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Thread: Depth of Field, Depth of Focus, and Film Flatness

  1. #61

    Depth of Field, Depth of Focus, and Film Flatness

    P.S. I apologize to Bill, and others, if my two posts above are a bit rambling. I jumped into this thread late and did not participate in the original. I think I managed to wade through most of the original thread before it was removed, but now that it's gone it's a bit hard to remember EXACTLY who said what. I have a good general recollection of what was said, but avoided mentioning anyone by name unless I am responding directly to something they have posted here in this version of the thread.

    Kerry

  2. #62

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    Depth of Field, Depth of Focus, and Film Flatness

    Kerry, no apologies required...... you have always been a generous, polite and knowledgeable contributor to the entire LF community. I applaud and appreciate your generosity to the LF community. Although I did not take your post as criticism towards me, I would accept criticism from you with open mind and open arms! Glad to hear you sold some nice large prints, your work is first rate.

    After tweaking my system through the years, I too have made many large prints, sometimes pushing 4x5 to 60" with excellent results. However, it took me some time till I found the right lenses, right DOF or lens tilt scenes, well tuned gear, scanners, etc. till I could push enlargements this far and acheive tack sharp prints..... ..and even then, many shots can't be pushed this far..... again, all part n parcel of on-film resolution which is what this post addressed. Hence why I will never surrender my 8x10 camera...horses for courses!

  3. #63

    Depth of Field, Depth of Focus, and Film Flatness

    Kerry writes, "My whole point is if you can't see a problem on your final output, then no problem exists. " And also, "It's only a problem when it's a problem."

    These sound self-evidently true, but I think not. Of course, no problem = no problem, but that's not really what he is saying. I understand his point to be that if you cannot see a problem, then there is no problem, and that is clearly false. There can be problems you cannot see until it is way too late.

    The heuristic principle that all problems are immediately visible is not really correct. Maybe exactly one of your film holders is off by enough that a 10x enlargement will be a big disappointment, but you will find out only after a delay of several years.

    In art, there is always a possibility that you could do something better, and occasionally, that something is a technical detail such as making sure your ground glass is well calibrated to all of your film holders or learning how to balance diffraction with depth of field.

  4. #64

    Depth of Field, Depth of Focus, and Film Flatness

    The heuristic principle that all problems are immediately visible is not really correct.

    Jerry,

    I never said the problem would be immediately visible. In fact it can't be in this case. The soonest you could see a depth of focus issue is after the film is processed. You could take measurement to check alignment and registration, but there will be no visible evidence of a problem until you shoot some film - and even then you may not detect the problem. Which is why I wrote:

    "My whole point is if you can't see a problem on your final output, then no problem exists."

    Maybe exactly one of your film holders is off by enough that a 10x enlargement will be a big disappointment, but you will find out only after a delay of several years.

    This is one reason I habitually check the sharpness of my chromes with a loupe when I get them back from the lab. If I'm not getting consistantly sharp results, I know there is a problem and I have a pretty good idea where to start looking (careful note taking helps).

    I'm not suggesting people shouldn't test their equipment or understand the variables that effect image sharpness. I think we're actually on the same page here. I know my equipment well enough, through both testing and years of actual use, to trust it. If I get a new piece of equipment, I don't totally trust it until have convinced myself it will perform as expected. Depending on the type of equipment, that may mean some controlled testing is in order, or it may mean just shooting a few sheets of film and checking the results with a loupe (which I do anyway as force of habit). Testing is one way to quickly get to know your equipment, determine its limitations and identify any problems. Actually using your equipment to make photographs is another way to get to know it. It may not be as efficient as testing, but some people may find it enjoyable. Both approaches are valid, and I personally rely on both. I don't see why this has to be an either/or issue. I have done a lot of testing of my equipment, but sometimes when I get a new lens or other piece of gear, I just can't wait to get out and make some photographs with it. I've made some of my best (IMHO) images with new gear that I failed to test prior to using it. Like a kid at Christmas, when I get a new toy I can't wait to start playing with it. Of course, if that new toy doesn't perform as expected, I will revert back to testing to figure out why.

    On the other hand, there are times when testing up front is most prudent and can nip any potential problems in the bud. I'm currently assembling a 7x17 camera. I don't trust woodworking skills enough to make the camera back. So, I will have it made for me by someone with more experience and better skills. I have already acquired two 7x17 holders (thanks Chris) and will send them out to have the back made to match. The first thing I'll do when I get receive the back is perform some tests to verify the registration and alignment of the back and both holders. If I get any more holders, I will also immediately test them. The back and the holders are all hand made, and by different individuals. So, there is an increased potential for error. Now, if I was buying a new 4x5 ARCA-SWISS or some other precision machined metal camera I'd be much less concerned about problems with the back being out of spec.

