Hyperfocal with Leica M8

[2Bébèrt]

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Hi everybody,

 

2 weeks ago I became the proud owner of a M8. Vigorously testing my voigtlander lenses

I noticed that the hyperfocal distance had changed, due to the 1.33 lens factor.

My Ultron 28mm becomes a 37mm, a cv 15mm akts as an 20mm and so on.

The marks on the barrel of the lens are suddenly useless, as far as I can see.

Is there an easy workaround to use an acurate scale "conversion" in daily practice, not

the DOF website's or widgits u use on your computer but real-life solutions.

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[wparsonsgisnet]

Bert, I have noticed results like you show, when using my only CV lens, the 15mm. I use this with John Milich's ltm adapter and his hood.

 

I find that unless I stop down to f11 or more, my pictures show a lack of focus.

 

This is the second lens I have gotten, and it produces a satisfactory image at f11. I don't, however, think the image is as good as I expect to see from Leica glass.

 

I would expect that the 1.3 multiplier would narrow the DOF of the lens, and have been setting the focus point accordingly. As it happens, the images look terrible to me unless I go to f11.

[johnalex141r]

What I have been doing is this: move the DOF 1 stop. ie, if you are shooting at f11, set the hyperfocal distance to the f8 mark.

 

I'm still pretty new to my M8, so I'm still experimenting; there may be others out there with more skill/knowledge than I, but I *think* this works pretty well.

 

JohnS.

[jothiratnam]

Hi, changing the size of the sensor should not affect the optical properties of a lens (in effect it would be like getting a piece of 35mm film and trimming off a border around it): On the one hand, the problem may be that the digital sensor requires one to focus more accurately - in general, I have found that I have had to become more careful about focussing, and now have one of my 1.25x loupes more or less permanently mounted on my M8; On the other hand, if one is using an adapter-ring that it is not on correctly, that could also introduce focussing inaccuracies - I found this to be an issue with one of my old screw-mount lenses. Hope this helps. Jothiratnam

[luigi bertolotti]

The problem of DOF with M8 is only partially related to the crop factor... is the problem itself that on digital becomes different, for the "circle of confusion" concept, that had a specific sense on films, has to be considered differently with pixels... I don't want to go further, for I would risk to say something wrong, but navigating in the forum you can find good tech explanations on this... and I seem that also the well known Erwin Puts pages have something about the topic... in the usual Puts' style... that can be sometimes not so practical, but is always well in depth on tech issues like this.

[2Bébèrt]

The Ultron 28mm mounted on my Bessa R2M has a hyperfocal at f11

from 1,2 meters to infinity. (hyperfocal = 2,5 meter)

For the M8 (lens factor 1.33 and 'APS' sensor)

the DOF calculator says hyperfocal from 2,8 m to infinty (Hyperfocal = 5.7m)

That's some %211 further. So if I am right, you multiply your reading on the lens by 2,11

and get the 'real' hyperfocal.

[2Bébèrt]

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Luigi, I just read Erwin's page but I am not yet conviced. Just have to do some more 'field' testing to get the right feeling with this issue.

Pict taken with Color Heliar 75mm, so x 1.33 gives 99mm viewing angle.

DOF unchanged ?

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[Jamie Roberts]

Bert, I have noticed results like you show, when using my only CV lens, the 15mm. I use this with John Milich's ltm adapter and his hood.

 

I find that unless I stop down to f11 or more, my pictures show a lack of focus.

 

This is the second lens I have gotten, and it produces a satisfactory image at f11. I don't, however, think the image is as good as I expect to see from Leica glass.

 

I would expect that the 1.3 multiplier would narrow the DOF of the lens, and have been setting the focus point accordingly. As it happens, the images look terrible to me unless I go to f11.

 

Bill, something just isn't right there. First, the crop factor actually increases the effective DOF (which is one reason point and shoots with fast lenses and high crop factors don't let you isolate the subject like a digital with a smaller crop factor does). So my M8 at f4 has more effective DOF than my 5d with the same sort of FOV.

 

And on the CV 15 with the M8, you should be sharp with that lens from about 2 and a half feet to infinity by f5.6 or so, and it's almost a pinhole for all intents and purposes by f8.

