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HD Pentax-DA 20-40mm F2.8-4 Limited DC WR

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52 211,321 Sat October 10, 2020
Recommended By Average Price Average User Rating
92% of reviewers $731.95 9.17
HD Pentax-DA 20-40mm F2.8-4 Limited DC WR

HD Pentax-DA 20-40mm F2.8-4 Limited DC WR
HD Pentax-DA 20-40mm F2.8-4 Limited DC WR
HD Pentax-DA 20-40mm F2.8-4 Limited DC WR
HD Pentax-DA 20-40mm F2.8-4 Limited DC WR
HD Pentax-DA 20-40mm F2.8-4 Limited DC WR

The HD Pentax-DA 20-40mm F2.8-4 Limited DC WR is the first zoom lens to join the Pentax lineup of ultra-compact "limited" lenses. This lens features a sleek all-metal barrel manufactured to very high standards.

This is also the first Limited series lens to feature silent DC autofocus as well as a weather-sealed design. Like the other HD Limited lenses, this lens features Pentax's latest lens coating promising less ghosting and flare.

As is standard for all premium Pentax lenses, this lens allows for full-time manual focus adjustments (Quick shift) and it is treated with Pentax's Super Protect coating to protect the front element from dust and scratches

The lens covers a wide-angle to normal focal length range, and is compatible with Pentax APS-C DSLRs. It will be available in both black and silver in December, 2013 for $999.

HD Pentax-DA 20-40mm F2.8-4 ED Limited DC WR
©, sharable with attribution
Image Format
Lens Mount
Pentax K
Aperture Ring
Automatic, 9 blades (rounded)
9 elements, 8 groups
Mount Variant
Check camera compatibility
Max. Aperture
Min. Aperture
AF (in-lens motor)
Min. Focus
28 cm
Max. Magnification
Filter Size
55 mm
Internal Focus
Field of View (Diag. / Horiz.)

APS-C: 39-70 ° / 33-62 °
MH-RA 55mm
Soft pouch P70-150
Lens Cap
Metal push-on O-LW65A
Weather Sealing
Yes (WR)
Other Features
Diam x Length
71 x 68.5 mm (2.8 x 2.7 in.)
283 g (10 oz.)
Production Years
2013 to present (in production)
$496 USD current price
Engraved Name
HD PENTAX-DA 1:2.8-4 20-40mm ED Limited DC WR
Product Code
23000 (black), 23010 (silver)
User reviews
In-depth review
Unofficial Full-Frame Compatibility Tests by Pentax Forums
★★☆ Full coverage at some F-stop and focal length combinations
Show details
One aspherical element, one ED and one extra-low dispersion element.
No autofocus on older bodies (*istD series, K100D, K110D, and film).

Black and silver

Supersonic AutofocusQuick ShiftWeather SealedAutomatic ApertureAPS-C Digital Only
Purchase: Buy the HD Pentax-DA 20-40mm F2.8-4 Limited DC WR
In-Depth Review: Read our HD Pentax-DA 20-40mm F2.8-4 Limited DC WR in-depth review!
Sample Photos: View Sample Photos

Add Review of HD Pentax-DA 20-40mm F2.8-4 Limited DC WR Buy the HD Pentax-DA 20-40mm F2.8-4 Limited DC WR
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Senior Member

Registered: May, 2011
Location: Hanoi
Posts: 213
Lens Review Date: August 27, 2015 I can recommend this lens: Yes | Price: $700.00 | Rating: 10 

Pros: perfect build, low light, autofocus
Cons: nil
Sharpness: 10    Aberrations: 10    Bokeh: 9    Autofocus: 10    Handling: 10    Value: 10    New or Used: Used    Camera Used: Pentax K30   

In my point of view, this is the best design of Pentax. I love the build and the way of autofocus which creates many impressive photos.

Nhat Tan 2015, on Flickr

Nhat Tan 2015, on Flickr

Nhat Tan 2015, on Flickr

Registered: March, 2010
Location: Vermont
Posts: 902

1 user found this helpful
Lens Review Date: August 13, 2015 I can recommend this lens: Yes | Price: N/A | Rating: 10 

Pros: Sharpness, color, contrast
Sharpness: 10    Aberrations: 10    Bokeh: 10    Autofocus: 10    Handling: 10    Value: 9    New or Used: New    Camera Used: K-3   

Just a super lens. Sharpness, color, contrast are nothing less than outstanding on my copy. Covering the range of other limited primes (21, 31, 35, and 40), WR sealing, silent DC motor, smaller size (compared to the DA*16-50 and Sigma 18-35), flare resistance, makes this lens very good solution for me. I've had this lens for a week and have yet to take it off my K-3.

