How to use bellows on a 35mm SLR?

Discussion in '35mm Cameras and Accessories' started by Erik Petersson, Apr 24, 2010.

  1. Erik Petersson

    Erik Petersson Subscriber

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    Hello!

    I have a bellows unit from Asahi, that fits to my Zenit ET. My lenses (mainly a Helios 44, 52 mm f1:2) achieve quite some enlargment when attached. The bellows unit can slide back and forth. The unit is marked with f=55 mm on one side and a scale with numbers from 0,7 to 2,3. On the other side it is marked f=58, and a scale with numbers from 0,6 to 2,2.

    The scales probably relates to light loss, but which of them should I use with my 52mm lens, the one on the left side or the one on the right?

    When using the unit, should I leave the lens focused on infinity, on the closest focus, or somewhere in between?

    Anything else to think about? I plan to use negative film in the first try, so exact exposure will not be extremely critical.

    Thanks in ahead for any replies! I hope to catch some of the spring flowers with this setup. The pictures just might be very nice.

    Erik
    Stockholm
     
  2. richard ide

    richard ide Member

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    Someone correct me if I am wrong, but I think the numbers refer to magnification with both a 55mm and 58mm lens. The bellows is being used for focussing instead of the lens barrel so you can ignore the setting marks on the lens. I am not familiar with your camera so if it has through the lens metering use the meter reading for exposure setting. If not, apply the appropriate correction for the magnification you are using.
     
  3. Rol_Lei Nut

    Rol_Lei Nut Member

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    Those should be the magnification factors.

    If you want to be accurate, the 55mm one would be closest to (but not exactly match) your 52mm.
    Also, leave your lens at infinity, if you want to know the magnification factor as accurately as possible. Otherwise it makes no difference where you have the focusing ring set (exception being lenses with CRC, but does not apply to yours).

    If your camera has through the lenses metering, you don't have to compensate your exposure. If not, you'll have to find a table for exposure compensation according to the magnification factor.
     
  4. Erik Petersson

    Erik Petersson Subscriber

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    Richard and Rol Lei Nut,
    thanks for your replies.

    Does exposure compensation relate directly to magnification? Does two times magnification mean that I should open up two stops?

    /Erik
     
  5. Rick A

    Rick A Subscriber

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    Exposure compensation does relate to magnification, but not the way you are thinking. If you have TTL metering, do not worry about this. there is a formula for figuring exposure comp, but I dont remember it off-hand. I recommend you find a copy of "The Manual of Close-Up Photography" by Lester Lefkowitz, has all the tables of info and methods of close-up work you could ever want. He even covers DIY gear for macro.
     
  6. Q.G.

    Q.G. Inactive

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    It does. And no.

    Exposure compensation can be calculated using magnification into an aperture factor, a shutterspeed factor and a correction in stops.

    The first, aperture factor, is: 1 / (magnification + 1)

    The second, shutterspeed factor, is: (magnification + 1)^2

    The third, correction in stops, can be derived from either of the two above:

    log(aperture factor) / log(sqr(2)), or
    log(shutterspeed factor) / log(2)


    So a two time magnification needs an aperture correction of 0.33 times the f-number the meter suggests (so set f/2.7 instead of f/8); or a shutterspeed factor of 9 times the shutterspeed the meters suggests (so set 1/15 (actually 1/13.89) instead of 1/125), or a correction of 3.16 stops applied in any way you like.
     
    Last edited by a moderator: Apr 24, 2010
  7. Erik Petersson

    Erik Petersson Subscriber

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    Thanks QG. There is no TTL on this camera.

    Let's see if I get it.

    2 times magnification - f8 adjusted to f2,7
    1 time magnification - f8 adjusted to f4
    1,4 times magnification - f8 adjusted to f3,3

    My lens has one click stop between the standard apertures, so I will probably find acceptable settings.

    the shutterspeed factor, is that (magnification + 1) multiplicated with 2?

    Erik
     
  8. Q.G.

    Q.G. Inactive

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    No, raised to the power 2.


    I usually take the long route and calculate the correction in stops.

    With the aperture being more important in close up than the shutterspeed, i then put the bulk of the correction into the shutterspeed, and use the aperture only for what then remains.
    That, not just because the aperture is more important, but also because shutterspeeds usually only come in whole stop intervals, apertures in 1/2 stop intervals.

    So, for instance, if a correction of 4.6 stops is called for, 4 stops go into a 4 stops slower shutterspeed, while the remaining 0.6 of a stop is taken care of by opening the lens 0.5 of a stop (the remaining 0.1 cannot be set, but also doesn't matter much).

    When shutterspeeds get long however (i.e. over 1 second), i put everything into a longer shutterspeed. Fractional stops perhaps translate into fractions of seconds. But with reciprocity failure kicking in, it stops being a precise art, and that again doesn't matter much. Just give it something extra, and it'll be fine.
     
  9. Erik Petersson

    Erik Petersson Subscriber

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    Ok, I think I know what I need now to try this out tomorrow. The main problem, now that the exposure compensation is clearer, will be to deal with the shallow depth of field. It will be fun to see what I can achieve with these bellows.

    Thanks everyone!

    Wait, I just realized that the lens will be fixed on f2 as the bellows does not stop down the lens. I will probably have to put a piece of tape on the "pin" on the back of the lens without making it sticky. Hmmm. Thanks anyway!