 

So open it up a bit, because you're just inviting camera shake and diffraction at f11 or over anyway

 

How are you setting the hyperfocal?

[wparsonsgisnet]

Jamie, my dof calculation was as follows:

 

My 35mm becomes a 47mm (or so). That's a longer lens. A 47 has a narrower dof than a 35, other things being equal.

 

If I get you, you're saying that my 47 is really as 35 and enjoys the 35's dof.

 

Which is the operative process?

 

 

 

As to the CV15, I've tried with and without a tripod. It's definitely NOT Leica glass (not a surprise at 10% of the cost). Perhaps I don't have the screw mount tight enuf. At f11, I can get a satisfactory image. At 5.6 or 8, I don't like what I get. This may be due to the fact that the out-of-focus part of the image sucks.

 

If you look at the image above, the grass in the background, where the pieces of grass in the foreground are in focus, doesn't resemble the background images I have come to expect from Leica glass.

 

I need a wide lens. Not finding a WATE to my specifications, I bot the CV15. As soon as Leica makes a 15mm f1.4, I'm giving the CV15 away (don't all shout at once; the candidate has been chosen) or selling it. If they goof off too long, I'll go for the Zeiss.

[bradreiman]

Bill-Something must be wrong with your 15 or adapter. This lens is basically always in focus. At f5.6 and turned to infinity everything but your shoes should be in focus (and really sharp in my experience) check that thing out....B

[rosuna]

You can read this article:

 

The Luminous Landscape: Leica M8 – Another Perspective

[mwalker649]

I have heard or read on this forum that a stop down from f5.6 (6.5?) is the sweet spot for the cv15, focus a hair under the infinity mark. This gives a DOF from2.5 ft to infinity making it the ultimate point and shoot. It has worked well for me resulting in very sharp images.

[Jamie Roberts]

Jamie, my dof calculation was as follows:

My 35mm becomes a 47mm (or so). That's a longer lens. A 47 has a narrower dof than a 35, other things being equal.

 

If I get you, you're saying that my 47 is really as 35 and enjoys the 35's dof.

 

{snipped}

 

As to the CV15, I've tried with and without a tripod. It's definitely NOT Leica glass (not a surprise at 10% of the cost). Perhaps I don't have the screw mount tight enuf. At f11, I can get a satisfactory image. At 5.6 or 8, I don't like what I get. This may be due to the fact that the out-of-focus part of the image sucks.

 

 

Bill--I do believe you've got a defective CV 15 or a defective adapter. One of the two.

 

Everyone else here is right, and as I said before, the CV 15 is basically very sharp at 5.6 from a couple of feet to infinity.

 

No, it's not Leica glass, but for the money it's exceptionally good. In some cases, the CV lenses are better corrected than some of the Leica offerings And the CV 15 is a true gem: sharp and contrasty, if hard to shoot (it's hard to shoot an 18mm lens effectively, I believe).

 

As for DOF, on a cropped body you actually have more of it with every lens (not every FOV) because of the crop and it's resulting effects.

 

In other words, every lens on the M8 has more effective DOF than it does on an M7. This is one reason why the Noctilux is so sweet on the M8. Yes, you give up a little FOV, but you gain DOF with the same light gathering characteristics of an F1 lens. Since the Nocti has out of focus mojo to spare, you don't even notice it's not quite as crazy as it would be on film

 

As for the crop, yes--your 35 crops to a 47mm FOV. But it's still a 35 and looks like one of those cropped. Again, on a cropped body, it will have yards of DOF it wouldn't have on a full-frame body; film or digital.

[ho_co]

For exact calculations of depth of field (though we know there is no such thing), remember to multiply the numeric aperture by the crop factor.

 

I know that bothers many, but an article in LFI 3/2006, pp 40-47, first brought it to my attention, and the concept was later confirmed in passing in the dispute at Luminous landscape.

 

That is, an f/5.6 lens used wide open on the M8 has depth of field identical to that of a lens of aperture f/7.5 ( = 5.6 * 4 / 3 ) used on a full-frame film camera.

