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How to focus manually by Thorsten von Overgaard

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Diffraction limited lenses have the limit at full aperture. One or two R lenses are, and the newest Karbe designs are close.

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1 hour ago, jaapv said:

Diffraction limited lenses have the limit at full aperture. One or two R lenses are, and the newest Karbe designs are close.

The point, quite rightly made, is that lens performance improves as you stop down, til you hit the point where diffraction comes into play.  Sure, with some (an extremely limited few, mostly telecentric lenses), wide open is as good as any other aperture, until you get down to the point where diffraction degrades the image.

The point remains, though, that for any lens, the reliably best part of the lens is the middle, which you strike between f/4 and about f/8 (in 135mm format).  

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On 5/24/2018 at 1:30 AM, Whitford said:

 

Except for the fact that Leica intends for their lenses to be shot wide open.

No. Leica gives one the option of being able to shoot wide open whilst maintaining excellent imaging.

Edited by MarkP

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My point: Not any lens, but the vast majority of lenses. One notable exception: The Apo-Telyt R 280/4.0 If you stop down, there is a small improvement in the corners, but the centre will show diffraction from 4.0 upwards.

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6 hours ago, jaapv said:

My point: Not any lens, but the vast majority of lenses. One notable exception: The Apo-Telyt R 280/4.0 If you stop down, there is a small improvement in the corners, but the centre will show diffraction from 4.0 upwards.

Which is a rather serious limitation, I’d have thought.  The 90-280 Vario-Elmar-SL doesn’t seem to suffer from diffraction til well down the aperture range, that I’ve noticed.  Remarkable, but very big and very heavy!  Nothing comes free!

When I learned photography, my father taught me to stop down as much as a useable shutter speed would allow, so I used the best part of a lens.  Narrow depths of field were the curse of telephotos, rather than a feature, and “bokeh” was unheard of ...

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That means that the 90-280 does not reach  the quality that the the 280/4.0 APO has wide open (which it doesn't, check the resolution figures.). It is the opposite of a limitation, one does not want to stop down a lens of such lens. So rendering the highest quality wide open is a bonus. A smaller aperture means risk of motion blur or high-ISO deterioration. Don't see this as a criticism of the 90-280, though. It is arguably the best zoom lens in its focal length.

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19 hours ago, IkarusJohn said:

One man’s limitation is another’s virtue.  I’ve never been remotely interested in the 280/4 ...

It was my go-to lens for many years.

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