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Thread: Image circle too large?

  1. #11
    Jac@stafford.net's Avatar
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    Re: Image circle too large?

    Quote Originally Posted by mingliaozi View Post
    Thanks to everyone. Yes, I do realize that I have lots of reading to do. However, as a mathematician I sometimes find some of the articles a bit handwavy and lengthy for the information they provide. So I was asking for a quick formula, and thanks a lot. So, I have a bulldog 4x5 DIY camera , my minimum lens extension is around 100mm and maximimum about 180mm ish. This doesn't seem to be very good, basically only allowing 90mm lenses, am I right?
    And also, which formula relates f stops to depth of focus? For pinhole cameras, everything is in focus. So, by stopping down heavily, I could account for the limitied lens extension ?!
    Please visit here for formulas and a lot more information. No sense in duplicating it here. You will find that depth of focus is different from depth of field. Good stuff. Enjoy the read.

    Regarding using a lens longer than bellows draw, one can use a lens board extension (which can sometimes be a recessed lens board mounted backwards). You can then use your 180mm and longer. Surf the big auction site, or google for examples.

  2. #12

    Re: Image circle too large?

    Thanks for the quick reply and the formula. Unfortunately, the Intrepid Camera seems to have been sold out, but I am considering making my own, apart from the bellows, it doesn't seem too difficult

  3. #13
    Jon Shiu's Avatar
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    Re: Image circle too large?

    Quote Originally Posted by mingliaozi View Post
    Thanks to everyone. Yes, I do realize that I have lots of reading to do. However, as a mathematician I sometimes find some of the articles a bit handwavy and lengthy for the information they provide. So I was asking for a quick formula, and thanks a lot. So, I have a bulldog 4x5 DIY camera , my minimum lens extension is around 100mm and maximimum about 180mm ish. This doesn't seem to be very good, basically only allowing 90mm lenses, am I right?
    And also, which formula relates f stops to depth of focus? For pinhole cameras, everything is in focus. So, by stopping down heavily, I could account for the limitied lens extension ?!

    Thanks to everyone!
    No, not good to use a 90mm lens with a camera with > 100 minimum extension, because it likely won't focus to infinity. For that camera it would probably be better to get a 120mm lens.
    my black and white photos of the Mendocino Coast: www.jonshiu.com

  4. #14

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    Re: Image circle too large?

    Quote Originally Posted by koh303 View Post
    That very polite, but misguided, sadly there are no females active on this forum.

    Now - back to technobabble.
    Excuse me? I really hate to interrupt the thread to answer this, but I'm quite female, thank you. I do try to be active on this forum. Sorry if nobody notices.
    Bethe King
    www.ewfisher.com

  5. #15

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    Re: Image circle too large?

    Quote Originally Posted by mingliaozi View Post
    Thanks to everyone. Yes, I do realize that I have lots of reading to do. However, as a mathematician I sometimes find some of the articles a bit handwavy and lengthy for the information they provide. So I was asking for a quick formula, and thanks a lot. So, I have a bulldog 4x5 DIY camera , my minimum lens extension is around 100mm and maximimum about 180mm ish. This doesn't seem to be very good, basically only allowing 90mm lenses, am I right?
    And also, which formula relates f stops to depth of focus? For pinhole cameras, everything is in focus. So, by stopping down heavily, I could account for the limitied lens extension ?!

    Thanks to everyone!
    If minimum extension is only 100mm then maximum lens focal length would be approx 100mm unless you can fit a recessed lens panel. It may be that the camera was designed for use with a 90mm lens, I don't know but if max extension is only approx 180mm then a 180mm focal length lens will only be able to focus at infinity or very close to it which is not much use.
    Those cameras are very basic. Don't get it wet. MDF expands when it gets wet and it will become a 10x8 before you know it

    This software may be a bit advanced for you at this stage but as a mathematician its probably right up your street.

    http://www.winlens.de/index.php?id=70

    you can play around with numbers. Just remember to put object(the subject) distances and magnification preceded with a negative sign.

    You can use it to calculate all distances, depth of field, depth of focus, circles of confusion, airy discs, what difference apertures will make to DoField and DoFocus, lens extension, distances near and far, etc etc.

    Also available for andorid at https://play.google.com/store/apps/d...e.calclensthin

  6. #16
    Jim Jones's Avatar
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    Re: Image circle too large?

    Quote Originally Posted by mingliaozi View Post
    . . . my minimum lens extension is around 100mm and maximimum about 180mm ish. . . .
    As Jon Shiu says in post #13, a lens about 120mm or a little more should be good on your camera. Press camera lenses with a focal length of 127 or 135mm might work, and are less expensive than many of the lenses intended for view cameras. Look up the back focus specification on any similar lens before investing. To focus closer with the lens you have, buy or improvise a top hat lens board to extend the lens further.

  7. #17

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    Re: Image circle too large?

    Quote Originally Posted by Winger View Post
    Excuse me? I really hate to interrupt the thread to answer this, but I'm quite female, thank you. I do try to be active on this forum. Sorry if nobody notices.
    I see you on here and APUG, Bethe. You don't say as much as some of us but what you do say is both helpful and interesting.

  8. #18

    Re: Image circle too large?

    Hey Jim Jones, thanks a lot! If I want to aquire a press camera lens, what terms should I use on ebay? And what do you mean by back focus specification?

  9. #19

    Join Date
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    Re: Image circle too large?

    Quote Originally Posted by mingliaozi View Post
    Hey Jim Jones, thanks a lot! If I want to aquire a press camera lens, what terms should I use on ebay? And what do you mean by back focus specification?
    What do you mean by "a press camera lens"? Any lens that can be mounted on a press camera could qualify.

    You don't care about back focus. To determine if a lens will work at infinity on your camera you need to know the flange focal length of the lens in question.

  10. #20

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    Re: Image circle too large?

    I agree with what most are saying in that a 90 to 120mm lens is what you need for that camera. If you can work out what the shortest lens that will focus at infinity is for that camera, then that would be best for you. The manufacturer should be able to tell you if a 90mm Angulon will focus at infinity.

    It would make sense if it does but is not guranteed so check with manufacturer what is shortest focal length lens the camera was designed to work with. If in doubt then a 100-120mm lens will probably be OK. A 90mm lens might be marginal. All depends on exact lens and exact minimum extension you really have.
    180mm lens definitely sounds like it is too long for that camera to be useful.

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