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Author Topic: Digital lenses: color cast on film?  (Read 1092 times)
epines
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« on: July 06, 2013, 03:58:43 PM »
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Does anyone know if lenses such as Schneider's 35mm digitar XL and 47mm digitar XL cause color cast on film? Or is it only a digital-sensor phenomenon? I have both of these lenses on an Arca Swiss 69 FC. I often shoot film for personal work, and I'd love to use them occasionally with film, especially for shift/rise/fall movements. I can't test this for myself, as I currently don't have a film back that will mount on to the camera.

thanks
ethan



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ErikKaffehr
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« Reply #1 on: July 06, 2013, 04:10:36 PM »
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Hi,

I am pretty sure the color cast is a digital problem. You still get vignetting on film.

Best regards
Erik

Does anyone know if lenses such as Schneider's 35mm digitar XL and 47mm digitar XL cause color cast on film? Or is it only a digital-sensor phenomenon? I have both of these lenses on an Arca Swiss 69 FC. I often shoot film for personal work, and I'd love to use them occasionally with film, especially for shift/rise/fall movements. I can't test this for myself, as I currently don't have a film back that will mount on to the camera.

thanks
ethan




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BartvanderWolf
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« Reply #2 on: July 06, 2013, 04:16:59 PM »
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Does anyone know if lenses such as Schneider's 35mm digitar XL and 47mm digitar XL cause color cast on film? Or is it only a digital-sensor phenomenon? I have both of these lenses on an Arca Swiss 69 FC. I often shoot film for personal work, and I'd love to use them occasionally with film, especially for shift/rise/fall movements. I can't test this for myself, as I currently don't have a film back that will mount on to the camera.

Hi Ethan,

In principle, there is no Color Cast as we know it from the sensel masking and cross-talk artifacts and Bayer Demosaicing in single shot sensors. Depending on the filmstock, there might be a tiny bit of internal scatter in the color layers though.

The main benefit of still shooting an occasional LCC frame, even with film, is that it also allows to calibrate for lens vignetting and light fall-off, including scanner effects. Of course that requires taking a film frame of a uniformly lit surface and/or using an LCC diffusor. Whether the cost delivers enough of a benefit is up to the user, but it would allow an almost perfect flat illumination whith Tilt/Shift images, as long as the scans are made of exactly the same area as the film with an actual image.

Again, more useful with digital captures, but not entirely useless with film (although with fewer benefits).

Cheers,
Bart
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epines
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« Reply #3 on: July 06, 2013, 05:00:19 PM »
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Thanks, Bart and Erik. Much appreciated. I suspected as much.

Bart -- I don't really mind a little vignetting, but if I do what you're suggesting and shoot a frame on film to calibrate for fall-off, etc., how would I use it to apply corrections to the scanned film frame? Could I import them both into Phocus or Capture One and then use the software's LCC correction function? Or does that only work with raw digital files? Or perhaps there's a layer/blending mode in Photoshop I could use for the correction?

ethan
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BartvanderWolf
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« Reply #4 on: July 06, 2013, 05:38:09 PM »
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Bart -- I don't really mind a little vignetting, but if I do what you're suggesting and shoot a frame on film to calibrate for fall-off, etc., how would I use it to apply corrections to the scanned film frame?

In the (apparently) theoretical case that you do want to go through the trouble of shooting a 'featureless' LCC frame, you'd have to process that frame identically to your actual image (i.e. same camera/lens and fixed scanning settings). The basic idea about LCCs is that they are linear gamma images, just like the Raw sensor captures, and in linear gamma space it is almost trivial to balance out luminance differences. Once a Gamma adjustment has taken place, it all becomes much less accurate.

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Could I import them both into Phocus or Capture One and then use the software's LCC correction function? Or does that only work with raw digital files? Or perhaps there's a layer/blending mode in Photoshop I could use for the correction?

For the best results, one needs to stay in a linear gamma colorspace (Raw luminance capture/scan, without gamma adjustment). Anything else becomes troublesome, so only software that's designed to handle LCCs or Flat-field calibration, should be used.

Cheers,
Bart
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Graham Welland
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« Reply #5 on: July 08, 2013, 08:48:26 PM »
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I sometimes shoot with my 35XL and 47XL on film with my Alpa. The results are stunning enough that even the folks in the lab want to know what was used to shoot them as the acuity of these lenses is that good.

The digital lenses are just simply sharper and better corrected for chromatic aberations than the analog versions. There may be some minor vignetting at wide open settings but to be honest I never shoot them there anyway. I really wouldn't worry at all.
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Graham
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« Reply #6 on: July 17, 2013, 03:25:16 PM »
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Color cast is not a an issue with film as far as a I know, not at all to the extent as in a digital sensor at least.

A different aspect: some of the wide angle digital lenses are corrected for the refraction in sensor glass, ie the chromatic abberation correction expects that there should be a glass filter behind the lens, which for film is not. This should in theory make the lens have more CA on film than on digital, but on the other hand I guess digital lenses is on a higher level of correction anyway so this factor can probably be ignored. I'm not sure if older digital lenses like the 47XL and 35XL actually does have this sensor glass correction at all, don't think so.
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