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Thread: Picking ideal lens and fl, for flat copy work

  1. #1

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    Picking ideal lens and fl, for flat copy work

    I need a lens to perform flat copy work. I will photographing very sharp prints about 32 x 40" down to 4x5 film. So about 1:8 . I am trying to pick a lens (and a lens fl) to perform this task which will yield the sharpest images to the entire film area. I tried researching flat field lenses, as this task is surely a flat field task. After reading this article by Ron Wisner, I am starting to beleive there is no real benefit of a flat field lens over a traditional lens. (except maybe for wide angle flat copy, which can be avoided by choosing a longer fl lens)

    http://www.wisner.com/myth.htm

    Here is my thinking so far, please feel free to correct or add to any of my thoughts.... I have no experience at doing repro work.

    1. Lens fl - First I take the image diagnol of the film, 150mm, and desire a fl lens which is at least equal to this. My theory is, the larger the angle of view of the lens, the more obstacles a lens must overcome, which prevents the lens from being as sharp as a normal fl lens. (normal fl being defined as, lens fl = film diag.) Of course, the same applies to camera lenses.

    2. MTF values - Next, I looked at the MTF curves of lenses within this "normal fl", and within the 1:8 magnfication working area.

    3. The obvious items, such as image circle, light fall off, distortion, etc.



    Now, my first thought was that a darkroom lens (not camera lenses) would be most suited for this task, and it's possible they are. But after reviewing the MTF values of Schneiders enlarging lenses, I began to second guess this. I found the Schneider 150 mm Digitar lens (camera lens) to be superior to the enlarging lenses in just about every aspect at this magnfication ratio??

    Then, I began to think it was the "flat field issue" that made the darkroom lenses superior for this task, but Ron Wisner article convinced me otherwise. (despite Bob Solomons small mention of this a few weeks back) Then I began to think, possibly the latest digital lenses simply trumped the previous lens technologies, whereas in the past, darkroom lenses would produce superior results vs. camera lenses, but possibly the latest lens designs and glass types may have given the digitar camera lenses an advantage, even in reproduction / darkroom applications? Of course, this only applies when the digitars specs can accomplish the reproduction requirements, which is not always the case.

    Or, I am missing something completely? Maybe when the digitars are suitable for reproduction, they are the best option available, even though they were designed for camera use? What criteria would you use to pick such a lens?

    If the digitar becomes the lens of choice, I am considering a vacuum back, as the 150mm digitar is optimized for this magnfication ratio at f8, which can make the ol "depth of focus" an un-welcome deal breaker.

    TYIA

  2. #2

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    Picking ideal lens and fl, for flat copy work

    One last thing I forgot to mention.

    The digitar lense I proposed to use, is designed to take a larger image and compress it onto the smaller film. Hence the MTF values should reflect such.

    However, the enlarging lenses I mentioned above are designed to take a small image and project it larger, therefore there MTF values reflect such, which is NOT the task I am requiring the lens to perform. The Schneider web site did not have any "copy lenses" listed on their web site.

    Now, I assume a "copy lens" is an enlarging lens designed to be used in the reverse manner, i.e. compressing an image vs. enlarging it. If this is correct, I could not find any MTF charts for "copy lenses". Can anyone provide a link to such? I would assume, if any lens is a tough competitor to the Digitar, it must be one of these "copy" lenses? Right?

  3. #3

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    Picking ideal lens and fl, for flat copy work

    Look, Bill, all decent lenses have high MTFs near the center of the field at all apertures. So use a lens that's longer than needed to avoid an MTF that falls off towards the edge of the field you need. Incidentally, that's why MTF at the edge increases with magnification.

    Both taking lenses and enlarging lenses are optimized for "large in front", "small behind." The lenses don't care whether light passes from front to rear, as when taking a picture, or from rear to front as when printing. That's why some of us use enlarging lenses for closeup photography.

    Enlarging lenses, except those made for printing murals, are typically optimzed for more-or-less the magnification you need.

    Just grit your teeth and ante up for a 210 Apo El Nikkor.

    Oh, and by the way, how do you plan to align subject and film plane?

  4. #4

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    Picking ideal lens and fl, for flat copy work

    > So use a lens that's longer than needed to avoid an MTF that falls off towards the edge of the field you need.

    Dan, the 150 Digitar has better MTF throughout the image circle, vs. any of the other suitable lenses I could find, including the Schneider enlarging lenses?

    Why grit my teeth and buy 210 Apo Nikkor? I can't find any information on it? Why do you suspect it being better then the digitar?

    As for alignment, I will save that possibly for a new thread, as this has been discussed in several threads.

  5. #5
    Jack Flesher's Avatar
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    Picking ideal lens and fl, for flat copy work

    The digitars, while exceedingly sharp, have relatively small image circles; the 120 won't fully cover 4x5 film. Hence a copy lens is probably going to be your best bet. Personally I would consider a Schneider G-Claron 210 -- they can be found used in shutters for under $400...
    Jack Flesher

    www.getdpi.com

  6. #6

    Picking ideal lens and fl, for flat copy work

    This will likely do a better job for your repro work:

    Chromatics Art Scanning Camera

    For the smaller subjects a flatbed scanner will work wonderfully. Unless having this work on film is the final desired output you won't beat scanning the original art.

    If film shot in your camera is a must then, in general, longer lenses will make your job easier. How about a repro lens? They are cheap, readily available and made for doing the kind of work you have in mind until you get down to the 4x5 size objects. At that point a duplicating lens is in order for the very finest result.

    Just because the 150 Digitar is best across its circle does not mean that its better than any other lens with a much larger circle. The larger circle lens MTF may fall off at 200mm but be extremely sharp over the area you'll be using.

    But again - why not scan this stuff? For any method of repro I can think of, scanning wil give a better result.

  7. #7

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    Picking ideal lens and fl, for flat copy work

    Jack the image circle of the digitars is 150mm, enough for 4x5.... the sharpness is extraordinary even at the edges....

    Henry, I failed to mention, the film is the final product.... I am coming from a digital file to film, not the reverse. I can not find a better MTF over the 150mm image circle I need.... no LF lenses even come close to the digitar, at least for all the modern Schneider offerings. I would use a longer digitar, but 150mm is the longest they currently make. I think Rodenstock may make one digital lens which is longer, but I have not seen its MTF chart.

  8. #8

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    Picking ideal lens and fl, for flat copy work

    WG, I have only been doing art copy work in my studio for 14 years now and I use the GClaron line of lenses, 150, 210, 270 and 305. They are perfect for the job from 4x5 to 8x10 transparencies. They are low in cost and easy to use and produce images that can be printed billboard size at highest quaity. Quit grousing over MTF's and go to work, you will like them. Paul

  9. #9

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    Picking ideal lens and fl, for flat copy work

    Paul, unless the entire MTF principle is bunk, the digitar MTF's out perform the G Claron MTF's by a factor of about 3x, yep, 300% better, not 30% better. If the MTF's are only marginaly accurate, well, for that type of improvement, I am willing to do some grousing (whatever that means)

  10. #10

    Picking ideal lens and fl, for flat copy work

    You seem pretty set on the digitar, eh? Why bother asking if you've already made up your mind..?

    That said, why use a lens at all? You want to go from a digital file to a piece of 4x5 film. Why have a print in between? Use a film plotter. There are various labs that will do that for you, for much less than the cost of the equipment you're considering.

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