Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 71,849   Posts: 1,582,824   Online: 730
      
Page 3 of 3 FirstFirst 123
Results 21 to 28 of 28
  1. #21
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    23,534
    Images
    65
    Quote Originally Posted by holmburgers View Post
    No worries, something's always better than nothing.
    I've got nothing. The folder included some prints, but none with R/G/B exposure so I remembered wrong. Sorry. If I do find something, I'll scan and post, but I doubt it now.

    PE

  2. #22
    Photo Engineer's Avatar
    Join Date
    Apr 2005
    Location
    Rochester, NY
    Shooter
    Multi Format
    Posts
    23,534
    Images
    65
    Quote Originally Posted by hrst View Post
    Is there a filter with three narrow passbands at R, G and B, that would change white light to trichromatic RGB "white"? It would give the same saturation boost by lowering crosstalk with white-light source, but with single exposure.

    Another option would be to use RGB LED source, but the most common ones wouldn't probably have the best possible wavelengths so we would again have some crosstalk.
    The basic problem here is that the final "white" that you want is not daylight "white", but rather a reddish Tungsten "white". And, to get this Tungsten balance, you have to fiddle with the quantity of light passed by each filter.

    To do that, you must give unequal exposures through each filter or use CC filters if you try to use the "white" produced by juxtaposition of the output of each of the 3 during exposure.

    PE

  3. #23

    Join Date
    Dec 2006
    Shooter
    Medium Format
    Posts
    348
    nyoung (neil young? ), if you try it, please let us know![/QUOTE]

    Sadly, all darkroom except for changing bags and developing tanks is packed away pending completion of the house remodel. I will try a comparison as soon as I get set up again but it will probably be in the deep winter (February).

    For those who aren't familiar with the Phillips enlargers, the color head uses three halogen lamps illuminating through three narrow pass filters that can be individually controlled so it would be very easy to expose the red channel, then the green and then the blue. Normally, you use all three at once.

  4. #24

    Join Date
    Sep 2008
    Shooter
    Multi Format
    Posts
    806
    If/when I get a condenser head, I could post examples. I have 4 of the Minolta/beseler 45A heads, that's my main color head. I've printed with dicrho heads and condensor head with filters in drawer also. I don't recall there being huge color differences between the methods. for B&W I use an Aristo head. (all on a 45-VXL)

    The Minolta/Beseler 45A is a nice head. One can be picked up on ebay, complete, for less than the price of one or two of the hard-to-find replacement flashtubes. Thats' why I have 4. One for use, and 3 for spares, complete with tubes. It was a $2500+ head back in the day.

    -Ed

  5. #25

    Join Date
    Sep 2005
    Location
    South East Middle Tennessee
    Shooter
    Multi Format
    Posts
    275
    Back in the 70's Unicolor had an color printing kit based on the Tri-color method. It had a color/exposure calculator that required only one test print for each negative. The Tri-color filter holder fit on the enlarging lens the way an under the lens Polycontrast filter holder fits. The system was a bit of a pain to use but the color was excellant especially with bigger negs. ( 6x6 to 4x5 ). I still have my set and I may use it again--someday. RandyB

  6. #26

    Join Date
    Dec 2006
    Shooter
    Medium Format
    Posts
    348
    Quote Originally Posted by hrst View Post
    Is there a filter with three narrow passbands at R, G and B, that would change white light to trichromatic RGB "white"? It would give the same saturation boost by lowering crosstalk with white-light source, but with single exposure.
    Find yourself a Phillips PCS 150 color head. That's exactly how they work.

  7. #27

    Join Date
    May 2009
    Shooter
    Medium Format
    Posts
    39
    RGB printing can be very fast and efficient, far more efficient than CMY subtractive printing, because instead of *filtering* colors out, subtractively, you are making three rapid additive exposures.

    That is with machines. In practice, manually, it will take longer. Ron raises an interesting point about the color temperature of the bulb.

    I'm not sure if there was a standard for professional color printers (of course, bulbs changed and darkened over their lives so nothing is perfect in terms of color temperature except in theor), but variance in lamp VOLTAGE will also vary color temp up to the rated voltage.


    Personally, I'd try to avoid a filter wheel unless I had a very firmly planted enlarger. I'd be temped to just hold the filters at roughly the same distance under the enlarger lens, but then my hands aren't perfectly shake-free either ;-)

    While there's "3x" the opportunity for shake to occur, the biggest advantage I can think of is less color drift with short exposures caused by the lamp cooling up and down that you get with subtractive printing. Pro lab printers had shutters even for RGB exposures, but I'd imagine that the bulb warm-up cool-dwn would be negligible with three exposures compared to a single subtractive one.

    If you have a subtractive enlarger already, just use it though. . .

  8. #28
    holmburgers's Avatar
    Join Date
    Aug 2009
    Location
    Rochester NY (native KS)
    Shooter
    Multi Format
    Posts
    4,423
    Images
    2
    Quote Originally Posted by jpberger View Post
    Just to clarify--- are we talking printing positives on ra-4 or negatives? This would be interesting to try with b/w separation negs, but methinks getting the registration right would be a project in itself.
    Wow, you could print b&w separation negatives on color paper in this manner.
    If you are the big tree, we are the small axe

Page 3 of 3 FirstFirst 123


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin