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Photo Forum / General Photo Topics / General Topics / January 2005Any advantage to scanning emulsion side of slides?
When scanning slides, I wonder if there could be any advantage to scanning the emulsion side of the slides and then reversing the image? >From my experience (which is reasonable, if not professional!) with film scanners up to 4000 dpi, nothing that I could spot. But it's possible it *could* make a small difference depending on the optics and light path. The difficulty will be detecting whether it really is different for that reason, or whether it has just focused slightly better/worse.. Why not try it on your scanner and see for yourself? Yes ... why would you want to scan **through** the base? > When scanning slides, I wonder if there could be any advantage to scanning > the emulsion side of the slides and then reversing the image? > Yes ... why would you want to scan **through** the base? That's why I made the inquiry. All the "here's how to scan slides" sites I've seen direct you to slide the non-emulsion side to give you the same perspective as the projected image, but after thinking about it, I wondered if that could degrade the image to some small degree. > > Yes ... why would you want to scan **through** the base? > > That's why I made the inquiry. All the "here's how to scan slides" sites > I've seen direct you to slide the non-emulsion side to give you the same > perspective as the projected image, but after thinking about it, I wondered > if that could degrade the image to some small degree. Surely because they are transparencies, the light projected through them should be the same either side, unless the coating on one side reflects the light. ?? >> > Yes ... why would you want to scan **through** the base? >> [quoted text clipped - 5 lines] >Surely because they are transparencies, the light projected through them should >be the same either side, unless the coating on one side reflects the light. ?? Yes, it can. but ... think this way ... In the enlarger and projector the light source is on the coated (non-emulsion) side and the emulsion is to the lens' rear port. You're doing the same thing by placing the emulsion closest to the glass, as most scanners today have a lens system to 'read' the item just above the glass. FWIW, I keep the slide in a Wess 'Duplicator' mount to keep anything from touching the actual film. This is a special mount that shows the entire exposed area, unlike standard plastic or cardboard mounts. Can you show any examples? Back when I was a very keen film-scanner (about 2 years back, don't do all that much now..) this question came up quite a few times on the filmscanner lists I was on, but no-one could show any convincing evidence either way. I'm genuinely interested.. (sorry if double-posted..) >Can you show any examples? Back when I was a very keen film-scanner >(about 2 years back, don't do all that much now..) this question came >up quite a few times on the filmscanner lists I was on, but no-one >could show any convincing evidence either way. I'm genuinely >interested.. My hunch and aging knowledge of physics tell me that it would make no discernable difference whatsoever. I've got a micrometer somewhere and could measure the thickness of a transparency, but there's no point, quite frankly. The depth of field of your typical scanner is >> the thickness of the film. It's not about "depth of field" ... it's about putting the crap, aberrations, dirt, and distortion of the *film base* between the scanner and the image. It was never designed to be used that way. The film base is simply a substrate to support the emulsion, and is/was never "controlled" as part of the optical chain. Yep, and there's also the issue of the light path and optics - the light paths in flatbed/film/drum scanners can be quite different to that of a projector (and of the taking lens for that matter). Just like in enlargers, some clearly use more/less parallel/diffuse light sources than others, some *do* have extremely limited depth of field (eg nikon LED scanners). So to dismiss the idea that turning the film around will have no visible effect may be a bit rash. To start another argument ((O;) it's a bit like saying that an optically flat UV filter will have no effect on the sharpness of your images. In fact, if you start looking at it very closely and looking at the light path and how it is affected by that (admittedly small, but *extra* refraction), you will see it may not be quite true.. But to contradict myself (grin) - like I said above, I have not actually seen direct evidence of a difference, and it would be pretty hard to prove that it wasn't just a slight difference in focus. |
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