OM 50mm problem with extension tube

Discussion in 'Adapted Lenses' started by Crushader, Jan 12, 2014.

  1. Crushader

    Crushader Mu-43 Regular

    62
    Dec 11, 2013
    Melbourne, Australia
    Tham
    I'm new to the photography scene, and so far I'm more interested in the old prime lens so I picked up a few old 50mm. One of it is the OM 50mm f1.8, the lens itself is in pretty good condition aside from some cosmetic wears, and I got a triplus extension tube for the OM mount as well and that is also in pristine condition.

    I tried the combination out with the 50mm and the tube for some macro shots, but somehow the focus is all wacky, it looks more like tilt shift when I have the tube on. There would be only a just a 1/4 of the screen in an angle like a / is filled with focus-able view, the rest is just blurry.

    I'm currently clueless what could be the problem, as the lens itself can focus just fine without the tube, and the tube has no gaps or any damage that could potentially affect the image either (test with 1, 2 and 3 parts of the tube connected). Maybe veterans like you guys could give me an idea of what could cause it.

    Currently I'm at work so unable to upload sample images, will do later when I return to home.
     
  2. chonbhoy

    chonbhoy Mu-43 Veteran

    430
    Apr 23, 2013
    Scottish Highlands
    Never used an extension tube but i gathered that there is no glass in them so all i can say is that the tube must be bent or not parallel.
     
  3. wjiang

    wjiang Mu-43 Hall of Famer

    A bent extension tube is basically a tilt shift...
     
  4. Petrochemist

    Petrochemist Mu-43 Top Veteran

    653
    Mar 21, 2013
    N Essex, UK
    Mike
    DOF in macro is VERY minimal, so it may be that as someone fairly new to macro photography this is all your problem is.

    Extension tubes normally come as a set of three, which can be used individually or in combinations. The focus getting progressively closer as the distance the lens is extended away increases. The DOF decreases rapidly as the magnification goes up, and can eaisly get to less than 1cm.

    Try using the shortest section of the tubes on it's own first, and work your way up to all of them together. Photographing a printed page with the camera parallel to the page, you should be able to get all the image in focus (though it might get a bit soft towards trhe corners). Whilst the DOF increases as the aperture is closed down (the image gets significantly darker too) even fully closed DOF will be fairly limited in extreme close up.

    I've never known a set of tubes to get bent significantly, but even if they are you should be able to get a flat subject in focus by tilting the camera slightly to compensate.

    There are some specialist techniques (such as focus stacking) for drastically increasing the DOF of macro shots, and these often give false expectations of what is possible in camera to new macro users. There are now many photos on the interent produced from hundreds of individual shots. I haven't the patience</SPAN></SPAN> to match these!
     
  5. inuini2005

    inuini2005 Mu-43 Regular

    103
    Nov 17, 2011
    If you attach an OM 25 extension tube on a 50mm lens, it acheives 1:1 reproduction ratio. I don't really understand what you mean by triplus, anyways, for my OM 50mm F2 macro, there is also little focusable area. Better if you could show a photo of your problem.
     
  6. Petrochemist

    Petrochemist Mu-43 Top Veteran

    653
    Mar 21, 2013
    N Essex, UK
    Mike
    I seem to remember Triplus is a brand of Extension tube.
     
    • Like Like x 1
  7. inuini2005

    inuini2005 Mu-43 Regular

    103
    Nov 17, 2011
    Thanks for pointing that out :)
     
  8. silver92b

    silver92b Mu-43 All-Pro

    Feb 7, 2013
    Atlanta, GA
    I've used the OM extension tubes with my OM 50mm f1.8. The DOF is very, very shallow and you must be very careful in the angle of the camera and subject to get the image you want. I found it extremely difficult to focus properly as I had to move the camera itself back and forth from the subject. Also, the camera and lens itself was so close to the subject that it blocked all the light!

    I ended up rigging all kinds of lights and moving the subject and the camera on the tripod in minute amounts until I got the pictures I wanted. I was able to get some large images of tiny sand grains about .5mm in dia.