 

So for general purposes the suggestion above of considering the next larger aperture is a good one. But since most of us were already using that aperture for calculating with film, the instruction becomes to use the aperture one-and-a-half to two larger. In other words, if you're working at f/8, consider the depth of field to be that indicated by the engravings for f/4.

 

Despite the fact that Peter Karbe was the original source of the mentioned LFI article, "Form Follows Format," Leica erroneously claims in the M8's instruction manual that depth of field is unchanged by the crop factor.

 

 

But the flatness of the digital sensor itself has made a major change in the ability to rely on engraved depth of field scales, and specifically on use of hyperfocal distance. There was an article on this topic, also on LuLa, which I can't find again at the moment, showing a sequence of images at successively smaller apertures and clearly demonstrating that the extension of depth of field rearward in digital is not as we have come to expect as we stop down with film. (Related ideas in LFI 6/2007, in the article concerning the differences the flat sensor has made for such lenses as the 35/1.4 asph M.)

 

--HC

[t0tor0]

I also have my own share of confusion with DOF and hyperfocal distances with the M8. In fact, they seems to contradict each other!

 

the more I read, the more confuse I become

 

Haha...

 

Anyway, after a certain point, I gave up on physics. However, there are 2 points which I come to accept and it works for me.

 

1. DOF increases with 1.33 crop as compared to full-frame (traditional 35mm).

Thus, if shooting with a 35mm on M8 ( which is about 47mm) vs a 50mm on full-frame, the 50mm will have a shallower DOF and more off focus

 

2. Hyperfocal distance decreases with crop factor!

I am unable to hyperfocus my CV15 using the marked distance indicators and usually use 1 or 1.5 (estimate) stops higher than the markers.

I know it is weird but if you compare a medium format system, the hyperfocal distance is much more than that of 35mm with the same focal length. Compare a Mamiya 7 50mm vs. the Leica 50mm. The markings are clearly different. The 50mm Mamiya can hyperfocal from almost 0.5M up to infinity.

 

I guess that hyperfocal distance is only a theoretical vaue base on the "Circle of confusion" theory. Thus, larger formats will have wider hyperfocal distances as it is not enlarge as much as smaller formats.

 

On the other hand, DOF is relative (to the off focus) so it is pretty much fixed on all formats.

 

My 2 cents worth. Please feel free to comment... or further confuse:)

 

Bill: my CV15 is also not perfect for hyperfocal distances. So you are not alone.

[pazonada]

I find it hard to believe that a lens' depth of field changes with film or sensor size. Lenses specifically designed for smaller sensors would have more depth of field but this is not what we are talking about since Leica lenses are designed for full frame so to speak. I can see how one could think you get more depth of field but you are in reality just cutting away information around the edges. The image the lens is projecting is the same. Any lens focused correctly would not change the way it renders in and out of focus areas just because of what is behind it. (Except for view cameras maybe but we are talking about fixed planes at the same distance) Anyway, that seems like common sense to me?

[t0tor0]

Hi pazonada:

 

Ya. This is sure confusing. I first notice this when I notice the distance marking on my Mamiya 7 lenses after using M-Systems for a few years. Since then, I have been trying to ask myself "Why?".

 

I can see how one could think you get more depth of field but you are in reality just cutting away information around the edges

 

You are right. But then the composition will be tighter.

 

I think mostly, people are comparing images with the same composition. Which means to say that 35mm (as 47mm on M8) vs 50mm on film on a similarly composed photo (say head and shoulders only). Then the DOF is different.

 

Any lens focused correctly would not change the way it renders in and out of focus areas just because of what is behind it.

 

Yes too.

 

However, natually, there is transition from focus to off focus. And when enlarged, the difference starts becoming obvious. We may not think much but a compact digital camera has actually a much smaller size sensor compared to a 1.33 crop sensor. So the enlargement factor (to say 1200 x 800) is significant.

 

Well, like I say, I am still confused... and these are the bits and pieces that I understand.

[adan]

"As for DOF, on a cropped body you actually have more of it with every lens (not every FOV) because of the crop and it's resulting effects.