IMGP9775.jpg by Short_Final!, on Flickr

IMGP9901.jpg by Short_Final!, on Flickr
Site Supporter

Registered: September, 2011
Location: Hampshire, UK
Posts: 1,682

1 user found this helpful
Lens Review Date: July 17, 2015 I can recommend this lens: Yes | Price: $750.00 | Rating: 10 

Pros: IQ, general solidity and 'feel', construction quality, zoom smoothness, manual focus over-ride smoothness
Cons: None
Sharpness: 10    Aberrations: 9    Bokeh: 9    Autofocus: 9    Handling: 10    Value: 10    New or Used: New    Camera Used: Pentax K-5   

I bought this lens during a special offer period, and it has hardly been off my K-5 since. My previous standard zoom was the 16-45 which was itself a step up from the kit zoom, but the images from the 20-40 have something about them. Flare resistance is incredible. The supplied hood is a little small but with the HD coating, this is not an issue. Any necessary additional shading can be provided with the hand. Sharpness is very good indeed across the range, and at the sweet spot of around f8 it really is a cut above my other lenses.

The K-5/20-40 package is very compact, and the lens is just such a pleasure to use. The zoom is silky as is the manual focus fine adjustment, and the all-metal construction just feels so right. I also like the simplicity of the design: no knobs, switches, levers - just the zoom ring and the fine focus ring. Yes, the focus ring turns when the autofocus operates, but that's not an issue. The DC autofocus itself is almost silent and locks quickly, even on my veteran K-5. Strongly recommended.
Site Supporter

Registered: July, 2011
Location: Eastern Oregon
Posts: 690

9 users found this helpful
Lens Review Date: April 21, 2015 I can recommend this lens: Yes | Price: $695.00 | Rating: 10 

Pros: Sharp, great contrast, thick lush color saturation
Cons: none
Sharpness: 10    Aberrations: 10    Bokeh: 10    Autofocus: 9    Handling: 10    Value: 10    New or Used: New    Camera Used: K3, K5IIs   

I LOVE this lens. The review(s) are wrong. They must have got a bad sample. This lens is as good as the primes it covers, namely the 21/31/35/40/43 LTD's. And most importantly it has that LTD magic photo dust sprinkled all over it, the shots are rich, lush and have that "artistic" something that we all crave. This lens (and the LTD's in general) make me want to photograph things just to see what they look like through it. This lens covers my 17-50 Tamron with WR and better IQ. I still use the 17-50 for weddings as a backup etc, but this 20-40 is my goto everything lens. With the 15 and 70, it is my travel/landscape foundation lens. I don't find the zoom range limiting at all. It's a very convenient fine tunable normal. If I need wide or tele, then I switch lenses. But for everything else it's perfect. Just buy one. At $695 USD it's a great deal.
New Member

Registered: April, 2014
Posts: 4

4 users found this helpful
Lens Review Date: March 2, 2015 I can recommend this lens: Yes | Price: $800.00 | Rating: 10 

Pros: Small size, build, styling, bokeh, image rendering, weather sealing
Cons: none
Sharpness: 10    Aberrations: 9    Bokeh: 10    Autofocus: 10    Handling: 10    Value: 9    New or Used: New    Camera Used: K3   

This lens is well worth having. Like another reviewer said, don't let some of the negative reviews scare you off. I found that none of the negative points are relevant. The f/4-2.5 aperture range is not a problem on a camera like the K3 with or K5 with their high ISO capability. The limited zoom range is not relevant either. The 20-40mm focal range covers the most-used normal-wide focal lengths on a crop sensor camera. All of the other lens makers, Canon, Nikon, Sigma, make zooms with similar restricted focal lengths and they sell just fine.

