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02-08-2014, 09:16 PM   #1
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Where sweet spot on 18-135 lens?

Have a new k3 and using this lens. I should aperture priority most of the time. Where is this lens and camera combo the best? F8 or f11?

Thanks.

Steve

02-08-2014, 09:37 PM   #2
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I've found both F8 and F11 to be great - anywhere around there. I find anywhere between F8-F16 to be the best.
02-08-2014, 10:17 PM   #3
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I usually keep it around F8, but 5.6 @ 18mm is fantastic.
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/179869-da-1...at-can-do.html
02-08-2014, 11:11 PM   #4
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Agree with above. I have found the lens is optimum when stopped down around 2 stops.
At 18, f3.5 + 2 stops = f7.1, at 135 f5.6 + 2 stops = f11.

So f8 is a pretty good compromise to aim for.

That said its pretty good stopped down just 1 stop (except corners at 135mm).

02-09-2014, 12:46 AM   #5
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You have a MTF program line, although I find it a bit optimistic.
02-09-2014, 11:12 AM   #6
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They have tested this 18-135mm on SLRgear web site. Check the interactive chart

Pentax Lens: Zooms - Pentax 18-135mm f/3.5-5.6 ED AL [IF] DC SMC DA WR (Tested) - SLRgear.com!
02-09-2014, 04:41 PM   #7
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not so fast. Without a lot of testing, it is hard to determine what the "best" setting for your particular lens + body combination is.
For example, here is a listing of the following data points from DxO for "similar" lenses:
  • Nikkor 18-135mm + Nikon D7100 = Best at f=24mm & f/3.8
  • Nikkor 18-140mm + Nikon D7100 = Best at f=18mm & f/4
  • Canon 18-135mm + Canon 7d = Best at f=18mm & f/3.5
  • Sony 18-135mm + Sony Alpha 77 = Best at f=18mm & f/4

I think it pretty safe to draw the following conclusion (by inference) -- the Pentax 18-135mm is likely "sharpest" somewhere between 18mm and 24mm and f/3.5 and f/4.

YMMV

Michael

Last edited by MJSfoto1956; 02-09-2014 at 08:10 PM.
02-09-2014, 06:30 PM   #8
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What's best for one lens is not best for another, and usually center sharpness is at a lower f-stop (numerically) than corners.

If you're just trying to maximize sharpness without regard to DOF, F/8 is usually a good place to start.

MJSfoto - the 18-135 is not good at the wide end IMO, and also IMO, DxO's lens testing leaves a lot to be desired. It's not that I disagree with the testing per se but the implicit conclusions they draw (like 'best' or their ratings) are poor.

02-09-2014, 06:58 PM   #9
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It's pretty sweet in the 24-70 range. Even wide open through there it looks pretty nice.

This is my favorite 18-135 shot, f8 at 70mm (EXIF says 68, but it never says 70 for whatever reason)




People fuss about the IQ of this lens, but all in all it's pretty decent weighed against the convenience.
02-09-2014, 07:13 PM   #10
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It's sweet spot is between 24mm and 35mm, and around f/7.1 to f/11
02-09-2014, 07:20 PM   #11
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It's sweet spot is 60-90mm and f5.6.
02-09-2014, 08:15 PM   #12
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you might want to play with this online widget to see how the Canon 18-135mm behaves with different f/stops and focal lengths. This is the kind of data that reveals how your lens actually behaves and explains why certain photographers "like" a certain combination better. Let's hope they publish more Pentax lens data like this.

Lens review data: Digital Photography Review

Michael
02-10-2014, 10:36 AM   #13
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QuoteOriginally posted by MJSfoto1956 Quote
not so fast. Without a lot of testing, it is hard to determine what the "best" setting for your particular lens + body combination is.
For example, here is a listing of the following data points from DxO for "similar" lenses:
  • Nikkor 18-135mm + Nikon D7100 = Best at f=24mm & f/3.8
  • Nikkor 18-140mm + Nikon D7100 = Best at f=18mm & f/4
  • Canon 18-135mm + Canon 7d = Best at f=18mm & f/3.5
  • Sony 18-135mm + Sony Alpha 77 = Best at f=18mm & f/4

I think it pretty safe to draw the following conclusion (by inference) -- the Pentax 18-135mm is likely "sharpest" somewhere between 18mm and 24mm and f/3.5 and f/4.

YMMV

Michael
I can concur, as others have posted that the best image should be over 24mm. It has quite nasty (IMO worse than the 18-55) barrel distortion bewtween 18 and 24mm. I rarely have the luxury to stop it down, but that of course improves sharpness.
02-10-2014, 12:15 PM   #14
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QuoteOriginally posted by MJSfoto1956 Quote
you might want to play with this online widget to see how the Canon 18-135mm behaves with different f/stops and focal lengths. This is the kind of data that reveals how your lens actually behaves and explains why certain photographers "like" a certain combination better. Let's hope they publish more Pentax lens data like this.

Lens review data: Digital Photography Review

Michael
MJSfoto. Interesting link you showed us. Wish more Pentax lenses were in there. Thanks.
02-10-2014, 01:07 PM   #15
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I think it depends on what you are trying to photograph. The lens is decently sharp across the zoom range.

I have used this lens almost completely wide open in mid-zoom for portraits while I'm out with my kids. The shot came out pretty good with nice bokeh and good subject isolation due to the shallower depth of field. I can easily make out the hairs on my kid's head. So, sharp enough for me!

I have also used this lens at f/7.1 to f/9 for landscapes at 18mm.

I have also used the lens at f/22 to slow down the shutter speed so I can blur and soften streams of water. Diffraction comes into play but the water is blurry and soft. Do I care about diffraction at that point? No.

I would not mix the lens settings between the different shooting scenarios.

Sharpness is a funny thing when DoF is mixed in. There is actual sharpness of the glass and perceived sharpness due to DoF.
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