On my 70D, why is 250mm by Canon a larger zoom than 250mm by Sigma?

Started 10 months ago | Questions thread
Howard
Senior MemberPosts: 1,438Gear list
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Re: On my 70D, why is 250mm by Canon a larger zoom than 250mm by Sigma?
In reply to Sir Atfus, 10 months ago

Some zoom lens only attain their claimed focal length when focused at infinity, their focal lengths become shorter when focused on something closer. I would think that lenses with higher zoom ration tend to "lose" focal length more because of the design compromise.

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Howard
cameras: 5DII, 50D, D60, Rebel 2000 (film)
lenses: 17-40 f/4 USM L, 24-105 f/4 USM L, 100-400 f/4.5-5.6 IS USM L, 24 f/3.5 TSE L, 35 f/2, 50 f/1.4 USM, 100 f/2.8 IS USM Macro L, 300 f/2.8 IS USM II, 430 EX II, 270 EX II, EF 1.4x TC III, EF 2x TC III, Kenko Pro 300 1.4x TC
personal website: http://www.travelerathome.com
blog: http://travelerathome.wordpress.com

 Howard's gear list:Howard's gear list
Canon EOS 5D Mark II Canon EOS 50D Canon EOS 70D Canon EF 35mm f/2.0 Canon EF 50mm f/1.4 USM +8 more
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