Sharpest possible aperture?

I am curious what the sharpest aperture one of my lenses would be. It's a sigma 70-200 f/2.8

If anyone knows the exact aperture that would be awesome, or of someone could point me to somewhere that I could find out I would be very happy as well. I shoot a lot of skimboarding and since I usually have an abundance of light to work with (at the beach) I figure I might as well find an aperture that I can optimize my results.

I think the sharpest aperture is generally considered to be two stops down from wide open, but maybe I'm just making that up...But from all the lens reviews I've read, it seems that most lenses tend to be sharpest around f/8, no matter what kind of lens it is. Anyways, www.photozone.de has a review of it, but it's not particularly detailed...

No such thing as a general best aperture. Every lens is different, and every sample of lens is different. If you really need to know, test your sample and find out.

A lot of people feel that one to two stops down from wide open will be the sharpest with most lenses. Personally, I think there are other considerations that will usually be much more important than making sure you're always at 5.6. For example, that aperture may give you too much/too little depth of field. It may also give you too fast or too slow of a shutter speed.

Unless you're shooting on a tripod with stationary subjects, I don't think you'll find any real difference between 2.8 and 5.6 (or anything else other than maybe some of the highest apertures like 22 and 32). The other considerations are more important IMO.

According to this one guy called Erwin Puts (big time lens testing buff) the biggest distrupter of good image is lower shutter speed.
He has tested for most lenses, a shutter of 1/250 is sufficient to render camera shake.

Of course he also tests lenses for their optimum aperture.
However, he only does tests on a small selection of stuff - mostly Leica stuff.
From his tests, he finds the following:

older Leica lenses - f/8 optimum
newer ASPH Leica lenses - f/4-5.6 optimum

this is not for all Leica lenses, but from his reports, it seems that this is the trend.

Past f/8, there is degradation of image quality due to the diffractions.
On the other hand, probably testing it out yourself is the best. Want things that need a lot a resolving power? try arm hair. Or is it contrast you are after? paint cards maybe?
colour rendition? well i dont think that changes with aperture anyway

Quote:

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Originally Posted by Ryguyinlj

I shoot a lot of skimboarding and since I usually have an abundance of light to work with (at the beach) I figure I might as well find an aperture that I can optimize my results.

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If you shoot manually then you can help the situation. Aperture priority shooting will let you set the aperture but the camera determines the shutter speed. If you shoot at the beach, then you will have some considerations to make about the brightness level and the amount of action stopping you need to apply.

Sharpness for fast moving subjects will require higher shutter speeds. Beach/water brightness tends to produce under exposed images if meter readings are followed. Opening the aperture a couple of stops will comensate for this effect. It may be that ISO settings will need changing to produce fast enough shutter speeds because when you open the aperture, the image forming light needs less time to record the image.

The aperture requirement will alter as you move from the short to the long end of the focal length of your lens. The higher the magnification, the more noticeable will be your camera shake so faster shutter speeds are often better in that situation. The ideal aperture is dependent on what artistic effect you seek. If you want to isolate the background from the subject then the largest aperture (smallest f number) is what you need. Sharpness in depth comes with smaller apertures (large f numbers) but you need to focus at a point that will guaranteee that your subject will be sharp.

If you search, you should find some information on hyperfocal distance and this will be of value when using a larger aperture. Althugh smaller apertures do produce diffraction effects, short of a lens testing rig, in my experience, most observers do not notice the effect, especially on small format cameras. Medium and large format cameras make the effect more visible.

So your answer... it depends on what effect you are trying to produce. If you are making images without pre-visualising what you want to see from your image captures, then it probably wont matter what aperture you use, although a recipe book approach to photographic technique will not help you to improve your understanding. If you know what you want to achieve and produce, then aperture control is one vital ingredient in the whole process and a single set aperture is unlikely to serve all of your needs well.

h

You know, I've found that the best way to find out how well your lens performs at a given aperture is to simply test it yourself, like Sebastian said. You've got a digi, so it won't take long and it won't cost a dime. Just set it up like any other experiment. Use your lowest ISO and try different apertures at different focal lengths until you find one that works best. Unless, of course, someone has already done this with your lens, which is likely. Hopefully they have posted their findings on the net.
Check out some of the reviews of that lens here on PR. Some people say it does well at most all apertures, but others list specific numbers. The MTF charts are also on Sigma's site, which may help you decide what focal length to use...
Good luck!

The MTF chart shows excellent results at f/8 @ 135mm.

Quote:

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Originally Posted by Ryguyinlj

I am curious what the sharpest aperture one of my lenses would be. It's a sigma 70-200 f/2.8

If anyone knows the exact aperture that would be awesome, or of someone could point me to somewhere that I could find out I would be very happy as well. I shoot a lot of skimboarding and since I usually have an abundance of light to work with (at the beach) I figure I might as well find an aperture that I can optimize my results.

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Quote:

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Originally Posted by mikishots

The MTF chart shows excellent results at f/8 @ 135mm.

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THat's another thing... Where are these charts and how do I read them?