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Thread: Scanner comparisson page and drum scan limits?

  1. #11

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    Re: Scanner comparisson page and drum scan limits?

    Well I can agree with what Sandy says but that was not quite my point. I put it poorly. So to explain another way.

    If I have a very fine grain film where even clumps cannot be resolved by the scanner and in fact the resolution on the film is totally determined by the film, then is there some kind of advantage in scanning beyond the resolution imposed by the taking lens? The advantage being this kind of elusive "quality" that Lenny mentions about very high resolution scans.

    Nate Potter, Austin TX.

  2. #12

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    Re: Scanner comparisson page and drum scan limits?

    As Sandy said, "the limit to resolution is always the weakest link in the chain"

    Let's say we are taking a photo of the earth from outer space, with a camera that can resolve 1 meter at most. Can we read the print on a newspaper ?

  3. #13

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    Re: Scanner comparisson page and drum scan limits?

    "If I have a very fine grain film where even clumps cannot be resolved by the scanner and in fact the resolution on the film is totally determined by the film..."

    Perhaps I misunderstand, but that sounds contradictory. If the film is so fine-grained that it's undetectable, then the taking lens (or the tripod) determines resolution, not the film.

  4. #14

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    Re: Scanner comparisson page and drum scan limits?

    Quote Originally Posted by Ken Lee View Post
    As Sandy said, "the limit to resolution is always the weakest link in the chain"

    Let's say we are taking a photo of the earth from outer space, with a camera that can resolve 1 meter at most. Can we read the print on a newspaper ?
    Hm, well, if not it seems CSI has some explanations to do...

  5. #15

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    Re: Scanner comparisson page and drum scan limits?

    Quote Originally Posted by Lenny Eiger View Post
    However, the old rule of "can't get more than 4,000" isn't true, in my opinion.
    I agree. A scanner designed for higher resolutions usually performs better at lower resolutions than a scanner being at its limit at 4,000 spi. Any idea how the old Linotype-Hell scanners performed at their stated maximum resolution of 24,000 spi?
    Quote Originally Posted by Lenny Eiger View Post
    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.
    I was only comparing the X5 in terms of resolution on 35mm film. Tonality is a different story. That's where I'd prefer a high-end drum scanner any time. I was comparing X5 scans with my own ICG scans at the highest optical resolution of 8,900 spi. I really have to say that the X5 was on par. I don't know if a Premier could do so much better when even the X5 is quite close to its 8000 spi spec. If you could show some sample how a Premier scan looks at 8,000 ppi maybe the difference compared to other scanners is obvious.
    Quote Originally Posted by Lenny Eiger View Post
    My scanner gets all the sharpness the film has, I zoom in to the grains and can see it.
    Seeing the grain pattern in a scan does not necessarily imply that you're getting all the detail. The grain clumps in a single emulsion are of various size. To detect some detail hidden in the smallest grain clumps you would have to use a very small aperture which is going to cause grain aliasing from the larger grain clumps. Your choice of aperture is a compromise between maximizing the amount of detail and minimizing artifacts. This may not be a problem for large format film because the LF lenses are unable to transfer enough contrast in the high spatial frequencies for most films to capture. But think about the resolving power of the best 35mm lenses. Choosing a high res film for these lenses can really make a difference in terms of resolving power. Like in our tests with microfilm we could record more than 250 lp/mm on film. You would require a sampling spot smaller than 2 microns and a very high MTF at that frequency to digitize these fine structures.
    Quote Originally Posted by Lenny Eiger View Post
    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.
    May I ask where you got those number about the 20K steps per PMT channel?
    As far as I understand the PMT signal generates an analogue current which is routed through a log amp before going into the A/D converter where it's digitized and the steps are introduced. But in general I agree that you start off with a strong signal from the PMT.
    One thing though that made me wonder was a comment by Karl Hudson in the ScanHi-End newsgroup where he made a statement about the Tango being able to resolve down to 4 microns with a 15.9 micron aperture.
    Quote Originally Posted by Karl Hudson
    Also remember there has to be SOME light falling on the photomultiplier to get any kind of dynamic range. How many photons can pass through 3 microns? I have no idea but I'm sure a lot more pass through a 15 micron aperture ...and after all the PMT's are going to "white out" on clear drum and set the 6 volt peak signal there. Then it's going to block the light and adjust the op amps to zero volts offset there. What's in between is your dynamic range. The less light you have to start with on white-out, the less dynamic range your scan will have.
    It got me thinking how useful a 3 micron aperture really is if it compromises the signal's dynamic range. Maybe this is another factor besides the grain aliasing causing the noise you get on 3 micron scans. How often do you actually use the 3 micron aperture?
    Quote Originally Posted by Lenny Eiger View Post
    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).
    If you're working with 16 bit/channel, is there any advantage applying the tonal separations in the scanner software compared to what you could do with a raw scan in Photoshop?

    Damn, with all these quotes the my original post went over 10,000 characters. Sorry about the length.

    -Dominique

  6. #16

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    Re: Scanner comparisson page and drum scan limits?