    Erik
     
  10. Rol_Lei Nut

    Rol_Lei Nut Member

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    There's a reason I suggested looking for a table... :D
     
  11. John Koehrer

    John Koehrer Subscriber

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    The scale with .7 to 2.3 is a magnification scale.
    A general rule of thumb is at 1:1 increase exposure 4X which is two increments of either shutter speed or aperture. At 1:2 the increase is 8X or 3 stops.
    These are just approximations but you will find them to get you right into the ballpark. I just use these values & bracket my exposures.

    The method QG uses is very good, using speed for full stop & aperture for fractions.
     
  12. Q.G.

    Q.G. Inactive

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    I don't know... i can do 'the drill' on a pocket calculator pretty fast.
    Excluding the input of both extension and focal length, all it takes are 13 keys in a fixed sequence on a standard pocket calculator.
    :wink:

    But yes of course, i have also compiled tables and carry those in my bag.
    But mainly because the 'general' formulae ignore lens asymmetry, and it does make a difference big enough to worry about, and i am not even trying to memorize the relevant data of all of the lenses i might want to use.
     
  13. Rol_Lei Nut

    Rol_Lei Nut Member

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    I tend to take a more "in the field" approach, meaning I'm unlikely to have a caculator in my bag.

    What I usually do is stick some gaffer's tape alongside the ratio scale (if there's space) and write the exposure compensation values in their proper places. ALso did that in my macro lenses.
     
  14. Rick A

    Rick A Subscriber

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    Does the lens you are using have a selector switch to set the aperture at auto or manual? If you can select manual, focus, compose, then set the aperture to the f-stop of choice. If you dont have the selector, go ahead and tape the actuating pin down and follow the previous steps.
     
  15. Erik Petersson

    Erik Petersson Subscriber

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    Yes, I will have to tape that pin down on this lens.

    I did not have a chance to do my photos today as I was not feeling well. Hopefully next weekend will be sunny as well.
     
  16. Erik Petersson

    Erik Petersson Subscriber

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    Your posts encouraged me to acquire a bellows unit to my Nikon system. I got it on the mail the other day, and now I am playing around with some lenses before going out to make photos. This is strange: I can only use lenses from 35mm and up. The 28, the 24 and the 20 will not focus when attached on the bellows. Only blur. I wanted to use them to get some more depth of field, but it seems impossible. Can something be done, such as mounting the lens backwards or so?
     
  17. Q.G.

    Q.G. Inactive

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    Mounting them backwards could work, yes.
    The problem with retrofocus lenses is that the principal plane can lie too far behind the front lens surface, so that subjects need to be inside the lens for a sharp image to be formed given the lens to film distance created by the bellows. And that obviously won't work. :wink:

    Depth of field depends on magnification and aperture. Not on focal length.
    So there is no need to try shorter lenses: you will not get an increase in depth of field at all.

    Depth of field is very small anyway.
    Effort put into getting more of it (by stopping down the lens - the only thing you can do) will not produce significantly more. That is: stopping down far enough may double or quadruple DoF, but it then still is minute, compared to the size of your subject. And image degradation due to diffraction will ruin the resolution inside what little DoF you have long before the little bit extra DoF will become apparent.
    So its better to make do with the little DoF there is and concentrate on how to use that to best effect, instead of spending time and energy chasing after what you will not get anyway.

    Welcome to the world of tiny things!
     
  18. Erik Petersson

    Erik Petersson Subscriber

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    As depth of field is not achievable on these small scales, I will have to do without then. Thanks for explaining!

    My idea is to catch a small weed just as it is leaving the soil, so I will have to think of a way to keep the camera clean as well...
     
  19. Q.G.

    Q.G. Inactive

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    Cheap clear plastic bags.
    Put them around everything, cutting or tearing holes where there need be.
    And a rag to wipe everything clean afterwards. :wink:

    Some shots are best set up in a controled setting. Perhaps your emerging seedling shot would be too: if in a container, you could set that on a support in front of the lens, without you having to lie on your belly with you and the camera pressed down in dirt or even mud. The background will be blurred beyond recognition, so you can put such a set up anywhere where you can find a good background (substitute). You could also create a black background by clever lighting and using black card or paper.
     
  20. Erik Petersson

    Erik Petersson Subscriber

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    Another question before I go. This leaves me with a 100mm and a 50mm. The 100mm focus further away from the camera than the 50mm, which is practical. Is there anything else to think of when choosing lenses?
     
  21. Q.G.

    Q.G. Inactive

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    Try to use ones of a 'standard' lens design, i.e. double Gauss derivatives.
    They keep up good performance with changing image scales, and offer excellent quality when used close up.

    And the thing you mention: longer lenses offer more working distance. But they also require more extension.


    When you're not metering through the lens, you ned to know that asymmetrical lenses (telephotos. As you have found you won't be using the retrofocus wide-angle designs, the other asymmetrical ones) require more exposure compensation than you would think.
    You need to find out the pupil magnification of those lenses to do the sums correctly and work out much more.
     
  22. Erik Petersson

    Erik Petersson Subscriber

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    The 50 it is then, a Nikkor 50mm Ais, it should not be too complicated the first time around. Thank's a bunch!
    Erik