[gump]

If anyone tells my wife about this thread you are off my christmas card list. I am proceeding from an assumption that the Sigma 17-50 or the Pentax 20-40 will be an improvement of the DAL 18-55 kit lens. Both lens do very well in reviews. The Pentax is WR, a feature I like and the Sigma is less expensive, a feature I love. I am patient and wait for a deal. I have a hunch I would be happy with either lens. Any further insights?

[Serkevan]

Yes: you know the saying "it's easier to ask for forgiveness than for permission"?
Does not apply to significant others.

Jokes aside, I have used the Tamron 17-50/2.8 (which seems pretty similar to the Sigma in terms of performance); I can confirm it stomps the 18-55 optically, but it's larger, heavier and not WR. I haven't had the pleasure of trying the 20-40, unfortunately.

[veato]

Have you considered the Pentax 16-85? It's both wider and longer than both of your choices, priced inbetween both and, despite being slower at f3.5-5.6, it's a great lens.

[stevebrot]

One might also want to throw the Sigma 17-70/2.8-4.0 (C) into the mix. It is often competitively priced and has worked well for me as my walk-around, does-most-things-well zoom.


Steve

[gump]

Have you considered the Pentax 16-85? It's both wider and longer than both of your choices, priced inbetween both and, despite being slower at f3.5-5.6, it's a great lens.

My planning, such as it is, was not to duplicate my 16mm prime and 55-300 PLM. I can see that some overlap might mean getting the shot you missed trying to do the quick lens change dance.. I certainly will look at all suggestions. I rely heavily if not completely on the reviews on PF, with sharpness and overall being the priority numbers. Not sure if i am sophisticated enough to be concerned with the difference between 9.0 and 9.3.

---------- Post added 11-27-19 at 11:04 AM ----------

Yes: you know the saying "it's easier to ask for forgiveness than for permission"?
Does not apply to significant others.

Jokes aside, I have used the Tamron 17-50/2.8 (which seems pretty similar to the Sigma in terms of performance); I can confirm it stomps the 18-55 optically, but it's larger, heavier and not WR. I haven't had the pleasure of trying the 20-40, unfortunately.

Thanks for your counsel. For some unknown reason I found the Tamron just before i checked back here. You saved me the trouble. It is certainly comparable in review,

[AstroDave]

I'll put in a vote for the Sigma 17-50. This was my walk-around lens (replacing my Pentax 16-50) until I got the Pentax 18-135, which now lives on my K-3. I think you will find that any of these performs much better than the kit 18-55. I feel the Sigma is a bit sharper than the Pentax 16-50, and definitely focuses much faster.

I can't compare with the 20-40, though, since I've never tried it.

[c.a.m]

Any further insights?

I acquired a 20-40mm Limited earlier this year, after considerable research and deliberation. I scoured many online sites and forums for reviews, comments, comparisons, sample images, and specifications. These two Sigma and Pentax lenses are often compared in the 'wide angle to short telephoto' class.

I also have a Pentax DA 18-135, which is a good lens but quite a few of my images seemed somewhat 'flat' to me. I considered the Sigma 17-50, Pentax 16-85, Pentax DFA 28-105, and the 20-40 Limited. My short list arrived at the Sigma and the 20-40.

In case you're interested, here are my summary notes concerning the two lenses. Some of the points are subjective on my part, while others are simply captured from what I read of others' experiences.

At the time of my purchase, the Sigma was selling for CAD $500 while the 20-40 was $730.

I have been very pleased with my 20-40.

- Craig

Notes taken from online forums, reviews, and sample images

Sigma 17-50 f/2.8

Pros
• Covers good FL range
• Constant f/2.8
• Generally positive reviews
• Sharp; slightly softer at long end
• Better IQ than DA 18-135
• Low field curvature
• Low price
• “Better value” than DA 20-40?

Cons
• Not WR
• Relatively large and heavy
• Report of poor landscape use (‘mushy’?)

Remarks
• Less ‘character’ than DA 20-40?