    Quote Originally Posted by sanking View Post
    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.
    It is not that simple that the system resolution is limited by the weakest link in the chain. It's rather a function of contrast of all the links combined, and the weakest link reduces the overall contrast more than the others. Please see below my response to Nate's post where I'm going to elaborate on that point further.
    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 it is only an illusion of sharpness that could be achieved with other methods of processing.
    That's correct, but it's hard to define where the resolution of a lens and film combination stops because the variance is huge depending on the contrast at hand. When you're photographing a test target with a line pattern it may give you an idea what your capture system is capable of when it comes to 2-4 stops contrast. The great work of Chris Perez and Kerry Thalmann may serve as a base as well for LF lenses and TMX or similar film. And when you're scanning the MTF of the scanner needs to taken into account. A scanner that maxes out on a scanner test target at 60 lp/mm will probably be unable to detect some barely resolved detail on film at that frequency.

    Quote Originally Posted by Nathan Potter View Post
    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.
    For real world photography it is an interesting question how a lens, a film and a scanner perform on a target of lesser contrast. A sine target gives a much more realistic result about the performance than a simple line target, but these are very expensive.

    When I tested my ICG drum scanner with a high contrast scanner target it was able to resolve more than 160 lp/mm. But with a test target shot on film the effective resolution was much less because the contrast of the finest detail on film was too low for the scanner to detect at the highest spatial frequencies. Thus I'd take the lp/mm values from scanner tests with a grain of salt though it might work as a relative comparison between the machines. But it's really the MTF that is important. Unfortunately these are not published. A drum scanner's MTF depends on the mechanical precision, the optics and the effective aperture. A real world photograph has much lower contrast in high spatial frequencies. To detect the highest spatial frequencies captured on film you would need a scanner that has a close to 100% MTF on those frequencies.

    Example:
    Let's just say we're trying to record some detail at 60 lp/mm that has a contrast of one stop. At f/22 and 1:20 magnification ratio a perfect diffraction limited LF lens transfers 14.7% contrast for that frequency. A modern slide film like Fuji Astia 100F transfers about 38% contrast at 60 cycle/mm according to the published MTF. I'm taking a transparency film for this because it doesn't compress the tonal range like most negative films do. So our one stop real contrast in the scene becomes just 1/18 of a stop on film if everything else is perfect. The scanner needs a very high MTF at the 60 lp/mm frequency to detect that sort of detail. A high res drum scanner has the necessary optics and mechanical precision to capture such fine detail. But the higher you go with your desired resolution you'll see that even the best drum scanners have their limitations. If you take negative film with its compressed tonality it's even harder for the scanner to detect those very subtle differences in density where the finest detail is hidden.

    As Ben pointed out oversampling helps to get a more precise image of the lower spatial frequencies. I can see it even in blurry areas with no detail at all that the tonal transitions are nicer if the scan was made at a higher optical resolution. If your desired print size requires a scan beyond 4000 ppi than I would always recommend to scan for the native resolution of the printer.
    Last week I was scanning very old 35mm slide film from the 60s that is going to be blown up to 2 x 3 meters. I used the maximum optical resolution of the scanner at 8,900 ppi which is enough for a 105 ppi print at that size. The client told me the printer wants 195 ppi. I could have used the 12,000 ppi setting of my scanner but it is in fact only 12,000 x 6,000 so I found the 8,900 x 8,900 to be the best solution I could offer, also considering scanning hours and file size.
    Lenny, would you have used the 16,000 x 8,000 setting of your Premier in a similar case?

    -Dominique

  7. #17

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    Re: Scanner comparisson page and drum scan limits?

    Quote Originally Posted by SCHWARZZEIT View Post
    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
    The text came up in English for me! Guess something out there knows whether we speak English or German?

    Sandy
    For discussion and information about carbon transfer please visit the carbon group at groups.io
    [url]https://groups.io/g/carbon

  8. #18

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    Re: Scanner comparisson page and drum scan limits?

    Some scan comparisons (scroll down):

    http://www.clarkvision.com/articles/...l#introduction

  9. #19
    pramm
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    Re: Scanner comparisson page and drum scan limits?

    Quote Originally Posted by SCHWARZZEIT View Post
    It is not that simple that the system resolution is limited by the weakest link in the chain. It's rather a function of contrast of all the links combined, and the weakest link reduces the overall contrast more than the others.
    -Dominique
    I am going back a long ways, but I believe system MTF is the product of the discrete component MTFs. Improving the weakest link is often the easiest way to get a proportional improvement.

    More generally, the expert eye has always been the best judge. Scanner SNR is directly related to so many factors that providing a broadly applicable quality metric would be very difficult. I do not recall ever seeing a thorough analysis back when PMT and CCD scanners were relevant to some lucrative markets. People bought what made their data look good - as they do today I guess.

    Practically, I believe a PMT-based system can be engineered to have better SNR at small apertures than any area-based detector. LN2-cooled or amplified CCDs can actually detect single photons and have some advantages (primarily speed), but a PMT-based detector is more sensitive (better SNR) at low flux levels.

    I am sure the engineers on this board can put it better but here's my simple summary. At anything under NASA price levels, PMTs maintain better SNR at small sampling apertures. This yields better MTF = perceptually better rendition of intensity variation overall and less visible "grain" in light image areas. Drum scanners are a fast way to position a PMT over large areas so we like 'em for LF. Wish I had a drum to play with today.

  10. #20

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    Re: Scanner comparisson page and drum scan limits?

    Quote Originally Posted by Ron Marshall View Post
    Some scan comparisons (scroll down)
    What item in particular please ?

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