75mm APO depth of field

[pico]

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If you look at the depth of field @ F16 marked on the current 75mm Summarit focussed @ Infinity you will see that it is 8 meters to Infinity. The equivalent depth of field on the 75mm Summicron is approximately 10 meters to Infinity. A significant reduction.

 

It could also be that Leica calculated DOF using a more conservative (smaller) Circle of Confusion in order to accommodate digital enthusiasts' tendency to work on large monitors and/or viewing at 1:1.

[Ozoyo]

Michael,

 

Thank you, that is a very interesting explanation and I was expecting something like that.

 

Another think I was wondering that could explain how a Leica 75mm 2.0 can have shallower DOF than a Nikkor 85mm 1.4 is the mirrorless aspect of the Leica (i.e. distance between sensor and back of the lens). But that is just a hunch.

 

Like some on this thread I believe only Physics can affect the DOF. I had an argument with someone who was telling me that exposure could also play a role but I can't see how...

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[Michael Geschlecht]

Hello Pico,

 

Thank you for your reply.

 

There are a number of examples where there is a difference in depth of field between floating & non-floating designs.

 

I'm sorry you missed my addition of the 280mm, F2.8 in my Post #20 above. I added it during the time you were Posting #21.

 

Best Regards,

 

Michael

[Michael Geschlecht]

Hello Ozoyo,

 

Having or not having a mirror is not the issue.

 

There is only 1 actual plane where the image is "in focus".

 

In front of this plane or behind it are a series of image planes of lesser focus.

 

Floating elements increase image sharpness AT THE PLANE OF FOCUS. They do this at the cost of lessening image sharpness as you move further away from the image plane in either direction.

 

This loss of image sharpness DECREASES apparent depth of field.

 

Best Regards,

 

Michael

[pgk]

There is no variability and I'm quite amazed at some of the comments here. It's PURELY physics.

Your statement would be accurate if lenses were perfectly corrected, but they are not. You can't get away for physics but you need to take ALL factors into account and not just work with the convenient and simplistic ones.

[CheshireCat]

Please, help me to understand. It's a matter of pure mathematics (all lenses of the same focal length have the same DOF and the differences are only due to the eye-brain mechanism) or there may be a real variability due to individual projects ?

 

There may be a real variability, and it depends on lens design.

People think about the field of focus as a plane but reality it can be a complex shape that depends on the lens design and varies with aperture and focusing distance.

This shape may strongly affect the bokeh and perceived DOF especially far from the image axis, where the bokeh is most noticeable.

[NB23]

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Your statement would be accurate if lenses were perfectly corrected, but they are not. You can't get away for physics but you need to take ALL factors into account and not just work with the convenient and simplistic ones.

 

But it IS simple. A focal length, an aperture. All must compute. The only way the manufacturers have found to vary the dof within a guven focal length with a given max aperture is to play with aberrations. The DC nikkors and the minolta T lens comes to mind. Nothing else. The 75 cron is very nice but it can't bend the laws of physics by a full stop.

 

I own the nikkor and the 75 aa. I will test them both. Df and M9. Just out of curiosity.

[jaapv]

There is no variability and I'm quite amazed at some of the comments here. It's PURELY physics.

 

Sorry, you're wrong. It is biology...

[Herr Barnack]

There is no variability and I'm quite amazed at some of the comments here. It's PURELY physics.

 

"But Cap'n - I canna' a change the laws of physics!!"

- Commander Montgomery Scott, U.S.S. Enterprise

 

 

 

 

 

(sorry, couldn't resist )

Edited September 13, 2014 by Carlos Danger

[Al_OOF]

If only!

 

Have you discounted the effects of different "Pupil Magnification" or are you suggesting that all 75mm lenses have the same Pupil Magnification?

Not being an expert in optics I was using the simple assertion that all the lenses of equal focal have the same depth of field, but what you wrote made ​​me doubt and has driven me to learn more.. So I tried to read something on the Pupil Magnification, that I didn’t know. If I have well understood it affects the depth of field (in the formula that defines it) and it is not necessarily equal in lenses of the same focal.

If the lens is highly symmetric the PM (equal to 1) doesn’t affect the DOF, while in telephoto it is less than 1 and in wide angle > 1. It’s correct ?

The discussion still seems up in the air but, In any case, thanks for having stimulated my curiosity !

[gvaliquette]

Depth of field is NOT PURELY PHYSICS. Physics tells us that there is one and only one plane of focus. Depth of field is the human visual PERCEPTION of sharpness, and is therefore totally dependent on image size, image subject, viewing conditions, viewing medium, and even, possibly, the phase of the moon!

