Lens Magnification on 35mm

Discussion in 'Beyond the Basics' started by PlasticSpanner, Jun 28, 2005.

  1. PlasticSpanner

    PlasticSpanner TPF Noob!

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    I know the size of a lens for a 35mm SLR is relative to it's focal point but can anyone tell me how to work out the magnification level?

    If 50mm is roughley what the eye sees then is 100mm equivelant to 2X magnification or is it more mathmatical than that?
     
  2. DocFrankenstein

    DocFrankenstein Clinically Insane?

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    What you said works when focused to infinity... or at least if the subject isn't too close.

    Correct me if I'm wrong though
     
  3. &Denekamp

    &Denekamp TPF Noob!

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    I don't know if you even calculate that.. If you would take a picture of someones head, which would be roughly say, 20 cm in hight, in portrait view, almost view filling. that would fill your negative for about 3.5 cm. that would be a demagnification of about 6x. When printed on 10x15 cm paper, the head would be around 12 cm on paper. so that makes a demagnification of 2.9x.. right?

    I think only macro magnify an object by more than 1x

    Again, correct me if i'm wrong
     
  4. &Denekamp

    &Denekamp TPF Noob!

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    oh, forgot to add:

    but on the other hand, when you enlage a picture, at some point the magnification will become greater that 1..

    ..

    I just got even more confused..:confused:
     
  5. PlasticSpanner

    PlasticSpanner TPF Noob!

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    Now that's realy confused things!
     
  6. &Denekamp

    &Denekamp TPF Noob!

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    Sorry..:)

    I've given that macro thingy some thought.. Lets say you were to photograph a flower that is 5 cm in diameter, camera in landscape view. under such an angle that you have the flower all over the photo, from side to side, top to botom. then, on the negative, the flower would be the full 35mm on the film (demagnification of (50/35=)1.4) then, when printed, it will fill the full 15cm of the photo, and that is a magnification of (15/5=) 3x..

    I don't know if i'm right, so please correct me if im wrong..

    by the way, why are we actualy trying to find this out.. it wont help us taking better pictures, will it..? :p
     
  7. hobbes28

    hobbes28 Incredible Supporting Member

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    Your original thought here is the correct one. I knew this but started to feel loopy after reading all of the reasoning that followed so I had to look it up again to make sure. :lmao:
     
  8. PlasticSpanner

    PlasticSpanner TPF Noob!

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    Now that it's got realy confusing here's another question.

    If I had a 50mm lens and used a 2X converter it would be a 100mm lens.

    If I added another 2x converter it would be a 200mm lens right? 50mm X2 =100mm X2=200mm.

    If I added yet another 2x converter what focal legnth would I be up to?

    50mm x2 = 100mm x2 = 200mm x2 = 400mm?

    or

    3 x 2X converters = a 6X converter x 50mm = 300mm?

    :confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused:
     
  9. spiralout

    spiralout TPF Noob!

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    Haha, no, it would be a 400mm, the lens magnification is exponential. e.g. 2^1=2, 2^2=4 2^3=8. Of course, that would be COMPLETELY useless! If you have 3 2x teleconverters on one lens, then you're certifiably insane! :lol:
     
  10. ThatCameraThingy

    ThatCameraThingy TPF Noob!

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    PlasticSpanner - please give us some more details as to the thinking behind the question ?

    What is it you want to figure out ?

    I hope it is not : " I have a 50mm lens and if I buy 3x Teleconverters(cheaper than lenses) then i can get up to 300mm or 400mm."

    Really curious about the thinking behind that question.



    Hanno
     
  11. PlasticSpanner

    PlasticSpanner TPF Noob!

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    The first question was because I would like to plan what lens I'd need to see what I can get on my Astronomy progran RedShift. The program is aimed towards telescopes and magnification factors. For example the Andromeda Galaxy is quite large at 3 times magnification but lenses are measured on the focal point so I would like to know what lens I'd need to get the equivelant 3x magnification on a 35mm SLR.

    The second question I thought up a couple of nights ago after a night of astrophotography and waiting for the sunrise. It was more of a hypothetical question realy with more emphesis on the mathmatics than the practicalities! Basicly it was a long night, I was bored and my brain started to wander!:lol:
     
  12. PlasticSpanner

    PlasticSpanner TPF Noob!

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    Also has anyone actually tried stacking converters like that? How bad is the distortion and image!?


    Not that I'm going to try it before anyone asks! I'd rather sellotape my camera to the end of a 2" refracting telescope first!:confused:
     

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