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  1. #1
    Faugh a' ballagh Sean Dempsey's Avatar
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    Focal Lengths - diminished return the higher you go?

    Is there a curve of focal lengths and zoom that flattens out? I have a 28-300 as my only real zoom, and the difference between 100 and 200 seems alot more than between 200 and 300. And today, my friend just got his Sigma 50-500, and I was ready to be like "okay, 500 is gonna be incredible!"... So I set the lens to 300, which is what I am used to, then cranked it up to 500!!... and the increase wasn't as much as I suspected.

    So now I am wondering, is the difference between 300 and 500 less than between 100 and 300? Do zoom lenses magnify in a less and less ration as you go up higher and higher? I hope this is making sense.
    A good craftsman never blames his tools.

  2. #2
    Hardcore...Nikon Speed's Avatar
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    Focal Length Is Focal Length

    Quote Originally Posted by Sean Dempsey
    Is there a curve of focal lengths and zoom that flattens out? I have a 28-300 as my only real zoom, and the difference between 100 and 200 seems alot more than between 200 and 300. And today, my friend just got his Sigma 50-500, and I was ready to be like "okay, 500 is gonna be incredible!"... So I set the lens to 300, which is what I am used to, then cranked it up to 500!!... and the increase wasn't as much as I suspected.

    So now I am wondering, is the difference between 300 and 500 less than between 100 and 300? Do zoom lenses magnify in a less and less ration as you go up higher and higher? I hope this is making sense.
    While I am not an expert on lenses, I do understand the basics, and focal length is focal length.

    You asked: "is the difference between 300 and 500 less than between 100 and 300?"

    No, the difference is 200mm between both of the ranges that you listed. What you are experiencing is more of a perceived drop in increase. Going from a 28mm to a 50mm seems like a bigger difference than going from 50mm to 100mm. It's all a matter of perception.

    Consider it this way. Every 50mm is equal to about 1X (or 1 power or 1 magnification). So a 100mm lens is a 2X, and a 300mm is 6X, while a 500mm is 10X. To the human eye, going from 100mm to 300mm is an increase in magnification of three times (going from 2X to 6X). Conversely, going from that same 300mm (6X) to 500mm (10X) isn't quite a doubling of the magnification. It's still a 200mm increase, and every 200mm gains you 2X. But the ratio of increase from your starting point isn't as much.

    I hope this makes sense, and that explains it clearly. Let me know if you get what I'm trying to say.
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  3. #3
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    The difference between angle of views, in degrees, is more when considering wider angles than tele's. Small changes in the wide angles results in large changes in angle of view.

    Take for instance:

    20mm = 94 degree vs 40mm = 57 degree

    200mm = 12 vs 400 = 6 degree


    However, as can be seen, the change in angle of view by doubling the focal length remains the same. Doubling the focal lenght halfs the angle of view. Note the numbers I'm showing are from real lenses. In reality these numbers are rounded. I've read the sigma 50-500 actually comes in at about 460 at the long end for example.

    Mike

  4. #4
    Hardcore...Nikon Speed's Avatar
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    I Meant To Mention...

    Quote Originally Posted by darkman
    The difference between angle of views, in degrees, is more when considering wider angles than tele's. Small changes in the wide angles results in large changes in angle of view.

    Take for instance:

    20mm = 94 degree vs 40mm = 57 degree

    200mm = 12 vs 400 = 6 degree


    However, as can be seen, the change in angle of view by doubling the focal length remains the same. Doubling the focal lenght halfs the angle of view. Note the numbers I'm showing are from real lenses. In reality these numbers are rounded. I've read the sigma 50-500 actually comes in at about 460 at the long end for example.

    Mike
    That the high end may not be exactly 500mm. I know with variable power binoculars and riflescopes, that the high end is usually rounded up a little. For instance, a riflescope listed as being a 6.5 to 20X may actually be 19.6X at the maximum magnification.

    I hadn't read that the Sigma 50-500mm was actually 460mm. Now that is stretching the rounding up bit! I wouldn't have been surprised at 490mm or so, but 460 is way short IMHO.

    Excellent point Mike. Thanks for mentioning that.
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  5. #5
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    Quote Originally Posted by Speed
    That the high end may not be exactly 500mm. I know with variable power binoculars and riflescopes, that the high end is usually rounded up a little. For instance, a riflescope listed as being a 6.5 to 20X may actually be 19.6X at the maximum magnification.

    I hadn't read that the Sigma 50-500mm was actually 460mm. Now that is stretching the rounding up bit! I wouldn't have been surprised at 490mm or so, but 460 is way short IMHO.

    Excellent point Mike. Thanks for mentioning that.
    I read that in a magazine test. They were suprised how far from 500 it was. I'll see if I can dig it up.

    Mike

  6. #6
    has-been... another view's Avatar
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    Right - 100 to 200 is a 100% increase; 200-300 is a 50% increase, 300-500 is about 60%, etc.

    The thing to be careful is that longer focal lengths magnify the image - and any camera movement or technique problems. There is a rule of shooting hand held with shutter speeds at least the reciprocal of the focal length (as in 1/500 sec for a 500mm lens). Personally this doesn't always work, I can do 1/30 with a 50mm but can't get that sharp with 1/500 on my 400mm. My 400mm is a lens like that, not a 400 f2.8 or anything... Even shooting on a tripod with a lens of this length will take some getting used to.

  7. #7
    Toon Army Foot Soldier straightarm's Avatar
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    You also have to think about ratios

    not just the difference in focal length.

    Going from 100 to 200mm is a doubling of focal length so the subject will be twice as big.

    Going from 200 to 300mm is again a 100mm change, but only a 50% increase, so the subject will be only 50% bigger.

    So yes in that sense there is a diminishing return

    Simon
    Simon, bombadier 1st class

  8. #8
    nature/wildlife co-moderator paulnj's Avatar
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    I may be misreading your theories... but i assure you your subject will get 4x as large in the frame going from a 200mm to a 400mm!!!!

    mount any lens (50mm) and then a lens of 2x the original length.....subject will be 4X the size in the frame

    even better.... go from 35mm to 70mm on a zoom......
    CAMERA BIRD NERD #1




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  9. #9
    Faugh a' ballagh Sean Dempsey's Avatar
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    So I think I get this...

    if I am looking at a bird that takes up 1/20th of the frame height at 100mm, and I go to 200mm, let's say that now it takes up 2/20th of the frame height, and it looks like it doubled. But now if I go to 200 to 300, it takes up another 3/20th's of the frame height, which is the same as before, but now the bird only appears to have grown by a 3rd, so eventually if it took up 19/20's at 400mm, at 500mm it would increase again by 1/20 to take up the full fram, but only looks like it zoomed a little.

    I think I get it now.
    A good craftsman never blames his tools.

  10. #10
    nature/wildlife co-moderator paulnj's Avatar
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    no....

    do this.....

    your 300mm on a tripod and next to it your friends 50-500mm(which is about 460mm at "500")

    look through both focused on the same subject...... 300-460mm should DOUBLE the subject size

    so 300mm 1/10.... 600mm 4/10ths


    seeing is the best way to understand it

    I just tested from 300mm to "500mm" on my sigma 170-500.....DOUBLED to my eye
    CAMERA BIRD NERD #1




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