Understanding Leica M 75mm (Summicron 75 f2 – Noctilux 75mm f1.25)

[nejad_b]

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75mm is the favourite lens of those who are interested in detail, portrait or landscape photography. With its moderate magnification it is a good choice for photographing flowers and other objects without distorting quality and scale of their image. 

Not all who use 75mm find it fully satisfying, the result, not always, seem to be to their expectation. You hear many stories from those who sold on their 75 and yet went back to it! The core of disappointment emanate from dissatisfaction on getting the focusing right. It’s a problem that occurs, on both, close range and distant images!

Users of Leica M 75 have a keen interest in “Bokeh”! Bokeh is the outcome of isolating subject from the background. It is achieved by placing the subject within the depth of field while rendering the background to a pleasant insignificance. Bokeh is not a concern for wide angle users as the wide angle ,somewhat, captures the bigger picture. Bokeh is not a big deal for those with 50mm either.

The widely held view within photographers that are using 75mm is the idea that to get the bokeh right they need to have the aperture wide open. Majority do not have a full understanding of the working perimeter of the lens at its extreme setting where the depth of field is unimaginably small. Incredibly some photographers have accepted their failings by ignoring focusing issues in their photographs

Depth of field:

Most photographers who progress from 35 or 50mm lens to 75, take the issue of depth of field very lightly and use the printed diagram on the lens as a way of “getting a feel for” extent of DOF. This practice might work for a wide angle or even standard lens but not for the 75, in particular at largest aperture setting. Printed diagram is vague yet DOF is narrow and very precise. It is like trying to measure millimetres with a ruler that is marked in meters!

Leica's "Technical Data" for each lens, that can be download, incorporates a table for Depth of Field. It lists closest and furthest distance for each aperture setting - but does not display the actual range- that can be calculated by deducting two given figures. The measurement are all in meters that is not helpful at all! The DOF table may serve a scientific purpose but not a practical one as the values presented are in an abstract format. For example first cell on 75mm Noctilux, for its minimum distance, (0.85) and largest aperture (f1.25) reads: 0.846 - 0.854, subtracting these two figures you get 0.008 which is hard to appreciate. You will be, however, alarmed when your penny drops that it means 8mm, a distance that is so narrow it is almost impossible to get any target in focus. Slightest movement whether it’s a breeze or photographer’s own breathing or body movement will shift the focus elsewhere and spoil the work! 

For a portrait photograph, using a 75mm lens, a working distance is between 1.2 and 1.5m (to frame the head and a bit of shoulder). The depth of field at this distance for Noctilux at f1.25 is 18 to 30mm (31 – 49mm for Summicron at f2). To work at these apertures you would need to consider; if your subject’s head is turned, you will only get one eye in focus, hair, ears and other features having similar fate regardless of posture!

To make a most of these lenses you need to know their limitations at every setting. For Noctilux despite its f1.25, f2 or f2.8 might be a better choice, working close to a subject (at 0.85m), similarly f2.8 or f4 might suit a portrait better(at 1.2 or 1.5m). For Summicron even smaller apertures like f5.6 must be taken into consideration! 

Figures in depth of field table are not negotiable and there are no remedies like changing shutter speed or iso to overcome the problem.

Putting a distance between lens and the subject results in increase in depth of field, for example, for Noctilux, at 3 meters DOF is over 5 inches (129mm). The trade-off, however, is the magnification which will be down from 1/8.8 to 1/37.4. 

 Focusing at infinity setting

Photographers who rely on printed depth of field on the lens, mistakenly believe in another myth i.e. continuity of focusing from the last largest number printed on the lens to infinity! Unlike some wide angle lenses setting to infinity does not give a “wall to wall” focusing, take Summicron, for example, at f2 anything within first 82.78 meters is out of focus. For Noctilux setting the aperture to 1.25 and the focusing to infinity will have the first 133.7 meters out of focus and there is no way of knowing that by looking at DOF scale printed on the lens! The implication of such limitation is that photographer cannot rely on setting the focusing to infinity in order to point and shoot. Most street scenes will be rendered out of focus for a considerable distance. 

These “limitations” are result of limitations of laws of physics and compromises that designers had to make in order for it to work. Being aware of these limitations would make us a better photographer. There is no alternative other than being aware and working around them. 

Noting the above it seems reasonable to go back to the idea that one size does not really fit all and any lens has its limitations and can only deliver what it is designed for and you may therefore need more than one to work with. Similarly contrary to what some “photographers” advocate having a lens that has F1.25 does not mean it has to be used on that setting all the time! Your car may have 220mp/h on it’s speed dial but you don’t drive it at that speed!

It might be prudent to carry a copy of DOF table or have it on your smart phone in order to better evaluate what you compose, until such time you become one with the lens!

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Noctilux VS Summicron?

