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75mm APO depth of field


Ozoyo

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I have been wondering recently about the DOF shallowness of the 75mm APO at full aperture.

 

It is the most shallow I have seen so far. I have been using a Nikkor 85mm 1.4 for years and the Leica 75mm 2.0 feels more shallow.

 

I can't see how that makes any sense but from experience that is what I get...

 

Also, out of curiosity, can anyone tell me how it compares with the 50 noct?

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I don't think you can beat the physics. Just use a DoF calculator, and you'll get the answer.

What might have tricked you was the fact 75mm Cron has minimum focus distance of 0.7m while Nocti has 1m. So yes, it can produce shallower DoF.

Edited by mirekti
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Ozoyo, you have anticipated me because I thought to open a thread on the same matter…

I have this lens since two months and, also if I need more time and training to better understand it, I have had the same feeling (also if I have not done any accurate test)

In comparison with Summicron 90 and Elmarit 90 its depth of field seems shorter, not only at 2.0 but also in other apertures.

I wondered if it was just my impression or a real thing…

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I have been wondering recently about the DOF shallowness of the 75mm APO at full aperture.

 

It is the most shallow I have seen so far. I have been using a Nikkor 85mm 1.4 for years and the Leica 75mm 2.0 feels more shallow.

 

Good observation. I have the same impression from sample DNGs and I have studied it from the physiological and optics perspective. With the excellent micro-contrast of Leica's APO lens, the eye is (in my old film-eye experience) virtually assaulted. The human eye-brain removes some small details in natural presentations in order to see the animal in the grass - so to speak. Introducing some stochastic noise can actually help by smoothing out micro-contrast. (The human ear-brain does the same thing which is why with some of us, adding white noise to hearing aids helps reduce tinnitus.)

 

The impression of more shallow DOF is often expressed as 'over-corrected' optics which probably is an insult to Leica's lens designer, whom I admire none-the-less. Somebody had to do it!

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I don't think you can beat the physics. Just use a DoF calculator, and you'll get the answer.

What might have tricked you was the fact 75mm Cron has minimum focus distance of 0.7m while Nocti has 1m. So yes, it can produce shallower DoF.

 

Yup - but DOF is not physics. It is a calculation that approximates the subjective impression of our eye and brain. Thus parameters that are not taken into consideration can make it inaccurate, like the type of subject you are photographing, the frequency of the image (i.e.high or low detail) the contrast of the image, the microcontrast of the lens.

Take it to the extreme: A photograph of something without contrast (like a featureless greycard) cannot have DOF at all, or infinite DOF, according to your whim.

So yes - a high (micro)contrast lens like the 75 APO can produce a more shallow DOF than one might expect on basis of the calculations.

Edited by jaapv
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The design is similar to the 50 lux so they should be similar. However I have never compared.

 

I will tell you I have dine test shots at 300 feet and F8. The main subject, a lamp post was sharp, but before and after was not. I bought the 1.25 eyepiece to limit user error considering how shallow debth is.

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I am not a lens tester nor would I know where to even begin but I've now been shooting with the 75 Cron for 4 months and every day I shoot with this lens I'm amazed at what it can do.

 

I just had my eye glass prescription updated this week and know it will assist in the short focus throw of this lens.

 

My everyday carry kit is the 35 Lux pre-FLE and the 75 Cron.

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As others have mentioned, the depth of field of a particular focal length is an optical effect, and does not materially differ from one manufacturer to another.

 

The factors that affect depth of field are focal length, aperture, and distance to subject. That's it. [Edited to add: film or sensor size also affects depth of field, but am assuming for purposes of this discussion that that is not a variable]

 

Depth of field aside, all lenses have their own unique signature. And the difference between the 75 Summicron and 50 Noctilux is very large. As an example, the first image below as with the 75 Cron; the second with the Noct.

 

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Simply register for free here – We are always happy to welcome new members!

 

 

Edited by Jager
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The factors that affect depth of field are focal length, aperture, and distance to subject. That's it.

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.

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The 75mm APO is one of the best corrected lenses in the Leica M range. The micro-contrast even at f/2 is very high particularly in the centre of the image. If this is combined with a suitable detailed subject then the perceived DoF can be very limited.

 

This limited DoF effect applies also to Leica's ultra wide angle lenses like the 18mm which the DoF charts would have you believe can be regarded as "sharp" from only a few metres to infinity. It is just not true. On something like an A2 print the plane of focus of the 18mm can be very evident.

