Scanning Resolution

[The Deer Gunter]

It surprises me so far no one talked about the resolving power of film, and more in particular the different film formats. It's not only a question of how thick the emulsions are and what film speed you're using, but also and mainly how much detail photo optics CAN deliver to the photographic emulsion. The bigger the format, the more information you get from the emulsion for sure, but the overall sharpness goes down due to a typical bigger circle of confusion.
In this respect I think it's always wise to use the highest optical resolution your scanner is capable of when scanning small format (35 mm film), but a 4x5 inch would have very little benefit, if no benefit at all, from a 5 000 ppi scan. The only thing you would gain, is weight, but no true image detail. Even more, I think oversized images are more difficult to sharpen, as the image's grain acutance becomes more fuzzy, causing the transitional contrasts harder to be detected and isolated.

Do you agree? And what do you think a reasonable scan resolution would be for a 4x5 inch slide?

[mdarnton]

Do you agree?

I don't think I do. Last spring I got my first 8x10 camera, and set it up pointing out my shop window. Twelve floors up, I can see several blocks. Putting the loupe to the GG I was very surprised at the detail I could see--with a better loupe it would have been very easy to read license plates a couple of blocks away. Then I had what was for me a big revelation: I was using a 300mm Tessar, a very sharp lens that resembled many 35mm teles, and looking at a 35mm size piece of film. Of course, that would not be an unusual situation for 35mm, and think of the detail you would naturally expect in that situation. There's no reason at all not to expect it in the middle of a larger piece of similar film behind a similar lens, right?

So if everything is well-aligned, I would expect if you can scan 35mm and get useful detail at 5000ppi, you would get useful detail from a similar film/lens combination at 5000ppi if the film happened to go farther out in every direction (i.e., 8x10). Whether you can use it making an 11x14 print is, of course, a different question. But it's there to use.

[The Deer Gunter]

There's no reason at all not to expect it in the middle of a larger piece of similar film behind a similar lens, right?

I'm afraid there is! If you would compare a true 8x10 inch lens (covering the 8x10 inch usable image circle) to a true 35 mm 'tele' lens giving you the same enlargement on the 35 mm film, you would see a significant difference in sharpness! And I'm not talking about whether you see that license plate on the ground glass or not. Viewing your ground glass with a magnifier is not a reference at that point. I'm talking about the acutance of the details of both shots when you scan at high res, or even when you view them with a 25x loupe on the light table. You would be surprised to see the differences between both recordings! 35 mm Lenses reach a higher degree of sharpness. The Circle of Confusion (CoC) for 35 mm lies typically around 0.029 mm, whereas an 8x10 inch format system would reach a CoC of 'only' 0.22 mm!

This is the reason why I think you would be overkilling your large format scan at extreme high scan resolutions, because the resolving power is simply not available.

[onnect17]

IMHO, 5000 dpi is OK with 4x5 with the right lens, emulsion and scanner.
Nowadays with apo, ed, and very fine grain we can get near 100 lp/mm with that particular format.
Perhaps would be wise to verify the real resolution of the scanner in use.

[Peter De Smidt]

It's not just resolution on subject, though, that matters for prints. It's also how the grain is presented. For instance, I've scanned 35mm film at a wide variety of resolutions with my Cezanne. The best results, by a significant margin, came at 6000 spi. At that setting the grain was much finer and more even than at 4000 spi. Of course if you're not enlarging enough to see grain, then that probably doesn't matter.

For me, the balance between quality and cost goes 6000 spi for 35mm, 4000 spi for 120, 4000 spi for 4x5, 2500 spi for 8x10; but this is something that everyone who scans should check out with their film and their scanner.

[Jim Jones]

. . . The Circle of Confusion (CoC) for 35 mm lies typically around 0.029 mm, whereas an 8x10 inch format system would reach a CoC of 'only' 0.22 mm! . . .

