2 random questions on printing

Discussion in 'The Darkroom' started by Alexandra, Jun 17, 2006.

  1. Alexandra

    Alexandra TPF Noob!

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    ok, these are just details, I know.
    I tried to figure it out on my own, but I'm all confused now. :meh:
    Here goes:

    1. I usually print 5x7's, but I've recently switched to 8x10. Comparing two prints of the same picture printed in the same chems and with the same exposure but one 5x7 and one 8x10, I noticed the 8x10 looked kinda fade.
    Here's my thought, correct me if I'm wrong. Since the enlarger's light is further above the paper at 8x10, it will have a weaker impact on it and the pic will be rather fade.
    Does this make any sense?
    If it does, then I have to change the exposure. I checked Ilford's site and apparently their papers are made for more or less 10 sec. exposures. I don't really like messing with timing, so then I'd have to set a larger aperture..? with 5x7's at 10sec. I used f/8. Here, I think f/5.6 would be rather extreme, right? So I still need a longer exposure?
    Does ANY of this make ANY sense at all?

    2.This is really unimportant (or is it?), but I was just wondering.
    What's the maximum time you can let go by between exposing the paper and developing it without it actually affecting the result? Will it really affect the results if you exceed that time?
     
  2. JamesD

    JamesD Between darkrooms

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    Open your aperture one stop, ie if the exposure for 5X7 is f/8, then for 8X10, use f/5.6. You may indeed have to tweak the time a little, since the actual ratio you need is about 2.25 X the exposure, ie 22.5 seconds; however, this is waaay less than a half stop of difference, and shouldn't be too noticeable. You might also want to try adjusting the contrast filter, if you're using VC paper, since larger enlargements are a bit lower in contrast.

    Short version: add one stop of exposure when going from 5X7 to 8X10.

    BTW: in case your interested, the formula I use to calculate this is not too hard. Measure the diagonal of each format (12.8 inches for 8X10 and 8.6 inches for 5X7). If the original is smaller, then divide the larger amount by the smaller amount (12.8 / 8.6 = 1.49). Do the opposite if you're going from larger original to smaller. Now, square the result (1.49 X 1.49 = 2.22). So, you need to multiply your exposure by 2.22. One stop = 2X the original exposure, so open up one stop. I use the diagonal because the aspect ratios (length divided by height) are different for 8X10 and 5X7, so using the diagonal is a bit more accurate. (1.25 & 1.4, respectively.) Note also that the numbers in the example above are rounded off, and are therefore approximations. The actual formula is this:

    E2 = E1 ( H2 / H1) ^2 ​

    where E1 and H1 are the exposure of and enlarger head height for the first print, and E2 and H2 are the exposure and enlarger head height for the second print. If you use an easle on top of the baseboard, don't forget to subtract the height of its surface over the baseboard from each enlarger head height.
     
  3. JamesD

    JamesD Between darkrooms

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    Also, deviating from the 10-second exposure for the paper won't make much difference as long as you don't go too short or too long. I use Ilford MC III, which isn't in production any longer, but I'd expect to be fairly representative. I use exposures anywhere from 10 seconds up to 120 seconds, depending on what kind of manipulations I want to do. Generally, the shortest I use is 15 seconds, and the longest is about 90 seconds.


    As for your second question, yes, the latent image formed by exposing the paper will dissipate over time. Generally, it's a good idea to process immediately after exposing, although it's better to say "as soon as practical." A couple of hours probably won't affect it much, so you can expose a bunch of prints, then process them simultaneously. If the latent image does dissipate, then you just won't get an image when you process the print. I don't know how long full dissipation takes.

    So, expose, then process within any reasonable amount of time.
     
  4. Alexandra

    Alexandra TPF Noob!

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    Thanks a lot, James! That formula will be pretty damn helpful :)
    I'll try this out tonight and I'll be able to tell if it worked

    (btw, love that quote in your signature)
     
  5. JamesD

    JamesD Between darkrooms

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    No problem, let us know how it works for you.

    As for the quote... it's expressive on so many levels.... :mrgreen:
     
  6. Alexandra

    Alexandra TPF Noob!

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    K, well I tried it and it works most AWESOMLY :biggrin:

    Actually, the exposure I gave you came from test prints even smaller than 5x7. After re-calculation, I ended up exposing them 17.5-22 seconds at f/5.6.

    The prints are beautiful!

    I wish i could still give you rep or something... :hug::
     
  7. JamesD

    JamesD Between darkrooms

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    LOL Glad to hear it worked out right. Knowing that is reward enough.

    Keep up the work, and post us some examples!
     
  8. Philip Weir

    Philip Weir TPF Noob!

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    Hi, to put my bit in. As a general principle, 10 seconds is a good time to expose print paper, but if you imagine printing a 20 x 24 from the same negative, you would probably be printing with the lens wide open [not adviseable] so don't be too concerned about printing with a longer exposure. Shooting with the aperture too wide could give you drop-off [focus] on the edges. You can check this when you are initially focusing the negative. If you focus in the middle of the image, the edges will probably drop-off a bit, that's one reason why you stop down, apart from adjusting the image density to the stage that you can print and have time to do any dodging. Imagine printing a dense negative and stopping down to your normal printing aperture, you would have to give more exposure...no problem. What does happen though, at very long exposures is reciprosity failure comes in...look it up or post a reply and I will explain it to you.

    Don't be a bit concerned about about leaving exposed paper for a length of time unless it was a couple of weeks. Next time you do a print, do an extra one and leave it undeveloped for a week or so, then develop it, you will probably not notice the difference.

    JamesS's calculations are correct, but basically a 10x8 is about double the size of a 5x7, so give double the exposure and do a test. But remember it's the area to consider i.e. a 5x4 might sound like half the size of a 10x8 [if you know what I mean] but in fact it's 1/4 of the area, four times the exposure or two more stops. Trust this helps. Philip.

    www.philipweirphotography.com
     
  9. Alexandra

    Alexandra TPF Noob!

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    I'd sure post some if my scanner didn't suck so hard... but I'll see what I can do with some heavy editing :)
     
  10. Alexandra

    Alexandra TPF Noob!

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    hmmokay. If I get this right, when you double the size, you have to either double the exposure time or to increase by one stop... but not both, to keep the reciprocity..?
     
  11. Philip Weir

    Philip Weir TPF Noob!

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    No, No, No, I think my explanation was somewhat lacking, my apologies. What I was trying to say was that, if you double the length of a print, the depth also doubles, giving you four times the area, i.e a 5x4 [20 square inches] enlarged to 10x8 [80 square inches] 4 times the area, hence 4 times the exposure.
    "Reciprocity" in relation to exposure means that if you were exposing a print in the enlarger or a film in the camera, and your exposure was say 20 seconds, when you stop down a stop, you may need to give not double the exposure but more. I probably shouldn't have mentioned it, I'm probably confusing you. Philip.
     
  12. Alexandra

    Alexandra TPF Noob!

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    nah, I'm not that confused... yet. ;)

    I'll stick with James' formula for the exposure time.

    my only unclear area right now is the aperture.
    when doubling exposure time, should I also adjust the aperture regardless the fact that the print size has doubled (or 4x'ed) too?
    Last time, I went from f/8 for a 5x4 to f/5.6 for a 8x10 (time was 10sec for the first and about 18sec for the second)

    So, is there any rule for aperture too, in realation with time?

    I usually go with the 'try different combinations and make a ton of prints until you hit the right effect' technique, but I suppose there's a better way, isn't there?
     

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