Sharpest f-stop

[BayAreaPhotog]

Where will you get the sharpest image? Will it be the smallest f-stop or is there a "sweet spot", so to speak. It's seems like I have heard in the past. that the mid range of a lens is sharpest - is this true?

[Bodog]

I think the answer to your question would be lens specific, but generally speaking a lens is sharpest 2-3 stops below its widest apeture.

[CyberDyneSystems]

Bodog is absolutley right,. it will vary from les to lens..

The general rule of thumb is stopped down a bit... but stopped down all the way is never the best either.. it's somewhere in the middle ground (usually)

Between f/8 and f/16 is usually the best...

[Andy_T]

You should try it out with your lenses!

Also consider, that the smaller the aperture, the more likely you are to get motion blur in bad lighting situations.

Best regards,
Andy

[kb244]

..
Between f/8 and f/16 is usually the best...

As bdog says, it varies, but the sweet spot for most of my f/2.8 lens is around f/4 to f8, and not 8 to 16, things actually start to get soft at f/11-f/14 Least thats the case on my Sigma 105mm f/2.8 Macro, on my 50mm f/1.8 generally between f/3.5 to 5.6, on my Canon 28-135 USM IS f/3.5-5.6 , about what you said on the telephoto end. I remeber there was a website that actually reviewed lenses, and showed you quality at certain apeture. But I also remeber you could technically find the sweet spot looking at the lens' MTF charts but I never did figure out how to read those.

[12345Michael54321]

Most lenses will perform at their best when stopped down around 2-3 stops from wide open. (This is just a general rule, but usually a fairly accurate one.) For example, the sharpest f-stop for a 28mm f/2.8 lens will typically be somewhere in the f/5.6 - f/8 range.

Of course, the smaller the aperture (larger the number), the greater your depth of field. So if it's maximum depth of field you want for a given situation, you'd want to stop down beyond f/8, despite the fact that f/8 may be your lens' "best" aperture. Similarly, if you wish to draw the eye to your subject, you may wish to minimize depth of field, which means you'll probably choose a large aperture, like f/2.8, even though your lens doesn't perform at its absolute best at f/2.8.

The point being, compositional considerations often - and rightly - far outweigh such considerations as whether a lens performs slightly better at one aperture or another.

Other factors worth considering are that a shallow depth of field may cause the viewer to perceive your subject as being extremely sharp, due to the contrast in sharpness with the blurred background. So even if f/2.8 isn't actually as sharp as f/8, it may provide the impression of great sharpness. Okay, not if you're shooting a test chart on a wall, but in real world photographic situations.

Also, diffraction effects come into play at smaller apertures. Many lenses can stop down to f/32 (or even smaller). But the lens opening is so tiny when stopped way down like that, that sharpness begins to significantly suffer. So there may be situations where you want to maximize depth of field, but have a personal rule you tend to obey that unless it's really, really necessary, you won't go down below f/16 or so, due to diffraction limitation. Conversely, you may decide "I know my lens isn't at its best when closed all the way down, but I'm shooting macro work and really need all the depth of field I can get, so I'm going to shoot at the smallest aperture my lens allows."

Finally, let's say there's a photographer who is utterly indifferent to depth of field. Shallow, extensive, he doesn't care - he just wants to shoot at the aperture his lens likes best. (He's an idiot, but he's got a large assortment of L series glass, so other photographers hang out with him in hopes he'll let them borrow his 600mm f/4.)

This photographer may decide that he'll shoot everything at f/8.

Problem is, if the light's a little dim, and he's shooting at f/8, he's going to have to use a shutter speed of, let's say, 1/30 sec., for proper exposure. Well, if he's shooting something fast moving, like 6 year olds at a birthday party, he's going to get blurred images. Oh, because it's his lens' "best" aperture, they'll presumably be high resolution, contrasty blurs. But blurs, nonetheless. Whereas had he been willing to shoot at f/4, his lens might not have performed quite so well (although it might have been almost as good), but he could've shot at 1/125 sec., and gotten nice, crisp pictures of little Damian running around Chuck-E-Cheese in search of more birthday cake. (This doesn't even get into the issue of whether the photographer can handhold sharp images at 1/30 sec.) (And yes, he could've just bumped up the ISO a couple of stops, or used a flash, but these solutions come with their own compromises.)

So basically, what it comes down to is that "sharpness" isn't simply one thing, save in the artificial sense of laboratory tests or test chart photography. In the real world, sharpness is better defined as an optimal balance of various photographic considerations, of which lens performance is but one element - and often a rather minor element.

Sorry for being so long-winded.

[aam1234]

That's a great answer 12345Michael54321. Thank you for the time and effort.

Personally, I think sharpness is a bit overrated. There is nothing wrong with a slightly soft image IMO.

[Sam]

I use this site often when I have a question about canon equipment http://www.the-digital-picture.com/Reviews/

Hope it helps.

[vjack]

This was a very useful discussion that has helped me to understand the relationship between sharpness and aperture. Thanks!

[Steven M. Anthony]

Personally, I think sharpness is a bit overrated. There is nothing wrong with a slightly soft image IMO.

I went for years thinking the world had a bit of a softness too it--then I realized I just needed glasses... :)

[amosher]

Cool site, will have to explore more when I have time.

[chtgrubbs]

You can never go wrong with F/8, as in the old photojournalist's adage for the perfect photo:
"F/8 and be there".

[Robert_Lay]

There was a time when a group that called themselves the f/64 group did all their photography at "you know what".

Then came the era in which the sweet spot (somewhere between wide open and stopped down all the way) reigned.

Both of those ideas are now dead.

Today, you have to understand the Modulation Transfer Function (MTF) and choose your lens as being optimized for either resolution or contrast - you can't have both.

[PhotosGuy]

Great " long-winded" post, Mike! "F/8 and be there". Wasn't that "F/16, and be there"? Anyway, just be there! ;-)

[Jesper]

Great " long-winded" post, Mike! Wasn't that "F/16, and be there"? Anyway, just be there! ;-)I think you're mixing it up with the Sunny f/16 rule... 8)