Reviews > Ramblings of the Fierce Bear of the North
The new fluorite generation: AFS 600 mm f/4 Nikkor FL E
Akira:
The IF design incorporates a focal length shortening trick. So, unless you focus at infinity, there is no guarranty that the focal lengths of two different models are the same. The designated focal length on the catalog only applies to the lens focused at infinity.
BW:
Thanks for your reply! That might explain the discrepancy I observed at close range. Maybe the closer, near focus limit on the 600 FL, might compensate? I had the feeling I was shooting with a shorter focal length at the time I did the comparison.
Bjørn Rørslett:
The industry tolerance on a property like nominal focal length is 5%. Thus, even at infinity there might be 10% difference between two lenses of the same specification. Do note the tolerance is to the design property, so a lens might range from 570 to 630 mm and still be designated 600 mm. However, individual samples of a given lens should be very similar in actual focal length when focused to the same distance.
For the near range, the detail magnification (in the focus plane) must be identical in order to compare angular view. Having the same distance to the subject is not sufficient on its own.
Akira:
--- Quote from: BW on December 31, 2015, 09:59:18 ---Thanks for your reply! That might explain the discrepancy I observed at close range. Maybe the closer, near focus limit on the 600 FL, might compensate? I had the feeling I was shooting with a shorter focal length at the time I did the comparison.
--- End quote ---
Yes, I suppose so. The shortened focal length was much discussed also when 70-200/2.8 VRII was released.
BW:
--- Quote from: Bjørn Rørslett on December 31, 2015, 10:30:32 ---The industry tolerance on a property like nominal focal length is 5%. Thus, even at infinity there might be 10% difference between two lenses of the same specification. Do note the tolerance is to the design property, so a lens might range from 570 to 630 mm and still be designated 600 mm. However, individual samples of a given lens should be very similar in actual focal length when focused to the same distance.
For the near range, the detail magnification (in the focus plane) must be identical in order to compare angular view. Having the same distance to the subject is not sufficient on its own.
--- End quote ---
Thanks for the clarification!
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