 

In other words, every lens on the M8 has more effective DOF than it does on an M7."

 

You've got it backwards, Jamie.

 

Put a 21 on both a film M and an M8 - same image at the image plane, right?

 

Now make two 10 x 15 prints from both the film and the M8 captures, using all the image.

 

You enlarged the film image 10x linearly, and the M8 image 13.33x linearly to reach those final prints - some small blur circles that still appear as sharp points in the film print will have been enlarged enough to show as blurs in the M8 print.

 

LESS DOF from the same lens on a cropped sensor using the same aperture - because final print enlargement MUST BE a part of the DOF calculations.

 

 

NOW - if you shoot a 21 on the M8 and a 28 on a film M (and perhaps a 7mm on a Digilux 2), the M8 will show more DOF than film, and the D2 will show more DOF than either. But that is because the focal length (in absolute mm) changed.

 

And if you've changed the focal length, you cannot claim the you get more DOF with "every lens" - because youv'e used different lenses. A 21 is not a 28, ever.

 

Two key points for further thought - first, there is NO SUCH THING as a (for example) "28mm field of view" - unless one specifies in the same breath the film or sensor format/size.

 

For someone inexperienced who has only used 35mm film, it may seem obvious that a 28mm lens is somehow "equivalent" to a 74-degree field of view, but that is just limited experience talking.

 

For another photographer, who has only used 6x6 film, 74 degrees = a "50mm" field of view

 

Next example - a 90 mm lens obviously projects the same image, regardless of the material behind it (air, sensor, groundglass, film). So - view three same-sized prints (print dimensions, not subject size), one shot with a 90 @ f/8 on a 4x5 (as a wide-angle), one shot with a 90 @ f/8 on a 6x9 roll film (as a normal), and one shot on a 90 @ f/8 on a 35mm camera (as a short tele) - the 35mm (smaller) format will show the most obvious blurrienss in OOF areas - due to the extra enlargement.

 

LASTLY - DOF is often calculated on a VERY conservative print size - 8 x 10 or smaller. If you are making bigger prints than that (or viewing the image huge on your screen) - the DOF calculations no longer apply: You will see blur where the DOF marks or tables say it should still look sharp.

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[ho_co]

Andy's explanations are excellent all round. My first two points are an amplification of what he said; then I'll show how his comments regarding the need for specification of format can be subsumed into a fuller use of the 'crop factor,' applying it to both aperture and focal length.

 

1) Regarding "field of view" in absolute terms: a 15mm on a 35mm camera is a super-wide, but a 15mm was the normal and only lens on a Minox (8x11 mm). Obviously, if you cut the center 8 x 11 mm segment out of a 35mm frame shot with a 15mm lens, it will be identical with the 8 x 11 mm image shot by a Minox. And if you blow up both to, say, 8x10, they will both show identical depth of field. But if you blow up a Minox shot to 8x10 and blow up a 24x36mm image from a 50mm lens ("normal" field of view in both cases), the Minox will show greater depth of field because it was made with a 15mm lens.

 

2) As you said, our depth of field markings are out of date. The DoF engravings on our lenses go back to Barnack's days. They're calculated for an enlargement of 4x6 using a far larger blur circle than we would use today, simply because lens technology is so much better.

 

But here's the interesting part:

3) Again, as Peter Karbe explained, when you start talking crop factor (which after all is exactly what we're talking about when we talk about 6x6 cm vs 24x36 mm vs 18x27 mm etc), the only way to do it fully is to multiply both the focal length and the aperture by the crop factor.

 

Crop factor is defined as the ratio of the diagonals of the two formats you are comparing. For example:

diagonal of 24 x 36 mm format = square root of (24^2 plus 36^2) = 43.27 mm

diagonal of 18 x 27 mm format = square root of (18^2 plus 27^2) = 32.45 mm

 

43.27 / 32.45 = 4/3

 

Thus, 4/3 (or 1.3333333...) is the crop factor of the M8 compared with 35mm film.

