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PostPosted: Sun Oct 12, 2008 12:27 am 
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This is a 35mm Velvia 100 frame, scanned at 4000 dpi on the Howtek drum scanner. It produced a 21 megapixel file. I shot it on a Canon Rebel G with the 24mm TS-E f/3.5L lens.

Below it I compare two scans. One is with an aperture of 6 microns (on the left) and on the right it's with an aperture of 25 microns. A 6 micron aperture is the smallest I can choose on this scanner, which means (in the context of a drum scanner) that 6 microns is the smallest detail size that I can resolve. Most films have a grain size of 10-15 microns. And there are roughly 4233 6-micron intervals in an inch, so this scanner has a true optical resolution of 4000 dpi.

The upshot of this is that you can use a drum scanner with a wider aperture in order to mask grain, which is especially important when scanning small formats like 35mm. This of course can come at the expense of detail and contrast, so the ideal situation is to closely match aperture and grain size.

I normally scan at 13 microns for fine grained film and 19 microns for coarser grained film, but I wanted to do a more severe comparison of 6 microns to 25 microns. The difference is amazing -- far less grain in the 25 micron scan, but far better contrast, detail, actuance in the 6 micron scan.

At the bottom is a 100% crop of the 6 micron scan image, with routine noise reduction (Noiseware) and sharpening applied in Photoshop. Even from 35mm film there is a tremendous amount of detail in a tiny crop.

I'd conclude that you easily get 21 megapixels from a fine grained film scan shot with a good lens. Scanning it at 8000 dpi (like on newer scanners that can go down to 3 microns) probably doesn't add any additional detail resolution, because at 4000 dpi you're already down to film grains.

Image

Image

Image

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PostPosted: Mon Oct 13, 2008 11:09 am 
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I'm trying to get this into context.

Does the 21MP scan capture all of the detail that the 35mm slide contained?

Will a print from the scan have more or less detail than a print made directly from the slide?

Will a print from the scan have more or less detail than a print made from an internegative?

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PostPosted: Mon Oct 13, 2008 1:10 pm 
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I think that a 21 MP scan of this particular film is probably all the detail you're going to get. If at an aperture of 6 microns you're clearly resolving film grains, then you're already resolving the base material at a level beyond any image detail. A higher res scan will not add any detail, but will probably make grain more visible.

I think this is comparable to an optical enlargement, perhaps better because there may be a 5-10% resolution loss through an enlarging lens. That would happen if enlarging an interneg, with the potential added lossiness of any coarser grain structure in the interneg.

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PostPosted: Tue Oct 14, 2008 10:57 am 
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Now do one for Shawn!

Good work, it held the range well. Looks to me like you could avergae between the two aperture settings and geta good compromise between detail and tonal smoothness.

Now, the howtek, it's giving you some colour noise, no? I mean, that colour noise isn't coming straight from the [low speed] film is it? What happens if you average a couple scans? Is the detector on your howtek a ccd or what?

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PostPosted: Tue Oct 14, 2008 11:30 am 
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That's not color noise, it's just dye clouds in the film. If I approach shadows on a transparency by increasing the gamma, it's treated optically so there's no "gain" effect. If I approach them by applying a curve that lightens shadows, however, that does seem to introduce noise.

The Howtek is a true drum scanner -- there is no CCD or CMOS. It's a pure PMT (photomultiplier tube) device.

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PostPosted: Tue Oct 14, 2008 11:49 am 
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That is pretty damn awesome.

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