I tested the rendering capability against the FA-43 and SMC K 30mm (sire of the FA-31). The 20-40's rendering capability is equal to those two legendary lenses. The bokeh is very smooth resulting from the rounded aperture blades. The lens weight is deceivingly light. The size is small so it's not obtrusive nor obnoxious to carry. So many of the other zoom lenses in this range are as big as water bottles. I really like the tasteful styling with the Takumar-style zoom ring. All in all, it's a very excellent lens, capable of excellent results, on par with all of the Pentax Limited primes, and looks good to boot. Highly recommended!
Site Supporter

Registered: May, 2014
Location: Minnesota
Posts: 1,588

7 users found this helpful
Lens Review Date: December 25, 2014 I can recommend this lens: Yes | Price: $574.00 | Rating: 9 

Pros: Small, Light, Weather sealed, Quiet
Cons: Limited range
Sharpness: 10    Aberrations: 9    Bokeh: 8    Autofocus: 9    Handling: 10    Value: 8    New or Used: Used    Camera Used: Pentax K-5 IIs   

First of all I can't give an extensive review for this lens since I only had it a couple of weeks. Maybe after a few months I'll update this review to give you a better perspective on how I feel about this lens. I have lusted for this lens for quite a while now, but the thing that held me back was the price. Due to the limited range and due to some negative reviews I was hesitant to fork over that much money for it. A few weeks ago I was looking at the BH website and saw that this lens was selling for only $574 Used in 9+ condition !

This was about the lowest price I had yet to see for this lens new or used, so I got it. I figured I could always send it back within 31 days if I did not like it.

So, lately I have been testing this lens under as many real-life conditions as possible, hoping I would not have to send it back. Like I said, it's only been a few weeks if that many, but so far I'm pleasantly surprised. This lens is a marvel of engineering and so fits well with my K-5 IIs which is a marvel of it's own.

First I will describe the Aperture which some people have complained about being too slow. At 20mm you can open up to f2.8, at 25-30mm f3.5, at 35-40mm f4.0. Not bad considering that even some limited primes within those focal ranges are not much faster.

I compared the Sharpness of this lens against my 16-45mm f4 and 35mm Macro f2.8. The good thing about this lens is that it does not extend much from the body like my 16-45mm does. At 20mm it extends about 2/3 of an inch. at the other focal lengths it does not extend past 1/2 of an inch from the body. The distance scale on this lens is quite limited in that after 5 feet it goes straight to infinity with nothing in between, but that might have to do with lens design for zooms which I now little about

From what I can tell, this lens is a tad sharper than my 16-45mm across all focal lengths except maybe the 30mm focal length, why I don't know ? What this lens got going for it, is the way it renders the colors and the contrast. Not artsy, not over-saturated, but amazingly life-like. At 35mm, my 35mm f2.8 Macro is sharper across the length of the frame, but to tell you the truth, there is not much difference between all 3 lenses unless you really pixel-peep. If you really want sharp though, set the camera to ISO 80. Then you start moving into 3D territory...

Handling : Although this lens is supposed to be all metal, it is very light to the point where I think it's some kind of aluminum instead of real metal ? Nevertheless it is very well built, but I wish it had the heft of my other limited lenses just my opinion... The focusing is very well damped as well as the Zoom dial. So there is no problem there. One thing is the very fancy lens cap. I am so afraid that I might drop it and lose it (@$40) that I keep it in my left hand when shooting. This lens is light and well balanced enough for me to do that thankfully.

Autofocus is nearly silent and pretty quick. You really have to put your ears pretty close to the camera to hear it. This is perfect for places like museums, operas, churches, funerals, where the loud buzzing whirl of other lenses might become annoying. One thing I noticed is that the AF is faster and much more accurate if you limit the auto focusing points. I set my AF to Sel Mode and only use one focusing point, so far this has worked best for me.

Bokeh is reasonable mild/smooth a little better than on my 16-45mm, but not better than on my 35mm, or 77mm. I have not had the time to test this much so I can't say much about it.

Aberrations: What I like about this lens is this new Pentax Anti Flare coating. This really helps when shooting into the light, not just sun light, I'm talking about street lights and car lights and things like that. This lens does not fall apart like my Limited and other lenses do in those conditions. Another thing I noticed though is that this lens produces a little bit more CA under certain circumstances than my 16-45mm. It could be my copy, but I'm still investigating.

