Critical focus question?

Discussion in 'Medium Format Cameras and Accessories' started by stradibarrius, Oct 5, 2009.

  1. stradibarrius

    stradibarrius Member

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    On my manual focus cameras like my RB67 or Yashica 124G when I get to the "critical focus spot" where it seems to be in focus...a tiny bit more and it is still in focus and then it starts to go OOF again.
    My question is about the tiny spot of critical focus where, for me, it is extremely difficult to tell the difference, even with the loupe. I know that for the exact focal length of a technical piece of equipment the is "the" spot where it is perfectly in focus.

    How do you decide when it is focused correctly?
    This may seem like a silly question...but???
     
  2. Bosaiya

    Bosaiya Member

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    Part of this is knowing ahead of time what you want the final image to look like. It may be planned out to the tiniest detail or it might be impromptu (for example you know you want a shot of a model looking off into the distance over her shoulder but the exact expression and angle aren't exactly known, you just have a general idea). Either way I look through the viewfinder or on the ground glass and wait for the right moment when it all comes together. Philosophically there is a "click" where everything just seems right. The trick for me is knowing my gear and what I want to achieve so that when the magic moment appears I can act on it.

    Mechanically when the part of the composition that I want to be sharp is in focus I release the shutter. Not much to it.
     
  3. Christopher Walrath

    Christopher Walrath Subscriber

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    I can see this as a relevant arguement if a razor sharp focal plane is called for. However for general grade photography I think it's not quite so elusive. I just zero in. Focus through clear and then back through clear, see-sawing back and through until I get the focus sharp and where I want it as to DOF. Barring LF photography and movements, there's honestly not that much more to it.
     
  4. Q.G.

    Q.G. Inactive

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    You approach focus by going back and forth in ever decreasing increments until you think that moving the focus knob/ring more will only make it go oof.
    You'll never know for sure, unless you check and move the thing a tiny bit more and see what happens. If you were spot on, it will defocus (and you will have to guess how much to go back again). If not, you will have to guess whether where you are now is the best you can get, or ...
    It takes confidence, the believe that you have it nailed.

    Focusing aids help.
    A split image rangefinder, for instance, is very accurate.
    But it then too still depends on your judgement, on whether you believe your eyes.

    Yet, it is not a big problem.
     
  5. stradibarrius

    stradibarrius Member

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    That is the method I use. I can get to the "focal point" quickly but I am always concern about razor sharpness. Maybe too much so? The RB in particular has such a beautiful viewfinder, almost 3D sometimes. I flip up the loupe and always fidget with the tiny-est detail. I am always concerned that the small scale of the ground glass will show up a mistake in the larger print.
     
  6. Bosaiya

    Bosaiya Member

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    It sounds like you are still uncomfortable with your gear. That will go away with time and practice. Learn your gear, learn what it does and how you interact with it until it becomes second-nature. Eventually all of that will just melt away and become invisible. Just keep working at it and don't change too many variables. Stick with one body and one or two lenses and learn how to use them so that they become a part of you. If you're thinking about your gear then you're not thinking about the shot.
     
  7. Denis K

    Denis K Member

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    If you only dwell on the plane of focus you will miss the more important issue of dept of field. You really need to think about the area of acceptable focus as a volumn, not just a plane. The visual focus point you refer to in your message is somewhere in the middle of that volumn. In your composition, it is up to you to decide what to bring into that volumn and what to throw out of it, but to do so you need to think about both the near and far boundaries, not just the plane of maximum focus.

    Denis K
     
  8. Q.G.

    Q.G. Inactive

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    Yet you have to focus, and the 'problem' arises.
    (I disagree, by the way, that depth of field is more important. Putting focus there where it should be is more important than - also important, but less so - deciding how the in-focus bit relates to the rest of the image 'focus/sharpness-wise'.)

    It's not a matter of being uncomfortable with your gear, i think. It's just a lack of a way to decide when you have reached the 'maximum' other than seeing it get worse again. And when you do, you know you're no longer there.
     
