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11-03-2015, 02:15 PM   #46
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QuoteOriginally posted by normhead Quote
Almost all Pentax lenses are sharpest at ƒ5.6. The three amigos are sharpest at ƒ4.
According to the optical engineers at Optyczne/Lenstip,
the FA 31 is sharpest in the center at f/5.6,
and f/8 at the edge of the APS-C frame.

Same for the FA 43.

The FA 77 is the only one that's sharpest at f/4, edge and center.

This discussion is all kind of theoretical, anyway.
In practice motion blur or cranking up the ISO
can eat away at the apparent sharpness gain from stopping down the lens.

11-03-2015, 04:30 PM   #47
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QuoteOriginally posted by lytrytyr Quote
According to the optical engineers at Optyczne/Lenstip,
the FA 31 is sharpest in the center at f/5.6,
and f/8 at the edge of the APS-C frame.

Same for the FA 43.

The FA 77 is the only one that's sharpest at f/4, edge and center.

This discussion is all kind of theoretical, anyway.
In practice motion blur or cranking up the ISO
can eat away at the apparent sharpness gain from stopping down the lens.
Well, the DA 35 F2.4 is also sharpest at F4 edge to centre if you believe the tests

Maybe I'm alone in being interested as to the most useful aperture range of my existing and future lenses... That's fine. It just seems kind of handy to know where I can grab a bit more light or DOF without sacrificing significant resolution.
11-03-2015, 05:11 PM   #48
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I take many of my shots at a range of apertures whenever I can. I like something like 2.8. 5.6, 8, 16 and sometimes all six in that range. I've so many times had my favourite one of a series be an odd focal length i wouldn't have expected, I wouldn't get comfortable thinking you know something. At this point I'd say, the specific alignment of the elements of the photo are completely changed by the aperture used. Unless you are willing to start including the distance of the subject from the lens, the distance of the subject from the background, placements of other objects in the frame in relation to the subject, a simple calculation based on the need for more light or whatever is not likely to give you the best shot very often. IN fact really only useful when you have time constraints and may only get one chance. Then best guess will have to two. The rest of the time, shoot as many f-stops as you have time for.
11-03-2015, 05:25 PM   #49
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QuoteOriginally posted by normhead Quote
I take many of my shots at a range of apertures whenever I can. I like something like 2.8. 5.6, 8, 16 and sometimes all six in that range. I've so many times had my favourite one of a series be an odd focal length i wouldn't have expected, I wouldn't get comfortable thinking you know something. At this point I'd say, the specific alignment of the elements of the photo are completely changed by the aperture used. Unless you are willing to start including the distance of the subject from the lens, the distance of the subject from the background, placements of other objects in the frame in relation to the subject, a simple calculation based on the need for more light or whatever is not likely to give you the best shot very often. IN fact really only useful when you have time constraints and may only get one chance. Then best guess will have to two. The rest of the time, shoot as many f-stops as you have time for.
That makes perfect sense. I wouldn't rely on or get comfy with the data I was looking for and am now compiling. And yes, you're right, when you need to take the shot, you take it, whatever. If possible, with some options to choose from later. I agree with all that

11-03-2015, 06:20 PM   #50
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QuoteOriginally posted by BigMackCam Quote
So... here's the kind of thing I was thinking of. This is a very, very rough summary of just the Limited primes, the DA35 F2.4 and DA50 1.8 - just to play with the basic layout... Data taken from Photozone reviews with the exception of the DA50 1.8 which was Lenstip. I haven't validated this yet - I may have made an error or two, but as I said, this was mainly to play with the format.

Any constructive input would be appreciated - this layout is fine for me, I think, but if I turn it into something for others to use also (and add a lot more lenses), I'd rather make it broadly appealing
I think that's a helpful chart to see quickly at at glance optimal center and edges. I suspect that there may be some variation depending on the camera and the integrity (based on quality control) of the lens used, but this chart matches exactly my findings I did by subjective testing with my camera and lenses I have. Popular Photography uses a chart like the one below. It is fairly easy to visualize the strength of a lens, but it doesn't reflect center/border quality like yours does. (BTW, the chart was for a Tokina AT-X 24-70 f2.8. I couldn't find a Pentax lens to show.)
11-04-2015, 04:05 AM   #51
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QuoteOriginally posted by mgvh Quote
I think that's a helpful chart to see quickly at at glance optimal center and edges. I suspect that there may be some variation depending on the camera and the integrity (based on quality control) of the lens used, but this chart matches exactly my findings I did by subjective testing with my camera and lenses I have. Popular Photography uses a chart like the one below. It is fairly easy to visualize the strength of a lens, but it doesn't reflect center/border quality like yours does. (BTW, the chart was for a Tokina AT-X 24-70 f2.8. I couldn't find a Pentax lens to show.)
Thanks for the feedback I agree, there will be variations due to tolerances, quality control, wear and tear etc. Plus, as others have already mentioned, the data used doesn't necessarily demonstrate the lenses' performance in relation to specific subjects or distances - but it's a starting point.

The Popular Photography charts look good.

I think I'll continue to add the current range of Pentax lenses to my sheet (at least where data is available) and see if there is any appetite from others for me to expand it further. If not, at least I'll have the reference I was originally looking for
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