If you take all the features into consideration, not just pixel-peeping sharpness, this is a wonderful lens and a marvel of engineering. Time and experience will tell whether I will send it back, but so far so good.
New Member

Registered: May, 2013
Posts: 13

8 users found this helpful
Lens Review Date: July 29, 2014 I can recommend this lens: Yes | Price: $825.00 | Rating: 9 

Pros: Sharp, Color, Weather Sealed, Light, Compact, Flare Resistance
Cons: Slow Autofocus, Price, Lens Cap
Sharpness: 9    Aberrations: 9    Bokeh: 10    Autofocus: 6    Handling: 10    Value: 8    New or Used: New    Camera Used: Pentax K-5IIs   

I bought this looking for an upgrade over the DA SMC 18-135 which I had used for a year or so and actually liked but I purchase a few of the limited series lens and was astounded at much better they rendered color and, in general, how much sharper they were over the 18-135. The HD 20-40 obviously doesn't have the zoom range and it isn't as useful in that regard but it renders colors so much better and is much sharper. I apparently got a good copy since I have found mine to be decently sharp wide open and very sharp when stopped down just a little more. The new HD coating works amazing well in tough, high contrast conditions. The autofocus motor is quiet. Not as quiet as SDM but much quieter than screw drive. It is a bit slow sometimes to lock onto a subject. Can be a tad frustrating at times.

Construction is top level and then lens feels good on the camera. Not too heavy but substantial enough. The weather sealing works very well. I was recently involved in a kayaking mishap where mine and my wife's tandem kayak sprung a leak in the middle of a bay in the Florida Keys. Eventually the kayak became too unstable to paddle and flipped. My wife saved the camera but it did get partially dunked in the bay. We were stranded out there for a couple hours till a boat came by and rescued us. The lens held up totally fine and the camera has of course okay as well. I was impressed! We of course were exhausted, dehydrated, and glad to be out of the water.

The price is steep for what it is but I wasn't willing to pay the equivalent to get the DA* 16-50 with potential SDM issues and the extra weight. I did find a good deal on this lens lurking Amazon but I do think the lens is a little too expensive for what it is. Maybe $799 for it brand new.

The lens cap is 62mm in size, the filter size is 55mm, and expensive! Don't lose it because it costs $40 to replace! It fits over the "lens hood" if you can call it a lens hood. My opinion is that flare is such a minimal problem with this lens that it could go without the lens hood the majority of the time.

I really enjoy using this lens. It stays on my camera 90% of the time.

Inactive Account

Registered: January, 2014
Posts: 76

1 user found this helpful
Lens Review Date: July 4, 2014 I can recommend this lens: No | Price: $1,060.00 | Rating: 6 

Pros: Built, Bokeh, design, WR
Cons: IQ, AF, hood
Sharpness: 7    Aberrations: 9    Bokeh: 10    Autofocus: 7    Handling: 10    Value: 6    New or Used: New    Camera Used: K-5ii   

This is my first pentax lens that I dislike.
First impression was very good. Lens is really nice piece of metal. Handling is very pleasant. But photos were lacking of something... And I didn't know what is not right. So I have done some testing (tripod, MUP...) between this DA20-40, DA L 18-55 Tamron 17-50 and DA18-135 and DA 35 AL. And that show, that this lens is really lack of sharpness! It isn't absolutely horrible, in fact it's quite mediocre - but for $1000 lens it is not acceptable. Kit lens has same IQ on 20mm as this lens, and my 18-135 is better! On 35mm is standing: Tamron, prime DA35 2.4, 18-135, DA-20-40, and kit lens. It has worse IQ thru all FL than my Tamron 17-50 and somewhere on par, somewhere worse than 18-135.

Autofocus is quite strange. Its quiet but not quick. My screwdrive lens are faster. And behavior of AF motor is like screwdrive, lik My other DC lens lock focus instantly, no need to microadjust, same on my SDM lens... And with multiple presses of AF button - multiple microadjustment - even on contrast scene.

What is good: This lens has very low CA, good flare resistance, nice built. And very, really very nice bokeh (maybe best for wide zoom that I ever seen). And it can handle images at higher ISO then others - I don't know how, but photos from this lens seems have less noise than photos from other lenses on same ISO.

