Distance & Exposure times....

Discussion in 'Enlarging' started by ChristopherCoy, Oct 31, 2011.

  1. ChristopherCoy

    ChristopherCoy Member

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    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. jeffreyg

    jeffreyg Subscriber

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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. Steve Smith

    Steve Smith Subscriber

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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.
     
  4. ChristopherCoy

    ChristopherCoy Member

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    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. ic-racer

    ic-racer Member

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    Most enlargers out there can do a 16x20 on the baseboard. What enalrger are you using?
     
  6. ChristopherCoy

    ChristopherCoy Member

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    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.
     
  7. Doremus Scudder

    Doremus Scudder Member

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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. ChristopherCoy

    ChristopherCoy Member

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    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. Steve Smith

    Steve Smith Subscriber

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    Not sure about the best, certainly the most used!


    Steve.
     
  10. TheFlyingCamera

    TheFlyingCamera Membership Council Council

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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.
     
  11. youngrichard

    youngrichard Member

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    Isn't this the same as the sticky thread "Factor for enlarger head height adjustment" at the top of this forum?
    Richard
     
  12. ChristopherCoy

    ChristopherCoy Member

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    Probably - I'm on a roll with erroneous threads today. But then, if everything has been posted previously, whats left for us to discuss? Shall we all log out?
     
  13. MattKing

    MattKing Subscriber

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    Christopher:

    Here are some suggestions:

    1) Cut one or two sheets of your 16x20 paper into four 8x10s;

    2) Work with them to get another good 8 x 10 print, using at least f/11 and possibly f/16 on your enlarger lens. Record the time you use for the resulting best print, and note an area on the print that is a highlight area with detail - that is the area you will attempt to match in your 16 x 20;

    3) Set up your enlarger (Beseler's site indicates the Printmaker 35 "can produce prints up to 11″ x 14″ on the baseboard or much larger when reversing the column and projecting on the floor") for the 16 x 20 size you want to print;

    4) Position an 8 x 10 easel so that it includes the highlight area that you are attempting to match;

    5) Open the lens two stops from the stop you most recently used for your smaller "reference" print. Use your test strip method to match the highlight using a #4 filter - the exposure time should be close to the time you used for your 8 x 10 reference print;

    6) When you determine the correct exposure time for the highlights, do a test on another 8 x 10 section of the image that shows how the shadows will appear with the new #4 filter. If they look good use that filter. If they are too light, increase the filter number and recheck both highlights and shadows. If they are too dark, decrease the filter number and recheck both highlights and shadows;

    7) Once you have both the shadows and highlights looking good in 8 x 10 sections that you have tested, move your attention to the mid-tones. Depending on the image, you may find that slight adjustments to the mid-tones may have the greatest effect on the results;

    8) When you are happy with the smaller 8 x 10 excerpts for highlights, shadows and mid-tones, you can try a full 16 x 20, to see if the "whole" is different from "the sum of its parts";

    9) Note that it is important to do the tests on the 16 x 20 paper (cut into smaller pieces) rather than paper that started out 8 x 10. Otherwise you may run into problems arising from differences in the emulsions.

    Finally, I would suggest avoiding exposures as short as 3 seconds. They are hard to repeat, and give no reasonable opportunity for dodging and burning.
     
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  15. ChristopherCoy

    ChristopherCoy Member

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    I knew the negative was underexposed when I contact printed the proof sheet at 5 seconds. I set the negative up and used a 5x7 for a test strip. I figured the shorter the exposure the less gray it would be. After a few test prints at 2 seconds, I had an image, but it was light. The true blacks in the image were gray. So I added a #2 filter and ran it for 2 seconds. The darks were slightly better but it was still to light. So I went up a step to the #3 filter at 2 seconds, again slightly better but the darks were still to light. So I went up to 3 seconds still with the #3 filter and the 8x10 came out to my liking. I'm sure that it isn't correct or proper, but it produced something that I was able to mat and give to a friend as a reminder of our old stomping grounds. It is by far gallery ready, but it worked. The short exposure left enough white, and the filter made the blacks dark enough. But this is how I learn things.