    Kerry

  5. #65

    Depth of Field, Depth of Focus, and Film Flatness

    Bill,

    Thanks for the kind words. I wasn't fishing for compliments, but I'll take 'em when I can get 'em.

    Glad to hear you sold some nice large prints, your work is first rate.

    Thanks. Every couple years I manage to land a project providing prints to an office or public building. This particular job is a new medical clinic. They are displaying three of my 40x50 prints in the lobby/waiting room. They may also be buying some 20x24s and 24x30s for some of the offices and exam rooms (fingers crossed). I also supplied several prints (smaller in size) to the (then new) federal courthouse here in Portland a few years ago. I hadn't been back until this past April when I got called to serve jury duty on a federal case. It was fun to see my work on display in such a beautiful building. A couple weeks later, my kids visited the courthouse on a field trip. So, they also got to see my work on display (which they thought was cool).

    For my own personal use, I rarely print larger than 20x24. 16x10 and even 11x14 are common (I only have so much wall space). But it's nice to know the work holds up when enlarged 8 or 10x. I also sell a few prints through a gallery and the smallest size they want is 20x24 and hey prefer 24x30 or 30x40 (they also sell a lot of artwork to businesses to display in their public areas).

    However, it took me some time till I found the right lenses, right DOF or lens tilt scenes, well tuned gear, scanners, etc.

    Yep, been there, done that. I'm very satisified with the quality of my gear at this point. I'm still not totally up to snuff on scanners. When I need something made really big, I have it drum scanned. It adds cost, but they only time I need anything made big enough to require a drum scan, it's for a paying job. So, I can justify the expense.

    Kerry

  6. #66

    Depth of Field, Depth of Focus, and Film Flatness

    Kerry,

    Well, when I wrote immediately I meant it in
    the context of the time frame mentioned in the next
    sentence---i.e., several years. I am not
    quite foolish enough to suggest a time frame of a few
    seconds after exposure. My immediately allows
    for the time needed to look at the developed film with a
    loupe.

    But I do not think that looking with a loupe will uncover every problem.
    I think you would agree, because you wrote, I recently
    sold some 40"x50" prints (made from 4x5 chromes)....I admit I was
    pretty happy with the way they turned out, too.
    If your
    undoubtedly very close inspection with a loupe had removed every possible worry that
    you might have had about the quality of the chrome, then you would not have
    been so happy with the way they turned out---there would have been no surprise
    at all.

    The point I have been trying to make, alas maybe not clearly enough, is that a good
    and experienced large-format photographer may have some depth-of-focus problems
    without knowing it. His work could maybe be better, even though he regularly
    examines his work with a loupe.

    I would not dream of criticizing your techniques; it was only two of your sentences that I thought
    could easily be misinterpreted into something you had not intended. You said,
    "if you can't see a problem on your final
    output, then no problem exists.
    " and "It's only a problem
    when it's a problem.
    " These sentences sound anti-testing and anti-understanding to me.

    Anyway, you subsequently made
    clear that photographers should ``test their equipment [and] understand
    the variables that effect image sharpness.
    '' And I agree. By testing, I am sure you
    mean to include careful examinations of shots you wanted to take anyway.

    Remember, the context of this discussion comes from the original thread
    (Image quality: Normal holders vs. Quickload), which
    contained this exchange:

    Writer A said this:

    My advice is to look for consistency in your working methods.
    Consistency of film plane is important ... Part of that consistency should be a
    consistent film plane depth so switching to and fro from quickloads and
    normal film holders will likely give a different film plane depth. i.e. if
    you are going to be using normal film holders then use all of the same
    make and vintage and check their depth and set your ground glass to
    correct depth for those film holders....


    Writer B said this in response:

    This is completly unnecessary. Film holders, of all types, have been shown
    to be satisfactory for years and years, and years. There will be the
    occasional bad apple but it is not related to the MFG or style. Show me a
    pro who makes his/her living practicing this type of obsessional behavior.
    They know better and don;t have time. It is not necessary. ... Your commentt
    [does] nothing to clarify the question or help him
    understand what large format photography is all about.


    Seems to me that your position, Kerry, is closer to A's advice, even though the
    two sentences I took issue with seem to me to support B's position. I could try
    to summarize my overall position as follows: Even if most of your images usually
    look pretty good under a loupe, you might be able to improve your results by
    checking your film-plane and ground glass alignments.

    By the way, Kerry, when are you going to write a book for us? I would be one the first
    waiting in line to buy it.

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