  9. Denis K

    Denis K Member

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    I think an example to demonstrate my point is when taking a picture with the lens nominally focused at infinity. If you simply focus at an object at infinity, as you describe, then you will throw away a great deal of potential depth of field for the comfort of seeing a maximally sharp image (of infinity) in the viewfinder. From the standpoint of your composition this may be what you want, but I doubt it. I can't think of any simple way of boiling down the process of setting the focal plane of an image that does not come to terms with the near and far points of acceptable focus based on your estimate of the depth of field. Even if your strategy involves setting the focal plane at a fixed distance and hoping for the best, this strategy does not work well at infinity. I do, however, agree that this simple strategy will work if your objective is to maximally render a flat plane, such as the tombstone in one of the original posters portfolio pictures.

    Denis K
     
  10. MattKing

    MattKing Subscriber

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    If you are having trouble determining critical focus, it would be worth your while to determine if the viewing system of the camera and your eyesight are matched to each other.

    There is a reason that eyeglasses are made for people, and correction diopter lenses are made for cameras :smile:.

    Matt
     
  11. Q.G.

    Q.G. Inactive

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    I don't describe simply focussing at infinity.
    I strongly feel we have to put focus there where focus must be. Focus is a tool used to set the focus of the image we create.

    'Hyperfocal', considering the near and far limits of focus, is a technical, numerical appraoch, that fails to acknowledge that the image is about something, instead acts your subject as if it is a distance range.

    So we must set focus where it is supposed to be (say, the eye in a portrait - you decide: it can be anything, as long as you decide what the focus of the image you are creating is!), then use the aperture to control how the bit in focus relates to the rest.
    There are limits to what you can do with the aperture. But i don't think that is bad: it protects us against ourselves, should we ever feel the desire to make too much part of the subject of our images, letting it drown in indecision.

    Nowhere in the process should near and far limits play any role. This is not a mathematical thing you are doing. So infinity or not, it does not make a difference. We shouldn't even think in those terms.
    The silliest thing i think you can do, by far (and then some), is to let focus be decided by mathematics. Let the number game, condicence, decide what is and what is not the focus of your image.

    So we do not "hope for the best". We carefully and deliberately place focus, and use the aperture to get the image the way we want it to be.


    Alll the above is, i think, extremely important. Yet beside the point: when you know what to focus on, it can be hard to decide whether you have it, critically, or not.
    Eyesight, as suggested, is a factor.
    Yet in the end, it remains a bit of a guessing game. Like anything that we want to do as good as possible.
     
    Last edited by a moderator: Oct 5, 2009
  12. Maris

    Maris Member

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    I think I've had the same experience as the OP and discovered it was the camera's fault!

    A very small amount of backlash, play, or slack in the focussing mechanism seems to cause a "flat" spot in the focussing response...focus, turn, no change, turn some more, out of focus. Very disconcerting.

    My Mamiya RB67 has a variable friction control on the focussing mechanism so if there is a bit of looseness in the focussing rack the fingers won't feel it. Only the eye on the focussing screen notices something wrong.
     
  13. BetterSense

    BetterSense Member

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    Critical focus is achieved by "mind over matter".

    If you don't mind, it don't matter.
     
  14. Anscojohn

    Anscojohn Subscriber

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    We were taught thusly: with the magnifier in place (124G), focus until you see the image "pop" in then go a bit beyond it. Return slowly to the point of focus; a bit beyond, but less than before. Another time or two and you are "locked in". Now, with my six decade old eyes, it is not as easy as it was; but it is still the way I do it.
     
  15. stradibarrius

    stradibarrius Member

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    John I can identify with the old tired eyes..LOL! You just described my method. I get to the "spot" and then go back and forth in smaller steps until I think it is as good as it is going to get.
    I like the idea of mind over matter!!!
     
  16. Anscojohn

    Anscojohn Subscriber

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    Yup. Even with young eyes, that's the way to do it.
     
  17. Sirius Glass

    Sirius Glass Subscriber

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    As others posted, move the focus back and forth fast enough so that the eyes do not work against you by compensating and working faster than you are focusing.

    Steve
     
  18. marcmarc

    marcmarc Member

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    As someone who shoots mostly street photography (often with an RZ!) I prefer to focus each and every shot. There are any number of reasons why negatives may be out of focus - film not flat (more likely with 120 film then 135) mirror out of alignment, after market focusing screens, etc. My RZ Pro II has a second fine focus knob which I find very useful.
     
  19. Sirius Glass

    Sirius Glass Subscriber

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    Can't make a generalization about that. It depends on the equipment and its condition. That was not a valid generalization. Much like saying all film cameras are inferior.

    Steve