Lens calibrated for digital

[Exodies]

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Were lenses designed to focus the colours in the correct layer of colour film?

Edited October 3, 2017 by Exodies

[TomB_tx]

While the basic focus setting hasn't changed, I think they realized more care in setting (precision) was necessary with today's users looking much closer and expecting perfection. My Summitars from 1939 and 1948 are near perfect on my M9. My V2 and V3 Summicrons are perfect at f2.8, which DAG noted were intended as focus changed depending on aperture (as with most lenses if you look closely enough). Since most photos then were at f4 to 5.6 the f2.8 compromise gave sharper shots at f4 than if optimized at f2.

A couple of my later Leica lenses (including a 90 Summarit 6-bit) needed tweeking by DAG. On the other hand, most of the Zeiss ZM and Voigtlander lenses have been perfect on my M9. So the real issue may be care in adjustment and testing by the workforce, not the more modern test equipment, since 30s & 40s lenses were as well adjusted (on average) as modern Leica lenses.

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[jaapv]

That is not surprising, since a tolerance span is just that, a range of acceptable settings. It is quite possible for an older lens to sit smack in the middle of the range, making it spot-on in all conditions. The trick with the newer gear is to narrow the band by more precise adjustment methods.

[willeica]

Just my few cents. I have a 35mm Summilux Asph pre-FLE lens which shows focus shift between f2.8 and f 5.6 on digital Ms, perfect at f1.4 and almost so at f2, fine again at f 8. It shows no sign of this whatsoever on film Ms. I put this down to the film thickness point made by UliWer above. It is possible, I suppose, to get a lens matched to taste on a digital M, but then it might be 'out on other cameras. Whether it is worth paying for this is down to the individual user.

 

William

[lct]

Focus shift is well known on the 35/1.4 asph pre-FLE but it is not a flaw lens calibration can fix IMHO.

[pico]

If the focus can be anywhere within the layer of the film material how does the scanner or enlarger know where to get the image data from?

Enlarger focusing is usually accomplished using a grain focusing device.

I use a long-mirror Peak device. Scanners have enough depth of focus.

Edited October 3, 2017 by pico

[Jared]

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Honestly, I think the largest factor in "calibrated for digital" is expectations.  In the film era, it wasn't possible to zoom in to 4:1 magnification at the touch of a button.  There was less emphasis on technical image quality, and more emphasis on lighting, composition, and artistic merit.  I'm not saying nobody cared about image quality in years gone by or that modern photographers don't care about the artistic aspects of photography.  I'm just discussing emphasis.  

 

With digital bodies in an age where millions of photographers have obsessed over focus accuracy the past few years, the expectations for digital M's are much higher than for film M's.  Leica has tightened up their tolerances with that obsession in mind.  That is all that has changed.  

 

Oh, one other factor I forgot to mention.  I think that in years gone by most rangefinder photographers were willing to learn their lenses.  Got something with focus shift?  You learn how far to move the focus tab when shooting wide open.  Got a lens whose calibration is off a touch?  You learn how far to move the focus tab when shooting that lens.  I know I had a 90mm Summicron some years back that was off just a touch.  I simply focused and shifted.  Worked great.  But it assumed the photographer was willing to adjust for the vagaries of the camera and lens.  The same was true for light meters years ago.  Many photographers would "rate" their camera's light meters, and if they were shooting chromes in particular they would adjust the ISO or set some exposure compensation (typically negative for chromes to increase saturation a touch).  People didn't expect perfection from their cameras.  Photographers were expected to learn their cameras and adjust their own technique to match.  Not saying it was "right" to make adjustments yourself rather than expecting the camera to be perfect; just saying that the expectations have changed.  

 

Years ago good photographers simply had to learn the little quirks of their equipment and adapt.  Now, the expectation is that it will either be right when it arrives, or that it will be repaired to be perfect. We no longer see it as the photographer's job to adapt to the sample variations of a camera or lens.  

[Jared]

End result?  "Calibration for Digital" should be thought of more as "Calibration for Modern Expectations".  It's not BS in that many (most?) older lenses can benefit from tighter tolerances and/or an adjustment for wear.  However, it has little to do with digital directly.  The back focus spacing has not changed one iota since the days of the M3.

[adan]

Were lenses designed to focus the colours in the correct layer of colour film?

 

Generally, no. Lens designers have much bigger problems to solve.

 

Although over the years, it's quite possible somebody tried this. It would require "tuned" longitudinal chromatic aberration - which is generally something lens designers try to avoid and eliminate, not enhance. (Thus the proliferation of APO and ED lenses over time - they get the colors to focus all in the same plane.)

 

https://www.edmundoptics.com/contentassets/f0a067fda6414ac5957aaf0f5818d07b/fig-2-cmoa.gif

 

It is possible that the reverse is true - that in creating the now-standard "color tripack" of three-plus layers in color film, the film engineers took into consideration existing and unavoidable Long. CA in lenses of the 30s-40s (the time period the tripack for color was originated, in Kodachrome (1936) and Agfa color negs, etc.

 

But highly unlikely - the stacking-order of layers in color film (blue-sensitive on top, then a yellow filter layer to block all energetic blue light from the lower two layers, then a green-sensitive layer (naturally insensitive to red - orthochromatic), then a red-sensitized layer - is pretty much pre-determined by silver's natural response to light - very sensitive to blue, less so to green, and very little at all to red (thus safelights are yellow or red).

 

http://www.dowjow.com/camera_beginners_workshop/kumon/img/k11-fig1e_i.jpg

 

You have to stack the color layers that way, to keep blue from contaminating the other colors.

 

Realistically, film engineers have tried to get the film as thin as possible (but not thinner, to borrow from Einstein), and lens designers have tried to get the plane of focus as thin as possible, through eliminating CA, field curvature, spherical aberration, etc. etc. I.E. both trying to meet in the middle at some "ideal," rather than compensate for each others' flaws.

[Exodies]

Thanks very much, adan. It's hard to get a feeling for what matters and the scales involved - thickness of sensitive film layers, variations in film flatness, quantities of CA, accuracy needed for placing the sensor, cell size and spacing, ... - these things measured in microns and then the distance scale on the lens in meters, light levels doubled or halved in two clicks. Fussing about with white balance and calibrating monitors, creating paper profiles then showing the prints in whatever lighting is available. It's a peculiar mixture of the rough and ready and the extremely precise.

[pico]

After reading many of adan's contributions I'm left with the comforting fact that I

am way too old, obsolete, to worry that he would be a the final editor of my

contributions to visual journalism.

 

Freedom, nothing left to lose and all that. (Thanks Chris Kristofferson.)

forgive spelling

Edited October 3, 2017 by pico

[Jeff S]

It's understandable, too, that various digital cameras from Canon, Nikon, etc, have 'micro focus adjust' settings in the camera menu to compensate for differences in camera and lens variances, even when both might technically be within tolerance. Some care, some don't, but this takes some work away from those who do.

 

Jeff

[sblutter]

When I switched to digital with M9 I had DAG calibrate 3 important lenses b/c of off results, 2 50's & a 90.  They continue to be perfect with the 240

 

Good investment