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  1. #1
    fhovie's Avatar
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    I just did a 20 x 24 from a color 4x5 of some flowers and I noticed in the corners, the image got soft. I used a polarizing filter. It is sharp every where but the corners. it is not dim in the corners. It is from a 75mm F5.6 Caltar II N (80s Grandagon by the Serial Number and the info on View Camera Magazine.) I am under the impression that this is as good a short lens as there is. I used a slight forward tilt, was focused at hyperfocal and was at F32 (pushing difraction here?) I suppose it is possible that the filter could cause it. It is a good double coated filter. I was just wondering if anyone else had this kind of experience with their 75 mm lens and at what aperature do you consider the limit (either way)

    Frank
    My photos are always without all that distracting color ...

  2. #2

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    Frank,
    The view camera magazine article indicates two 75 mm Caltar lenses. The earlier a Komura manufacture and the latter Rodenstock. The earlier lens had an image circle of 170 mm and the latter an image circle of 195 mm. Both were mounted in Copal O shutters.

    The fact that you indicate softness in the corners leads me to believe that you were exceeding the coverage of the lens. The diagonal of the 4X5 format is approximately 6.4 inches (sq root of "a" squared plus "b" squared) that converts to 162.56 mm. Thus a lens would need to have an image at least that large to cover the format. When you indicate that you used slight tilt (wouldn't make any difference if front or rear) you are increasing the effects on the size of the diagonal of the format. Tilt is the greatest user of a lenses covering ability.

    Most usually the coverage ability of a lens is not a sharp demarcation point. Rather it has an increasing degradation effect until the image circle is bypassed. The reason for this is the penumbra effect that you have noticed when you dodge a print. As the dodging tool is raised from the paper the shadow edges become less distinct. This softness that you noticed would become more noticeable the larger the degree of enlargement of your print.
    Art is a step from what is obvious and well-known toward what is arcane and concealed.

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  3. #3
    Loose Gravel's Avatar
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    We don't have enough info to really figure this out. I've had several soft-in-the-corners lenses over the years. Komura was one. A fast xenar was another. Wide angle lenses are tough to design and maintain critical focus across the field. To solve this, you will need to reproduce the setup, but photograph something flat, maybe a sheet of newspaper. Try it with and without the polarizer and let us know.

    Since you said it didn't become dim or have light fall off, I don't think you were running out of image circle. Also, with flowers you may have had a little bellows extension, giving you a larger image circle.
    Watch for Loose Gravel

  4. #4

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    Depends on how you define image circle. If he had 15 lp/mm in those corners wouldn't it look okay on the ground glass? But enlarge it 5x and those corners are going to get soft. Don't some lenses have relatively large circles of ilumination but relatively small circles of good definition?

  5. #5

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    fhovie, did you check with a good loupe whether the negative is the source of your lack of sharpness? It could as well be a misaligned enlarger or some lack of flatness in the carrier.

    It is not unusual that a short lens has a curved (not flat) field, esp. when using it close-up. But you should be able to check this on the groundglass. Use a small Maglite at the subject to check this at f32.

  6. #6
    David A. Goldfarb's Avatar
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    Unless these were enormous flowers, I suspect you were relatively close to them, and therefore nowhere near the edge of the image circle.

    Ultrawide lenses just aren't the best choice for macro work, where DOF is short anyway. A better choice would have been a macro lens or an enlarging lens (unless you have much more bellows than I would have guessed from your initial choice of a 75mm lens). It can even be a lens that doesn't cover the format at infinity, like a macro lens for 35mm or medium format or an 80mm enlarging lens. At macro distances, lenses for smaller formats will often cover 4x5".
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  7. #7

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    David raises a valid point. I wonder if Frank would not have gotten into bellows extension considerations if he were really that near the flowers?

    Considering his choice of materials (color) one would think that if he were that near the object his exposure complaint would have been one of underexposure. I guess we will wait for Frank to weigh in and tell us "the rest of the story".
    Art is a step from what is obvious and well-known toward what is arcane and concealed.

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  8. #8
    fhovie's Avatar
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    I don't know if this is the "rest of the story" but I was under the impression that if you ran out of image circle, you would get light fall off. The softness is in the negative. It is a Rodenstock Lens. The enlarging lens was a 105mm Nikkor. The scene is a field of flowers with the closest at 3 feet - The camera was 24" off the ground and I focused using a good loupe. The Image seemed sharp end to end at F5.6 and I stopped down to F32 because of the slight tilt. The image went from 3 feet at the foot to infinity and the mountains in the background in sharp focus. The flowers in the forground center are sharp, The flowers at the left and right and the mountains are sharp. The lower corners are soft where there is the greates distortion caused by the short lens. The exposure was 1/2 sec at F32 with Fuji Color sheet film at the rated ASA 160 and processed dip and dunk commercally at a local lab. I did the enlarging myself. I posted the image - poppy field
    Frank
    [/img]
    My photos are always without all that distracting color ...

  9. #9
    Loose Gravel's Avatar
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    That's a very short enlarging lens for a 4x5.
    Watch for Loose Gravel

  10. #10
    fhovie's Avatar
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    Quote Originally Posted by Loose Gravel
    That's a very short enlarging lens for a 4x5.
    Yes - agree - It is my friend's lab and that was his longest lens - I do regret not brining my 150mm Omegron.
    My photos are always without all that distracting color ...

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