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05-17-2009, 11:23 AM   #1
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Silly "sweet spot" question?...

This may be a silly question but...Is there an existing list specifying the particular known "sweet spots" (ie best performing apertures) of the various Pentax lenses?...

05-17-2009, 11:28 AM   #2
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Just viewing another thread "Lens results" and saw the attached link which answers my question (assuming the data is correct).

Measured Resolution Numbers

Any other thoughts are welcome...
05-17-2009, 11:48 AM   #3
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I'd seen that list before--I see that the one reviewer has f/11 and f/16 as the "best aperture" for a lot of lenses, but I'm wondering if he means "smallest aperture that's somewhat useable and stopping down more is disastrous."

Or something to that effect.

A lot of people read photozone.de tests for that info, and usually where the average sharpness across the frame is highest (like the average of center and border sharpness), that's where the sweet spot is.
05-17-2009, 12:15 PM   #4
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QuoteOriginally posted by beaumont Quote
This may be a silly question but...Is there an existing list specifying the particular known "sweet spots" (ie best performing apertures) of the various Pentax lenses?...
Set your camera on MTF program lie, and take pictures in average light with auto iso, and just note the aperture the camera selects. This should give you the optimum aperture for the Pentax lens on camera. I don't think it works properly for non Pentax lenses. I tried a few third party lenses, and my cameras more or less always go to the same aperture of 5.6.

05-18-2009, 12:15 AM   #5
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Of course, this all assumes that "sweet spot" is objectively measurable. It isn't. You can measure resolution, you can measure MTF, you can measure contrast, you can probably measure color, you probably can't measure bokeh, you definitely can't measure "rendering". All of these attributes may have differet "sweet spots" (and some may have different sweet spots for different observers).
05-18-2009, 07:10 AM   #6
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Point taken Marc! The reason I've asked is that I am often blown away by the "sharpness" that some picture demonstrate. "Sharpnes" that I am rarely able to duplicate. Therefore I'm wondering if there is such a thing as a sharpness sweet spot identified for the lenses?...
05-18-2009, 11:23 AM   #7
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What we perceive as "sharpness" is a combination of resolution and contrast, and is what MTF numbers are designed to show. So to get a good idea of that, you could check the MTF number measured by Photozone.de, or as Yves suggests, use the cameras program line to tell you.

Really, though, very few lenses are very far from maximum sharpness at f/8. The difference between f/8 and whatever the theoretical maximum is for a given lens is unlikely to be visible in web-sized images or in normal-sized prints, and might not really be noticeable to the human eye even at 100%. So I'd say don't sweat those fine distinctions. The real issues in getting maximum sharpness are in totally nailing focs, using the stablest tripod you can, shooting the lowest ISO you can, making sure your subject is not moving at all, etc. And of cours,e how much sharpening you apply during PP. That kind of stuff is *way* more often the different between a super-sharp picture and an ordinary one than shooting f/6.7 instead of f/8.
05-18-2009, 01:16 PM   #8
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QuoteOriginally posted by beaumont Quote
Point taken Marc! The reason I've asked is that I am often blown away by the "sharpness" that some picture demonstrate. "Sharpnes" that I am rarely able to duplicate.
Are you referring to pictures you've seen on the web? Because the "sharpness" of most web-sized pictures has little to do with the lens and much to do with how much sharpening has been applied in post-processing after they've been resized.

05-18-2009, 02:38 PM   #9
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Agreed on everything said,
postprocess skills is important (sigh),

but I might add if you nail the exposure really right, that also contributes to a 'sharp' picture. This has to do with covering the dynamic range, or else making pictures where all the content is within that range. That's why it's harder to get nice pics on high noon, too harsh lights and shadows (oh but we have HDR :-). Avoiding any flare by shooting out of the shadow or shading the lens effectively does contribute as well as trying to get a 90░ angle to the sun for the max. colorpop through natural polarization.

From the view of a manual prime user:
One last thing about the MTF curves. I would say that I too often assume something like f/8 to be optimum aperture when it is f/4 to f/5.6. This has to do with the curve's cutting at 14.3mm on APS-C (that is half the diagonal), so all the 'borders' and 'extreme borders' from the old full-frame tests are nonexistant on APS-C.

If you don't have have a manual prime but are after 'sharpness' (who isn't), go get something between say 35- 58mm focal length as a cheap start and see what your camera is capable of.

Best, Georg (the other)
05-18-2009, 03:21 PM   #10
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Thx all for the feedback.
I wondered about taking note of the aperture selected by the camera, but then thought this would only tell me what the camera is set up to do, as opposed to what the "sweet spot" of the lens would be? Yes/no?
Regarding a lot of it being through PP'ing, I can understand that but on the odd occasion I seem to nail it without applying PP (for example the attached) and when I do, it makes be realize how often I don't! As a result I've been wondering if it's the aperture for the various lenses. (Lately I've been using the focus button on the back of the camera so that I don't have to spot focus and recompose. This seems to help somewhat.)
Again, thanks for the feedback!

Last edited by beaumont; 01-01-2012 at 12:14 PM.
05-18-2009, 08:23 PM   #11
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QuoteOriginally posted by Marc Sabatella Quote
... <snip> ...
Really, though, very few lenses are very far from maximum sharpness at f/8. ... <snip> ...
The old journalist's maxim "F 8 and be there" has some validity. At f/8 you are not anywhere close to diffraction limits and you are not (generally) wide open either. Some others use the rule of thumb that the lens is best stopped down two stops from wide open. On my M macro, that just happens to be f/8.
05-19-2009, 04:52 PM   #12
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"The old journalist's maxim "F 8 and be there" has some validity. At f/8 you are not anywhere close to diffraction limits and you are not (generally) wide open either. Some others use the rule of thumb that the lens is best stopped down two stops from wide open. On my M macro, that just happens to be f/8. "

Thx for the feedback all...I will continue to endeavor to get better!
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