1. Asha

    Asha Blithering Idiot

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    Well I can read and ( just about) understand all the codswallop that you lot type in here so that'll make German a stroll in the park:D
     
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  2. StephenM

    StephenM I know a Blithering Idiot

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    I suppose I might as well add a missing advantage to plates over film. They are rigid, meaning that film flatness is a given; there is no possibility of the emulsion surface bowing in towards the lens. If depth of focus is a potential issue (as with wide angle lenses) this could possibly result in sharper images.
     
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  3. ChrisR

    ChrisR

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    Both points interesting, Stephen. I'm just a little confused, though. Is flatness of film an issue? I thought the film holders/DDS had the film pretty well confined on all four sides, and even Fomapan 100 (which apparently has a curly reputation in other formats) seems remarkably flat in its 4x5 polyester configuration. I haven't used any other film yet, though.

    On the second point, in 35mm (my normal area of comfort), wider lenses seem to produce a greater depth of field. Is there something I should understand to change this in 4x5? (Although again not an issue for me as I only have one 135mm lens.)
     
  4. Steve Smith

    Steve Smith Joe

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    It's more of an issue with longer focal lengths.


    Steve.
     
  5. StephenM

    StephenM I know a Blithering Idiot

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    Film flatness is a theoretical advantage - at least, in my limited experience. It may be more of a problem with the larger film sizes that used to be used than the miniature 5x4 of my experience.


    True; short focal length lenses do have more depth of field. But I said

    Depth of field is how much the subject can move and still look sharp; depth of focus is how much the film can move and still record an image that looks sharp.
     
    Last edited: Dec 10, 2018 at 9:22 AM
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  6. StephenM

    StephenM I know a Blithering Idiot

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    I originally put some additional text in the post above, and then removed it after a few minutes as being less clear than I would like. I'll now add as an afterthought the following extract from the Walker Cameras site:

    The Walker Titan XL 4x5 Field camera is primarily a wide angled camera with a fixed back which addresses the inevitable problem that afflicts all view cameras when used with extreme wide angle lenses, namely parallelism of the front and rear standards; critical depth of focus declines as focal length diminishes as does the need for swings and tilts.
     
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  7. Terrywoodenpic

    Terrywoodenpic

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    Extreme wide angle large format cameras are usually made in some sort of fixed cone or box form with helical rather than bellows focus with only a rise and fall or cross slide.

    Flatness of the film was a real issue with aerial photography as the film could be sucked toward the lens with a bellows camera.
    Rollies were sometimes issued with a glass front pressure plate to sandwich the film, to prevent this. I had two with this feature, when not needed it was kept in a pouch built into the case.
    depth of focus is less critical with short lenses when doing extreme macro work. as the film to lens distance can be longer than the lens to subject distance.
     
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  8. Asha

    Asha Blithering Idiot

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    This is the reason why some people who shoot old folding bellows cameras wait until they actually want to expose a frame before advancing the film.

    If the film is already advanced to the next unexposed frame, it can be sucked towards the lens when the camera is opened and the bellows extended, thus potentially bowing the film.

    I'm talking more about 120 / 620 roll film folders in this instance but as has been mentioned, it can apply to other formats including sheet film.
     
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  9. Steve Smith

    Steve Smith Joe

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    I think wide lenses have more tolerance to film position. I made a 6x12 camera with a 65mm Super Angulon. It has a focusing helical, but doesn't really need one. When I accidentally took a shot with it focused to eight feet, I couldn't tell the difference between that and one focused at infinity. That's a difference of about 6mm in lens to film distance.


    Steve.
     
  10. StephenM

    StephenM I know a Blithering Idiot

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    You seem to still be talking about the subject to camera distance...

    We'll have to agree to differ on this, as I still believe that there's a difference between depth of field and depth of focus.
     
  11. Terrywoodenpic

    Terrywoodenpic

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    Absolutely.. except in macro work, film to lens depth of focus, is always shallower than lens to subject depth of field. Surprisingly monorails and technical cameras are often set up with remarkably poor parallalism. And when using them, exact movements are not that critical, and are usually done by eye.
    I have spent hours zeroing the set up of lage monorails, and it has made little difference to the images produced. But it does make you feel happier to have it right, for a while at least.
     
  12. ChrisR

    ChrisR

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    I was trying to work this out in my head and came up with this... A wide lens has good depth of field (range of subject distances), ie it compresses a large range of distances into a small range of distances at the film plane. Conversely, a relatively small movement at the film plane would be equivalent to a large movement of the subject.

    Well, it makes sense to me!

    (But probably the wrong thread to discuss this...)
     
  13. StephenM

    StephenM I know a Blithering Idiot

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    Probably the simplest way to think of it is pictorially. As I can't draw easily with letters, try sketching this on a piece of paper.

    Draw a couple of curved lines to represent a lens, sketch in the parallel rays (from infinity) on one side, and the converging-to-a-point lines on the other side to the plane of focus. Now consider the angle made by the lines you've just drawn that converge. As you increase the distance to the plane of focus, that angle will become smaller - this, since we're focused on infinity, represents the focal length length increasing.

    Now, depth of field depends on our eyes interpreting a circle as a point, which always happens if the circle is small enough. From consideration of the diagram(s) you've just drawn, you can see that this circle increases much more rapidly with distance when the angle is large (i.e. a shorter focal length, usually referred to as a wide angle lens). And conversely, the longer the focal length, the further away you can go from the plane of focus before the circle becomes as large as the one from a shorter focal length.

    Q.E.D. (or something).

    Edit to add: do we need a new thread "The advantages of plates - or why we should ditch film"?:D

    DOF2.jpg

    This diagram doesn't show rays from infinity, but it should still make the point clear.
     
    Last edited: Dec 12, 2018 at 11:44 AM
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