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  1. #21
    Jeremy's Avatar
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    Quote Originally Posted by Claire Senft
    However, any lens that reaches its best performance at f 6 can not out perform a lens that reaches its best performance at a wider aperture..this is not my opinion this is the laws of physics and light.


    If one wants to make 15x or bigger enlargements than the best (2) lenses ever released into general commerce are the 40mm f 5.6 Zeiss S-Biogon and the 60mm S-Orthoplanar.
    If a lens that reaches best performance at a wider aperture is always better then wouldn't the 40mm f/5.6 Zeiss be a bad lens? Or does it also have to do with magnification factors? Also what if the best performance of one lens at say f/5.6 is worse than the Leitz at f/6--wouldn't it still be outperformed by the Leitz? I have never experienced such massive diffraction as you are talking about with a 50mm enlarger lens (granted I use them at f/5.6-8)

    I'm not meaning to be argumentative, but I'm working on <2 hours of sleep and I am not following the logic.
    Let's see what I've got in the magic trash can for Mateo!

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  2. #22
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    Hi Ed

    sorry to open old discussions,
    but on a previous thread, you suggested that if one focuses an enlarging lens wide open and notices the edges unsharp of the easel, all one would have to do is close down the apeture and the edges would *snap* into focus.
    Since that discussion I have consumed quantities of beer to wrap my head around that statement .
    Are you of the same opinion?????
    If so I will drink some more beer and try to understand.

  3. #23

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    Ed Dig up a copy of Post Exposure By Ctein. He has a chapter devoted to enlatging lenses and testing. I agree that an enlarging lens is just like a camera lens. They are just designed to work at different magnification ratios. It is NOT my opinion that enlarging lenses that work well in the 4-5.6 range are poor at all other stops. In fact some of them work fairly nicely wide open. I would also imagine that many photographers that work with glassless carrriers may, when there is a goodly amount of detail at the edges and corners may prefer an aperture of at least f8. I neither fault no criticize anyone for whatever methodology they want to use.

    How much difference f4, for instance, there is with f8, for the second instance, is going to also depend on other factors. How much details is in the negative, how well is the enlarger aligned, what is the light source, how big is the resulting print are some of the factors involved.

    It is worth remembering that with an 8x magnification that the effective f stop is f 36 if the lens is set at f4.

    As far as the S-Biogon is concerned it does not have an aperture. Secondarily, both lenses were desinged to have their best performance for reproduction rations from 15-70x. This is well outside of normal parameters.
    I have not used either lens. Zeiss states that these two lenses, used at these magnification ratios, will significantly out perform anything on the worlds market.

    I have high regards for both Leitz and Zeiss....among others.

  4. #24
    Ed Sukach's Avatar
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    Quote Originally Posted by Bob Carnie
    Hi Ed
    Hi.
    sorry to open old discussions,
    but on a previous thread, you suggested that if one focuses an enlarging lens wide open and notices the edges unsharp of the easel, all one would have to do is close down the apeture and the edges would *snap* into focus.
    Since that discussion I have consumed quantities of beer to wrap my head around that statement .
    Sounds to me to be a terrible oversimplification of what I must have written. That statement is not necessarily true at an *absolute* level.

    In operation, we use the Grain Focuser with the Aperture wide open, to minimize the effect of "depth of focus" - in this case a we want everything to "snap" into focus - as much as possible. Closing down the aperture will increase the depth of focus ... making the "best" focus more difficult to determine.

    If something on the borders of the field is not sharply "in focus" to start ... it will not NECESSARILY be corrected, invariably and always, by using a smaller aperture. There will be correction TO A DEGREE of "curvature of field" and "perpendicularity to optical axis" errors ... but not compete enough to say "everything will snap into focus" without reservation.

    But ... I'm not averse to quaffing a pint or two at times.
    Carpe erratum!!

    Ed Sukach, FFP.

  5. #25
    Ed Sukach's Avatar
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    Quote Originally Posted by Claire Senft
    I agree that an enlarging lens is just like a camera lens. They are just designed to work at different magnification ratios.
    Uh ... well I don't know if Magnification range would be the "best" way to describe what happens ... but .. OK. The more prominent difference is that between a "Capture" lens, and a "Projection" lens.

    It is NOT my opinion that enlarging lenses that work well in the 4-5.6 range are poor at all other stops. In fact some of them work fairly nicely wide open.
    I didn't take it that way, or did I say that either. I replied to the idea of a lens (of that approximate focal length) being "Diffraction Limited" at so large an aperture. I did "side comment" that some here are overly sensitive to enlarging lens "errors" - more than they are about camera lenses.

    I would also imagine that many photographers that work with glassless carrriers may, when there is a goodly amount of detail at the edges and corners may prefer an aperture of at least f8. I neither fault no criticize anyone for whatever methodology they want to use.
    How much difference f4, for instance, there is with f8, for the second instance, is going to also depend on other factors. How much details is in the negative, how well is the enlarger aligned, what is the light source, how big is the resulting print are some of the factors involved.
    Agreed.

    It is worth remembering that with an 8x magnification that the effective f stop is f 36 if the lens is set at f4.
    Woof!! You just lost me. The f/stop is defined as the ratio of (I'll grind fine here) the aperture-to-film distance divided by the aperture diameter: f/stop = f/d. The magnification ratio has nothing to do with it directly. There are tables that indicate the "effective aperture" change from "marked" apertures (at infinity) due to the increase in aperture-to-film distance in close-up photography; using magnfication as a result of focal distance, but they are calculated on the original "f/d". I don't think that is as simple as "magnification ratio times marked f/stop."

    So ... ???
    Carpe erratum!!

    Ed Sukach, FFP.

  6. #26

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    How about magnification+1? No more comments from me on this thread. Enjoy your discussion.

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