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03-22-2015, 07:05 PM   #1
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HD DA 20-40 buying tips please

Hi all,
I'm thinking of picking up the 20-40 lens, but am a bit frightened by the issues some folks have found with their copies. I understand some copies are great, others have issues. How does one account for this? Just buy from B&H and return if need arises? Avoid the used market with this one?
If getting new is the way to go then, how to test for consistency in order to determine if you have a lemon or a gem?
Loving your 20-40? If so, have you been having successful results at the wide and 'long' end?
Thanks for your thoughts! :-)

03-22-2015, 07:23 PM - 1 Like   #2
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B&H Photo is good about replacing defective gear. You want to check that autofocus is accurate within the camera's ability to adjust, and check for decentering. There are a number of ways to check decentering, google it and you'll find them.
03-23-2015, 02:31 AM - 1 Like   #3
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The lens is excellent.
But remember its design objectives: to render delicate portraits wide open, and beautiful landscapes at narrower apertures.
That means that it is to be expected it will be 'softer' wide open, and shaper when stepped down.
It has amazing colour separation and clarity, subtlety of tones, etc.
You cannot go wrong with it.
03-23-2015, 04:39 AM - 1 Like   #4
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Can't say I've heard many complaints lately about poor copies either, more just the first batch.

03-23-2015, 06:50 AM   #5
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Thanks all. Softer wide open and sharper when narrow is exactly what I'm looking for! 😊
A lens great for landscapes and family shots as well.
Love Pentax! Can't wait for this lens!
03-24-2015, 07:57 PM   #6
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QuoteOriginally posted by TrailRunner Quote
Thanks all. Softer wide open and sharper when narrow is exactly what I'm looking for! 😊
A lens great for landscapes and family shots as well.
Love Pentax! Can't wait for this lens!
K-3 and DA20-40 Ltd would be my dream go-anywhere digital kit.
It is rain-proof, dust-proof, almost bomb-proof. Nonsense-proof too.
Nothing more is needed ... maybe, only DA15 and DA70, but later.
03-25-2015, 02:11 AM - 2 Likes   #7
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20-40

Hi, the 20-40 is my most used and currently my favorite lens. I got mine for 696.95 with a $20 store credit and a three-year drop and spills warranty from Adorama. I passed on getting this lens from the used market at about $530 because of all the bad copies floating around. I figured if someone was getting rid of the lens it had a higher chance of being a bad copy. When I got my copy the felt on the lens cap was improperly installed and I had to get a replacement cap. But I did get a good copy of the lens! It is fair to say my copy is sharp wide open throughout the whole range.

This lens was designed to try to capture spatial presence, (I'm assuming nothing was lost in translation here) I find that very intriguing. My photographic style is abstract oriented meaning I emphasize space and motion over mass and volume. So learning what this lens was designed for I thought it would make a good companion for me.

To make sure you got a good copy just check for decentering as I believe that is the main reason for the poor performance of the bad copies.

Here is a mini tutorial I've made for you!
Attached Images
View Picture EXIF
PENTAX K-01  Photo 

Last edited by SGOMMO7; 03-25-2015 at 02:28 AM. Reason: Grammar
03-25-2015, 02:30 AM - 1 Like   #8
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QuoteOriginally posted by SGOMMO7 Quote
Here is a mini tutorial I've made for you!
It is also useful to lock the exposure. And no need to turn the camera upside down, just get the distant subject in all four corners of the frame in four shots.

03-25-2015, 07:07 AM - 1 Like   #9
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The DA 20-40 is a wonderful lens, it and the DA*55mm are what's on my K-3 99% on the time - great combo. Though I do have a DA15 & DA35 Ltd, hardly use them anymore since getting the 20-40.
03-25-2015, 08:11 AM   #10
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QuoteOriginally posted by SGOMMO7 Quote
Hi, the 20-40 is my most used and currently my favorite lens. I got mine for 696.95 with a $20 store credit and a three-year drop and spills warranty from Adorama. I passed on getting this lens from the used market at about $530 because of all the bad copies floating around. I figured if someone was getting rid of the lens it had a higher chance of being a bad copy. When I got my copy the felt on the lens cap was improperly installed and I had to get a replacement cap. But I did get a good copy of the lens! It is fair to say my copy is sharp wide open throughout the whole range.

