What Minolta to use w/extension tubes?

Discussion in 'Adapted Lenses' started by juangrande, Jan 26, 2013.

  1. juangrande

    juangrande Mu-43 Top Veteran

    805
    Dec 2, 2012
    COLORADO
    I've just bought a sparkling 50mm 1.4 MC RokkorX with a full set of extension tubes for macro. With the 50 the lens w/all 3 (12-20-36mm) is nearly unfocusable ( <1" away). It's do-able with the 12 0r 20mm seperately but the magnification is not great. Would a different focal length be more manageable as far as distance to object? How would a 28mm work? 100mm? BTW, what are the spring loaded sleeves on the tubes for?
     

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  2. dwig

    dwig Mu-43 Top Veteran

    623
    Jun 26, 2010
    Key West FL
    The effect of adding an extension tube is a matter of the ratio between the length of the tube and the focal length of the lens. The longer the FL of the lens the less affect any particular tube will have.

    With conventional lenses which focus to infinity when mounted directly, a extension tube, or tubes, whose length is equal to the primary lens' focal length will yield 1:1 magnification with that primary lens set to its infinity focusing position. Using your set (68mm total) you will get greater than 1:1 with a 50mm lens but only about half lifesize with a 135mm lens. A shorter wide angle lens will give greater magnification. If that 28mm lens is designed for an SLR it will have a retrofocus design (most or all of the glass is in front of rear nodal point). As a result the in focus subject will likely be inside of the lens.

    The "cure" for using 50mm and shorter lenses with a lot of extension is to reverse the lens. There are reversing rings made that thread into the filter ring on the "front" of the lens and provide a lens flange (Minolta MD mount in your case) so that the lens can be mounted reversed. Using this method the subject distance will never, even with infinite extension, be less than the distance from the body flange to the film/sensor on the body the lens was designed for. When shooting at greater than life size magnification, image quality is almost always better, often substantially, when the lens is reversed. You want to be sure that the reversing ring you get has the proper lens mount (Minolta MD/MC in your case) and the proper filter thread size. The latter can be adapted using the usual filter step-up or step-down rings if necessary.
     
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  3. arentol

    arentol Mu-43 Veteran

    269
    Jun 29, 2012
    As a general rule you don't want to use more mm worth of extension tubes than the focal length of the lens you are using because doing so tends to move the minimum focus distance of the lens inside the front element, meaning it can't focus at all. However, you don't want to use too long a lens because the greater the focal length of the lens the less effective the extension tubes are. Also, a lens that is already a macro lens is going to work the best.

    So the best possible combination would probably be a 70mm 1:1 macro lens, but nobody ever made one of those for the MD/MC mount. However Minolta did make 6 different 100mm macro lenses, and that what I would suggest. Search the internet, your local craigslist, and watch KEH, and you will find one eventually (Just make sure it is not the auto-bellows version, as that won't work right for you).

    One downside with the 100mm macro (or most other lenses) will be that your minimum focus distance is going to become very very short. So if your goal is to shoot living things like insects this combination may not always work well for you, though you could always leave the extension tube off and it would still be a very solid macro lens with enough reach to shoot most insects.

    Personally though I went a different route, which I think might work for you. I have a writeup on it here:

    https://www.mu-43.com/f40/interesti...eries-1-vivitar-2x-macro-teleconverter-30615/
     
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  4. arentol

    arentol Mu-43 Veteran

    269
    Jun 29, 2012
    This is correct.

    But this I have never heard before and regardless of whether it is correct it is entirely pointless. In macro photography what we primarily care about is magnification at Minimum Focus Distance (MFD), not at infinity. When you add extension tubes who's length is equal to that of the focal length of the lens you are using the magnification of that lens at MFD is increased by 1x. So if it originally provided 0.2x magnification it would now provide 1.2x. If it provided 0.5x (1:2 macro lens) it would now provide 1.5x. This is why using a lens that is already a 1:1 macro generally provides the best final result from using extension tubes. A 100mm 1:1 macro with 68mm of extension tubes would provide 1.68x magnification, with the option of having a reasonable working distance at 1:1 magnification by not using the tubes.
     
