Extension Tube question...

Discussion in 'Adapted Lenses' started by kstevieh, Jul 28, 2010.

  1. kstevieh

    kstevieh Mu-43 Regular

    Jan 21, 2010
    USA, West Virginia
    For Macro photography using extension tubes how do you determine how many to use?

    For example...I have an E-PL1. Pk-m 4/3 adapter- with a pentax 50mm lens f2(not macro)

    How do I determine the amount of extension tubes to use or just add/subtract to get the magnification you want.

    Would it be better to get a dedicated Macro lens and use tubes, a normal lens and use tubes or a Macro zoom?

    Thanks for any advice
  2. very legacy experience

    Hi Kstevieh -

    My experience dates back about 30 years, but I believe I remember correctly.

    I wanted to use a macro lens to copy old family photos, some of which were very small. I ended up with archival copies (on ultraslow B&W negative film) which I now have to scan some day.

    My first effort was to use my existing OM Zuiko 50mm 1.8 (non-macro) lens. I bought a 25mm extension tube, which let me focus closer (at the cost of not focusing at infinity), but the quality was not that good. In particular, it was hard to keep the whole image in focus, even at a fairly tight (f11) aperture. It wasn't out of focus so much as softly focused. (Or maybe it was some other artifact that I didn't understand at the time.)

    I then went ahead and bought a macro lens (OM Zuiko 50mm 3.5) which I still have today. Even without the extension tube, the lens focused from infinity to a fairly close size, enough to render an image on the negative that was 1/2 the size of the original. With the extension tube, I got to go even closer for smaller items, close enough to get a 1:1 ratio. (That is, I was taking photos of items that are the same size as the negative, or today the same size as the sensor.)

    The bottom line is that the photos were beautiful. Sharp and in focus across the whole image. I ended up shooting at around 5.6, as I dimly recall. (That was my favorite aperture back then. Go figure.)

    I still have that lens today, and have recently used it with an adapter.

    My recommendation:
    1) Buy a nice macro lens first. Legacy lenses are not that expensive, if you are willing to shop around different brands (Canon FD, Minolta Rokkor, Konica Hexanon, etc.)
    2) If you still need more magnification, get an extension tube. I haven't used mine in about 25 years, but now I feel like I have to try it again. :)

    This pic was taken last February, with the E-P2 and the old 50/3.5 macro.

    Attached Files:

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  3. photoSmart42

    photoSmart42 Mu-43 Top Veteran

    Feb 12, 2010
    San Diego, CA
    The magnification of a lens with extension tubes is generally calculated as the length of the tubes divided by the lens focal length (so 100mm of tubes with a 50mm lens should get you roughly 2:1). You'll also end up losing significant amounts of light as you add extension tubes, so you have to account for that in other ways (higher ISO, additional lighting, etc. You can also induce aberrations and other distortion effects in your image if you go too far with tubes.

    Your best bet is to use a dedicated macro lens, and if you use it with extensions then use the macro extender that goes with that lens - usually the extender itself has a lens that prevents some of the distortion effects to keep the image clean. If you use a normal lens, you're better off using it reversed to achieve higher magnifications than you would be having it normally and adding lots of extension tubes to get the same magnification.

    Macro zoom lenses don't have very high magnifications in macro mode - at best they're 1:2.5-ish, so not even close to 1:1. It's a secondary function of that lens.
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  4. amoebahydra

    amoebahydra Mu-43 Regular

    Jul 20, 2010
    Unless the lens is exactly symmetrical in design, focal length as seem from rear is usually shorter than the usual focal and as such the magnification is much higher when a lens is reverse-mounted when compare with normal mount configuration. Besides, unless a lens is designed for macro use, normal mounted lenses is optimised for infinity; but for reverse mount it will then be good for close-up work.

    With the Planar 1:2.8/80mm shown below, the normal mounted largest magnification is 0.6x but for reverse mount it giving stunning close-up images with magnification upto 1.5x. This lens is for the Rolleiflex SL66 series camera and the camera/lenses is already having reverse mount capability built-in.

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  5. dwig

    dwig Mu-43 Top Veteran

    Jun 26, 2010
    Key West FL
    Assuming you really know the focal length of the lens and that the lens' own focusing mechanism is set to infinity, you use the following formula:

    m = x / f

    where m=magnification, x=extension tube length, and f=focal length.
    example: 50mm lens with a 25mm extension tube will yield a 1/2 life size magnification (0.5 = 25 / 50)

    If you are using a "classic" lens that focuses by moving the whole optical system forward, you can set the focusing ring to any subject distance and treat "x" as being "total extension from infinity", which is extension tube length plus the amount the lens has been moved forward from its infinity position.

    Lenses that focus by moving internal or rear elements don't maintain a fixed focal length as the are focused closer than infinity. With these lenses there is no practical way to calculate the effect of an extension tube except when the lens is focused to infinity. With many modern AF camera systems, focusing the lens to infinity can be a bit tricky. With these lenses, the formula is only a rough guide in practice.
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  6. kstevieh

    kstevieh Mu-43 Regular

    Jan 21, 2010
    USA, West Virginia
    GREAT information as always on this site. Thanks for the replies!