Canon Macro 100/f2.8 - which F setting for sharpest pics?

[James Yeung]

Hello,

I tried a search, but came up empty.

What is the best aperature setting to get the sharpest pictures with this lens?

Thanks,

James

[Persian-Rice]

The smaller the aperture, the sharper the image. (bigger f number)

[Scott J]

The smaller the aperture, the sharper the image. (bigger f number)

Not necessarily. When you stop down beyond f16 you are only using a tiny central part of the lens and sharpness can suffer. There are also some issues with digital as opposed to film that mean you can get some noticeable softness (I think) after f16 regardless of which lens you are using.

I also own a 100/ f2.8 macro and it is the sharpest lens I've got -- better than 50mm 1.4 and 200mm 2.8.

For macro work you could safely use F16 as a default and change from that according to the depth of field you want.

[jbradc]

The smaller the aperture, the sharper the image. (bigger f number)
Well I wouldn't say that. I think what you mean is the smaller the aperture the more DOF you have, but that is not the same as sharpness.
The general rule is a lens is sharpest when stopped down 2 to 3 stops from wide open. Thus a 2.8 lens would be sharpest at F5.6 to F8.

Here is a quote from a good article on the subject:
"Use the lens' optimum aperture. This is typically not with the lens wide open, and never when stopped all the way down. Only the finest lenses are as sharp wide-open as when closed down somewhat, and no lens is at its best when stopped down to f/22 or f/32, due to diffraction effects. Most lenses have their optimum aperture at 2-3 stops down from wide open."

Read more at http://www.luminous-landscape.com/tutorials/sharp.shtml

[James Yeung]

Great, now that I have an idea,, I can start learning how to take the sharpest pics without trying out too many F-stops. Yeah, what I wanted to know was best F stop for sharpest images on focus, not DOF.

Thanks,

James

[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.) In the case of a 100mm f/2.8, that'd 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'll want 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.

[tim]

Test pics here (http://mrwild.co.nz/ExperimentalGallery/Tests/LensTests/index.html). See also this thread (http://photography-on-the.net/forum/showthread.php?t=53272&highlight=tests).

[tim]

Like Micheal says, DOF usually dictates the F-stop for me. Also, learn to get the most important part of your subject parallel to the sensor.