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05-15-2015, 05:39 PM   #1
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Pentax HD da 20-40mm Ldt sharpness at 2.8 and infinity?? focus ring position

Hi everyone,
Yesterday I got my new "baby" the HD 20-40mm, after having done some test shots, a couple of things I want to understand if they are just normal or still their can be my copy issue.

1.I made a photo (the bottom one) with the ring position when the lenses are focused to infinity? - question mark because the focused area is from around 30m far (not sure if this means infinity), is this the correct ring position? The focusing was done in Live View as well in Viewfinder to make sure, that is not a camera issue.

2. The pictures taken at 2.8 on very distant areas come a bit too soft for me in the center . The bellow posted 100% center crops are from RAW shots taken in Live View mode - I made screenshots as they appear in LR5 without any settings applied. The focusing with viewfinder give quite the same results.

If these are related to my copy, I still can replace it. Thank you all for your reply.

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05-15-2015, 05:50 PM   #2
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I do not think you can just put the lens on infinity using the focus ring and expect "infinity" to be in focus, you have to actually focus. The focus ring might go further than infinity. Also, most reviews of this lens I have read indicate it is much sharper at f/4. Actually I believe almost all lenses will be sharper stopped down a bit.

I would not evaluate any lens with shots like you have shown, there are just too many variables. Set up a proper test target in good light with the camera on a tripod and precisely aligned perpendicularly to the target. Use MLU and a remote. If you are testing the lens, you must remove all other variables. Make a series of test shots, (minimum of three) at each aperture and test the lens from f/2.8 to f/16. Then you have a good evaluation of what the lens is capable of.
05-15-2015, 06:17 PM   #3
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I don't think you need to worry about your copy as my copy of the same lens is like that too. When I purchase this lens, I also checked other copies while I was at the shop (in Tokyo). The scale that you see appears to past infinity, perhaps it does, but in reality it is not. I personally don't see a point of using 'infinity' as the hyper-focal point should kick in long before the infinity point. If you worry about the sharpness of this lens, perhaps you should check for BF/FF (back or front focus) using AF fine adjustment on the camera. On my k-3, I have +5 setting on this lens, it is tack sharp at 100% with lens wide-open at all focal length.

And of course, YMMV... enjoy your new lens.
05-15-2015, 06:21 PM   #4
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Try going into live view, focusing until something very very far away is sharp, then look at where your focus ring is at.

05-15-2015, 06:32 PM   #5
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If I understand you correctly - you used LV to autofocus on the objects in the distance, so no AF fine adjustment is possible or necessary with contrast detect.

But all other things aside, yes your images do look unacceptably soft to me. Return the lens if you can't get better results.

Last edited by Gray; 05-15-2015 at 11:00 PM.
05-15-2015, 08:56 PM   #6
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If you using the hyperfocal markings then you should close the aperture down, f8,10,11,16 etc.

05-16-2015, 01:54 AM   #7
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Thank you all for your help here.
I had packed it and sent itback, as I am currently in China, and the return policy is more an agreement between the seller and the purchaser for the online shops here, I had the choice between getting the money back or get a second one, with no return options after.
So I have chosen to get the money back, feel a little sad, but still could not take a second risk considering the price and my limited budget for this purpose.

jatrax I agree with you, there can be a lot of factors which can influence, so I tried on several apertures, and got the best sharpness at 5.6, then after from 8 on again some softness came back.

I am used now with the DA 18-135mm WR and considering that for this ones I have paid a third the price of the DA 20-40, I would expect more. I like very much the color saturation and character of the DA 20-40, is like another world compared with the 18-135, but still I feel too long the way to dig very deep to get a proper shot.

When for my amateurish purposes I take pics mostly on the streets, I don't have the time to study what's the best way to do this, it has to happen at least the way is happening with my now 18-135.

So byebye for now the DA 20-40, will miss your color, now waiting for the sigma 18-35 f1.8 which still not available for purchase with pentax mount here in China. When will come out will give it a try.
05-20-2015, 06:03 AM   #8
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Were you taking pictures through windows???

05-20-2015, 11:09 PM   #9
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QuoteOriginally posted by oculus Quote
Were you taking pictures through windows???
Haha, it looks like? then it was still the right choice to send that copy back.
Anyway after turning rounds and rounds in circles and looked up and down for another lenses, I opted on the very end, to take the risk and still buy again this one. Maybe the rainy days of the last time have contributed a little, now once I will get it will update this thread, it should arrive by tomorrow.
I see all the lenses available for purchase in China are made in Vietnam, prices variation is very high from the official Pentax online shop of 1060 US$ (crazy!) to 709 US$ (still crazy!).
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