This lens was designed to try to capture spatial presence, (I'm assuming nothing was lost in translation here) I find that very intriguing. My photographic style is abstract oriented meaning I emphasize space and motion over mass and volume. So learning what this lens was designed for I thought it would make a good companion for me.

To make sure you got a good copy just check for decentering as I believe that is the main reason for the poor performance of the bad copies.

Here is a mini tutorial I've made for you!
hugely appreciate all the info on the 20-40. really thoughtful of you. funny, I guess I'm also oriented toward capturing space and motion. my favorite time to shoot is dawn/dusk (duh), capturing trail runners on mountain peaks. pretty much fits the bill.

I'd been grappling with the choice of this lens or the Sigma 18 35, but like the size factor, WR treatment and bokeh of the 20 40 more.
again, greatly appreciated info :-)
03-25-2015, 02:35 PM   #11
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"Bad copy" I would always take with a grain of salt. It is a common excuse for basic ignorance.
Because there so many more utterly bad amateur faux-photographers, coming with wrong preconceptions, and who can't tell their bottoms from elbow.

However, in today's market, I think it is always good to get a new lens, because those bad photographers selling theirs can firstly damage it unknowingly by wrong use. For a lens of significant value and complications I would buy secondhand only from an experienced, honest photographer, whom I personally know. Even then, for the modern lens in question, I would think twice before buying second-hand.

For today's motorised lenses are more susceptible to show effects of even moderate wrong use than the traditional manual lenses, which are much sturdier and can tolerate abuse.
03-25-2015, 04:03 PM   #12
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QuoteOriginally posted by kh1234567890 Quote
It is also useful to lock the exposure. And no need to turn the camera upside down, just get the distant subject in all four corners of the frame in four shots.
Yes you are totally correct you only need to take one picture instead of turning the camera upside down for a second. However I prefer the upside down camera approach for a couple reasons; for example:

•1 The sun may be at the right of the frame and cause loss of contrast on that side, (even though it doesn't make a noticeable flare on the photograph) from this loss of contrast on the right side, the left side may appear sharper even though the lens is not decentered.

•2 The photographer may be mistaken that the objects on the left and right side are on the same focus plane, thus making one side appear sharper depending on which side the focus is weighted more correctly.

•3 Even if the objects on both sides are at true infinity for the lens and therefore on the same focus plane the object on one side might still be closer say 400 m vs. 480 m. Even though they're on the same focus plane the objects that are 400 m away may still appear sharper than the objects 480 m away just by virtue that more pixel real estate may be allotted to rendering detail on the nearer objects. And if the objects are at something like 1 mi. vs. 1.5 mi. atmospheric haze can become a problem.

•4 Additionally the light could be hitting the objects on one side differently than the other, (such as highlighting) affecting perceived sharpness, or the objects themselves might have different properties, such as a fur coat resting on a park bench vs. a stop sign, obviously with the stop sign having clear defined edges it is much more likely to appear sharp than a fur coat at equal distance.

I always recommend taking the same picture with the camera flipped as I believe this way is a more, "apples to apples comparison" and much more unlikely to create a false positive for the reasons mentioned above. [I know in your post you say, "distant subject" which should eliminate problem 2 but not problem 1]

Of course, again, you're totally correct that theoretically flipping the camera is unnecessary. And of course you're also correct about locking the exposure for even though it is unlikely that the camera would choose to change exposure for taking the same shot a few seconds later it is still possible and it is possible that that difference in exposure could affect perceived sharpness and that the photographer might not catch that the photos were exposed differently. And of course there are some other things we could add to this such as it may also be beneficial to stay out of auto-pic mode, (as it may choose to render each shot differently) etc.

This is why I say to, " repeat the process a few times to confirm conclusion" just in case something like this might have happened, (or if the photographer happens to be such a noob he can't recognize one of the two photos happens to be blurry from camera shake and misdiagnosis it as decentering).

However I wanted to be able to stick all the instructions on a little photo and still be readable so I simplified the instructions slightly but not to the extent that they either cannot diagnose decentering or are likely to arrive at a false positive.

Last edited by SGOMMO7; 03-25-2015 at 04:10 PM. Reason: Grammar
03-25-2015, 08:47 PM   #13
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Sample variation

QuoteOriginally posted by Michaelina2 Quote
This suggests to me, at least, that the probability is pretty low for getting a used, or new, "bad copy"... Don't you agree? Other than a few questionable anecdotal reports here and there, please provide credible sources for your "all the bad copies floating around" observation. Just curious... M
Sure! My concerns are mainly from the professional reviews. On our own Pentax Forums a review was done on the 20-40. On the sharpness page they state, "To help reduce the impact of sample variation, we shot our test photos with two copies of the 20-40mm lens and verified that the results were consistent."

