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  1. #21

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    This may be a stupid answer and maybe at the enlargement percentages most of you are doing it doesn't make a difference, but with the extreme enlargements I do, I found that my focus would appear to be dead on, but the print would not be sharp. Well, I finally figured out that I was focussing on the print platform with complete disregard for the depth of the paper itself, causing me to be minimum of 2-4 mm out of focus. With film (my film are 7mm thick) it is much worse. Anyway if you think this might help, just apply a scrap piece of similar medium under you focussing tool when focussing, and see if it makes a difference.


    Embrace **it! **it. . .just another name for fertilizer. . . Grow baby Grow!

  2. #22
    lee
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    HI Jill,
    Welcome aboard! It has been well documented that you need to account for the thickness of the paper when focusing on the printing easel. The depth of field is not very good on enlarging lens and even stopped down there is some error. So, since I use several different papers and I just keep a wasted piece (marked with the name of the paper) of each paper I use near the enlarger column. I just place the paper on the easel and mt focus tool on the paper and then I just focus my little heart out.

    lee\c

  3. #23

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    Hi Lee,

    Thank you and I will probably state the obvious more than once for a while as I had zero experience as either a photographer or a lab tech when I bought the shop. Soooo some of these things which are obvious to you all were last minute "I wonder if" s to me. I'll catch up though I'm quick.
    Embrace **it! **it. . .just another name for fertilizer. . . Grow baby Grow!

  4. #24

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    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (lee @ May 4 2003, 03:39 PM)</td></tr><tr><td id='QUOTE'>It has been well documented that you need to account for the thickness of the paper when focusing on the printing easel.</td></tr></table><span class='postcolor'>
    Lee,

    I cannot believe this and have not made any such observations. A simple DOF-calculation will show you, that there is plenty of DOF on your easel and EL-Lenses do usually have excellent field flatness. Sometimes when the focus knob on my EL-Head is too far away, I do focus by lowering or lifting the geared easel table on my Durst 139. I&#39;m always surprised about how much I can move the table without losing focus while watching though a 10x grain focuser.

  5. #25

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    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Darkroom ChromaCrafts @ May 4 2003, 08:39 AM)</td></tr><tr><td id='QUOTE'>This may be a stupid answer and maybe at the enlargement percentages most of you are doing it doesn&#39;t make a difference, but with the extreme enlargements I do, I found that my focus would appear to be dead on, but the print would not be sharp.&nbsp; Well, I finally figured out that I was focussing on the print platform with complete disregard for the depth of the paper itself, causing me to be minimum of 2-4 mm out of focus. </td></tr></table><span class='postcolor'>
    Jill,

    at an el-factor of 35x, DOF is on the paper side much much more than 4mm, even if we assume a circle of confusion below the resolution of our eyes. However, DOFocus, i.e. the tolerance of the negative, is always critical. I sometimes do 50x enlargements and never encountered a paper-side DOF problem, if the enlarger is well aligned. Lens performance might be another issue. Paper is UV sensitive and might see another picture as your eyes, if the lens has aberrations at these wavelengths.

  6. #26
    lee
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    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (tschmid @ May 4 2003, 11:48 AM)</td></tr><tr><td id='QUOTE'> </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (lee @ May 4 2003, 03:39 PM)</td></tr><tr><td id='QUOTE'>It has been well documented that you need to account for the thickness of the paper when focusing on the printing easel.</td></tr></table><span class='postcolor'>
    Lee,

    I cannot believe this and have not made any such observations. A simple DOF-calculation will show you, that there is plenty of DOF on your easel and EL-Lenses do usually have excellent field flatness. Sometimes when the focus knob on my EL-Head is too far away, I do focus by lowering or lifting the geared easel table on my Durst 139. I&#39;m always surprised about how much I can move the table without losing focus while watching though a 10x grain focuser. </td></tr></table><span class='postcolor'>
    what can I say, your experience is different than mine. I use a Peak and I can see the difference even at 8x10. YMMV....


    lee&#092;c

  7. #27

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    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (lee @ May 5 2003, 01:59 AM)</td></tr><tr><td id='QUOTE'>what can I say, your experience is different than mine.&nbsp; I use a Peak and I can see the difference even at 8x10.</td></tr></table><span class='postcolor'>
    You mean that if you focus on your easel and then place a piece of paper below your Peak, you will loose focus?
    If you state the details (lens, f-stop, and magnificaion), I would like to do a DOF calculation for that.

    Have you ever done a double blind test on these results? I often do that when theory dosn&#39;t seem to match practice. Most often it turns out as an illusion.

  8. #28

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    Thilo, this is a well documented fact or practice. Fred Picker even taped a piece of paper on the bottom of his focus gizmo so he did not have to put it on top of a paper.

    My experience is the same, focusing an aerial image with a piece of paper under the peak always yielded sharper prints.

    So if you want the info I used a Rodagon G, 2x magnification at f16. Of course with contact printing I dont worry about such pesky details anymore.

  9. #29

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    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Jorge @ May 5 2003, 08:01 AM)</td></tr><tr><td id='QUOTE'>Thilo, this is a well documented fact or practice. Fred Picker even taped a piece of paper on the bottom of his focus gizmo so he did not have to put it on top of a paper. </td></tr></table><span class='postcolor'>
    Jorge, it is not the case that I have never heard about that. But I have heard an read about a lot of things that have been handed down without further checking. There are a lot of urban legends around in photography. So please excuse my manner in this case.

    BTW: A Rodagon-G is optimized for el-factors above 15x. I dont&#39;t think it performs well at 2x. Mine (105 and 150) do not at these scales.

  10. #30
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    Is the plane of focus different when the grain focuser is used one-paper-thickness further away? Of course. Is it significant? It depends, but not usually.

    I routinely focus with the enlarger lens "wide open" to minimize depth of focus - as much as possible - and stop down for the exposure.

    If one is doing the "brick trick", tilting the easel to correct perspective, the effects of depth of focus become apparent. I have differences in paper height, from one side to the other, of as much as an inch and a half - 37 millimeters or so ... and printed "acceptably sharp" at f/16 or f/22, using the 50mm Rodenstock.

    What might be interesting is the "Softeners". I purchased two 40.5mm filters from a "bargain box" - out of a curious impulse - only because they *FIT* the Rodenstock enlarging lenses. The only information I have about them is that they are marked "Softener" and they were made in Japan. *Extremely* useful in printing portraits.
    Simply wonderful for removing "blemishes" - but *not good* trying to use the grain focuser with them.
    Carpe erratum!!

    Ed Sukach, FFP.

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