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05-26-2010, 08:13 PM   #1
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sharpness

so in your opinion is it a rule of thumb that the higher the aperture the sharper the image tendency? i know that the higher the aperture the deeper the focal field and the more telephoto the narrower the depth of field but not sure if there is any benefit to aperture setting other than light control.
thanks for any response

05-26-2010, 08:42 PM   #2
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QuoteOriginally posted by jeghead1 Quote
so in your opinion is it a rule of thumb that the higher the aperture the sharper the image tendency? i know that the higher the aperture the deeper the focal field and the more telephoto the narrower the depth of field but not sure if there is any benefit to aperture setting other than light control.
thanks for any response
I think most of the time, there is a sweet spot. I think, generally, that as long as you aren't wide open with a lens, it will be sharper. Of course, if you get too high of an aperture, then diffraction will cause a loss of sharpness. I'm sure experts in here will clarify this more, but this is what I understand to be accurate.
05-26-2010, 08:44 PM   #3
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This very much depends on the lense but generally the sharpness is better at mid aperture settings (like f8).
Usually image quality starts to degrade again as very small (high number) apertures.
05-26-2010, 08:45 PM   #4
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Of course- the smaller the aperture, the sharper the image, up to a certain point. Obviously, this depends on the lens itself, but you can use F8 as a rule of thumb for the sharpest aperture. Really small apertures, such as F22, 32, and 45, can start causing distortion. Lenses that are almost as sharp wide-open as they would be around F8 or 6.7 are considered as "great lenses", and typically that's what you can expect of FA*'s and Limiteds.

Let's take my A 15mm F3.5 as an example. If I shot my bookshelf at F3.5, most of the titles would be blurred and show a slight fringe. At F8, however, all that would be gone, and we'd have crisp letters!


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05-26-2010, 09:18 PM   #5
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thankyou alll
05-26-2010, 09:44 PM   #6
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As all else, sometimes a compromise is called for.
Loosing some sharpness to diffraction to get more overall sharpness will often trump shooting at the sharpest aperture.
05-27-2010, 04:29 AM   #7
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It very much depends on the lens. For what it is worth, Klaus at photozone tests lenses at various apertures and reports the mtf data on the lens for those. For instance, this is his report on the DA 40 (here). From this data, it looks like the sweet spot is between f4 and f5.6 and after that the sharpness actually drops off somewhat. The better the lens, the more comfortable you can be to shoot it wide open, but even the best lenses sharpen up considerably when stopped down a stop.
05-27-2010, 06:56 AM   #8
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QuoteOriginally posted by Rondec Quote
It very much depends on the lens. For what it is worth, Klaus at photozone tests lenses at various apertures and reports the mtf data on the lens for those.
The tendency I see is that most primes peak at f/4 for center and f/5.6 for borders. Good zooms peak more often at f/5.6 and some slow zooms (f/5.6-f/6.3) usually peak around f/8-f/11.

One nice thing about Pentax DSLR is their MTF Program line. The camera will try to select the best aperture it can.

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