Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 71,056   Posts: 1,561,474   Online: 976
      
Page 1 of 3 123 LastLast
Results 1 to 10 of 22
  1. #1
    CBG
    CBG is offline

    Join Date
    Nov 2004
    Shooter
    Multi Format
    Posts
    894

    Ramble on a new darkroom. And LEDs for contact printing.

    Miscellaneous thoughts as I start up a new darkroom, my first in thirty plus years.

    I am setting up to do contact printing but do not wish to use an enlarger as a light source. I'll be working with 8x10 negs primarily, and 5x7s otherwise, and don't want to use an enlarger as an overly complex lamp. It occurred to me that I could use blue and green lights as exposing light sources and avail myself of the benefits of split grade printing. So I obtained one each of a blue and a green LED unit pre wired as a screw in bulb. Each screw in unit has some 24 individual LEDs in it.

    Despite many years lapsed, things feel utterly familiar, except for the contact printing. In the past I always used an enlarger as the light source to do contact prints, and 4x5 film or smaller. Now, with 8x10 negs and a very different light source, the mechanics of making a print change.

    After hearing so much about how little light LEDs supposedly put out, I was surprised that my LEDs are so bright that I am having to cut way down on their intensity to get workable exposure times. To obtain soft even illumination of the printing frame, I bounced the LEDs off my rather low ceiling, and have exposure times about 2 seconds. Way too short for any meaningful control I bought the blue and green units on this: www.superbrightleds.com/specs/E27-W24.htm page. Each unit runs off a separate Time-O-Lite timer to keep things simple. Now I'm in process of putting a dark gray painted area on the ceiling where I am bouncing the LED light so I can get some thing more like the 20 to 40 second area.

    Even with the way too short times I can see that the contrast range should be very workable. The test prints range from verrrry soft with the green LED to very hard with the blue LED. If I find I want to extend the contrast range further, I'll try painting the bounce zones on the ceiling blue purple and yellow green to max out the respective hard and soft contrast emulsion layers.

    I also bought a red LED unit to test as a safelight. I have not yet had time to evaluate that. It seems very bright and very red so I'm hopeful.

    So far, I dislike the contact printing frame I just bought from PF. I got the 11x14 frame so I can do 8x10 negs within a 11x14 paper size to get really wide borders. Basically it seems well constructed, but I don't like the snapping metal clamps that hold the back on. The clamps are noisy, unkind to borderline arthritic hands, and slow since there are six clamps to do and undo for every test.. Does anyone else know of any other brands on the market with more humane clamping action???

    I want to explore the use of print pre-flashing for contrast control after I get the basic contact printing setup working.

    Guess I'll need to post photos in the darkroom portraits thread soon. It's going to be an interesting voyage.

  2. #2
    Jerevan's Avatar
    Join Date
    Nov 2004
    Location
    Sweden
    Shooter
    35mm
    Posts
    1,859
    Images
    9
    From the description of your set-up, I assume you do silver printing on variable contrast paper. In that case, I think it is easier to use a heavy plate of glass, putting the negative right on to the paper. If you use some sort of mat or foam under the paper you will get good contact between the neg and the paper. Otherwise your ideas seem great! Post more of your experiences with the LEDs as you go along.
    “Do your work, then step back. The only path to serenity.” - Lao Tzu

  3. #3
    glbeas's Avatar
    Join Date
    Sep 2002
    Location
    Roswell, Ga. USA
    Shooter
    Multi Format
    Posts
    3,307
    Images
    109
    Have you tried the leds with a dimmer yet? Extended exposure times will allow for burning and dodging of the contact print as well as local contrast control.
    Gary Beasley

  4. #4
    Lee L's Avatar
    Join Date
    Nov 2004
    Shooter
    Multi Format
    Posts
    3,244
    Quote Originally Posted by glbeas View Post
    Have you tried the leds with a dimmer yet? Extended exposure times will allow for burning and dodging of the contact print as well as local contrast control.
    The electronic circuitry built into these units for converting 120VAC to the 2-5 VDC with limited current for driving the LEDS allows only limited control with a dimmer, and it may be hard to adjust accurately. In addition, the vendor posts this warning in the product description:

    CAUTION: ALL 120 AND 240 VAC BULBS ARE FOR USE WITH STANDARD ON/OFF SWITCHES ONLY Use with any type of dimmer, relay or other control circuit will VOID WARRANTY - LEDs are very sensitive and subject to premature failure from electrical noise spikes
    It might be better to try these http://superbrightleds.com/specs/e27-w8.htm as an alternative. (BTW, the blue and green dominant wavelengths are switched on this data page.) These lamps have 8 LEDs rather than 24, and appear to be the same output and same color per LED.