Bottomline: I'm glad, that I had bought this lens from shop, where wasn't problem to return it and change it for another lens. But he had only one piece of 20-40, so I picked another lens. Maybe I'm just "lucky" for dud - but, apparently, I'm not alone.
New Member

Registered: February, 2013
Posts: 14

2 users found this helpful
Lens Review Date: May 7, 2014 I can recommend this lens: Yes | Price: $1,300.00 | Rating: 10 

Pros: IQ, bokeh, build quality, WR
Cons: Not constant 2.8, not internal focusing
Sharpness: 10    Aberrations: 9    Bokeh: 10    Autofocus: 9    Handling: 10    Value: 9    New or Used: New    Camera Used: K-5   

Before this lens, my main lenses was DA*16-50 and DA*50-135, but usually I left the 16-50 at home. It was too big and I felt the pictures it produced varied too much in quality.
I bought this as soon as it came out and fell totally in love with it. It's been constantly on my camera ever since and I have no desire to remove it.

The "weired" zoom range, wich I was a bit afraid would turn me off, really doesnt bother me anymore.
I tend to threat it as a 30mm prime with "adjustment possibilities".

I've used it alot with extensiontubes, and it produces great macro results with the tubes. The transition between the sharp and the blurred, I find to be just lovely.
The only trouble I have is that I cannot access the menu on my K-5 with the extensiontubes and it refuses to go beyond f. 3.5. Wich is weired because all my other lenses communicate perfect with my camera through the extensiontubes. It might be the DC, it might be a software issues with the firmware. I don't know.

All in all I find this to be a great lens. It has reignited my interest in photography and cured my LBA. So now it's all about the pictures, instead of the gear, for me.

It might not be everyones cup of tea, but for me this is the gem I've been looking for (with a few minor flaws).

(Sorry for the bad grammar. English is not my mother tongue.)
Site Supporter

Registered: May, 2011
Location: Arlington, VA USA
Posts: 927
Lens Review Date: April 22, 2014 I can recommend this lens: Yes | Price: $900.00 | Rating: 10 

Pros: Excellent build, quiet fast focus and very good image quality
Cons: The lens hood

This is a lens you have to hold and feel, the quality is amazing, a welcome new addition to the Limited line up in my opinion. I admit with all the unfavorable discussion on this lens, I was a bit hesitant. Thankfully my local camera store had their semi annual sale and I was able to try for I buy. I was sold when I was using it. I have put the lens through its paces and I am very pleased. The sharpness is very good through out the range, very little distortion, and very quite focus. Focus is accurate and decisive. Blazing fast, no, but still fast. It also gets in pretty close for decent close ups!. Anyway, I can see this being my main lens for my URBEX photography as it lightens my gear a bit. I know the price is on the high side, but it is a well crafted lens that deserves a second look.
New Member

Registered: May, 2012
Posts: 3

3 users found this helpful
Lens Review Date: March 31, 2014 I can recommend this lens: Yes | Price: $1,000.00 | Rating: 10 

Pros: sharp, build quality, silent
Cons: size, hood
Sharpness: 10    Aberrations: 10    Bokeh: 10    Autofocus: 10    Handling: 9    Value: 9    New or Used: New    Camera Used: K5   

I have had this lens for a week and the following are just some of my observations and opinions. I am a bit of a "pixel peeper" thus was looking something that would be smaller than 16-50, give some flexibility and be SHARP!

My take on commonly debated points:
1. SIze: Yes, it is bigger. Get over it! It's an awesome lens, much smaller than any zoom with such IQ. And as it is so light, it doesn't weight down the front end so I forgot the size of it and treated it the same way as rest of my Limited's. People seem to forget that Limited's are incredibly small primes, this should be compared to zooms of equivalent IQ and it fares incredibly well in terms of size.
2. Aperture: At this size and IQ I am fine with the non-fixed aperture. If you want fixed aperture, set it to f4 and be happy If you want extreme aperture get FA 43 or A 50 f1.2
3. AF: Slouch? No, but it is slower than the rest of DA lenses. This is not an action lens, it is a lens where you take your time to compose the shot and AF is more of a helping hand so the slower speed doesn't bother me. I did not feel the need for it to be any faster at any point.
4. Zoom: People compare it's size to primes and zoom range to 16-50? Really? I see this lens as a "flexible prime". It gives the handling and IQ of a prime while allowing some flexibility, not much but some when changing lenses is too slow or a very bad idea.

