Bronica E28 Extension Tube - cannot focus

Discussion in 'Medium Format Cameras and Accessories' started by smudwhisk, Feb 26, 2006.

  1. smudwhisk

    smudwhisk Member

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    OK, this is probably me doing something stupid but when I tried to use my recently acquired E28 extension tube today on both my ETR and ETRSi bodies, I couldn't get the lens to focus. I don't have a manual but the seller jotted down some instructions on connecting it to the lens and body, which I followed and appeared to do correctly since all connected up OK. However when I turned the lens to focus nothing changed and everything was out of focus. Now I did try it with my 50mm lens since it was the only one to hand, would it be this (I need to dig out my 75mm lens to test) or is something else not quite right? Any suggestions appreciated.
     
  2. Dave Parker

    Dave Parker Inactive

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    How close to your subject are you when you are trying to focus?, the purpose of the extension tube is to allow you to be closer to your subject when focusing, you will not be able to focus at infinity with the lens tube attached, focus your lens all the way out, and then move into a subject to find out how close you can focus, an extension tube is for macro work, and not normal focusing.

    Dave
     
  3. Nick Zentena

    Nick Zentena Member

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    How close were you focussing? The 28 adds how much extension? 28mm would be too simple I bet :D 28mm added to 50mm is pretty close focussing.
     
  4. MikeK

    MikeK Member

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    With a 50mm lens and a 28mm extension tube you will need to be very close to your subject. Even with a 75mm lens the subject will need to be quite close to the camera.

    Quick test with your 50mm lens, identify a subject and move the camera closer and closer until you get focus - it will be inches from the end of the lens. Hope this helps

    Mike
     
  5. smudwhisk

    smudwhisk Member

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    I'll give it another try but was trying to focus on the net curtain (seemed as good a target for macro as anything) at the window while standing in front of it, I could see the curtain fairly clearly but couldn't quite get to focus properly. Possibly too close, I'll give it another go.
     
  6. Dan Fromm

    Dan Fromm Member

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    This discussion is parallel to one in the LF forum. The orignal poster there was also trying to use a wide angle lens with a lot of extension and couldn't discern focus. Turns out he had two problems. Basically he didn't know how to focus a view camera. And his lens performed badly at the magnification he was trying to use it at.

    You know how to focus -- moving the camera is THE way -- but you're using a retrofocus lens at roughly 1:2. This is closer than its maker intended so it may give such a fuzzy image that discerning when it is in good focus is difficult. Also, wide open at 1:2 there's not much depth of field so when teetering back and forth its easy to miss the instant when the lens is focused on the subject.

    Good luck, don't practice lens abuse,

    Dan
     
  7. smudwhisk

    smudwhisk Member

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    Thank you for the comments. I am fully conversent with how to focus a camera, having used a number for many years. Just having difficulties working with an extension tube, since previously have only used macro filters successfully. I may well have been too close to the subject, something I have taken in mind.
     
  8. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    With a 50mm lens and a 28mm tube, that's going to put you pretty close to the subject.

    Set the focus for the lens at infinity and leave it there to start with. Don't turn the focus ring. Move the camera closer or farther from the subject to focus. To do this precisely it helps to have a macro focus rail.

    For greater magnification set the focus closer on the focus ring, but then focus by moving the camera, not by adjusting the ring. It's much easier that way.
     
  9. David Henderson

    David Henderson Member

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    I went through this with a 36mm tube for my SQ-Ai a year or so ago. After a while decided that the hassle of establishing focus whilst perched on a rock face or wherever simply wasn't worth it and that the macro lens which gives me 1:4 pretty much gets me what I need. I may have persevered a little more if I were using it in a studio or at least in a comfortable working position. From my notes I see I could achieve focus with my 80mm lens only when the lens was focussed to or near its minimum focus distance and that I could achieve what looked like decent focus only with the subject at 14"-15.5" from the film plane. With a 50mm lens I got focus at around 9.5" from the film plane.
     
  10. Dave Parker

    Dave Parker Inactive

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    One of the most useful items I have for doing macro work both in the studio as well as in the field is a macro focusing rail, I picked it up several years ago, it is a bogen make with micro adjustments, mount your camera lens combo then mount to your tripod, focus your camera at infinity, then you can use the rail to adjust the fine focus, makes macro work for me a whole lot easier..

    Dave
     
  11. Dan Fromm

    Dan Fromm Member

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    With a 50 mm lens at its infinity position on a 28 mm extension tube, magnification will be 0.56:1 and front node-to-subject distance will be 141 mm. Since your lens is retrofocus, I have no idea where its front node is; with normal lenses, it is approximately, great stress approximately, coincident with the diaphragm. If you extend the lens by setting it to a marked distance closer than infinity, magnification will be higher and lens to subject distance smaller.

    There's no magic to extension tubes or bellows. All they do is allow a lens to focus closer than it can on its own mount by adding more extension than the mount alone offers. Your "macro filters" accomplish the same thing, increasing extension/(focal length), by reducing the lens' focal length.

    If you knew what you were doing, why did you ask for help?
     
  12. Bob F.

    Bob F. Member

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    Using my SQA and 36mm tube (I do not have the 28mm one) with my 50mm lens, the focal point is about 6cm from the front lens element. Depth of focus is only a couple of mm with the lens wide open so, as others far more experienced than I have already said, it is very tight and easy to miss.

    Put the camera down flat on a table focused on infinity and move a pencil towards the lens from about 30cm out - you will see it snap in to focus. You will also see why Dave's idea of getting a macro focusing rail is a good one - probably essential for a pro (I'm not, and they cost a fortune! - OK, not a "fortune", but more than I'm willing to pay for the very few times I do MF macro) - it's often easier to move the subject than the camera & tripod...

    Good luck, Bob.
     
  13. smudwhisk

    smudwhisk Member

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    Because while it worked OK with the macro rings on a 35mm SLR, I couldn't seem to get it to work on the Bronnie correctly and wondered if, since it was a tube on the end of the lens rather than a ring on the front of the lens, if there was any difference particularly as on the Canon SLR I was using a zoom lens rather than fixed.