 

Now apply the crop factor to both focal length and aperture to define a lens exactly in regard to both field of view and depth of field:

50/1 becomes "equivalent to" a 67/1.3

28/2 becomes "equivalent to" a 37/2.7

12/5.6 becomes "equivalent to" a 16/7.5

 

In other words, applying the crop factor to both focal length and aperture does the same thing as specifying focal length, crop factor, and format covered.

 

Second example: 15mm lens on Minox as compared to 35mm:

diagonal of 8x11 frame is 13.6 mm, so "crop" or "magnification" factor compared to full-frame is 3.18.

 

Thus, the 15/3.5 lens of the Minox is (in depth of field and field of view) "equivalent to" a 48/11 on full frame.

 

Carrying out the comparison this way makes it immediately obvious why the Minox shows so much more depth of field than a 'normal' on 35mm: Set a 50mm lens to f/11 on a full-frame camera, and you'll have the same depth of field as you have with the Minox 15/3.5.

 

Third example: 7mm f/2 lens on Digilux 2 compared to 35mm:

diagonal of D2 frame is 11 mm, so 'crop factor' is 3.9 compared to full frame. Thus, the 7/2 lens of the D2 is "equivalent to" a 28/8 on full frame. Thus at its widest, the D2 approximates the field of view of a 28mm on full frame; and wide open at that 7mm focal length, it has the same depth of field as a 28mm lens at f/8 on full frame.

 

See the article in LFI that I mentioned above for a very strenuous proof of the idea (or the LuLa debate link for a passing nod to the relationship, as if it were well known among photographers ).

 

In my opinion, Peter Karbe deserves great credit for discovering (or at least for explaining) this relationship.

 

--HC

[lars_bergquist]

This has been a very confused debate. Most "facts" cited are plain wrong. I will not cite individual posters, for reasons of space.

 

First, cropping does neither increase nor decrease d.o.f. Saying that "a 35mm lens on the M8 is equivalent to a 50mm lens on film" refers to angle of acceptance (field) only. Cropping does not change the focal length of the lens. Magnification (print size divided by sensor size) does affect what looks sharp or not in the print. See below for the reasoning.

 

The d.o.f. tables and scales have been unchanged since the 1920's. They are based on a circle of confusion of 1/30th of a millimeter (.033mm). The choice of that measure was based on the assumption that the 24x36mm neg would be enlarged at most 3x, so that the print could compete with the then-popular contact prints from 6x9cm roll film (a.k.a. 120).

—This measure went totally obsolete already during the 1930's, as photographers started to make large prints. Leitz however did never dare change their tables and scales, seemingly fearing that stupid customers would believe that shrinking d.o.f. meant that lenses had gotten less good! Leica cameras, as we know, are used by idiots (NOTE! NOTE! Sarcasm!)

 

So very long ago, knowledgeable photographers started following the practice mentioned in this thread, setting their lenses to one stop wider on the scales, than the one actually used. I.e. aperture 8 set, read depth of field at 5.6 on the scale. This was adequate for a 5x7" print from film. The smaller sensor of the M8 means that the magnification factor (print size for print size) goes up however. So, we do need to stop down even more. To repeat, not because optical science has changed in the digital world, but simply because of increased magnification.

—For this is a fact: d.o.f. varies with two factors only: aperture and magnification. Tele lenses have less d.o.f. than wide angles, not because of the focal length per se, but because they magnify the subject more than wide lenses do. A smaller "sensor" such as 18x24mm on film, or 18x27mm in the M8, tends to decrease the d.o.f. in the print (apertures being equal) because it necessitates a higher degree of magnification (print size being equal). So, existing fuzziness is enlarged more. So, fuzziness has to be decreased.

 

Already before the switch to the M8 I read my aperture scales at TWO f-stops wider than the set aperture. I.e. if f:8 is set, read at f:4. This does effectively halve the permissible circle of confusion to 1/60th of a mm. Now this means of course that both zone focusing and hyperfocal focusing cannot in practice be used with lenses longer than 35mm. That is a fact of life. But this is all the d.o.f. in town ...

 

A permitted c.o.c. of 1/50th (.02mm) would probably have been adequate, but this cannot be conveniently read off the d.o.f. scales.

 

The old man from the Age of Box Cameras