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Author Topic: Statement in Luminous Landscape  (Read 2450 times)  bookmark this topic!
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Posts: 538

Statement in Luminous Landscape
« on: August 09, 2013, 12:11:01 PM »

There has been some buzz about the new Zeiss 135mm lens. It appears to be very close to lens perfection, not that I will ever touch one!

but in the Luminous Landscape review:

Michael Reichmann states:
"Theoretically, a lens should perform at its best wide open. But, that's theory and almost never the case in the real world."
Is this true, or does "theory" accept the fact that smaller apertures will improve lens characteristics?
Bob Atkins
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Posts: 1232

Re: Statement in Luminous Landscape
« Reply #1 on: August 09, 2013, 04:16:09 PM »

It's true. For a perfect, diffraction limited, lens, the larger the aperture the higher the resolution.

In fact the resolution would be around 1600/(fstop) line pairs/mm for such a lens (I mention this in an article at

The catch is that the faster the lens, the more difficult it is to correct all aberrations and spherical aberration is usually the killer for very fast lenses. Stopping down reduced the aberrations, especially spherical aberration. Few, if any, photographic lenses are diffraction limited wide open. Maybe something like a 500/4 or 600/4 could be close.

There are diffraction limited lenses - typically very expensive telescopes - but they are rarely faster than f5 and usually much slower.
« Last Edit: August 09, 2013, 06:09:52 PM by Bob Atkins » Logged
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