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Thread: De Vere 810H - Lens questions among other questions...

  1. #21
    Peter De Smidt's Avatar
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    Re: De Vere 810H - Lens questions among other questions...

    Quote Originally Posted by ic-racer View Post
    How close are your rails to the wall?
    That was a decade ago, or more, and so I wish a remembered more precisely. I had about 8 feet of track. It stopped about 2 feet from the easel. Getting the track flat, fixed and perpendicular to the easel took some time, even with a Versalab, but that was mainly because my very old concrete floor was uneven.
    If you get the manual, it'll tell you lens and track length needed for a given enlargement.
    J. Haidt's 3 great untruths:
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    Always trust your feelings.
    Life is a battle between good people and evil people.

  2. #22

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    Re: De Vere 810H - Lens questions among other questions...

    Quote Originally Posted by Pere Casals View Post
    Saying numbers, for 8x10 a 240mm enlarger lens will have a fall-off of around 3 stops in the corner for big prints, if wide open.

    With the 240 lens well stopped fall-off (big prints) is reduced to around 1.5 stops in the corner, which still it's a lot.


    _________________________

    Using a 240mm for 8x10 it's geometrically the same than using a 120mm for 4x5: not recomended.

    A 240mm it is suitable for 8x10 in next cases:

    > If we enlarge a crop.

    > For small enlargements, as we give bellows draw to focus... the image circle in the negative plane grows. As we take the center fall-off is lower.

    > If we had fall-off in the negative, say a Nikon SW 120 shot, the fall-off in the enlargement corrects the flaw in the negative.


    For a big print a 240 is troubles, we have to stop more than we want to decrease fall-off, requiring even longer exposures than the ususal long ones in big prints, this complicates contrast control because reciprocity failure in the paper toe (scene highlights)... And we still have a remarkable fall-off !


    Exactly the same than 120 for 4x5... it can be used, but the thing has drawbacks. 150 or 180 is better for 4x5 than 120. So for 8x10 proportionally it's 300 or 360.

    It is true that for printing 16x20 we can use the 240, in the same way that we may use a 120mm to print 8x10 from 4x5 negatives, because the bellows draw is to help.
    You seem to have a lot of theory but not enough experience!

    For instance, a 120mm Rodagon WA on 45 will out perform a 135 or 150mm Rodagon for the normal range of print sizes. The only lens that would out perform it is the 150 Apo Rodagon N.
    The 240 Rodagon is fully capable of delivering out standing quality results as long as it is used at optimal aperture and within it optimized magnification range. That means not stopping it way down.

  3. #23

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    Re: De Vere 810H - Lens questions among other questions...

    Quote Originally Posted by ic-racer View Post
    Nice post, plus not all 240s are equal in coverage.
    Of course... But fall-off is similar, 1-cos^4 , as enlarger lenses are relatively simple designs. (Biogons etc may sport a tilting pupil to decrease fall-off...)

    And the WA versions are shorter focals...

  4. #24

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    Re: De Vere 810H - Lens questions among other questions...

    Quote Originally Posted by Bob Salomon View Post
    You seem to have a lot of theory but not enough experience!
    Bob, you nailed it, I'm still a rookie printer, but I want to be a good student !


    Quote Originally Posted by Bob Salomon View Post
    For instance, a 120mm Rodagon WA on 45 will out perform a 135 or 150mm Rodagon for the normal range of print sizes. The only lens that would out perform it is the 150 Apo Rodagon N.
    The 240 Rodagon is fully capable of delivering out standing quality results as long as it is used at optimal aperture and within it optimized magnification range. That means not stopping it way down.
    Yes... but what happens with fall-off ????

    Taking a look to Rodenstock datasheets it makes clear what an insane amount of fall-off we'll have with a short lens.

    https://onedrive.live.com/?id=8D71BC...71BC33C77D1008

    We have to remember that 810 corners are 156mm off-center, see that in the 240 graphs, it's unacceptable amount of fall-off... if we are not in the 3 cases I mentioned in the other post #18...

  5. #25
    Jac@stafford.net's Avatar
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    Re: De Vere 810H - Lens questions among other questions...

    Quote Originally Posted by Pere Casals View Post
    Of course... But fall-off is similar, 1-cos^4 , as enlarger lenses are relatively simple designs. (Biogons etc may sport a tilting pupil to decrease fall-off...)
    Simple designs? Rodenstock enlarging lenses are hugely different depending upon their specific intentions.

    Is there a Biogon enlarging lens? How strange that would be.

    FWIW, 1-cos^4 can be partially mitigated in a semi-symmetrical lens with an over-size rear cluster.

  6. #26

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    Re: De Vere 810H - Lens questions among other questions...

    Quote Originally Posted by Jac@stafford.net View Post
    Simple designs? Rodenstock enlarging lenses are hugely different depending upon their specific intentions. (I have never been disappointed with a Rodenstock.)

    Is there a Biogon enlarging lens?
    What I was saying is that enlarging lenses are not complex enough to sport a tilting pupil to decrease fall-off, as biogons do, so a too short lens for the job will have remarkable fall-off.

    (Time ago Dan teached me about the tilting pupil concept...)


    Quote Originally Posted by Jac@stafford.net View Post
    FWIW, 1-cos^4 can be partially mitigated in a semi-symmetrical lens with an over-size rear cluster.

    See fall-off graphs in datasheets:
    https://onedrive.live.com/?id=8D71BC...71BC33C77D1008

    The 1-cos^4 curve is plotted in all graphs as a reference, and you will see that enlarging lenses fall-off match the 1-cos^4 curve when well stopped, having a lot more wide open.
    Last edited by Pere Casals; 29-Mar-2019 at 11:20.

  7. #27

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    Re: De Vere 810H - Lens questions among other questions...

    Quote Originally Posted by ic-racer View Post
    This is a really good chart for your purposes. Finding a lens might be difficult these days. My enlarger came with a box of lenses (including 240, 300 and 360), but that was ten years ago.
    http://www.durst-pro-usa.com/pdf/MAK...%20APENDIX.pdf
    awesome, thanks again. I have been looking using the various channels for old, obsolete photo gear having varying results. I honesty think a 300mm lens will be perfect. But the fact that it came with a 240mm suggests that the manufacture was thinking the labs perhaps weren't very long, so using a wider lens perhaps was their thinking...


    I think the only thing I need to worry about now is how to get the 500lb machine into my space. :/

  8. #28

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    Re: De Vere 810H - Lens questions among other questions...

    Quote Originally Posted by Bob Salomon View Post
    Thatís a process lens not an enlarging lens, the 180mm was the longest Apo Rodagon enlarging lens and that was for 4x5. It was replaced by the much better 150mm Apo Rodagon N.
    You're right, Bob, I didn't notice that, now I see!

  9. #29

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    Re: De Vere 810H - Lens questions among other questions...

    Quote Originally Posted by ajp View Post
    But the fact that it came with a 240mm suggests
    When you print 16x20" (which is a nice print) the 240 will be perfect. We often need some fall-off in the enlargement to correct the taking lens fall-off. Problem is when because of fall-off we have burn the corners, we may waste some paper before the print is ok, and it also complicates burning/dodging.

  10. #30
    Jac@stafford.net's Avatar
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    Re: De Vere 810H - Lens questions among other questions...

    Quote Originally Posted by Pere Casals View Post
    When you print 16x20" (which is a nice print) the 240 will be perfect. We often need some fall-off in the enlargement to correct the taking lens fall-off.
    Pardon my ignorance, Pere, but doesn't that compound the problem?

    (silly me, but would center-fill filters help with enlarger lenses?) \

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