1. Bokeh! This thing is wonderful, the rounded blades definitely do help. In comparison to FA 43 the bokeh of the background tree branches was a bit too nervous, but that is me splitting hairs already.
2. Sharpness. Mine is sharpest at 40mm, almost the same at 30 and a softer at 20mm. At f8 it has more resolution at any focal length than K5 "can handle", when wide open it softens up but only marginally. This thing gives the FA 43 run for its money and I personally think DA SMC 21 is on par with this thing in terms of IQ.
3. Build quality: The metal construction is sweet, it came to me as a surprise that the zoom ring is not metal, its rubber or plastic not sure, but very good quality one. I was not sure about the non-metal ring at first, but then realised that zooming all the time will rub the paint off the zoom ring and this thing will look...not so great. So now I think the non-metal ring is an awesome idea.
4. AF: Ouh, the sweet silence
6. WR: As it is new I am babying this thing, but friend of mine dropped a full cup of coffee over the lens and camera. Result? Wash under the tap and continue the walk Works like nothing happened and all good

1. Quickshift: Even though this lens has quickshift, the focus ring rotates when focusing and sometimes catches my fingers when doing that. Full time clutch like the one on other DA lenses would of been useful.
2. Hood: This thing is there for show and protect the front element. I think I will replace mine with 55-58 step-up ring and de-glassed filter to make a DIY hood and simple clip on cap. Just as useful and no drama when lost. Also makes the lens more wear proof as lens cap is usually first one to wear.
3. Price: This thing is expensive! I got a deal on it 200 off so was worth it, but at 850 it is just simply not worth the money!

In total this is a good addition to the Limited series and worth the money at around 650, not sure at 850 though. Incredible optics in a nice and small body
It's impossible to make a lens that satisfies everyone and every situation and I think comparing the zoom range to 16-50 and size to other Limited's is just non-sense. Zooms are always bigger and this one is small considering it's IQ.
Junior Member

Registered: January, 2013
Location: Texas
Posts: 32
Lens Review Date: March 10, 2014 I can recommend this lens: Yes | Price: $950.00 | Rating: 9 

Pros: Build Quality, Light Weight, Image Quality
Cons: Price, limited range
Sharpness: 9    Aberrations: 9    Bokeh: 9    Autofocus: 9    Handling: 10    Value: 8    New or Used: New    Camera Used: Pentax K30   

Except for the limited zoom range, this lens is very practical: small, light, all-metal, low minimum focusing distance, 49mm filters, very good autofocus and manual focus.

I took only 5 'test' photos with it, the brick house of my neighbor. The results are really excellent, and I don't understand some other reviews:
- I cannot see vignetting!
- Sharpness:
- at 20mm / 2.8: Center 90, Edges 80
- at 20mm / 4.0: Center 100,Edges 90
- at 20mm,5.6: Center 100,Edges 90
- at 40mm/4.0: Center 90,Edges 80
- at 40mm/5.6: Center 100,Edges 90

'100' being near-perfect.

I love it!
Senior Member

Registered: November, 2009
Location: San Jose, CA
Posts: 103

7 users found this helpful
Lens Review Date: February 24, 2014 I can recommend this lens: Yes | Price: $996.00 | Rating: 10 

Pros: light, sharp, great build, WR, zoom range
Cons: lens hood, price
New or Used: New   

For me, this is a great lens. And I may be the only one who actually likes the strange zoom range, but I do. First a little background. I have all the DA limiteds and use them whenever I have the time to play around with composition and enjoy shooting - which mostly means whenever I am by myself. When I go out with group of non-photography friends though, or whenever the weather isn't exactly right, I would end up going out with my 18-135. Which is WR and very small for the zoom range, but slow, not very great optically and no fun to use. It's much more fun to use limited primes (limited in more then one sense), because creativity often comes from that limitation. With 18-135, I just get complacent, zoom from where I stand and shoot.

But 20-40 changes all of that. It's a zoom, but still very limited. It gives me that possibility to go from 20-40 without changing the lens, and it gives me beautiful photos, very much comparable to limited primes.

