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28 Summicron vs 28 Elmarit...

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The laws of optics prohibits the 28 cron having less DOF than the elmarit at the same aperture and distance from the subject. ...........Peter

 

Unfortunately this is a common misapprehension. Lenses of the same focal length and used at the same aperture focused on the same distance do not necessarily have the same Depth of Field.

 

The misapprehension arises because it is generally assumed that the ratios of the diameter of the entry and exit pupils of different lens are the same. If this pupil magnification, as it is known, is not the same then the lenses will have different DoF. That is why Leica publish detailed DoF charts for each and every lens. If you look at them carefully you will see differences between lenses of the same focal length. In particular look at those M lenses which have retrofocus R equivalents

 

I have no idea if the pupil magnifications of the current 28mm Summicron-M and Elmarit-M are or are not the same, nor do I know if any particular difference would be detectable but digital sensors are much more critical in this regard than is film.

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Unfortunately this is a common misapprehension. Lenses of the same focal length and used at the same aperture focused on the same distance do not necessarily have the same Depth of Field.

 

The misapprehension arises because it is generally assumed that the ratios of the diameter of the entry and exit pupils of different lens are the same. If this pupil magnification, as it is known, is not the same then the lenses will have different DoF. That is why Leica publish detailed DoF charts for each and every lens. If you look at them carefully you will see differences between lenses of the same focal length. In particular look at those M lenses which have retrofocus R equivalents

 

I have no idea if the pupil magnifications of the current 28mm Summicron-M and Elmarit-M are or are not the same, nor do I know if any particular difference would be detectable but digital sensors are much more critical in this regard than is film.

Thank you Peter, it's great to learn new things! I was not aware of this issue at all, and I appreciate your getting me, and others, up to speed.

As an addendum, if the 28 cron does have a shallower DOF than expected, it may be one of the reasons I like it so much, as it does separate the subject so well at f2.0. Even at 2.8, a shallower DOF than the elmarit would be a plus for me. For my taste, it may be a reason to select the 28 cron rather than elmarit. best...Peter

Edited by innerimager

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Unfortunately this is a common misapprehension. Lenses of the same focal length and used at the same aperture focused on the same distance do not necessarily have the same Depth of Field.

 

The misapprehension arises because it is generally assumed that the ratios of the diameter of the entry and exit pupils of different lens are the same. If this pupil magnification, as it is known, is not the same then the lenses will have different DoF. That is why Leica publish detailed DoF charts for each and every lens. If you look at them carefully you will see differences between lenses of the same focal length. In particular look at those M lenses which have retrofocus R equivalents

 

I have no idea if the pupil magnifications of the current 28mm Summicron-M and Elmarit-M are or are not the same, nor do I know if any particular difference would be detectable but digital sensors are much more critical in this regard than is film.

 

Yes but the DoF would be minimally different and more then likely unnoticeable to the naked eye. The 2 different lenses of the same stated focal length would need to grossly different in magnification for this to be apparent.

 

I have 3 50mm lenses, 2.8, 2 & 1.4 and they are all of very similar true focal length.

My 2 28mm lenses are the Leica Elmarit ASPH and a CV f/2 Ultron M mount and those too are very similar. As you can see.

First is the Leica then the CV.

 

 

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Yes but the DoF would be minimally different and more then likely unnoticeable to the naked eye. The 2 different lenses of the same stated focal length would need to grossly different in magnification for this to be apparent.

 

.............]

 

I am making a completely different point.

 

It is not the focal lengths that are different, though in practice they do differ by a fraction of a mm. I agree that to detect differences in focal length using pictures would be very difficult if not impossible.

 

There is a fundamental property of all lenses known as the Pupil Magnification. If you stop down a lens by a stop or so and then view the apparent diameter of the diaphram from both sides you will see that it is rarely the same. This is very noticable in tele and retro lenses. The ratio of the two apparent diameters is the Pupil Magnification.

 

Without going into the complications of the optics, which are set out in any number of text books on the subject for those minded to learn more, the result is differing Depth of Field. As I commented in my original post this is precisely why Leica publish DoF data for each and every lens. If it had no effect they would not need to bother. DoF tables in books of a general nature are usually based on the assumption that the Pupil Magnification is unity.

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...Without going into the complications of the optics, which are set out in any number of text books on the subject for those minded to learn more, the result is differing Depth of Field....

Interesting indeed. I was under the feeling that DoF depends on 3 factors: the focal length (f), the f number (N) and the circle of confusion ©. Hence formulas like that of the hyperfocal distance H = f2/Nc + f. Do you agree with this or do you refer to a 4th factor?

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Interesting indeed. I was under the feeling that DoF depends on 3 factors: the focal length (f), the f number (N) and the circle of confusion ©. Hence formulas like that of the hyperfocal distance H = f2/Nc + f. Do you agree with this or do you refer to a 4th factor?

 

Please correct me if I'm wrong, but I believe that Peter was explaining that the difference in pupil magnification, caused by the various entry/exit pupil sizes, affects these factors, and that any 'standard' formula for DoF is a compromise based upon a fixed ratio. Whereas use of such a formula will be a good starting point, the actual DoF can, and does, vary between different designs of lens of the same focal length.

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Just asking a question, Nicole. I'd like to comprehend if there is a 4th factor which could possibly interfere with the well known others. Any formula taking into account this factor or interference, Peter?

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Just asking a question, Nicole. I'd like to comprehend if there is a 4th factor which could possibly interfere with the well known others. Any formula taking into account this factor or interference, Peter?

 

Sorry lct,

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Please correct me if I'm wrong, but I believe that Peter was explaining that the difference in pupil magnification, caused by the various entry/exit pupil sizes, affects these factors, and that any 'standard' formula for DoF is a compromise based upon a fixed ratio. Whereas use of such a formula will be a good starting point, the actual DoF can, and does, vary between different designs of lens of the same focal length.[/quote

 

That is correct.

 

If people want to get into this topic then I suggest they get a text book from the library. The formulae are not simple and you have to know the Pupil Magnification quite accurately. A Google search on the internet is not particularly helpful.

 

I need perhaps to repeat that I have no idea about the technical data for the two lenses in question so I don’t know if differences, if they exist, would be detectable.

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Anyone tested both lenses on the M9?

 

If you can afford it buy the 28 Cron. If not then go for the Elmarit as it is a great lens.

 

Tests done by someone else does not mean you will like the lens or your copy of the lens.

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Anyone tested both lenses on the M9?

Only on R-D1 and M8.2. Hard to tell a difference at f/2.8 and on. The bokeh of the Elmarit asph is slightly sharper and its overal contrast looks a bit higher as well. But i need to do side by side comparos to see this.

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