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How and Why does 50 APO perform better than other 50s


MrFriendly
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From an optical engineering perspective, could someone please explain how and why the APO-Summicron-M 50mm performs better than other Leica M 50mm lenses (namely the Summilux-M 50mm and Summicron-M 50mm).  I know MTF charts don't tell the whole story, but I'm mainly interested in the differences between the MTF charts and other measurable differences.

My memory is a bit hazy in regards to the details, but I remember while back I was watching Mr. Karbe speak, which at the moment I can't find the source, where he said something to the effect that most of the extra cost of the 50 APO (iirc, compared to the 50 Summilux) went into the assembly and the housing of the lens, and not the design or the glass.  What does that mean? and why does the assembly cost $5K more than the Summilux?

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I am no optical engineer, others may chip in, but general consensus is that to manufacture lens at reasonable cost it has to be designed in such a way that manufactured components and assembly can be done with realistic tolerances while delivering ideal design parameters.  This can, apparently, be achieved easier with physically bigger lenses, don’t ask how is this related as I don’t know. It is perhaps principal reasons why modern lenses that are designed to provide quality image on unforgiving digital sensor including Leica L mount are big. 

APO Summicron M 50mm is high performance and very small lens at the same time.  Precise machining and micro-meter assembly tolerances plus QC that goes with it are key contributors to the final cost.

Leica being Leica with QC being more marketing than shopfloor endeavour managed to drop the ball with early batches by omitting to prevent optical elements not being pained black entering into final lens assembly that caused internal flaring - being discussed here following lens launch.  

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5 hours ago, MrFriendly said:

went into the assembly and the housing

I don't think that is correct. I think somewhere it is said one of the glass types for a single element made that element more expensive than the total cost of elements for the Summilux. The lens does need more accurate assembly which does of course cost.

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6 hours ago, MrFriendly said:

From an optical engineering perspective, could someone please explain how and why the APO-Summicron-M 50mm performs better than other Leica M 50mm lenses (namely the Summilux-M 50mm and Summicron-M 50mm).

The "APO" in the 50/2 APO-Summicron asph means that it has apochromatic lens elements that refract the wavelengths of light so that they faithfully hit the same spot on the image. 

Wavelengths are affected by refraction (think of a pencil in a glass of water where the pencil appears to be at a different angle below the water line).  The amount of refraction (the 'steepness' in the change of angle) varies depending on the particular wavelength of light.  

In standard and telephoto lenses the red, green, and blue wavelengths in the 400 nm to 700 nm waveband don't hit exactly the same spot owing to the inherent refractive indices of the glass  in the lens elements and therefore don't overlap very well, which creates a fuzzy spot with red green and blue edges where the overlap is less than ideal.  Apochromatic lens elements, which refract the wavelengths in the RGB waveband by the same amount, are used to improve the overlapping of the wavelengths to create spots on the image without the fuzziness and this produces 'sharper' images.  

I should note that the current 50/1.4 Summilux-M asph is actually a 50/1.4 APO-Summilux asph lens but, for reasons only known to them, Leica left the "APO" off the name.

The "asph" in the 50/2 APO-Summicron asph and other lenses refers to aspherical lens elements, which are produced so that their curved surface is not a perfect sphere.  The aspherical (ie non-spherical) surface helps to rectify spherical aberrations, which cause the light rays passing through the outer edges of a lens to strike the image at a different 'depth'.  This means that the light ray (which is really a cone of light) will strike the image with different sized spots, and the inevitable overlapping of the spots produces a fuzziness.  The aspherical element(s) cause the rays from the outer edges and the centre to strike the image at the same depth and produce 'sharper' images.

Apologies for the long post but I hope this provides some answers.

Pete.

 

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In practical terms, the micro contrast is incredibly high at f2. The lines are 1,5 cm apart from the central one. The camera is circa 1m away and 30 cm higher than the table.

Have a look at the central line at 100% - Taken with the SL2. It is a 47 Mpixel picture.  

It's black, not grey. It's solid black at f2 in low light. The keyword is low light. All lenses seem contrasty in direct sunlight. Only the APO Summicron exhibits such micro contrast in low light.

 

 

 

 

 

Edited by Fgcm
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The very high micro contrast gives great colors and natural skin colors and texture.

I'm not allowed to upload more pictures now. Later I will upload a couple of pictures which I think give a clear Idea of how good the APO Summicron is in terms of skin texture

By the way: the APO Summicron 50 SL is even better.

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9 hours ago, MrFriendly said:

From an optical engineering perspective, could someone please explain how and why the APO-Summicron-M 50mm performs better than other Leica M 50mm lenses (namely the Summilux-M 50mm and Summicron-M 50mm).

Extremely high specifications which are met in the design stage, tighter tolerances in manufacturer than the others and more QC (testing, testing, testing) during assembly - probably. As we don't know exactly how Leica operate it all has to be conjecture, but the above makes sense, perhaps/maybe/possibly.

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One more picture to show skin tone and texture. It's a crop at 100% of a lager photo. Neither the common Summicron, nor the Summilux asph are so good. 

 

 

Edited by Fgcm
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The Karbe interview does, however, speak to general points related to costs for producing any premium M lens, including glass types and availability, size constraints, design/performance goals, build tolerances and reliable production capability. He emphasized the latter...consistent execution capability...  in his recent web presentations regarding M (and SL) lenses, as well as size constraints (the extra room being a key reason why the SL35 Summicron is his ‘best performing’ lens)

Jeff

Edited by Jeff S
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5 hours ago, farnz said:

The "APO" in the 50/2 APO-Summicron asph means that it has apochromatic lens elements that refract the wavelengths of light so that they faithfully hit the same spot on the image. 

Apochromat means that three wavelengths of light focus to the same spot; other than the three specific wavelengths, all other wavelengths are focused to slightly different spots.  Superachromats focus four wavelengths of light to the same spot.

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43 minutes ago, zeitz said:

Apochromat means that three wavelengths of light focus to the same spot; other than the three specific wavelengths, all other wavelengths are focused to slightly different spots.  Superachromats focus four wavelengths of light to the same spot.

But the four wavelengths of a Superachromat are all in the 400 nm to 720 nm visible spectrum are they?

Pete.

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10 hours ago, padam said:

Yes, thank you, that's the source I was trying to find.

Quote

"It has a lot to do with precision in production to get the results we wanted. The most of the high price of this lens – $8,250 – is the result of the precision assembling. It’s not exotic glass or something; it’s the assembling that is very precise.“

 

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