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Thread: Scanner comparisson page and drum scan limits?

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    Scanner comparisson page and drum scan limits?

    I have been looking at the scanner comparisson page http://www.largeformatphotography.info/scan-comparison/

    And it got me thinking.... the scanning comparison page we were looking compares the scans at 2400ppi, the highest optical resolution of the v700 (which I am contemplating purchasing), however the drum scanners can go beyond 8000ppi!!! Even at the 2400ppi the drum scans are so much cleaner than the flatbed or the flextight which lies in between in my opinion. The comparisson image was a 4x5 film that * had a 10x enlargement if printed at 240ppi 40x50 print! I am wonder how much data does the 4x5 hold if the tango is so much cleaner. In other words at which ppi is the practical resolution of the film reached with the drum scan?....

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    Kirk Gittings's Avatar
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    Re: Scanner comparisson page and drum scan limits?

    Thanks,
    Kirk

    "When did photography become a desk job?" Kirk Gittings 2009

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    Re: Scanner comparisson page and drum scan limits?

    Quote Originally Posted by l2oBiN View Post
    In other words at which ppi is the practical resolution of the film reached with the drum scan?....
    It really depends on the lens and film combination you're using but first of all on what's practical to you.

    Take a sharp Zeiss lens on high resolution 35mm film like Spur Orthopan UR (ASA 12) which is based on an Agfa microfilm emulsion, and you're able to get finer detail on film than any scanner can detect. Recently we did a test comparing this combination to Fuji Acros on 4x5" shot with the 110XL. The 35mm microfilm was surprisingly close in terms of overall detail. You would need something in the range of 14,000 spi optically to get the finest information from that microfilm digitized.
    On 8x10" I found the best lenses offer diffraction limited resolution on film at f/22 in the center for high contrast detail. So getting all the detail into the file requires a scan of up to 3500 spi resulting in a 5.5 GB file. Of course for lower contrast detail the effective resolution on film is lower.
    With their smaller image circle 4x5" lenses are usually slightly sharper. So 4000-4500 spi will probably be sufficient to get all the detail.

    But in practical terms with normal modern fine grained films you'll get most of the information from the film with an optical scan at 2000-4000 spi provided that the scanner still has a high MTF within that range. It's only areas with high contrast detail that require higher sampling resolutions.
    If, however, you're planning to print really large it's always better to scan at least to the desired printing resolution. The tonal transitions are much nicer when scanned optically from film than interpolated by software.

    BTW when it comes to scanner resolution the latest Flextight X5 is in the same league as the best drum scanners for 35mm film. It was tested recently at ScanDig and came out with an effective resolution of 6900 ppi. Unfortunately the text is in German only, but when you scroll down you can take a look at the scan sample of the USAF1951 target.

    -Dominique

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    Re: Scanner comparisson page and drum scan limits?

    Quote Originally Posted by l2oBiN View Post
    In other words at which ppi is the practical resolution of the film reached with the drum scan?....
    It depends on the quality of the drum scanner, and its ability to set the aperture to match the grain size on the film. There is a huge difference between flatbeds and drums. Flatbed's scan blurry, and the image is then sharpened (sometimes quite successfully for the size). Drum scanner's start out sharp. You can get 8,000 ppi out of them, but of course, that depends on how you quantify it. There are a lot of variables, and where one of us is clear about one part of the equation we may be not so clear about another. What I can tell you is that things look better in a scanner capable of 8,000 (or 3 microns) vs one that is set to 4,000. In sharpness, with test targets, a Premier beats a Tango hands down. In real life scanning with real film it's hard to quantify, harder to prove and as sharpening gets better, sometimes hard to justify. However, the old rule of "can't get more than 4,000" isn't true, in my opinion.

    I have been fortunate to have a drum scanner, I like to start out sharp. Contrary to what Dominique referred to, an Imacon/Hassleblad is closer to a flatbed scanner - in that it uses ccd technology. It has a better lens than most flatbeds and the results are better. But it does not match a drum scan.

    There is one other issue that I will mention that is a pet peeve of mine. We constantly talk (ok, haggle) about resolution. We have a lot of sharp lenses these days, skilled camera operators who know how to tip a front standard (for example) and good film and developers. My scanner gets all the sharpness the film has, I zoom in to the grains and can see it. The amount of sharpness in a digital print from a scan of this type is limited by the printers ability to put down dots in a tight enough pattern, without the slightest banding, overinking, etc.

    The real issue for me has been full tonal reproduction. There are some inherent conversion issues that plague the digital world. A PMT (photo multiplier tube) is capable of picking up a few photons of light inside the dark box. They are extremely sensitive, sensing about 20K steps per channel or 64K for RGB. The ccd's pale in comparison. Consider what you work with in Photoshop, where you have steps from 1 to 255. That's quite a dip in tonal representation. Getting "all of the juice" requires a strategic approach.

    Many people make a scan to look like the print they are going to make. This is a mistake. I was doing some scans with a friend last night and we were playing with pulling out the tonal separations inherent in the film. As we raised and lowered the midtones, we could see some of the tones blending together. We moved the values until they separated, which may have been lighter or darker than the actual print in that area. The clear goal is to supply the raw materials (tonally separated) so that someone can make a great print from the scan (after a little adjustment).

