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300mm F4

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    300mm F4

    I decided to buy a FD 300mm F4 plus FD 2x-A extender and FD to Ef adapter to use for birds-wildlife video on my 70D by obvious reasons, price and because my final product is footage 1920x1080. I had a similar (L series) 40 years ago with which I made a coffee table book on birds and later I used it on Betacam and DVcam camcorders. There is no way to shoot wildlife video with long lenses but by manual focusing and IS off.
    My question is simple: is it really 300x1.6 factor = 480mm or longer. My doubt is because if I shoot with a 18-250mm EF lens at 250 mm (same 1.6 factor) the sise of the frame looks much more smaller when compared with the 300mm. I does not look like the 50mm diff in focal length it should be between both lenses.
    How can I measure with certainty the real focal length on the assembly 300mmm-FD to EF adapter. I gess there should be a table where at a certain distance to the focal plane it should give a certain size.
    Thanks
    Carlo

    #2
    Re: 300mm F4

    It's down to the FD/EF adapter: because FD lenses have a shorter back focus than EF ones, it needs an optical component that acts as teleconverter. To know the effective focal length of your combination, you need to know the multiplication factor of your particular adapter. From memory, a figure I remember is 1.13x, but my memory could be defective and your adapter could be different anyway.
    There's no way to tell that I can think of simply by measuring extension.
    Please don't ask about my kit, it's embarrassing!

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      #3
      Re: 300mm F4

      The number 1.13 sound to me more on the line of what I saw visually between the 250 and the 300.
      Thanks

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