05-02-2011, 01:50 PM
[quote name='popo' timestamp='1304336056' post='7997']
The more descriptive name for it I prefer is "focal length shrinkage" at close® focus distances. Depending on the design of the lens, the focal length of the lens may reduce from nominal as you focus closer. If you shoot a lot at closer distances, just be aware the actual focal length may be less than you think, with consequent effects.
[/quote]
And this will mean two things.
1. The field of view gets a lot wider, with the SIgma and the Nikon, when you focus on something close by. It gets more narrow again, when you focus at something further away. With my Canon, the field of view gets a bit more narrow, when focussing at something close by.
2. Because of the shrinking focal length, the subject is smaller on the image than you would suspect, when looking at the set focal length. It is similar to the difference you get when you shoot a subject with your Tamron 70-300 VC with the lens set at 200mm, and the lens set at 300mm. The Nikon and Sigma show an image of a 135mm lens, instead of 200mm (at minimum focus distance).
It will only matter when you actually want to make a close-ish-up shot with 200mm focal length. If you never do that, but use the lens as telelens only, it will matter less.
The more descriptive name for it I prefer is "focal length shrinkage" at close® focus distances. Depending on the design of the lens, the focal length of the lens may reduce from nominal as you focus closer. If you shoot a lot at closer distances, just be aware the actual focal length may be less than you think, with consequent effects.
[/quote]
And this will mean two things.
1. The field of view gets a lot wider, with the SIgma and the Nikon, when you focus on something close by. It gets more narrow again, when you focus at something further away. With my Canon, the field of view gets a bit more narrow, when focussing at something close by.
2. Because of the shrinking focal length, the subject is smaller on the image than you would suspect, when looking at the set focal length. It is similar to the difference you get when you shoot a subject with your Tamron 70-300 VC with the lens set at 200mm, and the lens set at 300mm. The Nikon and Sigma show an image of a 135mm lens, instead of 200mm (at minimum focus distance).
It will only matter when you actually want to make a close-ish-up shot with 200mm focal length. If you never do that, but use the lens as telelens only, it will matter less.