75 Summilux Quandary

[NB23]

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Well, although a different look, both depth of field are the same. Depth is same. Physics.

 

I've tried multiple copies of the 75 Summilux on the M9. A definite pattern emerges that those upgraded with six-bit coding also had more consistent focusing. No doubt simply that Leica bench-tests the adjustment after replacing the lens mount.

____________________

 

As to 75mm (and other) DoF - physics is all very well in an ideal world. In the real world, there are significant other factors. Below are two crops from shots I made when transitioning from the 75 f/1.4 to the 75 f/2 recently (weight issue, not imaging).

 

Just for grins.

 

Due to the effects of spherical aberrations ("Leica Glow"), the Summilux (left or top, stronger color fringing) actually has more practical DoF (wider "field" of legible lettering and numbers) than the Summicron-APO. At a wider aperture (1.4 vs. 2.0) and identical focus distance/magnification.

 

There is a huge difference in "drawing," which effects DoF.

 

Especially when comparing older lens designs and newer ones, I'd strongly recommend actual experience with the lenses in question. An ounce of experimental evidence is worth a gigatonne of theory.

[lct]

[...] Due to the effects of spherical aberrations ("Leica Glow"), the Summilux (left or top, stronger color fringing) actually has more practical DoF (wider "field" of legible lettering and numbers) than the Summicron-APO. At a wider aperture (1.4 vs. 2.0) and identical focus distance/magnification. [...]

 

Not sure to understand what you mean sorry. Were you comparing an f/1.4 to an f/2 shot?

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[pico]

Due to the effects of spherical aberrations ("Leica Glow"), the Summilux (left or top, stronger color fringing) actually has more practical DoF (wider "field" of legible lettering and numbers) than the Summicron-APO. At a wider aperture (1.4 vs. 2.0) and identical focus distance/magnification.

 

Horrors! Would you reject a picture because it showed color fringing?

.

[jdlaing]

Horrors! Would you reject a picture because it showed color fringing?

.

Maybe.

[Jeff S]

You may find it clear but I don't.

 

And that's exactly why Leica asks folks (like you) to send in everything....to avoid any misunderstandings and to allow them to separately*

(as I noted) check everything.

 

* Separate......(Thesauraus)....unconnected, unrelated, different, distinct, discrete....

 

Jeff

[pgk]

Well, although a different look, both depth of field are the same. Depth is same. Physics.

 

 

Its all about 'appearance' (look). 'Appearance' is actually what photographic images are all about, so depth of field can vary (minutely) from lens to lens even at the same focal length as Adan illustrates. And the physics depends on definitions such as the size of the circle of confusion. A lens which spreads the image through a larger depth of focus due to its inability to concentrate all wavelength images together (i.e. a non-app lens) can appear to give greater depth of field (than a 'better corrected' - i.e. Apo Lens) if the circle of confusion is covered so that the apparently greater depth of field appears 'sharp' to the viewer. Depth of field is not due to physics, its down to how we define it and this is in itself a variable.

 

All that said, we ARE talking nuances here - and THAT said, nuances can have an effect of the overall image sometimes.

 

FWIW. As it happens I have just had an image taken on my 75 Summilux, wide open, printed. Shot into the sun with the sun in frame, the subject of the image lacks the biting crispness that the Summicron exhibits at f/2, but has all the detail well shown nevertheless, but with a very slight 'mellowness' to it. The effect is exactly as desired and depth of field whilst shallow has surprised me on the 15" x 10" print. Obviously I can't post the print here and any jpegs are subject to interpretation so you will just have to accept that the image is as I state.

[lct]

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You've lost me here folks. Are you really comparing DoF/OoF of the 75/1.4 at f/1.4 vs 75/2 at f/2?

[adan]

lct - yes.

 

The proposition was made that DoF is purely a function of "physics", and not the lens in use. "All lenses will show the same DoF at the same aperture", according to that proposition.

 

An unstated proposition - but if you disagree with it, say so - is that DoF at f/1.4 is always narrower than DoF at f/2, for a given focal length and focus distance.

 

The images I posted show that, while this is theoretically correct, it is not always borne out by practical experience with real-world (and thus not "ideal") lenses.

 

The Summilux design @ f/1.4 already produces a wider range of apparent sharpness (and DoF is exactly and precisely "that which appears sharp") than the 75mm f/2 APO does at f/2. Unless it would show less DoF if stopped down to f/2 (thus violating proposition 2), it is an effective comparison.

