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  1. #1
    ChristopherCoy's Avatar
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    Distance & Exposure times....

    During my trip to New Orleans a week or so ago, I took a very nice picture of the St. Charles Avenue trolley. It was just a bit underexposed, and the entire thing was rather bland and gray. Through experimentation with my contrast filters, I was able to print an 8x10 using a #3 filter at 3 seconds exposure, around f/5.6 I think, and produce something that I like.

    Last night I was thinking about trying a 16x20 of the same print, but I've only printed two 16x20's in my life and it was during my high school darkroom class. We mounted the paper on the wall, turned enlarger some wonky way, and winged it.

    I know that I can reverse my enlarger and project it onto the floor, but that would at least double the distance between the enlarger head and the paper. Would that also change my exposure time? I'm assuming that its going to at least double it.

    I am asking because It took me 3 5x7 sheets, and 3 8x10 sheets to get this one 8x10 right. I want to try and have an idea of how the distance may change my exposure time, before I start wasting 16x20 sheets...

  2. #2

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    Christopher,

    It's best to make a test print to establish the exposure settings as well as for contrast. You could try the test prints on 8x10 paper but the "final" test prints once you establish the exposure and contrast should be on 16x20 because the entire image won't be seen on the smaller paper. The 16x20 tests should be fully processed and dry and viewed under appropriate lighting so that you can see what the dry down effect is plus other modifications you might want to make. Often the larger print will take different handling than small ones. So be sure it is one that you want to spend the time with.

    http://www.jeffreyglasser.com/

  3. #3
    Steve Smith's Avatar
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    In theory, you are spreading the image over four times its previous area. Therefore your new exposure time will be four times that of the 8x10.

    Doubling the distance between the enlarger head and the paper is what you want to do.

    Once you have the image projected the right size for the 20 x 16 sheet, you can do test exposures with small pieces of paper rather than using a whole sheet.


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

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    ChristopherCoy's Avatar
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    Quote Originally Posted by Steve Smith View Post
    Once you have the image projected the right size for the 20 x 16 sheet, you can do test exposures with small pieces of paper rather than using a whole sheet.


    Steve.


    Typically I do, but you can't see the entire image, as was the case with the 5x7's and 8x10's. I did small test prints on the 5x7's but after I did the 8x10's I had to tweak it a bit.

  5. #5
    ic-racer's Avatar
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    Most enlargers out there can do a 16x20 on the baseboard. What enalrger are you using?

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    ChristopherCoy's Avatar
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    Quote Originally Posted by ic-racer View Post
    Most enlargers out there can do a 16x20 on the baseboard. What enalrger are you using?

    The one that's currently on the table is a Print Maker 35. The other one is an Omega B600 I think? I haven't used that one yet though.

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    Only 3 5x7 sheets, and 3 8x10 sheets to get one 8x10 right? Seems like a lot less paper than I use getting to a final print! After test strips, it's usually 4 or 5 sheets just to get close, then starts the fine adjustments.

    That said, since you have the dodging and burning and contrast already "in the ballpark," you should not have to make too many 16y20s to get where you want.

    However you need to use your enlarger to get a 16x20, the head will be farther from the baseboard and the enlarging exposure appropriately more (inverse square law ... can't break it!)

    Use the 4x enlargment factor as a starting point, keeping in mind that larger prints often need a bit different contrast (you may want to tweak that a bit). Think of your dodging and burning as percentages of the total exposure and scale them up to fit your new print size (you may want to tweak them a bit too).

    Don't be afraid to use some paper to get a print you are happy with! The best tool in your darkroom is the trash can!

    Best,

  8. #8
    ChristopherCoy's Avatar
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    Quote Originally Posted by Doremus Scudder View Post
    Seems like a lot less paper than I use getting to a final print!

    Yes, but my final print and your final print are probably two very different final prints. You've probably been knee deep in it for a while, and I've barely got my pinky toe wet, so print quality isn't at the top of my list right now. If I can get anything from the camera to the paper, I'm thrilled.

  9. #9
    Steve Smith's Avatar
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    Quote Originally Posted by Doremus Scudder View Post
    The best tool in your darkroom is the trash can!
    Not sure about the best, certainly the most used!


    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  10. #10
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    I don't think you can make a 16x20 with the Printmaker 35, baseboard or otherwise. The bellows won't compress enough. You're better off trying with the Omega. As a general rule, in addition to increasing the exposure time as you go bigger, you'll have to increase the contrast filtration - if it printed well at grade 3 as an 8x10, you'll probably need to use grade 4 (or even higher - maybe a 4 1/2) filtration to get a good 16x20 out of it. If you start printing at variable sizes, I would highly recommend getting something like an Ilford EM-10 enlarging meter. They're quite simple to use - you first get your enlarger set up, and make a good print from a known negative. With the lens aperture and negative-to-paper distance set, put the EM-10's sensor under a (preferably) middle-gray area of the negative on the baseboard. Turn the calibration dial until only the center green light is lit. Note the number so if you have to re-set it later you can. Then you are all set to print the same negative at a different size and/or a different negative at the same size. With the same negative, just re-position the enlarger head at the appropriate height, re-focus, and make sure the probe is in the same area of the negative that you measured. Turn the lens aperture until the single green light is illuminated on the EM-10. With a new negative, put the EM-10's probe in an image area that should have the same tonal value as the area you metered on the original negative. Then adjust the enlarger lens aperture until you have only a single green light. In both cases you don't have to adjust exposure time - just the lens aperture. It's somewhat primitive because it may be better to adjust time than aperture, especially if you are dealing with a very dense negative, and you don't want to print at wide-open. Of course you can calculate the aperture/time changes yourself after you set the exposure based on the meter.

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