Pentax HD Pentax-DA 20-40mm f/2.8-4 Limited

Pros
• Smallest and lightest
• Superb build
• WR
• f/2.8 at wide end
• More flexible than 21/35/43
• Similar IQ to DA Ltd primes
• HD coating
• Suitable for indoors
• Doesn’t draw in much air when zooming
• 'Enjoyable to use'
• Fairly sharp wide open across its range
• Superb flare resistance
• Decent for close-ups
• Better walk-around indoor lens than DA 18-135 or 16-85
• Filter 55 mm
• Better colour and contrast
• Shorter MFD: 28 cm; 18-135 40 cm; 16-85 35 cm.

Cons
• Possible field curvature at long end (distant subjects) (manageable?)
• Relatively expensive
• Narrow FL range
• Minimum FL 20mm; not as wide as other options
• Vignetting at 40mm
• Some edge softness wide open
• Lens cap prone to falling off
• Noticeable distortion at wide end (can be corrected in PP)

Remarks
• Pair with 50-135 for two-lens kit
• Pair with DA 15 for wider angle
• Compact, higher-quality
• Nicer bokeh than DA 18-135.
• Sharper than 18-135
• Very resistant to flare
• '3D character'
• “handles like a prime”
• “sweet shooting experience”
• Lightweight travel lens
• For wider shots, could stitch 2-3 shots at 20 mm
• Similar to DA 21 Ltd in colours and rendition

---

Last edited by c.a.m; 11-27-2019 at 12:44 PM.

[gump]

I acquired a 20-40mm Limited earlier this year, after considerable research and deliberation. I scoured many online sites and forums for reviews, comments, comparisons, sample images, and specifications.

I also have a Pentax DA 18-135, which is a good lens but quite a few of my images seemed somewhat 'flat' to me. I considered the Sigma 17-50, Pentax 16-85, Pentax DFA 28-105, and the 20-40 Limited. My short list arrived at the Sigma and the 20-40.

In case you're interested, here are my summary notes concerning the two lenses. Some of the points are subjective on my part, while others are simply captured from what I read of others' experiences.

I have been very pleased with my 20-40.

- Craig


Sigma 17-50 f/2.8

Pros
• Covers good FL range
• Constant f/2.8
• Generally positive reviews
• Sharp; slightly softer at long end
• Better IQ than DA 18-135
• Low field curvature
• Low price
• “Better value” than DA 20-40?

Cons
• Not WR
• Relatively large and heavy
• Report of poor landscape use (‘mushy’?)

Remarks
• Less ‘character’ than DA 20-40?


Pentax HD Pentax-DA 20-40mm f/2.8-4 Limited

Pros
• Smallest and lightest
• Superb build
• WR
• f/2.8 at wide end
• More flexible than 21/35/43
• Similar IQ to DA Ltd primes
• HD coating
• Suitable for indoors
• Doesn’t draw in much air when zooming
• 'Enjoyable to use'
• Fairly sharp wide open across its range
• Superb flare resistance
• Decent for close-ups
• Better walk-around indoor lens than DA 18-135 or 16-85
• Filter 55 mm
• Better colour and contrast
• Shorter MFD: 28 cm; 18-135 40 cm; 16-85 35 cm.

Cons
• Possible field curvature at long end (distant subjects) (manageable?)
• Relatively expensive
• Narrow FL range
• Minimum FL 20mm; not as wide as other options
• Vignetting at 40mm
• Some edge softness wide open
• Lens cap prone to falling off
• Noticeable distortion at wide end (can be corrected in PP)

Remarks
• Pair with 50-135 for two-lens kit
• Pair with DA 15 for wider angle
• Compact, higher-quality
• Nicer bokeh than DA 18-135.
• Sharper than 18-135
• Very resistant to flare
• '3D character'
• “handles like a prime”
• “sweet shooting experience”
• Lightweight travel lens
• For wider shots, could stitch 2-3 shots at 20 mm
• Similar to DA 21 Ltd in colours and rendition

C.A.M.,

Another thing i like is when someone does the work for me. Your research/tests confirms many of the generalities in my thinking. Thanks for taking the time to write the response.

[mlt]

One other plus for the 20-40, it is relatively usable on full frame K-1.

