario - the smaller area that will be captured at the minimum close-focus distance, approximately. Except in the digital bodies, but see next point. Since the framelines do not change size (just position) when focus changes, pictures taken at long distances will show more in the final picture than the framelines indicated.

3) Film images are usually cropped even more by mechanical devices after the fact: Whether it be slide mounts, enlarger film holders, scanner film holders or minilab machines, very few are designed to show the entire image right out to the unexposed borders. So again, in sizing the camera framelines, Leica's lines crop another 1-2% or so, to avoid nasty surprises in the lab.

4) The great viewfinder change: In 1984, with the M4-P, Leica added the framelines for 28mm and 75mm to the classic M4 lines for 35/50/90/135. Squeezing in those lines required - adjustments - to the other framelines, which made them generally a bit smaller (even more cropped) to allow adequate spacing.

It pays here to remember the mechanics of the frameline system - two sandwiched masks or stencils, with slits cut in them to pass the light that shows up as the bright framelines. One mask is the actual slits you see as the framelines. The other slides around, when mounting a lens or using the frame-selector lever, to hide two of the slit sets, so that you only see one pair at any one time (28/90, 35/135, 50/75). And of course the whole thing slides up-left/down-right for some parallax correction.

If the slits are cut too close together, the stencils can fall apart, so Leica has to "fudge" the framing accuracy a bit to maintain some minimum spacing between the slits for all six focal-lengths.

The net result of all those "margins for error" does mean the framelines will be tighter than what the lens will actually capture. The 90mm lines frame about like a "105mm lens" (16% error) in my film experience. The 50mm lines (set for 0.7m on film) may come close to the 75mm field of view at landscape distances (although I suspect it's more like a 60mm view).

On the digital Ms, with no film-reproduction effects (3) and the ability to check the images immediately for framing errors (1,2,4), Leica has standardized all framelines to be precise at 2 meters, rather than the "old, film" minimum focus distance (0.7, 0.9, 1.0 or 1.5m). Better for landscapes - but may result in less in the final picture than expected, below 2m.

Those who know video can think of the film-M framelines as the "action-safe area" at close distances and the "title-safe area" at longer distances.

Edited October 8, 2021 by adan

[Perceval]

I did mean to say that, when the 50mm and 75mm frame lines are present in the viewfinder (of my M6ttl, (0.72 finder ) then the picture area produced with a 75mm lens is better represented by the 50mm frame lines. 

One can check the coverage of the 50mm lines by comparing the same view with something like a Nikon F3,  (+50mm lens) which shows exact coverage.

Incidentally, my copy of the M4-P (serial number below 164XXXX has the frame lines covering a bigger area in the viewfinder than other M4-P's. Quite a useful feature and particularly beneficial for anyone using the 75mm frame lines.

[Jeff S]

2 hours ago, Perceval said:

I did mean to say that, when the 50mm and 75mm frame lines are present in the viewfinder (of my M6ttl, (0.72 finder ) then the picture area produced with a 75mm lens is better represented by the 50mm frame lines. 

 

If you’re shooting at distances longer than .7m (optimized frame line distance on the M6), you will get more image than the frame lines depict (closer to the 50mm frame lines), for the reasons Andy (adan) explained. At closer distances, the 75mm frame lines should more closely represent the picture captured.

This is also explained in the FAQ….

Jeff

Edited October 9, 2021 by Jeff S

[a.noctilux]

Out of topic to go in Jeff's explanation of framing 75mm at 70cm,

 

A while back, I had bad surprise with my M10 plus Apo-Summicron-M 75mm and closest 0.7m using OVF,

a non symetrical crop of my "careful framing with 75 in 50".

Now, if I have to do, my framing with OVF on M10+75 , I frame large (or check with EVF/Visoflex 020 to include everything ).