VueScan question on scan resolution

[ryee3]

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Ed Hamrick, the author of VueScan recently emailed me when I asked how much is overkill when scanning photos and when scanning film. He recommended 300 dpi for photos and 2400 dpi for film.

 

He felt 600 dpi was overkill for reflective and anything more than 4000 dpi is overkill. What are the recommendations of our experience forum members and it would be helpful if you add why you chose what you are currently doing.

 

Thanks to all who reply:)

[Jerry_R]

He felt 600 dpi was overkill for reflective

Yes and no. He is right - above 300 dpi you will not get more details.

But any work with noise removal, sharpening, some adjustments, etc. - more pixels may help.

 

Of course - I assume you scan to DNG.

[adan]

1) I'll assume by "photos" you mean "prints" - since pictures on film are also "photographs".

 

2) Scanning resolution is the last step in a long chain of "resolutions" for any picture - the camera lens, the film resolution, (for prints, the enlarging lens resolution, and the print resolution), the scanner lens resolution, and finally the scan resolution itself.

 

The short version of which is - if the detail isn't there in the thing being scanned, no amount of extra scanning resolution will restore it.

 

And the same holds true for every other "generation" in the chain: no film can improve the resolution of a weak lens, no enlarger can restore detail the film didn't resolve. The resolution will never be higher than the weakest link.

 

One also has to define which film: An ISO 25 microfilm can resolve probably well above 200 lppm - but that is not representative of most film, especially involving color. Velvia 50 resolves around 80-125 lppm depending on subject contrast, Kodak Ektar 100 is "red-limited" at about a 30% mtf at 50 lppm, TMax 100 maintains a 30% mtf out to 150 lppm (figures from Kodak's own publications).

 

Most lenses these days don't list resolution beyond the 40 lppm of their mtf charts - but it is fair to say that a really good lens at its best aperture likely hits around 80-100 lppm. The Schneider Xenotar f/2.8 for the Rollei twin-lens cameras tested out at about 120 lppm (in the center of the image, at one aperture). Medium Format Cameras - Testing Lenses

 

3) So, let's do the math:

 

Amazing-case scenario: ISO 25 micro-film with some rare APO lens that can also achieve 200 lppm. That equates to 5080 lines per inch, assuming perfect technique. To be sure of capturing all that detail without aliasing, the minimum scan resolution would be 2 pixels per line, or 10160 ppi.

 

"Excellent" scenario: T-Max 100 and the same lens. 150 lppm = 3810 lines per inch. Scan at 7620 ppi.

 

"Very good" scenario - lens available to mere mortals, ISO 50-100 color film: Likely limited to 100 lppm = 2540 lines per inch, scan at 5080 ppi.

 

General-photography scenario 1 - "Very good" lens (top-end Canon, Nikon, most Leica), excellent generally-available film (Ektar, Velvia 50, Tmax 100/400, Pan F) = 80 lppm = 2032 lines per inch = scan at 4064 ppi.

 

General-photography scenario 2 - film-limited ("old tech" Tri-X, Plus-X, HP5, FP4, ISO 100-160 color neg films other than Ektar) to ~60 lppm = 1524 lines per inch = scan at 3048 ppi

 

Low-light scenario - ISO > 400, wide-open lenses, likely 40 lppm or less. About 1000 lines per inch, or a scan at 2000 ppi.

 

So I'd agree with EH that for "general" photography, over 4000 ppi is overkill, and 2700 (the original Nikon Coolscan standard) was functional for most people. I saw a very small increase in real detail moving up to 4000 from 2700 (and a bigger increase in artifacts, such as "pepper grain").

 

I think he is low on print scanning, simply because that is SO variable (what enlarging lens? Hand or mini-lab prints? How big a print? Glossy or matte?) - but I've got to run, so I'll return to that later.

[adan]

...just to finish up...

 

Prints by definition have already gone through a second generation (except Polaroids or Daguerrotypes) and lost a fair amount of detail in the process of going through a second lens and a second layer of gelatin.

 

(Anyone who doubts that can try scanning a contact print from a 35mm frame and comparing that to a scan from the original negative).

 

A crisp glossy print can usually be enlarged, from the print, about 2-3x. So, assuming one is aiming for 300 ppi in a final enlargement from the scan, 600-900 ppi when scanning is adequate, and anything over 1000 ppi is overkill.

 

The surface grain of luster or pearl print papers imposes its own limits on resolution - anything over 200 ppi is overkill for textured prints.

 

I agree with Jerry that there are times when it doesn't hurt to overscan at a higher resolution than the mathematical requirements

[plasticman]

...and I'd just like to add that those two answers from Andy amount to an incredible wealth of information. Pretty much all of his answers should really be stickies and used as reference.