 

And - BTW - comports very well with one of Peter Karbe's stated goals for the 75 ASMA - a more rapid fall-off in sharpness on either side of the plane of focus, compared to the Summilux.

 

My images of a subject are simply a demonstration and confirmation of the effects of spherical aberration, as diagrammed in the two technical illustrations linked below. SA "smears out" the depth of "pretty good focus" over a range of distances, rather than a single plane of focus. Thereby affecting DoF in ways contrary to what theory says about an "ideal" perfect lens that has no SA.

 

http://www.olympusmicro.com/primer/images/aberrations/sphericalfig1.jpg

 

https://upload.wikimedia.org/wikipedia/commons/1/10/Spherical-aberration-slice.jpg

 

@ NB23. I won't repeat what pgk already said. I simply point out that what appears sharp enough to be legible and readable covers a deeper "field" with the 75 Summilux @ f/1.4 than with the 75 ASMA @ f/2

 

Readable in the 75 Summilux image: "...ICA APO-SUMMICRON-M" and "....z eloxiert/black anodized finish/a....." and "1:2/75mm ASPH."

 

Readable in the 75 ASMA image: "...PO-SUMMICRON-M" and "...anodized finish/a..." and "...2/75mm ASPH."

 

The 75 ASMA's correction for SA truncates the range of distances over which the lettering is sharp enough to read - i.e. it truncates the DoF (that which appears sharp). Even at a smaller aperture.

[lct]

Hi Andy we all know that bokeh does not look the same out of some lenses (say Zeiss vs Leica) at the same focal length and aperture but knowing you a bit i would have expected to see a difference, if any, between the 75/1.4 and the 75/2 at the same aperture. Comparing different apertures sounds like comparing apples to oranges to me and makes me suspect that there is in fact zero difference between the two lenses at the same aperture. I may be wrong of course but i don't own a 75/1.4 so i cannot do that simple comparo myself. 

Edited September 17, 2016 by lct

[otto.f]

Very interesting Andy, thanks!

Edited September 17, 2016 by otto.f

[ZHNL]

lct - yes.

 

The proposition was made that DoF is purely a function of "physics", and not the lens in use. "All lenses will show the same DoF at the same aperture", according to that proposition.

 

An unstated proposition - but if you disagree with it, say so - is that DoF at f/1.4 is always narrower than DoF at f/2, for a given focal length and focus distance.

 

The images I posted show that, while this is theoretically correct, it is not always borne out by practical experience with real-world (and thus not "ideal") lenses.

 

The Summilux design @ f/1.4 already produces a wider range of apparent sharpness (and DoF is exactly and precisely "that which appears sharp") than the 75mm f/2 APO does at f/2. Unless it would show less DoF if stopped down to f/2 (thus violating proposition 2), it is an effective comparison.

 

And - BTW - comports very well with one of Peter Karbe's stated goals for the 75 ASMA - a more rapid fall-off in sharpness on either side of the plane of focus, compared to the Summilux.

 

My images of a subject are simply a demonstration and confirmation of the effects of spherical aberration, as diagrammed in the two technical illustrations linked below. SA "smears out" the depth of "pretty good focus" over a range of distances, rather than a single plane of focus. Thereby affecting DoF in ways contrary to what theory says about an "ideal" perfect lens that has no SA.

 

http://www.olympusmicro.com/primer/images/aberrations/sphericalfig1.jpg

 

https://upload.wikimedia.org/wikipedia/commons/1/10/Spherical-aberration-slice.jpg

 

@ NB23. I won't repeat what pgk already said. I simply point out that what appears sharp enough to be legible and readable covers a deeper "field" with the 75 Summilux @ f/1.4 than with the 75 ASMA @ f/2

 

Readable in the 75 Summilux image: "...ICA APO-SUMMICRON-M" and "....z eloxiert/black anodized finish/a....." and "1:2/75mm ASPH."

 

Readable in the 75 ASMA image: "...PO-SUMMICRON-M" and "...anodized finish/a..." and "...2/75mm ASPH."

 

The 75 ASMA's correction for SA truncates the range of distances over which the lettering is sharp enough to read - i.e. it truncates the DoF (that which appears sharp). Even at a smaller aperture.

A very Good post. I see this all the time use manual focus Leica R 50mm summilux lens and OTUS 55. R is way more easy to use to get usable image. Lens Astigmatism can even have multiple focus plain in acceptable focus during use. Hence many older lens really are better tool for manual focus.

[jrp]

This as all assuming that the example was taken at the centre of the image, otherwise field curvature can also impact results.

