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Old Monday 28th November 2011, 22:36   #1
OUT&ABOUT
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Reproduction Ratio and Telephoto's

Hello to everyone, I am hoping that you will be able to impart some wisdom on me so please excuse the novice question.
I understand reproduction ratio's concerning Macro lenses but am not sure how it affects zoom lenses. If I was to compare a Sigma, Canon, Tamron etc , all with an end focal length of 400mm am I to take for granted that all will magnify my image exactly the same.
I'm currently using a 150-500 Sigma and want to try something else (yup that old dilemma), so I just want to get some basics straight in my head.
Any help will be greatly appreciated
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Old Tuesday 29th November 2011, 00:47   #2
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First of all, welcome to birdforum!

Secondly, any 400 mm prime lens should give the same field of view on the same camera body (and therefore "magnify" equally). Most x-400mm zoom lenses will "magnify" slightly less at 400 mm if I have understood previous threads on this forum correctly.

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Old Tuesday 29th November 2011, 12:35   #3
Roy C
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Quote:
Originally Posted by OUT&ABOUT View Post
If I was to compare a Sigma, Canon, Tamron etc , all with an end focal length of 400mm am I to take for granted that all will magnify my image exactly the same.
With zoom lenses it depends on how near you are to the subject - the nearer you are then the less the actual focal length will be (when compared to a prime lens for instance). Most zoom will only give you the true max focal length when shooting at infinity distance and even then there could be up to a 10% margin of error. I strongly suspect there would be differences between the various makes but by how much I do not know. The Canon 100-400 is reckoned to be around 380mm at the long end but I guess this would be shooting distance reliant.
When shooting at normal distances for birds (if there is such a thing!) I doubt if there is a single zoom lens that will match up to a similar focal length prime lens as far as magnification goes.
I saw a test several years ago where a Canon 400/5.6 was tested against the Sigma 50-500, the zoom being set to 500mm - the target was around 20 feet away and there was hardly any difference in the magnification (the guess was that zoom lens was actually around 430mm).
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Old Tuesday 29th November 2011, 14:22   #4
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Thank you for the replies and clarifications. Does however raise a question about what you are actually getting when you buy a lens. Considering most us spend so much time before we actually buy lenses it would be nice to know that my 500mm might be 430mm etc.Better someone bought the 400 prime. Sometimes their can be a lot of cost difference for that extra 100mm of focal length and you might not get it all anyway. My point is I don't see this type of information during my readings. Is their anywhere you can point me too for this type of info.
Thanks to everyone

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Old Tuesday 29th November 2011, 14:41   #5
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It does seem wrong that this could be the case, very miss leading from the manufacturers!
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Old Tuesday 29th November 2011, 20:04   #6
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More a case of fine print. The lens' maximum focal length will be quoted +/- some %error and at infinity. Focusing at anything closer to infinity will change the focal length/magnification in any zoom lens, they're hardly going to quote this for all focal length settings and all focus distances (although you could argue they should quote the field of view at MFD and infinity).

Also, AFAICT any internally focusing prime with floating elements (or any prime with a TC on) will also exhibit focal length/magnification changes with focusing distance, but not as pronounced. We're usually dealing with lenses with multiple elements with complex interrelationships for zoom and focus, rather than the ideal 'one lens with a focal length of f' arrangement we want to use for comparisons.

If I get time I'm going to compare the field of view of some of my zoom/primes at different distances, it might be useful when choosing my next lens.
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