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Author Topic: Focus Distance  (Read 5410 times)

opgr

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Focus Distance
« on: May 18, 2006, 04:24:11 AM »

Doesn't focussing distance influence the performance of a lens?

And if so, is the experience of the testers with lens performance different for in-the-field use as opposed to the studio setup?

I'm asking because I missed that from the text, and at least Michael is usually quite pragmatic about this. I can imagine that these lenses may perform better for landscape work at large focus distances than they do for the studio setup shown.
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Oscar Rysdyk
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Ray

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Focus Distance
« Reply #1 on: May 18, 2006, 10:12:09 AM »

The fact that lens performance might vary with focussing distance is a huge complication, isn't it? Photodo stopped testing lenses some years ago, presumably because there is insufficient interest by the photographic public to justify the cost.

I always felt they should have tested lenses at f11 as well. Perhaps they should also have tested lenses at near and medium focus distances as well as at infinity.

We'd have a lot more charts to look at, but perhaps some useful information for purchasing decisions.

I wonder how field curvature would affect those graphs (at close focussing distances) which usually fall off considerably towards the edges when the lens is focussed at infinity.
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Gary Ferguson

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Focus Distance
« Reply #2 on: May 19, 2006, 09:48:50 AM »

Quote
Doesn't focussing distance influence the performance of a lens?


Yes, camera to subject distance will affect performance.

Leica's official stance is that any lens testing should be done at 100x the focal length of the lens, although on occasions they've relented and said 50x is acceptable. And if Leica say 50x is acceptable then I guess a bit less than 50x is probably acceptable too!

When I first saw this test I thought a 15.5" target filling the frame was a bit on the small side. But if it was a problem then we would have seen the macro lenses take an advantage. That didn't happen so, no harm no foul.

I'd have thought the bigger advantage of shooting this subject from a longer distance would have been to better illustrate any differences between the cameras and lenses used. But maybe the studio dimensions didn't allow for this.
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