Reverse mount a macro lens?

Discussion in 'Macro Photography' started by molested_cow, Feb 14, 2012.

  1. molested_cow

    molested_cow TPF Supporters Supporting Member

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    Out of curiosity, and since I don't have a macro lens to play with, what happens when you mount a macro lens backwards?

    (note: this is NOT about reverse mount a prime to get macro)


     
  2. Judobreaker

    Judobreaker TPF Supporters Supporting Member

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    Exactly the same as when you reverse mount a normal prime.
    I say normal prime because a macro lens is basically a prime which can focus very close.

    To be able to answer this question it's good to first determine what exactly happens when you reverse mount a prime lens.
    The exact details of the aperture isn't important here as the aperture of a normal prime and a macro lens isn't any different.
    The difference is in the focus, which is why we need to focus on that. (Ok, that made me laugh... xD)

    When we look at focusing this is basically moving an element in the lens backwards or forwards to adjust the focus (more or less).
    Say we move it forwards to get further focus and backwards to get closer focus.
    This distance is fixed and limited. The closest focus distance varies per lens, but the furthest is always infinity.
    The manufacturers have limited the movement of the element inside there because face it, who the heck is going to focus beyond infinity anyway...

    Now we turn this lens around. What will happen to our focus?
    Surprise, surprise... It is reversed!
    This means that the position of the element which would normally be its infinity focus is now your closest focus distance and your the position that would normally be your closest focus distance is now the furthest.
    In normal primes the new furthest focus is far from infinity because they have limited that direction a lot.
    Macro lenses however are specifically designed to be a lot less limited in that direction.

    Basically what I am saying is that, instead of being able to focus closer and get more magnification, reverse mounting a macro lens will simply give you more focus distance on the far end. You'll be able to focus at something further away.
    I don't know if you can reach infinity with it though, I don't think anyone has ever tried and figured this out. I'd do it if I had a reverse mount just to see what would happen. :p


    Please keep in mind that I think I am correct, but I may be wrong.
    This is all logical reasoning but seeing as I am not perfect the truth may be different.
    I strongly believe this is what will happen though, I'd love to see anyone try this out for me. If not I might just get a reverse mount myself... Just for the heck of it. xD
     

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