75mm APO depth of field

[NB23]

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Well, lct's graphs show that from lens to lens, the dof is the same.

 

The opposite would have been quite impossible, anyway.

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[Peter Branch]

Well, lct's graphs show that from lens to lens, the dof is the same.

 

The opposite would have been quite impossible, anyway.

 

Except that they don't do anything of the sort.

 

The claim being made was that they would be identical - but they are not.

 

Look closely at the 50mm Summilux-M f/1.4 ASPH and the 50mm Summilux-R f/1.4 at 3 metres.

 

The choice of the f/16 data is questionable in this context as at that aperture all lenses tend to act like a pin-hole camera.

 

If the data for some of the R lenses with "Retro-focus like" construction is compared with the equivalent M lenses the differences are more apparent.

[jaapv]

The question of the structure of the subject matter seems to have been swept under the carpet....

[pop]

Does anyone here happen to know the accurate & actual focal lengths of the three 50mm lenses under discussion?

[NB23]

Some guys here really wish to get a Noctilux in a 50 cron. And firmly believe it.

 

Good luck. I'm out of this insanely misinformed and silly thread.

[pico]

Does anyone here happen to know the accurate & actual focal lengths of the three 50mm lenses under discussion?

 

I was wondering about that, too. Does Leica still engrave the small-type two-digit code giving the fractional actual FL? And what difference would 1.5mm make?

 

My 75mm Summilux has 00 engraved. The 50mm Summicron has 19. The rest are too old to have the engraving.

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I was wondering about that, too. Does Leica still engrave the small-type two-digit code giving the fractional actual FL? And what difference would 1.5mm make?

 

My 75mm Summilux has 00 engraved. The 50mm Summicron has 19. The rest are too old to have the engraving.

 

1.5mm would be 3% of the focal length. The closer limits for the infinity setting seem to vary by about that amount (5.1m vs 5.2m). That might speak for similarly shaped triangles at slightly different scales, however those are called in English.

[lct]

The choice of the f/16 data is questionable in this context as at that aperture all lenses tend to act like a pin-hole camera.

If the data for some of the R lenses with "Retro-focus like" construction is compared with the equivalent M lenses the differences are more apparent.

Should i redo the same with faster apertures and/or wider lenses to convince you that there is no significant difference whatsoever? There are indeed minor differences, which depend probably upon the actual focal length of the lenses, but they are negligible in practice, in my modest experience at least.

[Michael Geschlecht]

Hello Philipp,

 

What is it that you mean by "similarly shaped triangles"?

 

By the way, your English, as usual, is just fine.

 

Best Regards,

 

Michael

[pop]

Hello Phillip,

 

What is it that you mean by "similarly shaped triangles"?

 

By the way, your English, as usual, is just fine.

 

Best Regards,

 

Michael

Thank you, Michael.

 

The term which eludes me describes triangles of different sizes with equal angles.

[CheshireCat]

Should i redo the same with faster apertures and/or wider lenses to convince you that there is no significant difference whatsoever?

 

Thanks, but no thanks.

 

These diagrams are useless, as they are computed using unknown but certainly naive formulas that do not even take into account all relevant optical design parameters, let alone subjective human feelings.

 

What we need now is to compare two shots of the same identical subject made with the 75 Summicron and 75 Summilux at f/2.

Unfortunately, I only own the 75 Summicron. Anyone has both (and some spare time ) ?

[Michael Geschlecht]

Hello Philipp,

 

Those are called equilateral triangles.

 

In which context were you using them?

 

Best Regards,

 

Michael

[lct]

These diagrams are useless, as they are computed using unknown but certainly naive formulas

I admire you if you know better than Leica but i cannot compete at this strastospheric level sorry so i let you draw your own conclusions.

[pop]

Thanks, but no thanks.

 

These diagrams are useless, as they are computed using unknown but certainly naive formulas that do not even take into account all relevant optical design parameters, let alone subjective human feelings.

 

What we need now is to compare two shots of the same identical subject made with the 75 Summicron and 75 Summilux at f/2.

Unfortunately, I only own the 75 Summicron. Anyone has both (and some spare time ) ?

What subjective human feelings make the blurred images of points grow or shrink?

[CheshireCat]

First of all, depth-of-field most definitely is nothing but physics. No magic, sorcery, or witchcraft involved.

 

Indeed, but the physics is so complex that it fades into magic, sorcery and witchcraft

 

For example, especially for non-apochromatic lenses (like the 75 Summilux), different light frequencies will have different CoC sizes, and there will be no exact "point of focus", unless the subject is monochromatic.

[CheshireCat]

What subjective human feelings make the blurred images of points grow or shrink?

 

What makes you think that the human perception of sharpness can be expressed by the size of a blurred image of points ?

 

The funny thing is that not even the size of the "blurred image of points" can be properly expressed by means of these simplistic diagrams.

[pico]

Equilateral triangle

[CheshireCat]

Does anyone here happen to know the accurate & actual focal lengths of the three 50mm lenses under discussion?

 

Another interesting thing is understanding how much the effective FL changes with focus distance, depending on the lens design.

"Focus breathing" is quite noticeable on the 75 Summicron.

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Hallo,

Look here: Leica M

[pop]

What makes you think that the human perception of sharpness can be expressed by the size of a blurred image of points ?

 

The funny thing is that not even the size of the "blurred image of points" can be properly expressed by means of these simplistic diagrams.

To be quite sure, the markings on the lens barrel do not relate to any kind of "human perception of sharpness". The whole concept of DOF is based on physical properties of point images. I am also quite sure that there is an adequate definition of the measures of a blurred point image, even if I do not know it off the top of my head.

 

Thanks, BTW, for the suggested names. In fact, "similar" appears to be the term I was looking for. Two triangles where the corresponding angles are the same are said to be similar.

[John Black]

What we need now is to compare two shots of the same identical subject made with the 75 Summicron and 75 Summilux at f/2.

 

I do not care how many numbers or equations are debated, it's ultimately this type of side by side shooting that will tell tale. And I doubt anybody will be looking at the DOF. Instead the discussion would be the deltas in the sharpness / contrast, the bokeh (nervous bokeh vs gaussian bokeh) and how much CA (which the 75 Lux will have more of). If one lens had more DOF vs the other, I don't think that would be the criteria I'd use to select the "winner". But that's me.

 

I happen to have a couple old DNGs comparing 75 Lux @ F2 and 75 APO @ F2. I'm know I'm going to regret this somehow, but here they are... (dropbox).