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  1. #11

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    Ed - the Beseler/Minolta is an extremely weak flash tube system which presents
    distinct problems dodging and burning. It has indeed been successfully used for relatively small C-prints, but probably isn't bright enough for either large prints or
    something like Cibachrome. Similarly, a long time ago Phillips made a small simple rheostatic additive colorhead which was simply too weak for most professional
    applications. So once you up the ante things start getting complicated. To my
    knowledge, the only 8x10 colorheads in the world are my own and six owned by
    the NSA adapted for 9-inch aerial spyplane film (I don't know who built them or
    if they still use them).

  2. #12

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    Sorry, I obviously meant to say, the only 8x10 "additive" colorheads... But expensive laser digital printers and the Chromira concept work on a similar RGB premise.

  3. #13

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    One more postscipt - big additive enlargers (up to 11x14 film size) using powerful xenon flash tubes were once available for color separation work with pin-registered easels, but these would be classified as sequential additive rather than simultaneous. Similarly, one could simply print on a conventional enlarger
    using deep tricolor filters in sequence, but this would be quite slow and clumsy, and require a lot of trial and error testing. It has been done.

  4. #14
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    In college I used an Nord enlarging system that was RGB , took no time to adabpt, Lambda digital Printer is an RGB system but uses CMY control board plus density.
    In fact it is identical to an 8x10 Durst Enlarger in application.

  5. #15

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    Drew, tell us more about your color head. Indeed, beseler 45a has some limitations, but for up to 4x5 negs and prints up to say 20x24 it seems to work ok so far. I do wish the tubes had more power though.

  6. #16

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    The whole problem with additive enlargers is that the narrow-band filters are so dense that it takes a lot
    more light to do the job, and then you end up with serious heat issues. Too much heat not only ruins the
    filters prematurely, but drives up the utility bills and potentially fades the original neg or chrome. Real
    powerful flash tubes would ideally need to have the colorhead water-jacket-cooled and can cause electrical havoc. I used a powerful spectrophotometer once that blew its capacitor and every surge
    protector in sequence, then destroyed a whole room full of computers. Joe Holmes up the hill from me
    made a 4x5 additive head using a bank of tunsten-halogen bulbs each controlled by rheostats. It delivered
    nice color but his Ciba exposures were running eight or nine minutes. So to keep the color within parameters he had to resort to excessively narrow-bandpass filters which slowed things even more, with
    the inevitable reciprocity failure problems. At the end of their pro mfg, Durst adapted their top of the
    line 8X10 colorheads to additive, but never marketed them because labs were switching to digital printing.
    I suspects the remaining components for these were used by the NSA for their bank of enlargers, along
    with controls from ZBE. The problem with both the Durst and ZBE colorheads per se was again the terrible
    heat. Under lab use, filters might last only six months and cost hundreds to replace each time. So I'll
    explain my own approach in a following thread, when I get another moment....

  7. #17

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    Crystal Archive Type II and Type DPII are completely different papers.
    I just checked the data sheets for both of them and Type II is "designed for both analog and digital printers", whereas Type DP is "designed exclusively for digital output".
    Their spectral sensitivity curves are also very different.

    It's possible that Type DPII is not sold in the US at all, or has a different name.
    I know that DPII is being used for optical printing here in UK, but i'd love to find out how this paper responds.

    Many thanks for all the replies so far.

    I'm also very curious about the benefits of additive printing and enlargers (I'm using medium format negatives).

  8. #18

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    To continue ... as some of you might know, Beseler attempted to introduce a more powerful additive
    colorhead using multiple tungsten-halogen bulbs. There were several things good about the design and
    several things terribly wrong that gave it a bad rap. I don't know who the subcontractor was, but they
    didn't spell out our understand the implications of EMI (electro-magnetic interference) with multiple
    solid-state circuits, and the need for dedicated or isolated power; then they had a bad batch of triacs in some of the controllers; and the diffusion system was very poorly designed; plus, around the same time, Beseler changed ownership and the new owners had very little interest in honoring warranties on confusing equipment. But the control panel was very useful for converting YMC to RGB and was not itself
    problematic. I cannibalized some of this stuff to make a prototype colorhead for my 5X7 Durst chassis,
    but competely redesigned everything else, including a mirror box which essential tripled the light output
    (important for slow-printing Ciba work, which was my specialty at that time). This equipment works perfectly to this day, but that was the simple project, and next I had to figure out how to convert the
    idea into an 8x10 system. I'm neither an electrical engineer or a rich guy, so had to do it right the first time with only a fifteen grand budget... (to be cont'd)...

  9. #19

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    The last round of big Durst colorheads used a 2000W bulb which stairstepped down through two or more
    stages of diffusers. In the additive form, if it ever reached the market, the price for the colorhead would
    have probably been around 45K back then or a lot more at todays inflated prices. From my previous experience having custom mfg air compressors, I learned that the best way to control heat is to divide
    and conquer. So for my 8x10 enlarger I split the colorhead into a Y formation feeding into a common mirror
    box. This kept is running cool but presented a different set of problems. I had to integrate the light output
    of each; fortunately, ZBE had already engineered a device which monitored this kind of thing, and I could
    simply calibrate the heads together. Size and weight were obviously also going to be an issue. I built the
    colorhead housing out of 3/8 black Garolite phenolic, and it has to be raised or lowed for maintenance using a block and tackle. I wanted the enlarger chassis to be bombproof in this seismic neighborhood.
    It stands about 12ft tall and is made out of expoxy-impregnated structural beam material which is extremely dimensionally stable and strong. I load the enlarger using a rolling platform ladder. The focus
    device was cannibalized from a Sinar P studio camera, the yaw correction from a $0 military surplus micrometer-driven mortar aiming device (it would have costed thousands to custom mfg), the precision
    30X40 pin-registered vacuum easel was cannibalized $0 from a 22 ft long process camera when a print
    shop was being remodeled. The mirror box was tricky. I was able to distribute the light laterally using a
    linear array fresnel (no resemblance to a typical focussing fresnel lens), then grind a series of graduated
    diffusers per different lenses for falloff correction. Sometimes I still need to edge and corner dodge or burn, so this could use a little more fine-tuning. The electronics were an utter beast to psychoanalyze.
    Won't go into that. Today I would use sine-wave technology like they use for stage light setups in rock concerts etc, but that simply wasn't available yet.

  10. #20

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    listen mate, why won't you start your own thread?

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