The CoC is not an inherent quality of the lens; it is an arbitrary figure created to facilitate using the lens. Even though some lenses are designed for optimum sharpness in small formats, extensive lens tests done by others show some long LF lenses having fairly comparable sharpness over their larger film area.

[The Deer Gunter]

It's not just resolution on subject, though, that matters for prints. It's also how the grain is presented. For instance, I've scanned 35mm film at a wide variety of resolutions with my Cezanne. The best results, by a significant margin, came at 6000 spi. At that setting the grain was much finer and more even than at 4000 spi. Of course if you're not enlarging enough to see grain, then that probably doesn't matter.

For me, the balance between quality and cost goes 6000 spi for 35mm, 4000 spi for 120, 4000 spi for 4x5, 2500 spi for 8x10; but this is something that everyone who scans should check out with their film and their scanner.

I think you may be very close to reality Peter! The only thing I would estimate higher is the medium format resolution. I still found extra usable image information at 5 500+ spi when scanning Mamiya 7 shots. I never took it higher up, but I felt all the detail the film could offer was squeezed out of the lemon at that point.

[fishbulb]

...this is something that everyone who scans should check out with their film and their scanner.

I quite agree.

...you would be overkilling your large format scan at extreme high scan resolutions, because the resolving power is simply not available.

This is only true if the photo was taken very stopped down (f/32, f/64, etc.) At wider apertures, there is a great resolution benefit to scanning large format at 4000dpi, and even minor benefits for scanning at even higher resolutions.

With my own tests of 4x5 Delta 100, I saw significant increases in detail when scanning the same negative at 1000dpi to 2000dpi to 3000dpi to 4000dpi on my Howtek 4500 drum scanner. So I scan everything at 4000dpi and scale it down as needed. (I rarely stop down more than f/22).

This conclusion is supported in detail here: https://www.onlandscape.co.uk/2011/1...ra-comparison/ Check out the first data table. 4000dpi is about where you get about the maximum resolution on 4x5 and 8x10 film. 8000dpi adds a little more real resolution (line pairs) on finely-grained film like Delta 100, but not much more on other films.

Take a look at the second data table in that link. 4x5 and 8x10 suffer large drops in resolution as they are stopped down, so your hypothesis is correct IF the particular photos were taken at small apertures (large f/numbers). Which is may be likely - it's common to see large format images taken at f/32 or f/64. So 2000dpi is probably more than enough for those apertures.

However, when I see a photo taken at f/64, I wonder if the photographer could have used some movements to adjust the plane of focus and taken it at f/32 or even f/16, and really increased the resolution of their image.

A later update to the above linked article includes 35mm film (Canon A1) and 36mp digital (Nikon D800e). https://www.onlandscape.co.uk/2014/1...vs-6x7-velvia/
And this one has more info on print sizes, how big you can print, etc.: https://www.onlandscape.co.uk/2015/03/resolution/

[8x10 user]

360 PPI from a 2880 DPI print engine (screen) is quite nice. I've had reports from major suppliers of RA4 imagers that the actual resolution that they are obtaining is closer to 160 PPI. The samples I got from the US based RA4 imaging supplier sucked when compared to the newest inkjet technology. There is a European based equipment manufacture that makes an RA4 machine that is even higher quality, IMO, then todays inkjet.

In terms of scanning resolution I feel that if you have a good scanner that it is worth it to scan at the highest resolution possible. Even if you reduce the resolution later it will give you better tonality and will capture fine details and film grain with more accuracy. If you capture the grain better then it is easier to remove. Ideally your sample size should match the average grain clump size but the rate of sampling should be up to 3 times higher (due to the stochastic nature of film).

[paulr]

Ideally your sample size should match the average grain clump size but the rate of sampling should be up to 3 times higher (due to the stochastic nature of film).

I'm assuming you're talking about drum scanning. With flatbed scanners, the maximum sampling frequency is usually much higher than the optical resolution. This gives automatic anti-aliassing, and is good for marketing. But it also means that the only real utility to oversampling is noise reduction.