Maximum useable resolution.

[pebbles]

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I have read various items on the forum on a similar subject but my question is :-

 

What is the maximum usable resolutions of XP2 and Portra.? That is what is the maximum scanning DPI that will give the finest resolution ? My scanner will scan to 12800 dpi but is it usable  to any advantage on 35mm film ?

[adan]

You didn't say which Portra (160 or 400), but Kodak's data sheets quit charting MTF for either film at about 80 lpmm (contrast well below 50%).

 

Ilford doesn't publish MTF/resolution data for XP2, but it will be similar (since it is also a chromogenic - dye-producing C-41 - film), or slightly better, due only having one imaging layer.

 

Giving the benefit of the doubt, we'll take 100 lpmm as the films' resolution. Then you want to scan at twice that, to be sure of avoiding aliasing of the finest details. Or 200 lpmm x 25.4 (mm per inch), or about 5000 ppi (per inch).

 

With a scanner that CAN do 12800 ppi, there is probably a half-resolution setting for 6400 ppi, which should be more than adequate, and cut scan time by 50% and file size by 75%.

 

HOWEVER - the ability to nudge the scanner bar along in steps of 12800 or 6400 to the inch, does NOT mean the scanner's lens itself can resolve anything like that much. Any more than putting ultra-slow high-resolution film in a Holga will improve the Holga's lens resolution. Now of course your scanner lens is NOT a Holga lens, but no lens has infinite resolution.

 

I'd probably do tests at 3200, 6400 and 12800 ppi and SEE if there is visibly any more detail at 6400 or 12800, and not just bigger blurry files.

Edited June 4, 2016 by adan

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[pico]

HOWEVER - the ability to nudge the scanner bar along in steps of 12800 or 6400 to the inch, does NOT mean the scanner's lens itself can resolve anything like that much.

 

I have seen a scanned negative that performs adequately on our current monitors, but our monitors are impoverished. Those who choose to shoot digital are limited to the technology of the manufacturing date, while some film mavens have a brighter future waiting for proper scan technology.

 

Regardless, the stupid metric of lp/mm a good image will prevail regardless of fidelity. The metrics of lp/mm and so-forth are only contemporary marketing bullsh*t. To me it as if there were critics who argue about the sharpness and font choice for 'net poetry.

 

Good night.

[250swb]

I agree with Andy that although a scanner can do 12800 dpi half that is usually enough and represents a true scan of the image rather than the interpolation of information the high scan settings create, but it depends on the scanner. In fact even lower scan settings are fine if 'good enough' is required, say 2800 dpi, you wont see very much difference in a straight out the box image. But what increasing the dpi (and file size) does do is allow for more accurate or extreme post processing by adding pixels that can be assigned a tonal value to work with.

[pebbles]

Thanks guys. Really helpful answers. i will do the test at the varying DPI.