 

Assuming so, this is a good example of the Karbe approach to lens design which (taking sharpness as a given) focuses on -- no pun intended -- the speed with which focus descends into out of focus / contrast as an objective.

[pico]

Thank you, Adan, for the cogent explanation. I overlooked how often early LF lenses have curved-like DOF.

Edited September 17, 2016 by pico

[michaelwj]

This as all assuming that the example was taken at the centre of the image, otherwise field curvature can also impact results.

 

Assuming so, this is a good example of the Karbe approach to lens design which (taking sharpness as a given) focuses on -- no pun intended -- the speed with which focus descends into out of focus / contrast as an objective.

 

 

I wonder if the "Karbe approach" is a function of a wide aperture no longer being required for light gathering, but more and more used to create a subject floating in bokeh?

[pico]

I wonder if the "Karbe approach" is a function of a wide aperture no longer being required for light gathering, but more and more used to create a subject floating in bokeh?

 

Karbe did at least once state that choice of aperture was to done to determine rendering.

 

That said, I dislike his later designs specifically for their OOF rendering.

But who am I but just another old pharte using Leica lenses forever.

Edited September 17, 2016 by pico

[adan]

Could be (responding to michaelwj). But I suspect Karbe simply wants to design lenses that come as close as possible to the "ideal," theoretical lens of perfect focus in one plane/distance, with even fall-off of focus anywhere else.

 

Given that he now has the tools (relatively cheaper, easier to produce ASPH surfaces; better design computers; CNC machining of lens moving parts) that were not as available to Dr. Mandler or other designers prior to the 1990s.

 

Technically speaking - spherical aberration usually produces the softer bokeh. Thus the love for the 75 f/1.4 and its cousin the pre-APO E55 90 Summicron and 50 Summilux pre-ASPH (and many other lenses with SA). But introduces problems, such as quite variable bokeh at different subject/background distances, or at different apertures, or the kind of "Leica Glow" seen in my sample (a double image - soft overlaying sharp), or very different bokeh in front of the subject vs. behind the subject, or focus shift. As well as limiting absolute resolution at full aperture to "pretty good" or "soft sharpness", which Erwin Puts deprecates as simply a flaw.

 

Compare the foreground/background bokeh in my samples (since we have them available): the ASMA has very even, nearly identical blur in the OOF areas on either side of the focal plane. The Summilux's "back blur" is totally different from the "front blur." For example, comparing the "O" in "APO" and the "-M" lower right in both shots, the ASMA blurs them almost identically, the Summilux treats them very differently (leaving aside the color fringing, which is a CA effect, not SA).

 

The Summilux's output can be beautifully dreamy - or hyperactive - or godawful - depending on circumstances. The ASMA's output is consistently and simply "blurred, or not blurred" - all the time. After that, it becomes a matter of taste.

Edited September 17, 2016 by adan

[michaelwj]

Hi Andy,

I don't limit this just to Karbe, but all lens designers and companies. I agree that the high ISO abilities and fast shutters of modern cameras, combined with improvements in lens design and manufacture have changed aperture from a tool to gather light, to a tool to influence the image.

I think if Mandler had the tools, he would have produced very Karbe-like lenses. As in, I think he also strove to make the best lenses he could. He also worked in a time where the RF was not doing so well, so would have had greater financial pressure too. Would he have been able to sell at $10k 2/50 APO even if he could make it?

Edited September 17, 2016 by michaelwj

[Michael Geschlecht]

Hello Everybody,

 

In the 1980's when floating element designs began to appear in 24 X 36 photography it was observed that: Floating element designs tended to produce higher quality images at the image plane with depth of field that trailed off more rapidly in front of & behind the image plane while previous designs exhibited less sharpness at the image plane & had a depth of field that extended further & tended to produce more pleasant less in focus images on either side of the image plane.

 

Best Regards,  

 

Michael

Edited September 17, 2016 by Michael Geschlecht

[IWC Doppel]

The images show the speed of in to out of focus. Older lenses usually being more gradual. I'd say you can see the f1.4 is a narrower DOF, with a much slower transition to out of focus. This slower transition often (for me) gives a  are natural look to the Bokeh

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Hallo,

Look here: Leica M

[lct]

Couple of OOC snaps to add to the discussion.

Focal lengths and bokeh are slightly different but DOF looks similar to me. 

75/1.4 @ f/2: https://photos.smugmug.com/Other/Samples/i-TtdjQFp/0/O/DSC03364.jpg

75/2.0 @ f/2: https://photos.smugmug.com/Other/Samples/i-JMmVXf5/0/O/DSC03370.jpg

(3MB files)