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Author Topic: Aperture Sweet Spot  (Read 3108 times)

mikeclary

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Aperture Sweet Spot
« on: June 10, 2013, 02:06:35 PM »
Can anyone confirm that a lens' sweet spot is typically 2 stops closed from the lens' maximum aperture? IOW, if my max is f/2.8, f/5.6 is at least a starting point to test for the lens' sweet spot. Comments?

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Aperture Sweet Spot
« on: June 10, 2013, 02:06:35 PM »

Dantana

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Re: Aperture Sweet Spot
« Reply #1 on: June 10, 2013, 02:15:07 PM »
My experience has been that it varies from lens to lens. I'm not sure you can make a blanket statement like that and have it pan out.
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hgraf

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Re: Aperture Sweet Spot
« Reply #2 on: June 10, 2013, 03:15:07 PM »
Can anyone confirm that a lens' sweet spot is typically 2 stops closed from the lens' maximum aperture? IOW, if my max is f/2.8, f/5.6 is at least a starting point to test for the lens' sweet spot. Comments?

Completely depends on the lens, and your definition of "sweet spot".

If by "sweet spot" you mean the best possible sharpness, then for many lenses it's usually around 2-3 stops away from widest. If you're not sure, set the aperture to f/8 and you'll likely be near the sweet spot.

My 18-135 IS STM is very good wide open, excellent at 5.6.
My 50 f/1.8 is quite good at 2.2, excellent at 2.8.
My 18-50 f/2.8 Sigma isn't amazing at any aperture, it's as good at f/2.8 then at any other aperture.
My 8mm f/3.5 is decent at 3.5, amazing at 5.6.

Note that these are findings I've made with my particular lens, your copy might be different. I've seen alot of variation in lenses over the years.

First thing I do with a new lens (or when trying out a used one) is take a bunch of comparison shots are various zoom levels. I always considered my 55-250 a pretty poor lens, and wide open it was quite soft. But one stop from wide open that thing sharpens up a ton. At 250mm f/5.6 it's soft, and f/8 it's very good, f/11 doesn't seem to help it more.

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qwerty

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Re: Aperture Sweet Spot
« Reply #3 on: June 10, 2013, 05:16:27 PM »
All sweeping generalizations are wrong (especially generalizations about generalizations).

For example, m43 zoom lenses are usually sharpest wide open, mostly due to the effects of diffraction (f/4 on a m43 sensor is like f/8 on a ff sensor as far as the overall image is concerned).

An older rule of thumb was that lenses were sharpest around f/8 (regardless of whether that was 1 or 5 stops from wide open).  However, in x years, when lenses and sensors are amazing, most lenses will be sharpest wide open, due again to diffraction effects.  (However, the increased DOF will make some lenses also appear sharper away from the focus point after stopping down due to nonplanar focal planes.)

Easiest option is to either find published tests for the lens in question; better yet, take some photos yourself.  It only takes a few seconds to take a set from f/0.95 through f/32 and look through them to see which is the best for you.  (And if you can't easily tell which aperture is the absolute sharpest, then the difference is probably too small to matter for you.)

AlanF

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Re: Aperture Sweet Spot
« Reply #4 on: June 10, 2013, 05:41:03 PM »
There are websites that give data for various lenses, but not all. Slrgear.com has lots of quantitative data. http://www.reikan.co.uk/focalweb/index.php/online-tools/lenscamera-information/ has some limited data.  The-digital-picture is comprehensive for Canon lenses but you have to peer closely at the photos of the charts. 
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Mt Spokane Photography

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Re: Aperture Sweet Spot
« Reply #5 on: June 10, 2013, 06:28:18 PM »
Lenses tend to get better at the edges as you stop down, and may get better or worse in the center.  Most lenses are are better 1 stop down, but there are some which are extremely good at max aperture.
 

pj1974

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Re: Aperture Sweet Spot
« Reply #6 on: June 10, 2013, 08:43:13 PM »
There are so many variables here - by lenses (both primes and zoom)... as has already been written, it's impossible to make one statement about 'aperture sweet spot' in terms of image quality (IQ).

A few examples (and comparisons) from my person experience with various lenses:

1) Canon EF 28-135mm f/3.5-5.6 IS USM. My copy was 'decent' (but not fabulous) wide open across the zoom range, but noticeably sharper and had more contrast 1 stop down. I've since sold the lens (as I bought the Canon EF-S 15-85mm f/3.5-5.6 IS USM which is superior and has better IQ across the zoom range - even wide open)

2) Canon EF 100-300mm f/4.5-5.6 USM. This lens was quite sharp & had good contrast wide open at the wide end (ie 100 to ~170mm).  It got progressively worse (soft, low contrast and higher CA) towards the tele-end. At 300mm I had to stop down to about f/10 for the 'best' IQ.
Note: f/10 without IS at 300mm (480mm FF equivalent) needs IS in many situations - or high ISO - which often degrades quality anyway.
Again I sold this 'old' lens - when I replaced it with the Canon EF 70-300mm L f/4-5.6 IS USM - which is much sharper and has great constrast wide open at all focal lengths - even at 300mm f/5.6 my copy if great - just a touch of stellar when pixel peeping... So that's fantastic!! (Note: that 4-stop IS helps so much!)

3) Canon EF 100mm f/2.8 USM - my copy is very sharp already at f/2.8 and is perhaps the sharpest between f/4-5.6, though often I either shoot wide open (ie at f/2.8 for subject isolation) or at around f/11 - f/22 for when I need more depth of field in some macro situations. The lens is still reasonably sharp at f/14-f/22 but defraction is somewhat noticeable and sets in more.

4) Sigma AF 10-20mm f/4-5.6 EX DC HSM - my copy has 'reasonable' sharpness and contrast at 10mm wide open (f/4), and is a bit better by f/5.6.... Similarly at the tele end of 20mm - sharpness and contrast are somewhat better at f/7.1 than f/5.6.  Thankfully the sharpness / contrast is already quite good wide open, and at these ultra wide angles, depth of field even at f/5.6 is considerably deep!

5) Canon EF 50mm f/1.8 mk II - I had 2 copies - both were 'ok' at f/1.8 - but not as sharp or as contrasty as would be ideal (the main issue I had with both copies- 1st lens worse than the 2nd) - was AF - slow, inaccurate and inconsistent.  Stopped down between f/2.2-f/2.8 it had noticeably better IQ.  Then from f/2.8 to f8 it was very sharp (if AF was 'on').  So what do I want? A new Canon EF 50mm prime which has great IQ wide open, including lovely bokeh!

Well, that is my contribution. Hope it's helpful.

Paul
I'm not a brand-fanatic. What I do appreciate is using my 7D and 350D cameras along with a host of lenses & many accessories to capture quality photos, and share with friends.

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Re: Aperture Sweet Spot
« Reply #6 on: June 10, 2013, 08:43:13 PM »

Rienzphotoz

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Re: Aperture Sweet Spot
« Reply #7 on: June 12, 2013, 02:36:36 AM »
My experience has been that it varies from lens to lens. I'm not sure you can make a blanket statement like that and have it pan out.
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Re: Aperture Sweet Spot
« Reply #7 on: June 12, 2013, 02:36:36 AM »