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07-20-2011, 01:25 PM   #1
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Pentax DA L 50-200mm Sharpest aperture

Hi everyone, I have a Pentax IstDs with a Pentax DA L 50-200mm lens and I would like to know the recommended aperture for optimal sharpness of an Image, can somebody please help me? I would appreciate any help I can get.

07-20-2011, 01:53 PM   #2
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I don't think your question is as easily answered as it sounds. To try and give the simplest of solutions: Aperture will control depth of field (sharpness from front of photo to the back) but if you want to aim primarily for sharpness above anything else, I would suggest you use TV (speed priority) setting and use a rather fast setting.
The aperture will be set automatically.
Do not use an ISO setting above what is necessary. 100 to 400 ISO is best range for general shooting.

Hope this helps, as this one way of getting sharpness.
07-20-2011, 02:42 PM   #3

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Normally it's around the middle of the range, say f5.6 to f8.
07-20-2011, 02:43 PM   #4
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The old rule: f/8 and be there.

Which means: set the aperture wider than f/16 -- diffraction starts showing up in pixel-peeping after f/9 but isn't really apparent at f/11 -- and pay attention to what's around you.

So if ABSOLUTE SHARPNESS is critical to you, set the aperture to f/8, put the camera on a sturdy tripod, switch SR off, and use a 3-second delay. Maybe put a sandbag on the camera.

If you are shooting handheld with SR on and the aperture between f/5.6 and f/22, your handling of the camera will affect sharpness more than will the aperture setting.

In other words: Don't worry about it. Practice practice practice.

07-20-2011, 03:04 PM   #5
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2 stops down from wide open was an old rule of thumb.

There, now you have all the answers :-)
07-20-2011, 03:14 PM   #6
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Centre sharpness, corner sharpness or overall compromise sharpness ? At which focal length ?

You are welcome to browse through Collection: SMC Pentax DA 50-200mm f4-5.6 ED WR. This is for the WR variant but the L should be similar.

I'd say that at infinity focus it is about f8 at 50mm, f9.5 at 95mm and f16 at 200mm.
07-21-2011, 09:09 AM   #7
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If you have a K5 or K7 you can get he camera to select the best aperture for a given focal length by setting the P line to "MTF Priority" (on the K5 it's "Rec. Mode 3" menu.) In this mode, hitting the green button while in P mode will cause the camera to select the best aperture for the lens/focal length.
07-23-2011, 11:00 AM   #8
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If shooting on a tripod, then the MTF data published as part of some reviews would probably yield good info. As mentioned already, the answer varies depending on focal length, also depending on if you are talking about centers or corners. And of course, you have to consider whether you're OK with the DOF you get at the aperture suggested by MTF or if you'd rather sacrifice some sharpness right at the plane of focus in order to have more of the image appear in focus at all.

If shooting handheld, throw all that out the window - shoot whatever aperture you need to get a fast enough shutter speed.


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