And they conclude using two lenses mind you that, "One of the areas in which this lens doesn't shine is sharpness. Even though the center of the frame is looks good at the wider zoom settings, at 40mm you need to stop down to F6.7 or F8 (1.5-2 stops) for optimal performance, as contrast suffers at wider apertures. The corners never really catch up with the center of the frame, but they do become acceptably-sharp at 20mm and 30mm when stopped-down. At 40mm, however, distortion in the corners makes them appear very soft at virtually all aperture settings."

Compare this to the review done by SLRgear:"Overall, the Pentax 20-40mm is a sharp lens, particularly when stopped down a bit.", "At the longer focal lengths of 34mm and 40mm, the lens displays similarly sharp images with ever lessening corner softness at their respective wide-open apertures.", "Zoomed out to 24mm seems to be the "weak spot" for this lens in terms of sharpness, as it shows more softness at É/3.5 -- the widest aperture at this focal length -- and the greatest diffraction limiting softness at É/29. This is a bit odd because once you're at 30mm, the lens displays much more impressive sharpness, which is similar to, if not slightly better than, 20mm."

Lenstip, " Whatís interesting, at 20 and 30 mm the stopping down of aperture helps only a little with the limiting optical aberrations so the MTFs donít get noticeably higher. As a result we werenít bowled over by the maximum results of the lens. The maximum MTF values, reaching 47-48 lpmm, are a performance you can expect from a 18-55 or a 18-135 Ďkití lens. From a Ďlimitedí device with a narrow focal range you have every right to demand more."

Ephotozine, and SLRgear on the other hand make specific note of how much this lens DOES improve when stopped down at the 20, 30, ( and 40).

Then listen to this one by Pcmag, "It's an impressive performer, bettering the 1,800 lines per picture height that we require of a sharp image at every tested focal length and aperture. At 20mm f/2.8 it manages 1,861 lines using a center-weighted test, but there's a bit of softness towards the edges of the frame. Stopping down to f/4 improves things all around; the average score is 1,959 lines there. It improves to 2.068 lines at f/5.6 and peaks at 2,248 lines at f/8."

I have read a user review that supports SLRgear's observation of a bad spot at 24/25 mm but otherwise good throughout its range. And I've read user reviews confirming Pentax Forumsí findings of lack of performance at 40 mm. While other reviews I've read, (yourself included) have agreed with Pcmag's review of a lens that is sharp throughout its whole range!

Now I am aware that some differences in professional reviews isn't totally out of the ordinary but this is ridiculous. It is obvious that some sample variation is at play here. To what degree? To the degree that Pentax forums can get two bad copies in a row! Which is enough for me to recommend to others that they might want a warranty with their purchase.
03-28-2015, 02:16 AM   #14
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On the other end I never saw a pixel sharp picture form that DA20-40. This I get routinely from a DA35 f/2.4, FA43, DA35 macro, FA50... Never saw a pixel sharp picture of DA20-40.

It seems to offer great colors, lot of clarity, great flare resistance. The subject separation capabilities are really pleasant to look but the Uluru comment that it is made for portraiture is clearly overstated. 40mm f/4 is not great for portraiture to me.

I was really thinking to get it, potentially replace the DA21 and avoiding to buy a DA35 f/2.8 but finally the apperture at the long end and the overall sharpness performance disapointed me because all the sample I saw wheren't that sharp when zoomed and quite many looked like the sharpness that was here was done by software. As I tend to often crop, and wanted at least f/2.8, I decided to finally not take it after months of trying to decide myself.

The lense render great overall and can be a great deal, don't see my world as a conclusion this is a bad lense.

This is just that for the colors/clarity I do think that the DA35/DA21 manage well too, as for flare resistance. On the out of focus transistion, the lense is interresting but the apperture and focal range mean that for my use it will not be the primary usage of the lense. It would have been more a longer focal length for that and I have the 77 to handle this that manage very well too.
03-28-2015, 03:04 AM - 2 Likes   #15
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Either of these count as pixel sharp?

https://farm9.staticflickr.com/8708/16952477151_1f12647da3_o.jpg
https://farm9.staticflickr.com/8692/16953425335_948c2c5c3e_o.jpg
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