    And, we wont even talk about dodging and burning yet. As I said earlier I'm just happy to get an image from the camera to the paper. Right now I'm concentrating on trying to get images with good shadows, highlights, and mid tones. Once I feel like I have gotten that down good enough, I'll venture into the little things like dodging and burning, and tweaking prints to perfection.


    But I definitely appreciate all the information you posted above! It's definitely a good reference for me.
     
  16. MattKing

    MattKing Subscriber

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    Christopher:

    There is nothing wrong with a three second exposure at f/5.6, it is just more difficult/awkward/inconvenient/less flexible to work with than a twelve second exposure at f/11.

    And I for one would hate to have you lose interest in what you are doing because of anything that is more difficult/awkward/inconvenient/less flexible to work with than it need be.
     
  17. ChristopherCoy

    ChristopherCoy Member

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    Trust me, I don't know that there is anything that can make me loose interest now that I've returned to the dark room. It is every bit as exciting as I remember it being in high school. Maybe even more so now because I actually care, and comprehend what I'm learning and doing.

    But, that's how I learn. I never thought of raising the aperture on the enlarging lens to increase the exposure time, to allow for some dodging and burning, until you just mentioned it. And now that you did, that's opened up an entire other thought process on how to make that print better. hmmmmm...... I may have to wet some trays tonight after work.

    I never think of adjusting the aperture on the enlarger, because not once can I ever remember changing the one in class. And I constantly think about the exposure triangle when I'm shooting, I don't know why I don't think about it in the darkroom.....
     
    Last edited by a moderator: Oct 31, 2011
  18. RalphLambrecht

    RalphLambrecht Subscriber

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    same here
     
  19. RalphLambrecht

    RalphLambrecht Subscriber

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    there is more to iy than that. you also need to account for the belloes exrtension of the enlarging lens

    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)[/QUOTE]might as well record them as f/stops ang get used to f/stop timing!.

    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,[/QUOTE]
     
  20. TheFlyingCamera

    TheFlyingCamera Membership Council Council

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    The inverse square rule applies to enlargement the same way it does to studio lighting - double the distance, lose a stop, halve the distance, gain a stop. So going up to a 16x20 from an 8x10 is roughly 4x the distance, or two stops. If your base exposure is 3 seconds at f5.6, then give it 12 seconds as a starting point on your test strip (still do test strips!). you'll probably want to go up at least one grade in filtration, maybe a grade and a half. So you'll have to add another half to whole stop for the filter grade increase too. Try starting at grade 4, 24 seconds, and give your test strips three exposures at 12, 24, 36 and 48 seconds to see where the truth lies.
     
  21. Steve Smith

    Steve Smith Subscriber

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    Double the distance loses two stops as the light is now illuminating four times the original area.

    The clue is in the title: Inverse Square Rule!


    Steve.
     
  22. RalphLambrecht

    RalphLambrecht Subscriber

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    i 2nd the em10 recommendation
     
  23. keithwms

    keithwms Member

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    Some calcualtions will get you in the ballpark, but there are other things besides inverse square that matter too, so it's always best to do a test print.

    Just go ahead and project, seek out some portion of the projected image that contains the tones you want, and do a test on a small fragment of paper. There is seldom a need to test the entire image.

    When I get a new box of paper, I often sacrifice one sheet to make some test pieces for this kind of thing. The test pieces get exposed developed, topped, fixed, washed, dried... before I draw any conclusions about exposure of the "real" prints.

    You shouldn't have to waste hardly any paper at all- test strips can tell you almost everything you need.... before you do the real thing.
     
  24. Jim Jones

    Jim Jones Subscriber

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    Yes, inded -- until you refocus. Then you should use an enlarging meter like the Ilford EM-10, calculate the exposure using a formula that includes the change in effective f/number due to focus change, or calculate a chart that instantly tells you the proper exposure compensation. Math is one of our allies, not our nemesis.
     
  25. Steve Smith

    Steve Smith Subscriber

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    Not relevant as we were referring to moving lights, not the focus (well, I was anyway!) and inverse square rule in general. But yes, on an enlarger the re-focussing will affect it a bit. but only because it will also change the coverage so the inverse square rule will still apply.


    Steve.
     
  26. TheFlyingCamera

    TheFlyingCamera Membership Council Council

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    This is why I was not a math major in college. And another reason why I'm mostly a contact printer these days :smile: