testing lenses

Discussion in 'Medium Format Cameras and Accessories' started by nwilkins, Sep 27, 2013.

  1. nwilkins

    nwilkins Member

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    Hi everyone,

    U just got a 65mm KL lens for my RB67 and I want to find out if it is noticeably better in terms of sharpness and CA than the 50mm C lens, because I will probably not be able to justify keeping them both. I normally forego any kind of testing and just make the photos I would normally make, then form an impression over time. However, if I did want to take some test shots to compare I assume it would be best to focus on an object that is in the middle distance or maybe closer to the foreground? In that case, which of the following would be a more fair comparison

    a) focusing on an object a given distance away from the camera (ie not moving the camera between shots)
    b) focusing on an object which I would keep the same size on the negative (ie moving the camera a bit closer for the 50mm shot)

    thanks!
     
  2. E. von Hoegh

    E. von Hoegh Member

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    Stick some newsprint on a wall, about 20 feet away. Arrange it so you have small type in the center and edges of the frame, carefully focus, use a tripod, use several different apertures, etc.
     
  3. jeffreyg

    jeffreyg Subscriber

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    I'm not familiar with the RB67 and those lenses but I tested lenses I have bought for my Hasselblads. I put the camera on a tripod and under a steady light condition, I took a series of exposures at the different apertures with the appropriate corresponding shutter speeds then developed the film to see that the equipment was functionally correct. I focused on the same spot not moving the camera. To be sure of your decision why not test both ways a & b.

    http://www.jeffreyglasser.com/
     
  4. Peltigera

    Peltigera Member

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    I would think it will depend on what type of photograph you want to take - i.e. landscapes focused on infinity or portraits focused closer. For me, it does not matter at all how well a lens performs close to as I never take photographs that way. For others, how a lens performs when focused more than a few feet away will not matter.
     
  5. mesantacruz

    mesantacruz Subscriber

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    While i have ideas of what i would love for you to test, i think it's best for you to test in conditions in which you find yourself using either lens more often. I also think you should test both ways. What i would do is find a composition that has subjects along the edge in order for you/us to see CA/ or lack of... a composition that if you were to switch lenses, would still have these or similar edge subjects there.
     
  6. Mark Feldstein

    Mark Feldstein Member

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    That's the way I'd do it too although I usually work at shorter distances. You want to make sure your camera is plumb, level and square to the target too. I usually use a couple of string lines to set equal distance from the edges of the print. This is also a good method for squaring the camera to art work you're photographing for reproduction. Having a bubble level in the accessory shoe on your camera is really helpful too.

    I take multiple shots at close range, medium and infinity keeping notes as to where the camera is set and bracket the exposures 1/2 stop either side.
    Look at the negs with a strong loupe not the finished prints.
    Mark
     
  7. E. von Hoegh

    E. von Hoegh Member

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    It's actually a pretty meaningful real-world test, a pro told me about doing it that way back in the 80s. 20 feet is roughly 100x the focal length of the lens, so it's near enough infinity to tell you something. It's also the only test I've ever used. Try it on a modern kit zoom from a DSLR - you'll be appalled!:laugh:
     
  8. RalphLambrecht

    RalphLambrecht Subscriber

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    I would shoot any of the typical test targetssuch as the UASAF1951 ata distance of50timesthe focal length and compare the max resolution with a loupe or on an 11x14 inch print.
     
  9. EdSawyer

    EdSawyer Member

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    generally the 65 will be better, it's a less ambitious lens in terms of angle of view. but, it depends on what your criteria are. For the "sharpest" RB lens, it's not going to be either one of those 2 probably. Ideally, keep both - they differ enough in angle of view that it is useful to have both of them. I have the RZ versions and there's not much overlap in terms of functionality.
     
  10. David Brown

    David Brown Subscriber

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    Agreed. I have and use both for the RB. They are not interchangeable (IMO). If you prefer one over the other, that's fine, but just basing it on "sharpness" is apples and oranges.
     
  11. jerrybro

    jerrybro Subscriber

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    Better is the enemy of good enough. Which viewing angle better fits your photographic view of the world? Can you see yourself coming upon scenes where you would need one more often than the other?
     
  12. MattKing

    MattKing Subscriber

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    I have both 50mm and 65mm lenses for my RB67.

    I wouldn't want to have just one of them - they both make excellent negatives and slides for me (when I use them properly), but they make very different negatives and slides for me.

    I own and use way more wide angle lenses than longer focal length lenses.
     
  13. snederhiser

    snederhiser Member

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    Hello;
    I would be concerned about if the lenses were focusing properly on my camera. A depth of field tests or placing a ground glass on the inner film rails would be my greatest concern. Does not matter how sharp a lens is when the image is not focused on the film. By the way, I would keep both lenses, Steven.