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  5. juangrande

    juangrande Mu-43 Top Veteran

    805
    Dec 2, 2012
    COLORADO
    So what I think you all are saying: even though those tubes came with the 50mm, they're not meant for it.( It came from an estate sale). I have a tokina "bokina" 90 w/MD mount + the 1:1 magnifier (optical). Might the tubes work better on it? I'll check it out. I was just hoping to come up with a simpler and cheaper macro solution as it's just for my own entertainment. That bokina could become another lens if it weren't needed.
     
  6. addieleman

    addieleman Mu-43 All-Pro

    Aug 5, 2010
    The Netherlands
    Ad
    Apparently you want to achieve magnifications higher than 1:1. In that case I would go for the reversal ring approach, where the lens is mounted with its filter thread on the reversal ring, so that the bayonet mount side of the lens is up front. You can add extension rings between the adapter bayonet and the reversal ring's bayonet mount to achieve even higher magnifications. I just tried a 28mm on a reversal ring adding 56mm worth of extension rings and that got me up to a magnification of 3.5, meaning an subject of 3.3x5mm is filling the frame. The shorter the focal length and the longer the extension, the more magnification you'll get this way. To get higher magnifications you can also think of a bellows, these can be had for scrap prices if you go for brands like Albinar, Hama, Unigor, whatever; Minolta stuff can be quite expensive. This way even a 50mm can give you a 5x magnification.

    Maybe the Tokina 90mm with its 1:1 extender and extra rings will get you there as well, although I don't know what will be left of image quality and where to insert the extender rings.

    The sleeves on the outside of your extension ring set are meant to transfer the aperture value on the lens to the camera. They have no function with an ยต4/3 -> MD adapter.
     
  7. dwig

    dwig Mu-43 Top Veteran

    623
    Jun 26, 2010
    Key West FL
    It is far from pointless!

    Knowing the minimum magnification available with a particular lens+tube combination provides a starting place for estimating whether the tube choice is appropriate for the situation. Second, calculating what the maximum magnification would be with any particular lens+tube combination is often impossible as the lens' focusing system is an unknown. Some lenses focus purely by moving all elements in unison and calculations are possible but lenses frequently focus by moving only some elements and these often shift somewhat in focal length as they focus. Without knowing in detail how the FL changes you can't calculate magnifications except at the infinity focus setting. Everything else is by trial-and-terror.
     
  8. juangrande

    juangrande Mu-43 Top Veteran

    805
    Dec 2, 2012
    COLORADO
    I just got a series 1, Kiron made 70-210 f3.5 for $24. Converter is next.
     
  9. dwig

    dwig Mu-43 Top Veteran

    623
    Jun 26, 2010
    Key West FL
    No, that is not what we are saying.

    The tubes are made to be used with a variety of lenses in a variety of configurations. The 12 and 36 add up to 48mm extension. That and a little twist of the focusing ring on a "50mm" lens (quotes because that 50's actual FL may be as short as 48 and as long as 52 or 53) would easily get you to 1:1, the maximum at which you want to use a 50mm lens without reversing it. If you spring for a reversing ring you can make use of the whole stack for greater than lifesize work. By using the 12 or 20 by themselves, the 50mm can be pressed into a range of non-macro closeup work.

    In addition to working with the 50mm, they can be used in a range of situations with other lenses. With the typical 85 and 100mm lenses, the 12mm tube can be useful when needing to get only slightly closer than the lens is capable of by itself.
     
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  10. juangrande

    juangrande Mu-43 Top Veteran

    805
    Dec 2, 2012
    COLORADO
    Can you tell me what the purpose of the spring loaded sleeves w/tab on the tubes are for?
     
  11. dwig

    dwig Mu-43 Top Veteran

    623
    Jun 26, 2010
    Key West FL
    They are Minolta's "MC" class meter coupling. They connect the lens' aperture ring's tab with the mating pin on the body. They are of no use when adapting them to a m43 body.
     
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