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04-21-2012, 06:57 PM   #1
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lens "sweet spot"?...

I'm not sure if I should be posting this in the lens, or the DSLR forum, but here goes...
I was doing a search, trying to determine the various "sweet spot apertures" for my Pentax lenses, and came across an old post that stated:

"using MTF programming. Every lens has a sweet spot that will result in the best shot using a particular aperture and shutter speed for a given situation. For all Pentax DA, D FA, FA and FA J lenses, this information is encoded and if you set the program line in "Custom Settings" to MTF, the camera will automatically choose the best settings for each lens. I know that this may be a statement of the obvious for the more experienced Pentax users but I wanted to mention this topic for the Pentax newbies who own a K10D or K20D and may have glossed over this item while reading the owners manual (or maybe haven't read that part) and potential buyers of Pentax cameras or lenses. So often I see a thread asking whether to buy a Pentax lens or a third party lense of about the same focal length and I think that for me, I usually prefer the Pentax brand because they make great lenses and you also get this extra. I know that experienced users have reasons to set the aperture or shutter speed to a different setting for many reasons but isn't it nice to have a reference point to work from, especially if you are new to DSLR's as so many people are these days. If this is function is important to you, it may also be a reason to buy a K20D over a K200D as I don't believe this function is available on the K200D. Anyway, hopefully this post will be helpful and informative for someone who wasn't aware of it."

Is this also true of the K5? Or is there a list identifying the sweet spots for the various lenses?
Thanks in advance...

04-21-2012, 07:25 PM   #2

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QuoteOriginally posted by beaumont Quote
Is this also true of the K5?
Yes, it is. There's a setting in the menu for it. Now what those best settings are, I don't know. Lenses are generally sharpest in the center at f4 to f5.6, but they may not be sharpest corner to corner until f8. So the "best settings" for a specific lens may depend on what is more important: corner to corner resolution or center resolution.
04-21-2012, 07:39 PM   #3
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I'm embarrassed to say that while searching for threads on this topic, I came across one I posted a few years back asking this same question. (I guess my wife is correct, I am losing it.)
Thanks for the feedback. I will search through the menu of my K5 and see if it jumps out at me. (In the meantime, I'll keep watching this thread for futher wisdom.)
04-21-2012, 07:48 PM   #4
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Press the menu button.
Column three in camera settings.
Fifth option down is "Program Line"
Select MTF.

04-21-2012, 09:36 PM   #5
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Would be useful if this information could be extracted from the firmware, no?
04-22-2012, 12:25 PM   #6
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Thanks for the info Sandy.
With regards to hcarvalhoalves comment, at the very least we could generate a spreadsheet if it hasn't already been done...
04-22-2012, 12:25 PM   #7
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I wonder if Pentax would provide this information, if asked?

04-22-2012, 12:33 PM   #8
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Check the www.photozone,de site, for example:

Pentax SMC-FA 31mm f/1.8 AL Limited - Review / Test Report - Analysis

Many modern lens reviews now note MTF data.


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