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Maximum sharpness of old lenses
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PostPosted: Mon Sep 04, 2017 6:48 pm    Post subject: Maximum sharpness of old lenses Reply with quote

Hi,
I recently read in a forum that, as a general rule, modern lenses have their maximum sharpness around f5.6-f8, while old lenses peak typically between f8 and f11.

Is that a correct statement in your opinion?

Thanks.


PostPosted: Mon Sep 04, 2017 6:59 pm    Post subject: Reply with quote

No, they all vary depending on the design criteria.


PostPosted: Mon Sep 04, 2017 7:14 pm    Post subject: Reply with quote

In my experience, the triplet and tessar designe, are better at F/8 to 16

While the planar design is better at F/4 to 8.

The tessar design should be sharper than the planar one at F/16


PostPosted: Mon Sep 04, 2017 7:32 pm    Post subject: Reply with quote

It's impossible to make accurate generalisations as different Planars and Tessars were designed with different requirements in mind, for instance, the Planar 1.7/50 was designed to be good at both infinity and middle distance, whereas the Makro-Planar 2.8/60 is optimised for very close up. Same with Tessars, such as the 'normal' Jena 2.8/50 or one of the tessar-type macro lenses such as the Macro-Prakticar 2.8/55.

Some lenses were designed to be optimal at large apertures, some were designed to be optimal at smaller ones, so you really can't make blanket statements with any degree of accuracy.


PostPosted: Mon Sep 04, 2017 9:01 pm    Post subject: Reply with quote

Some setting between wide open and stopped down to diffraction limit. Varies. f/1.4 lens @ f/5.6 should be sharper than f/2 lens @ f/5.6...some macro designs love being stopped way way down, like f/22...


PostPosted: Mon Sep 04, 2017 9:05 pm    Post subject: Reply with quote

It really depends on the lens in question, anyone trying to categorize all legacy lenses as less sharp is biased.


PostPosted: Mon Sep 04, 2017 9:59 pm    Post subject: Reply with quote

I've often heard that lenses tend to be at their best 1-2 stops closed down from fully open. I'm sure that's something else that will vary with the lens in question but it's probably a better guide than the old vs new lens one.


PostPosted: Tue Sep 05, 2017 6:04 am    Post subject: Reply with quote

A lot of lenses get better in terms of MTF when stopped down, for example 2-4 stops (depends on pixel size too). This is what I see in my MTF measurements.
But for example I suppose (not yet tested, but seen from others) lenses with aspheric surfaces or very high quality lenses (modern Leica) could be best wideopen or only one f-stop closed.
So no general statement possible.
As others said, it depends on what the lens designer has intended in the design. Projection lenses or other lenses with no iris should better be good wide open Smile


PostPosted: Tue Sep 05, 2017 6:48 am    Post subject: Reply with quote

It also depends on focal length to a certain degree. Shorter lenses have smaller apertures in absolute terms for the same F number than longer lenses and diffraction is a function of absolute aperture size, not relative. This means that while every lens improves when stopped down, in a wideangle lens diffraction negates this improvement much sooner than in a tele lens. For example from experience I can say that my crop format Samyang 12mm/2.0 (the shortest focal length I have) is probably sharpest at around f/2.8 and definitely not above f/4 where diffraction already starts to play a big part in the final result. On the other hand most tele lenses, 135mm and above, keep improving as you stop down until f/11 or more, simply because of the larger physical size of the aperture.


PostPosted: Tue Sep 05, 2017 10:11 am    Post subject: Reply with quote

As a simple rule, stop down the lens until it gives you the depth of field you need firstly, and then adjust to have the lowest ISO/highest shutter speed combination to give you your required exposure and to minimise hand shake. Basic photography.

If you have some latitude left, I'd say the lower the F-number the better, due to diffraction.

Think of image sharpness as a competition between the lens' real resolution and the diffraction limit constant. Some lenses simply lose the race earlier than others, focal length and aperture being equal. In that respect, it is as it has always been - test test test! But testing is boring... and difficult because a tested outcome cannot be generally applied to all real photographic scenarios. Stopping down enough may make the edge of the image sharper, but at the expense of the centre.


PostPosted: Wed Sep 06, 2017 12:41 am    Post subject: Reply with quote

Almost every lens made, with very few exceptions has a sweet spot that falls somewhere between f/5.6 and f/11. So what if there's a 5.6-8 bias with one lens and an 8-11 bias with another. Is it really gonna matter? Just go out and shoot and be happy. Let somebody else obsess over grain counting or pixel peeping.


PostPosted: Wed Sep 06, 2017 4:11 am    Post subject: Reply with quote

If you're shooting digital, most likely you can't take advantage of larger apertures anyway due to the pixel pitch. I use a Canon T2i for studio work, and with its 4.3um pixel pitch it has a DLA of f6.7. A stock T2i has an AA filter (mine has been removed) and this decreases the effective DLA by at least a stop to maybe f10. So on a stock T2i, you won't be able to see the sharpness difference between a lens shooting at f4 and f5.6 because the sensor simply can't reproduce the required detail. So why worry about "sharpness"??


PostPosted: Wed Sep 06, 2017 5:06 am    Post subject: Reply with quote

Ray Parkhurst wrote:
If you're shooting digital, most likely you can't take advantage of larger apertures anyway due to the pixel pitch. I use a Canon T2i for studio work, and with its 4.3um pixel pitch it has a DLA of f6.7. A stock T2i has an AA filter (mine has been removed) and this decreases the effective DLA by at least a stop to maybe f10. So on a stock T2i, you won't be able to see the sharpness difference between a lens shooting at f4 and f5.6 because the sensor simply can't reproduce the required detail. So why worry about "sharpness"??


I'm not understanding. Seems like sensor dla works the other way around - that lens can be stopped to f10 on stock t2i, that f10 shows more detail than f8.