Best B&W film and developer for a lens and camera focus test

Discussion in 'B&W: Film, Paper, Chemistry' started by rbultman, Feb 20, 2013.

  1. rbultman

    rbultman Subscriber

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    I am having some focusing issues with a 150mm lens on a Mamiya 645 Super. The lens is new to me while I have had the body and the rest of the kit for a number of years. The kit has worked fine for me with a 45mm and 80mm lens and metering prism. I plan to do a series of tests both with and without film to find the problem. The question is, which emulsion type and speed and developer should I use? I have rolls of Delta 100 and 400, FP4+ and HP5+, Fomapan 100 and 400, Kodak Tri-X, and Fuji Acros 100. I have Xtol (ECO-PRO) and Rodinal (Adonal).

    As additional background, I shot one roll of film with this lens. Each frame had good exposure but every frame was out of focus. I used Fomapan 100 souped in ECO-PRO 1:1.

    As a subject, I plan to use wine bottles arranged diagonally when viewed from above so that I can see depth of field. Goodness of focus will be determined by the clarity of text on a bottle label. I have a ground glass than can be set in place of the film insert, but I don't have a small loupe that can be used to check focus with the glass, so that will only be a "suck/doesn't suck" test. I will of course be using a tripod. I plan to use the 80mm and 150mm lenses, repositioning the tripod in order to achieve similar framing with each lens. I plan to vary the aperture setting and use the metering prism for exposure. I plan to scan the film using a Nikon LS-8000 scanner with the ANR glass holder.

    The object of the test will be to find the source of the error, be it lens, body (including mirror, focus screen, prism, and back) or my ability to focus accurately. Only the 150mm lens was added to an otherwise well-working kit. Please restrict the film and developer selection to those listed in this post. Any suggestions on the experimental setup or other suggestions that might help me meet the objective will also be appreciated.

    Regards,
    Rob
     
  2. rbultman

    rbultman Subscriber

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    I'll bite, what improvements would you propose?
     
  3. JaZ99

    JaZ99 Member

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    Hi! I'd suggest the methodology described here: http://www.normankoren.com/Tutorials/MTF5.html

    I followed it myself, and it is very easy. The lower ISO film you use, the higher numbers you get, obviously.
    The best results you can get with E-6 film (velvia or provia 100F or any outdated Kodak Ektachrome).

    The scanner is the perfect tool to get the results, IMHO (provided it is working ok).

    JaZ
     
  4. Mr Bill

    Mr Bill Member

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    Hi Rob. I'm sort of wondering how the 150mm lens could be off while the other two are ok (you use the same finder screen for all lenses, right?). You say it was a single roll of film, right, so is it possible that a film-load issue or the film back could have caused a problem?

    Since you have a ground glass insert (replaces the film mag), I would personally start out by checking the two for agreement (use your 45mm lens as a loupe if need be). You'll need a way to decide what the difference is. It seems that your lenses have rotating focus barrels (?), you might try a small piece of masking tape on the moving part so you can make a pencil mark at the focus position. Try focusing several times to see how close together the marks are, this will give a good idea of how repeatable you are. Ultimately, you want to compare the average focus position for the viewing hood vs the film-plane ground glass.

    If it passes the previous test, then for film. I would personally test with one of the slow speed films (EI 100), using whatever you most commonly use (perhaps the stiffness or curl of the film base has an affect on film position). Rather than wine bottles, I'd suggest special test targets that you can rate objectively. Small USAF resolution target segments are good, or perhaps a half-dozen lines of text in decreasing font sizes. Prop them up, or tape them to a child's play blocks, or the like.

    If you arrange a handful of these with spacing of several inches, you can make a good estimate of where the best film focus is. For example, if you focused on the 3rd target, but find that the best focus is on the 2nd, you might say that your lens seems to be focused 3 inches (or whatever it is) too close. If you find that two targets seem to be equally sharp, you can probably assume the best focus point is midway between. I can't say offhand how far apart to space the targets, but perhaps test for a distance where you can detect a focus difference (thru the prism finder), then space the targets at half that distance.