[Wingincamera]

I have two of the lens that are mentioned here, the DA20-40 and 18-135mm. I very seldom use the 18-135 anymore, unless it's an event where I know I will not be able to change lens and will need the zoom capability.
The 20-40 I have mixed feelings about. I like the range of it and the F2.8 is handy at times, But I have problems getting sharp focus keepers at times, especially at the longer end and lower light situations. Don't get me wrong, it can be very sharp, but not always. This might be operator error. My DA35 & 15 and one of my 50's fills in pretty good.

[ramseybuckeye]

I have the 18-135, a good lens, but I also bought the Sigma 17-50 some time ago, as it is faster and supposed to have better IQ than the 18-135. I used the Sigma quite a bit when I didn't need extra length or weather resistance. In August I bought the 20-40 because I wanted a faster short zoom with WR, specifically as I was going to travel to London in October, I knew there would be a lot of rain, I wanted something fast, weatherized, and on the small side. Shortly after getting the 20-40 I sold the Sigma. Although it has a smaller zoom range, I feel it outperforms the Sigma. Even though it has a variable aperture, the 20-40 seems pretty sharp wide open, the Sigma needed to be stopped down some. I'm not saying the Sigma was bad, it's a good lens, but I prefer the 20-40 and I know I would not use the Sigma anymore. Currently my most used lens are the 55-300 PLM, 20-40, and 15 Ltd, with the DA* 300 right behind. That cover most of my shooting. And yes, both lenses you asked about are big upgrades from the kit lens.

[mikesbike]

I have both the Sigma 17-50mm f/2.8 EX DC HSM and the Pentax DA HD 20-40mm f/2.8-4 Limited. I use the Limited probably more often due to its fine IQ, lightweight but excellent build and WR, smaller size, great on my compact KP. I like it for general use, and when doing a lot of hiking or biking, shooting scenics, due to its lighter weight and fine performance.

But I still often choose to take out my Sigma lens instead. It is not a huge or real heavy lens, but it is definitely heavier and more bulky than my Limited zoom lens. After all, it is a pro-level, fast-aperture constant f/2.8 capable zoom lens. It does have significantly greater zoom range. You'd have a greater choice of focal length, either much wider angle or significantly more reach. If you want to grab a quick portrait, for instance, it would be a much better choice. Nothing like having f/2.8 when it is needed for low light and/or moving subjects for higher shutter speed, and for reducing depth-of-field to blur background more to make your subject stand out from it as needed. Brighter viewing in the VF too. If I had to choose between the two, this lens can do more under a greater variety of conditions. It provides excellent sharpness, virtually absent field curvature- very rare for a zoom lens in this range, very good AF, and very good build quality. You would not be disappointed.

It couples very well with the excellent DA* 50-135mm f/2.8 tele zoom- which does also feature WR construction, for a pro-style constant aperture f/2.8 capability 2-lens combo. (although I do also sometimes couple my 20-40mm LTD with it as an alternative, for conserving carrying weight when I don't need the f/2.8 all the way through or the wider angle)

I've found both lenses are sharp, pretty much so even wide open. But lenses are not generally at their best wide open particularly at edges of frame. I think the Sigma is a little better here, still good at edges but reduced just in corners (wide open aperture), while the Limited lens is likewise good centrally wide open but not so good at edges as is the Sigma. Also, except at 20mm, the aperture wide open for the Limited would be a stopped-down aperture for the Sigma. f/4 at 40mm is wide open for the Limited, but is stopped down by a whole stop for the Sigma, where its performance will be increased. At 40mm the Sigma lens can deliver twice the shutter speed at f/2.8 aperture, over the Limited lens's f/4 under the same lighting conditions and ISO setting.

If your old kit lens is of the WR variety, that could still be retained for times when that is a concern.

[timb64]

+ another one for considering the 16-85 in the mix.

BTW What body are you using?

[gump]

+ another one for considering the 16-85 in the mix.

BTW What body are you using?

Sorry for the omission. K-70.

[dcpropilot]

I have excellent copies of both the Sigma 17-50 and the DA 20-40. Both great lenses. I'd say for portability and WR, the 20-40 can't be beat. For lower light and constant 2.8, while also having excellent sharpness, the Sigma is worthy of being on the K-3.