It also creates beautiful travel kit with other DAs. My goto ultra light travel kit could easily be 15 for wide angle, 20-40 as basic walkaround and WR lens if it starts raining, 70 for short small telephoto. Replace 70 with macro for little extra reach and macro at the price of added weight. Or with 55-300 for real telephoto. Can't ask for much more. See I do like to travel light.

Scared by reviews here, I did some of my testing when I got the lens. It's sharp as sword in the center! And, I do not think there's a significant issue with corner sharpness, at least on my copy. The lens does have, though, a significant field curvature. If you focus the center at the open aperture, corners, especially at the close focus will be very much out of focus. You can focus the corners - then of course center will be out of focus. I believe for this type of lens it's normal behavior and refuse to be bothered by that. It pretty much disappears once you close the aperture enough, it gets much better at distance. Would I take this lens to take pictures of the artwork in the dimly lit gallery? Hell no, but that's not its purpose either. That's what macro lenses are for. Other then that, the lens is perfectly sharp on my K-3.

Some comparisons.

Compared to DA 21
21 pros:
  • tiny (this may actually play big role sometimes)
20-40 pros:
  • better sharpness over the field
  • WR
  • zoom

Compared to DA 40
40 pros:
  • tiny
  • fast @2.8
20-40 pros:
  • WR
  • closer focus
  • zoom

Compared to DA 35 Macro
35 pros:
  • macro
  • uniform sharpness across the field
  • I believe picture quality is a tiny bit better overall
20-40 pros:
  • WR
  • faster focus, especially when macro start hunting

Compared to 18-135
18-135 pros:
  • zoom range
  • price
  • internal focus
20-40 pros:
  • much better optically (it better be for twice the price though)
  • faster
  • lighter
  • parfocal! - this lens is completely parfocal, which allows you to do nice things, like focus on the (40mm) end, then zoom out and the focus stays the same.

New Member

Registered: December, 2013
Posts: 2

1 user found this helpful
Lens Review Date: February 7, 2014 I can recommend this lens: Yes | Price: $996.00 | Rating: 9 

Pros: Sharp,great built, compact, good contrast
Cons: Poor quality control - first sample required RMA exchange, marginally useful lens hood
Sharpness: 9    Aberrations: 9    Bokeh: 10    Autofocus: 8    Handling: 10    Value: 7    New or Used: Used    Camera Used: K-3   

My first copy was badly decentered, with the left side very soft and a weird lack of sharpness at 30mm, f/5.6. BH Photo was very good about making a prompt and hassle-free RMA exchange.

The second copy was noticeably better, with excellent sharpness across entire field at all focal lengths when used between f/5.6 and f/7.1 except for lower right corner at 20mm. Closed down, this lens is very good, but it's not really suitable for dim indoor light due to the need to stop down for best results. A bit of localized sharpening and increased clarity in Lightroom generally solved this problem.

Excellent build, weather-sealing, and compact size/light weight were the deciding factors when compared with the much larger and heavier Sigma 18-35mm, which I might have bought otherwise. It is somewhat sharper than my non-VC Tamron 17-50mm toward the edges, but not by a great margin.

It took some time to determine the best way to use this lens for maximum image quality, but I now find it very suitable for general use. Overall, it's sharper than I expected from the Pentax Forum and DXO reviews.
Senior Member

Registered: July, 2008
Location: montreal
Posts: 136

1 user found this helpful
Lens Review Date: January 16, 2014 I can recommend this lens: Yes | Price: $1,000.00 | Rating: 10 

Pros: small, WR, build quality, IQ
Cons: Some vignetting at 40mm but easily corrected.
Sharpness: 9    Aberrations: 10    Bokeh: 10    Autofocus: 9    Handling: 10    Value: 9    New or Used: New    Camera Used: K-01 and K20D   

I rated it a 10 for me because it does exactely what i wanted from it, that's why i bought it. Sharpness is very good at any focal length and apertures, except at 20mm at f/2.8 in the corners but i don't care. At 40mm there is still some vignetting even at f/13 but it's easily corrected in LR.
I really like it's small size, Limited build quality but with the addition of WR, just perfect !
Add Review of HD Pentax-DA 20-40mm F2.8-4 Limited DC WR Buy the HD Pentax-DA 20-40mm F2.8-4 Limited DC WR

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