    It might be worth trying 3-4 shots to make sure they are consistent. In industry, I've seen cameras where this changes, which indicates a film magazine problem, most likely related to the pressure plate. But it could be a poor design, etc.

    ps; I see that JaZ99 suggests a Norman Koren test that could give solid rating numbers, but I don't think you need to go that far. Your issue is that you found an obvious focus problem and want to identify the issue - it seems to me that something should stick out like a sore thumb.

    pps; I didn't mention to use a solid tripod 'cuz you already mentioned that part. Also, shooting wide open gives the most sensitivity to a focus distance error; you might try one stopped down a bit to make sure no shift takes place (although you won't have good precision in detecting this). Good luck, hope something simple shows up.
     
  5. tkamiya

    tkamiya Member

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    I've done a similar test to yours on (used to be mine) Mamiya 645 Super and Pro. I used Tmax400. You can basically use any film and any developer. The resolution capability of any film is far greater than the resolution capability of the lens you are testing.
     
  6. jeffreyg

    jeffreyg Subscriber

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    Rob,

    I'm a bit puzzled as to what the focusing problem is. I would think that a simple test on a flat subject (that has sharp graphics to focus on) that can be shot at different distances at each F stop/shutter speed combo using any one of the 100 ISO films will show if there is an issue with the lens. Some time ago a friend asked me to take pictures of him and his wife with his camera and lens. Every one of them was out of focus. I could not believe I would make such an error. He later recalled that he had dropped the lens but it did not appear to have any damage. After sending it back to Nikon for repair it was found to have a lens element out of alignment. If you bought it used this could easily be the problem.

    http://www.jeffreyglasser.com/
     
  7. Jim Noel

    Jim Noel Member

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    I strongly agree with Jeffrey. The lens has been disassembled and then reassembled incorrectly. I would not waste time testing, but return it to seller.
     
  8. Gerald C Koch

    Gerald C Koch Member

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    Top determine depth of field at short distances set a yard stick at a 45o incline. Focus at the 18 inch mark. After developing the film look at the marks on ech side of this center.
     
  9. ic-racer

    ic-racer Member

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    Choice of film could be important. If your mirror and focus screen check out to be in the correct position, then you are left with a film flatness issue.
     
  10. rbultman

    rbultman Subscriber

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    Thanks for all of the replies. I really appreciate them.

    I assumed that since it is an SLR, a sharp image in the viewfinder meant that the lens was not damaged. I'm past the return date so the lens is mine now.

    Assuming the ground glass test passes, I'll shoot a variety of targets, apertures, and lenses since I need to burn 15 frames anyway.
    Sent from my PI86100 using Board Express
     
  11. rbultman

    rbultman Subscriber

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    Mirror stop not stopping mirror at appropriate position

    I found your post from 2010 time frame regarding the problem with the mirror and everyone telling you it is not the mirror. I am pretty sure it is the mirror stop on my Super. With the ground glass against the film rails and the using a release cable to hold the shutter open, I focused on the ground glass using my 45mm lens as a magnifier. I then released the shutter. With the prism removed and using the 45mm and looking at the focus screen, the focus does not match. By moving the mirror lock-up knob slightly and thereby lifting the mirror slightly the image comes into focus on the focus screen. If I could adjust the mirror stop, I could correct the focus issue.

    I think the focus has always been off, but with the wider lenses and stopped down, I never noticed. I know remember why I stopped using the camera for several years. I was not happy with the sharpness of the images.

    I suppose at this point I could either try to fix it or buy a used Pro or Pro TL body. Suggestions?

    p.s. Thanks again for the great ideas.
     
  12. flatulent1

    flatulent1 Subscriber

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    It's probably going to be cheaper to replace the body than it would be to repair it. Have the old one repaired later, and use as a spare.
     
  13. Mr Bill

    Mr Bill Member

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    Since you know that lifting the mirror slightly seems to correct the focus, this means that the viewing image is formed short of the ground glass. I'd cross my fingers hoping that someone has simply put the ground glass in upside down.

    If you find that 1) the ground surface is facing up, and 2) the error is roughly 2/3 thickness of the ground glass, this would mean that it's most likely upside down.

    I'll cross my fingers for you. Good luck.
     
  14. rbultman

    rbultman Subscriber

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    Update

    After confirming that the mirror stop was broken and beyond my ability to repair, I bought a Pro body. It arrived yesterday. I repeated the same tests using the ground glass. The focus on the focus screen and the ground glass were identical, which confirms the diagnosis. Thanks again for the inputs and insights.

    Regards,
    Rob