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M8 DOF focus barrel testing with M6 - results


ampguy

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First photo is with my M6, 2nd two photos are with M8. Both are using the same 35/1.4 pre-asph lux at f8, and both are at 1/30th. Both are on the stationary tripod (note that the M8 has tripod threads under the center, M6 has tripod mount on side).

 

Focus for the first two images is on the "Scotch" tape wording on the tape on the white comforter, 6 feet away.

 

Focus for the 3rd image, or 2nd M8 image, focus barrel was moved exactly 1 stop on the DOF markings towards wider open, further focus of about 7 ft.

 

This author found no improved benefits for the DOF barrel move, to match the DOF of the film image.

 

Conclusion? Internet Myth Busted. Leica is correct in that no lens adjustment is needed with 35mm M-mount lens on the M8, in order to equal DOF of M FF systems.

 

Images and Results are here

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That is the point - the M8 image with same lens, same distance, same aperture, sitting on same tripod as the film exposure, shows the same DOF.

 

i.e. No adjustment of DOF barrel marking is needed between FF and M8.

 

Thanks.

 

I don't see much in the way of DOF at all in that image.:confused:
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No adjustment of DOF barrel marking is needed between FF and M8.

No-one ever suggested such nonsense anyway. When you set the distance wrong then you won't get more depth-of-field but out-of-focus images. Obviously you have no clue what depth-of-field actually is. Maybe you should do your homework before you try 'busting myths' :rolleyes:

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It would be more informative if you published some images that show clear DOF transitions. And if you kept the plane of focus in the same place. As it is, I <may> see the expected DOF difference between a film shot and an M8 shot in the two first images, but it is hard to tell. The recording character of film and a sensor is significantly different as well, so the character of the DOF will be different between a film and a sensor. It would make more sense to compare M8 and M9 shots, and ones with clearly demarcated subject matter.

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Hi there,

 

I apologize for my sensationalist wording. Please allow me to explain in more detail. On this forum, and some other forums, there has been some discussion that for when using the DOF scales on Leica lens barrels, that when using these lenses on the M8, for equivalent DOF, one needs to utilize one stop closer than the lens indicates.

 

I've done the DOF math, I know what Leica's CoC targets are, and I know what Leica wrote in my M8 manual on page 82.

 

I'm well aware of DOF and CoC assumptions and calcuations. But I simply wanted to point out that in addition to the math I worked out, that the actual *printed* and viewed on my monitor images, don't pan out the statement that adjustment of DOF range necessitates adjusting *my* Leica lens barrels.

 

I hope this gives you a little more info., and if you haven't come across the statements that I have, consider yourself fortunate, and have a great weekend.

 

Thanks!

 

 

 

No-one ever suggested such nonsense anyway. When you set the distance wrong then you won't get more depth-of-field but out-of-focus images. Obviously you have no clue what depth-of-field actually is. Maybe you should do your homework before you try 'busting myths' :rolleyes:
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... there has been some discussion that for when using the DOF scales on Leica lens barrels, that when using these lenses on the M8, for equivalent DOF ...

Same DOF.

 

 

... one needs to utilize one stop closer than the lens indicates.

Right. That's no myth but a matter of fact. Still it's possible that in real life one would hardly see the difference that one f-stop is going to make in an image. In particular not if one is digital and the other is scanned film.

 

 

I simply wanted to point out that in addition to the math I worked out, that the actual *printed* and viewed on my monitor images, don't pan out the statement that adjustment of DOF range necessitates adjusting *my* Leica lens barrels.

*Your* math obviously is different from anyone else's. Anyway, you busted a myth that exists in your head only.

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i.e. No adjustment of DOF barrel marking is needed between FF and M8.

 

I'm puzzled by your conclusions. Even using film M's I found the DOF markings to be optimistic and always used at least one more 'stop' of DOF than indicated on the lens to make sure things were in acceptable focus - i.e. if shooting at f4 I'd use the f2.8 markings.

 

Maybe if you tried repeating your tests at f2-2.8 rather than f8 you may be able to see that they are indeed not that accurate.

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OP, apparently you are confusing depth of field and depth of focus. The location of the engravings does have something to do with depth of focus. But the engravings should be used to read off the depth of field. It makes no sense to focus one test at 6 ft. and the other at 7 ft.

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OP, apparently you are confusing depth of field and depth of focus.

No, he doesn't.

 

 

The location of the engravings does have something to do with depth of focus.

No, it hasn't.

 

 

It makes no sense to focus one test at 6 ft and the other at 7 ft.

That's right—no sense at all.

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Unlike others, I think the basic concept of the test is just fine. Are the DoF scale lines a good indicator of how far something can be out-of-perfect-focus (shifting the focus setting from 6 to 7 feet, if that is what the DoF scale says is "safe") and still appear sharp?

 

I thnk the test procedure has some major flaws that render it totally ineffective, however.