Noctilux 75mm f1.25 has two basic advantages over the Summicron f2: 

First, it has 11 aperture blades, where Summicron has 9. The difference between two is the quality of out of focus areas (bokeh) which is distinctly better in Noctilux images. In addition the 9 blades has a tendency to produce what is some call as ninja stars in the bokeh appearing when there are reflections from shiny surfaces present at the scene;

Second advantage is larger diameter of the glass / surface area of glass. Logically, the bigger the diameter of the glass the more light passes through and hits the surface of the sensor. 

The aperture size is not defined by the amount of light it lets through, it is defined by a physical standard - size! It makes sense, therefore, to assume that at f16, as an example, Noctilux lets more light in comparison to Summicron for similar setting! This could mean a faster shutter speed. 

Whether you agree with the above conjecture or not, faster lens is only made possible with use of bigger and better glass that can only add to the quality and clarity of the image!

Edited July 10, 2020 by nejad_b
Wrong image was attached

[Mark T]

Thanks for the above advice. I have and love the 75mm Summicron and I think you outline quite well the reasons why people have difficulties with these lenses. I'm not really sure what the purpose of this post was and I don't agree with your second last paragraph. I'm pretty sure the aperture at f/16 is the same physical size in both the Summicron and the Noctilux. Many happy returns with your 75mm shooting!

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[rsolomon]

Love the 75 cron, amazingly sharp, love the images that come from it

[otto.f]

Oh.

[nejad_b]

5 hours ago, Mark T said:

Thanks for the above advice. I have and love the 75mm Summicron and I think you outline quite well the reasons why people have difficulties with these lenses. I'm not really sure what the purpose of this post was and I don't agree with your second last paragraph. I'm pretty sure the aperture at f/16 is the same physical size in both the Summicron and the Noctilux. Many happy returns with your 75mm shooting!

I thought that was what I was trying to say, physical size of the aperture is the same (standard) but better lens lets more light through. I guess it can only be proven, for fact, if they test the lenses at CERN and measure number of Protons passing through!

[nejad_b]

5 hours ago, rsolomon said:

Love the 75 cron, amazingly sharp, love the images that come from it

I agree. I just hope photographers (some) stop their obsession with one and only f1.25 and use it as any other lens - and stop posting their out of focus images online as their reviews!!!

[tom.w.bn]

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vor 23 Minuten schrieb nejad_b:

I thought that was what I was trying to say, physical size of the aperture is the same (standard) but better lens lets more light through. I guess it can only be proven, for fact, if they test the lenses at CERN and measure number of Protons passing through!

In the 2nd last paragraph you wrote that you would notice a difference in exposure. Setup a camera with fixed iso and time. Put a Noctilux at f16 in front of the camera and a Summicron at f16 and take a test shot. If you are correct you should notice a visible difference in brightness of the image. I think both won't differ so much.

Edited July 11, 2020 by tom.w.bn

[tom.w.bn]

vor 9 Stunden schrieb nejad_b:

Bokeh is not a concern for wide angle users as the wide angle ,somewhat, captures the bigger picture. Bokeh is not a big deal for those with 50mm either.

If you look around in this forum you will not find lot's of people who agree here.

[farnz]

I have no wish to trash the opening post because English might not be the author's first language and it probably contains useful information but it uses too many assumptions and generalisations to support a meaningful view and couldn't hold my attention through to the end.  I'm still unsure what the purpose of the piece is.  Some examples:

• "75mm is the favourite lens of those who are interested in detail, portrait or landscape photography."
• "You hear many stories from ..."
• "The core of disappointment emanate from ..."
• "Users of Leica M 75 have a keen interest in “Bokeh”!"
• "Bokeh is not a concern for wide angle users ..."
• "Bokeh is not a big deal for those with 50mm either."
• "The widely held view within photographers that are using 75mm is ..."
• "Majority do not have a full understanding of..."
• "Most photographers who progress from 35 or 50mm lens to 75 ..."

Pete.

[darylgo]

Pete, you read further than I did.  
 

To the op: regarding light transmission, a T stop would be a more accurate setting and used in cinematography. 

[tom.w.bn]

I think the main takeaway is: don't use a fast lens always wide open. I does not make your images better automatically. Seems trivial but some people use shallow depth of field excessively. and when the oof area is the main content of an image or faces/eyes are only partially sharp then there is something wrong (to me). It's more noticeable in video though. When filming with DSLRs was new, people played with threir fast prime lenses always wide open. When during one take a face constantly moves through many focus areas, you want to grab the camera operator and give him a f4 lens instead of a 1.4 lens. Does not look so bad then he uses that wide open.

[Guest]

Good bokeh is a very subjective thing really.

Its not a factual thing as such.

I have no interest in getting a 75mm lens as i prefer 90mm but thats just me.

 

[lct]

Not sure what the OP means by "myths". DoF markings and tables are calculated on average values and are not made for nailing focus nor pixel peeping. BTW i have no focusing problems with my 75/1.4, 75/2 and 75/2.5 lenses but i don't use DoF tables to focus at full aperture obviously. I have no experience with the 75/1.25 though. I suspect it is not easy to focus at full aperture as it is close to the limits of the RF accuracy but i don't quite see what DoF markings and tables have to do with that. Now perhaps i'm missing something as often... don't say always please .