    As has been said many times on this forum and others, this is the reason that "a scan is not just a scan". The operator is the key vs the machine. Working with someone on a long term basis to pull out all the "juice" from your work is the answer to a lot of these questions, especially for people who want exquisite prints. (Or practicing one's self - with a good drum, if finances allow.)

    There is nothing wrong with doing one's own scans. Anyone can learn, of course. However, while I am not sure your question is the right one to ask, there is certainly more than 2,400 in the film, on a couple of fronts.

    This was a longer answer than the question, I apologize for the long-windedness and I hope the info is useful to some.

    Lenny Eiger
    EigerStudios

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    Re: Scanner comparisson page and drum scan limits?

    If a large format lens delivers 60 lines per millimeter on film, we consider it pretty good.

    Since there are 25.4 mm per inch, that is 60 x 25.4 = 1524 lines per inch. To effectively resolve 1524 lines per inch, we need a scanner that can resolve 3048 lines per inch, isn't that right ?

    Given an image made with such a lens, if we scan at greater than 3000 spi, what are we getting ?

    Or is my math wrong ?

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    Re: Scanner comparisson page and drum scan limits?

    Quote Originally Posted by Ken Lee View Post
    Given an image made with such a lens, if we scan at greater than 3000 spi, what are we getting ?

    Or is my math wrong ?
    Wen you have a device that can see in to the grains - and can reproduce them as samples you get what the film has. I have seen this kind of math used to describe things, way too often, but it simply does not match to real life...

    Once again, the conversation is about sharpness. What about tonal reproduction?

    Respectfully, I just don't think this is right, or the whole picture.

    Lenny

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    Re: Scanner comparisson page and drum scan limits?

    Ken raises a critical point and one that has been nagging me. I think his math is correct if one talks about lines per mm on a high contrast target (that is near 100% contrast). But what about a target that has much less contrast say 50% or 25%, or even a sine function target?

    Now if we want to resolve the fine density gradations between lines on a sine target we will need some degree of higher resolution than is simply implied by the target lines/mm - maybe a much higher resolution. The same logic also holds for small variations in density on film, that is dimensions beyond the resolving power of the taking lens. Another way of saying this; is it useful to scan at a resolution that will detect artifacts that emanate from a resolvable point on the original subject and that has been recorded on the film.

    I wonder if this is something that Lenny is alluding to when he comments on the value of extreme resolution scanners that employ PMTs, like Aztec.

    In fact is the issue of scanner resolution tied more to the resolving power of the film than to the taking lens?

    Nate Potter, Austin TX.

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    Re: Scanner comparisson page and drum scan limits?

    Quote Originally Posted by Ken Lee View Post
    Since there are 25.4 mm per inch, that is 60 x 25.4 = 1524 lines per inch. To effectively resolve 1524 lines per inch, we need a scanner that can resolve 3048 lines per inch, isn't that right ?

    Given an image made with such a lens, if we scan at greater than 3000 spi, what are we getting ?
    Ken, your math and assumptions are both correct, with one big caveat. 3048 is the absolute smallest number of samples necessary to represent 1524 cycles. In reality, various factors prevent your scanner from resolving every pixel perfectly. Some scanners will be able to resolve 1524 cycles per inch by increasing the number of samples (ie, scanning at 4000 DPI/SPI or beyond). However some scanners won't see any improvement, because the scanner optics or sensor are already limiting resolution at 3000 SPI. For example, my Epson flatbed will never resolve 60 lp/mm, no matter what the SPI is set to.

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    Re: Scanner comparisson page and drum scan limits?

    Quote Originally Posted by Nathan Potter View Post
    In fact is the issue of scanner resolution tied more to the resolving power of the film than to the taking lens?

    Nate Potter, Austin TX.
    In my opinion, no, the limit to resolution is always the weakest link in the chain. In the case of a scan, the chain is 1) film, 2) lens and 4) the optical scanning resolution. I assume optimum conditions to get maximum resolution, i.e. camera on tripod, lens at best aperture, etc.

    If you scan at an optical resolution beyond the potential of the film and the lens you look deeper and deeper into the film and see finer and finer grain clumps. But this is not resolution, and it is not sharpness, though depending on how it is processed it may appear to produce sharpness, when in fact is is only an illusion of sharpness that could be achieved with other methods of processing.

    When I write "optical resolution" I mean the true effective resolution, not the stated resolution in dpi. As others have pointed out there is a huge difference in effective yield between various scanners.

    Sandy King
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    Re: Scanner comparisson page and drum scan limits?

    Quote Originally Posted by sanking View Post
    If you scan at an optical resolution beyond the potential of the film and the lens you look deeper and deeper into the film and see finer and finer grain clumps. But this is not resolution, and it is not sharpness, though depending on how it is processed it may appear to produce sharpness, when in fact is is only an illusion of sharpness that could be achieved with other methods of processing.
    Thank you - That confirms my experience when scanning 35mm film at 4800 spi with a Minolta Dimage Multi Pro scanner: once I exceeded the limit of the taking lens + film, all the rest was just... grain.
    Last edited by Ken Lee; 3-Sep-2010 at 16:10.

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