 

The Noctilux ,for all its special virtues, is never going to produce images as sharp as those that are possible with the 75mm APO. Perhaps paradoxically it therefore can create the perception of having greater DoF.

 

This effect has become especially apparent with modern digital sensors and very high grade modern lenses, such as those produced by Leica. What applied to film simply does not apply to the digital world. My personal view is that DoF table have effectively become obsolete in the modern digital world - except perhaps for low resolution web based images.

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I agree that microcontrast is the key to "perceived DOF" (the only real one that counts, after all, together with the OOF effects, which are another matter) : personally, I got the same feeling comparing two lenses of very different times : my Summarit 75 (very "modern" rendering") at 2,8 seems to have less DOF than my venerable Summarex 85 at f2 (of course, comparision on digital M, same subject same end dimension, slightly greater distance for the 85)

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

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

 

 

I respectfully disagree. Like you, I shoot film and wet print (for most work) so the DOF of most lens designs are much the same, but digital enthusiasts see unmitigated rendering especially at 1:1 on a large monitor up close.

 

Wet printers' images are pleasantly moderated by the enlarging lens and grain even if it hardly shows.

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I do not think DOF is a constant between two given 75mm lenses at F2. Thinking of the Canon 100mm F2 EF lens and a Zeiss 100mm F2 Macro Planar ZE, they have very different bokeh. The transition in and out the focus plane is very different - the Zeiss is a quicker transition, which separates the the subject better. Whereas the Canon is a more gradual transition, which results in a more 2D-like rendition. The 35 Lux ASPH FLE and 35 Lux ASPH render quite differently. The gradual ingress / egress from the focus plane impacts the CoC and what the perceived DOF can be.

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It could be because of the sharpness of the 75/APO. It is so sharp that it accentuates the effect between in and out of focus...

But according to the physics, the 85/1.4 has a shallower DOF by a good margin.

 

 

I have been wondering recently about the DOF shallowness of the 75mm APO at full aperture.

 

 

 

It is the most shallow I have seen so far. I have been using a Nikkor 85mm 1.4 for years and the Leica 75mm 2.0 feels more shallow.

 

 

 

I can't see how that makes any sense but from experience that is what I get...

 

 

 

Also, out of curiosity, can anyone tell me how it compares with the 50 noct?

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I've posted this before:

 

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

 

Spherical aberration (or lack of spherical aberration) can change the effective DoF somewhat. In that image the top and bottom samples are the path of light rays through lenses WITH spherical aberration. The center image shows the light rays passing through a lens with better corrected SA (more like the 75 ASMA).

 

The top and bottom lenses are less sharp in an absolute sense - the fatness of the white band, top to bottom; but have a wider coverage area of "equally sharp" or "apparently sharp" - the width of the white band, left to right.

 

(Which is why I prefer fast teles on rangefinders to have a bit of spherical aberration left uncorrected - they give more leeway with a focusing system (RF) that is hitting the ragged edge at 75+mm and f/2 or wider apertures.)

 

Mathematics is about ideal situations. In the real world, all lenses are better or worse APPROXIMATIONS of the ideal, but never perfect. So while the math is the same for any 75mm lens @ f/2 - the real-world imaging may show some deviation from the math.

 

When the 90 APO was introduced, people had the same reaction - the difference between the sharp and unsharp areas was PERCEIVED to be more stark than with previous 90 f/2 lenses. More or less as paulsydaus mentions above regarding the 75 - the APO contrast and resolution (and also the type of bokeh - soft-edged vs. double-image) accentuated sharp vs. unsharp areas.

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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 ?

 

If only!

 

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

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Hello Ozoyo,

 

Welcome to the Forum.

 

Your observation of a more limited depth of field is accurate.

 

The 75mm Summicron is a "floating element" design. With a "floating element" design some of the lens elements move differentially in regard to EACH OTHER during some or all of the focussing travel.

 

Floating element design in 35mm photography began in the last Century as a method of improving image quality @ THE PLANE OF FOCUS. This improvement in image quality at the plane of focus was at the cost of lessening of depth of field in front of & behind this plane.

 

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.

 

Another example might be the 280mm, F2.8 first introduced in 1984 for the Leitz Reflex cameras. If you compare the depth of field at COMPARABLE apertures with the 280mm, F4.8 lenses made for the Visoflex you will find the depth of field for the 280mm, F2.8 for the reflex to be significantly reduced

 

Best Regards,

 

Michael

Edited by Michael Geschlecht
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