 

These formulae that give you a "depth of field", based on focal length, aperture, and print size (screen magnification) do not take into consideration the human eye, with its characteristics and defects, such as need for corrective glasses and use of these glasses or not, even when they should be used, cataracts, retinal degeneration, and, not least, the brain that puts it all together.

 

...unless this is all an aberration in the matrix!

 

Guy

 

[NB23]

Yeah, it's biology. Sorry...

[jaapv]

[hoppyman]

Hi Ozoyo. Apart from the technical discussion in the thread, there are some other factors that may influence what you are seeing there. Those include your conditions and subjects of course, but also your technique, the calibration state of the individual lens and the camera itself. I have used the Nikon 85 (the f/1.8 version) on a full frame dSLR too in similar conditions. My personal experience is that my APO 75 has been superbly accurate on my M8, M9 and now the M. the Nikon required an AF adjustment via the camera body function. The AF function of the APO 75 is capable of finer accuracy in my experience.

 

Personally I typically use this focal length around f/4 for the DoF I want for portraits. That is to say with near eye sharpest and fall off from there without a too un-natural effect.

Portraits Gallery Photo Gallery by Geoff Hopkinson at pbase.com

 

But the measurement of the DoF in the most critical conditions for each lens that you have mentioned is:

not much

[MarkP]

 

Personally I typically use this focal length around f/4 for the DoF I want for portraits. That is to say with near eye sharpest and fall off from there without a too un-natural effect.

 

+1

[250swb]

You can't get away for physics but you need to take ALL factors into account and not just work with the convenient and simplistic ones.

 

Strange then that nobody has mentioned the photographer yet. The unknowable element Leica can't take account of, and who has access to all sorts of software tools to alter micro contrast, overall contrast, colour contrast, and sharpening. Somebody with only modest skills can play their own games with perceived DOF without even resorting to the 'Blur' option.

 

Steve

[jankap]

Unfortunately its not quite that simple. This might be true of a perfectly corrected lens with a perfectly circular aperture, but in the real world lenses are not perfectly corrected (not even the 75mm APO;)) and apertures are not perfectly circular so other nuances come into play. Zeiss published a pdf (CLN35_Bokeh_en) which explains the interaction between various factors which influence DoF and Bokeh but its not bedtime reading.

 

An interesting article (on Sunday morning), especially the last part is interesting for this thread.

At this point the mathematic model changes to the real world of the imperfect lenses.

 

I was not able to retrieve the download examples at the very end. Does somebody know, where those pictures can be downloaded?

Jan

 

By the way Fuji has introduced an lens with an apodizing element (see also the Sony/Minolta 135 mm 2.8 STF).

[pgk]

Strange then that nobody has mentioned the photographer yet.

They have, by referring to perception, something which has been studied but which is another variable. Try "Visual concepts for Photographers" by Stroebel, Todd and Zakia (Focal Press) 1980, which has a lot of interesting and relevant information in it. The problem we are 'seeing' in this thread is that one faction believes that everything can be summed up in simple mathematical equations whilst others of us see the grand complexity of imperfect systems interpreted by varied eyes/brains which do not operate identically.

 

That said I have the 75 Apo-Summicron which IMO is an extraordinarily good lens. Its clarity of micro-detail, relative flat field and high level of correction produce very different images to the 80 Summilux I used to own. Wide open, one produces wafer-like clarity, the other a soft and ethereal zone. Trying to determine which has a greater depth-of-field wide-open is like trying to decide between apples and pears - its difficult to compare because they simply don't define in the same way/aren't the same. Trying to compare these two by a simple mathematical formula might seem appealing but will only tell you what you might expect - feed simple data in and you'll get simple data out.

[jankap]

Simple mathematical formulas only hold for ideal models.

In the simplified vision all 75mm naturally have the same properties.

 

The ideal model is not buyable in the real world, so the mathematical formulas should be extended, and then they are not simple any more.

 

Not to speak of tolerances in the real world.

Jan

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Hallo,

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[Al_OOF]

Also if I have the curiosity to understand why, for me it is essentially a practical matter.

If I do some photos with the Summicron 90 and with the 75 Apo, in those with the 90 the subject seems to fall more easily into a zone of depth of field (or "appears" to fall), especially if I shot with a certain diagonal and not flat to the subject.

So I greatly appreciate the quality of the 75 AA but for me it's more of a challenge to focus properly. I have the same feeling comparing photos taken with a Summicron 50 III and a Summilux 50 at the same apertures.