 

Test critique:

 

1) You haven't done the fourth "control shot" - M6 and film with focus shifted to 7 feet. It may be irrelevant, in that ISO 800 color neg film in this case is fuzzing the image so severely that one can't tell what is within the DoF or not anyway. But for completeness, we need to know how well the DoF scale works on a 24 x 36 camera in the first place, to tell if it is the same or better or worse on the M8.

 

2) In general, for any kind of resolution or focus test, it is best to use the lowest possible ISO, film or digital. Noise or grain can always disguise small sharpness differences.

 

3) The tape in both the M8 shots does not look all that sharp in either image. Are your originals jpegs (and if so, with what sharpening level set?) or RAW (and if so, with what sharpening in post-processing?)

 

3a) That could be diffraction setting in - or

 

3b) the pre-ASPH 35 'lux may have inherent focus shift, and unless you know for sure that the DoF scale is set up for the focus of the lens as displaced optically (not your own shift from 6 to 7 feet) at f/8, you may not have been actually focussed on the tape to begin with - or

 

3c) your lens individually may be slightly out of focus calibration

 

In 3b) or 3c), therefore, all you may have done is really change focus from a true 5.5 feet to a true 6.5 feet. I.E. from one side of the DoF available to the other, rather than from the center of the DoF range to the far limit.

 

A further control would be needed - shooting at f/1.4 to be sure you are actually focused on the tape with NO DoF to speak of - but if your lens has focus shift (3b) between f/1.4 and f/8 even that may not be a good crosscheck. True and accurate focus on the tape at f/1.4 may not mean that the same barrel position means true and accurate focus at f/8.

 

4) It is true that real DoF is dependent on final enlargement - what looks sharp in a 4 x 6 print may be visibly no longer actually sharp in a 40 x 60 print. You need to figure out a way to represent that key component of DoF on the Web.

 

Recommendations:

 

Repeat test

- with lower ISO and slower film to minimize any extraneous blurring that may disguise sharpness changes related to focus or DoF. Or use an M9 'sted M6 + film (but we know that's a pricey and hard-to-come-by alternative).

- with a lens guaranteed to be free of focus shift from wide-open to stopped down (recommendations, anyone? 50 f/2? 90 APO?)

- check your processing technique to be sure it is maximizing resolution

- do control shots wide-open to be sure your whole focus chain is actually in calibration

- with the full range of control shots duplicated on 24x36 (film/M9) also, if you want to show the M8 is identical to the larger format or how it differs.

- research diffraction effects for the lens to be used, to be sure you are not stopping down so far that diffraction blur is hiding any sharpness change due to your change in focus setting.

- account for the effect of enlargement on what does or does not appear sharp. On the Web, that would mean downsampling (NOT cropping) a full M9 or M6/film image to be the same pixel dimensions as the full M8 shot (3916 x 2634) - or downsampling BOTH M8 and 24x36 images to the same pxiel dimensions (e.g. 2000 x 3000 or whatever).

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Unlike others, I think the basic concept of the test is just fine.

No, it's not.

 

 

Are the DoF scale lines a good indicator of how far something can be out-of-perfect-focus (shifting the focus setting from 6 to 7 feet, if that is what the DoF scale says is "safe") and still appear sharp?

In theory, yes. In practice, no. Because when shifting the focus away from the proper setting, the image will always look less sharp at the point of reference (assuming the original focus was correct and no focus-shift problems). There is no way of telling just by visual inspection of the image whether the observed degree of blur still is within DOF limits or slightly beyond.

 

The correct way to do it is to always leave the lens properly focused and then test if the apparent DOF is the same at a) the same aperture setting, as our "myth buster" believes, or B) at approx. one stop smaller, as theory predicts. But here's a pitfall lurking: When closely inspecting magnified crops of the original images and when comparing the very same image areas (i. e. the 35-mm frame being slightly more magnified in relation to the M8 frame) then DOF naturally will be the same which will falsely seem to support the "busted myth" notion.

 

Anyway, the difference in DOF between 35-mm format and M8 format (format factor 1.33×) is pretty small to begin with. It's always said it corresponds to about one stop (which isn't much) but in fact it's 0.8 stops (which is even less). You'd be hard-pressed to tell an image taken at, say, f/8 from another taken at f/10.6 (or f/11) purely by the difference in apparent DOF—in particular when the image content is not the same (which is the case when comparing the same lens at the same distance on different cameras) or when the characteristics and degrees of noise are different (as is the case when comparing digital to scanned film). And at wider apertures, the absolute differences in DOF are even smaller.

 

So if Leica says the DOF scales don't need to be modified for the M8 then they are not too far from the truth—not because DOF would really be equal but because the difference simply is too small to have any significant impact on real life.

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Unlike others, I think the basic concept of the test is just fine. Are the DoF scale lines a good indicator of how far something can be out-of-perfect-focus (shifting the focus setting from 6 to 7 feet, if that is what the DoF scale says is "safe") and still appear sharp?

...

 

o.k., this is reasoned, but I'm not sure it's the original intent. The test was supposed to measure something which never gets measured, as in the previous test on "focus shift" by the same poster.

 

I thought there was some confusion over the DOF scale, but I'm sorry if I read too much into it.

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