2X converters

Discussion in 'Photography Equipment & Products' started by calmwater, Jul 31, 2020 at 2:47 PM.

  1. calmwater

    calmwater TPF Noob!

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    This may seem like a dumb question. If you add a 2X converter to a 150mm lens it (effectively) becomes a 300mm. (2x by 150=300) Question.-If you added a second 2X converter to that would that change it to 450mm (2x by 150=300 by 2x=150 by 3 == 450) or would it change it to 600mm? (2x by150=300 by 2x-600)


     
  2. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    It would be three things.

    1. Effective focal length: 600mm
    2. 4 full stops of light loss.
    3. Totally crap for image quality.

    Oh, wait.... 4 things.

    4. Unable to autofocus 99% of the time. And a viewfinder so dim you'd be lucky to even manually focus.
     
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  3. Derrel

    Derrel Mr. Rain Cloud

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    600, and substandard image quality.
     
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  4. Original katomi

    Original katomi TPF Supporters Supporting Member

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    Very dark, loss of 4 or 5 f stops and you are opening up a window to problems with the contacts between lens converters and camera.
     
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  5. zombiesniper

    zombiesniper Furtographer Extraordinaire! Supporting Member

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    Not to mention if you buy 2 QUALITY converters you're already into the 300mm f4 range that will give you a better final image.
     
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  6. Soocom1

    Soocom1 Been spending a lot of time on here!

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    What's being missed here however is that the mechanism of the teleconverter is taking an image of a very specific circle size post rear element and altering it, in this case TWICE!

    That alone is cause to not do such.

    Because I have done it, I wind up with a horrible looking tunnel.

    I say bite the bullet and buy an old Vivitar 1000mm TP tube lens and call it a day...


    :)
     
  7. Strodav

    Strodav TPF Supporters Supporting Member

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    As you can see from the other posts, it's a bad idea. Just to pile on, teleconverters are only compatible with specific lenses. You should only buy a known compatible teleconverter from the lens manufacturer. An incompatible teleconverter might have the front element of the teleconverter come in contact with the rear element of the lens. Not a good thing, so I'm thinking two teleconverters might crunch into each other as well.
     
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  8. cgw

    cgw No longer a newbie, moving up!

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    They're cheap and plentiful, especially the really bad ones, so try it with 2 2x TCs and promise to post the results, OK?
     
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  9. Derrel

    Derrel Mr. Rain Cloud

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    A 500mm f/8 preset long focus lens or a used 500/8 mirror lens might give better Optical quality at about the same effective F – stop and for around $100 in price.
     
  10. photoflyer

    photoflyer TPF Supporters Supporting Member

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    That reminds me of Junior High. This was a long time ago and the screw mount on my Pentax enabled a buddy and me to stack a 2x on a 3X on a 135 F 3.5.

    We had no idea about what this did to the aperture. We only knew that the viewfinder was very dark.
     
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  11. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    Mathematically.... f/20.
     
  12. Original katomi

    Original katomi TPF Supporters Supporting Member

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    Post 10
    F stop .. view finder well . midnight in a coal cellar Comes to mind
     

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