    Because the output of the lamps is well matched to the sensitivity of the VC layers of the paper, they are more efficient than you might assume.

    Lee
    Last edited by Lee L; 06-11-2009 at 07:20 AM. Click to view previous post history.

  5. #5
    CBG
    CBG is offline

    Join Date
    Nov 2004
    Shooter
    Multi Format
    Posts
    894
    Quote Originally Posted by glbeas View Post
    Have you tried the leds with a dimmer yet? Extended exposure times will allow for burning and dodging of the contact print as well as local contrast control.
    Unfortunately, these LEDs have a dire warning about dimmers and any other control circuits so dimming is probably not an option for them. Too bad since dimming had been a back up strategy...

  6. #6
    CBG
    CBG is offline

    Join Date
    Nov 2004
    Shooter
    Multi Format
    Posts
    894
    Quote Originally Posted by Lee L View Post
    The electronic circuitry built into these units for converting 120VAC to the 2-5 VDC with limited current for driving the LEDS allows only limited control with a dimmer, and it may be hard to adjust accurately. In addition, the vendor posts this warning in the product description:

    It might be better to try these http://superbrightleds.com/specs/e27-w8.htm as an alternative. (BTW, the blue and green dominant wavelengths are switched on this data page.) These lamps have 8 LEDs rather than 24, and appear to be the same output and same color per LED.

    Because the output of the lamps is well matched to the sensitivity of the VC layers of the paper, they are more efficient than you might assume.

    Lee
    Yup. I hadn't read down before I made my last post. You found that text too.

    I'll check out that other set of bulbs - it never struck me that I might be getting bulbs too strong. In the meantime I have darkened the area I use for bouncing the light off of. Haven't had time to test.

  7. #7
    Struan Gray's Avatar
    Join Date
    Nov 2004
    Location
    Lund, Sweden
    Shooter
    Multi Format
    Posts
    914
    There are LED light panels sold for - don't laugh - discos and DJs which would make a nice light source for contact printing. They dim, can have variable colour, and will even pulse on and off in time to your darkroom music. There are UV ones which are (just) deep enough to do some alt process work.

    http://prolight.co.uk/item/ledj63/
    http://prolight.co.uk/item/ledj66/

    You can of course make your own using simple electronics breadboarding kits and packs of LEDs and limit resistors from eBay. This is a nice project (hint: it doesn't have to be UV):

    http://www.instructables.com/id/UV-LED-Exposure-Box/

  8. #8
    Lee L's Avatar
    Join Date
    Nov 2004
    Shooter
    Multi Format
    Posts
    3,244
    superbrightleds.com also has 12VDC light bars and various other 12VDC configurations that can be easily and properly dimmed with a potentiometer (standard 'volume' control) and a 12VDC power source. I do this with 12VDC LED safelights and a variable DC power supply from partsexpress.com like this one: http://www.parts-express.com/pe/show...number=120-536 which provides switchable 3 - 4.5 - 6 - 7.5 - 9 - 12 VDC

    You could run that power supply at 12VDC and put a potentiometer in line for continuously variable output from a 12VDC LED array.

    Lee

  9. #9

    Join Date
    Feb 2005
    Location
    Richmond, VA
    Shooter
    Multi Format
    Posts
    1,066
    These LED light source options are kind of interesting, especially for a non electro-techie like me.
    Would it make sense to have a forum dedicated to this technology for the future, so that all threads would be in one place?

  10. #10

    Join Date
    Oct 2003
    Location
    Richmond, VA
    Shooter
    Large Format
    Posts
    878
    I have found a vacuum easel much easier to work with than a printing frame.
    John Bowen

Page 1 of 3 123 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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