[othar]

I don't own any of those two lenses, but I don't think you will see much difference in sharpness between them.
I think you should concentrate more on lens size, weight and zoom range as an criteria for your pick

[Des]

I'm leaning towards the limited, as I think it will provide sharper images.

I don't have the 16-85, but I have the DA 20-40 and a bunch of other sharp lenses. If you want pure corner to corner resolution more than anything else, it's not your best choice. The 20-40 has a lot of field curvature, which can be challenging. I found the humble DA 35mm f2.4 has more resolution (tests by DxOMark will show the same).

The 20-40 is quite sharp enough, but that is not its real charm. As with the DA 15 Limited, the reasons to buy it for its image quality are more subtle: excellent colours, contrast and microcontrast. It also has quite smooth transitions and very pleasant bokeh. (That is aside from its physical properties: compact, beautifully built, HD, WR, 28cm MFD etc.) I rarely use the DA 35 f2.4; I use the 20-40 a lot and love what it does. Not everyone shares this preference - you either like the qualities of the Limiteds (and accept the compromises) or you don't. And for many shots the differences won't be apparent.

Our member @Northcoastgreg has excellent reviews of the 16-85 and DA 21 Limited (amongst others) on his web site. What he says about the 21 is broadly applicable to the 20-40.
HD Pentax DA 21 f3.2 Limited | Reviews | The Northcoast Photographer
Pentax DA 16-85 f3.5-5.6 | Reviews | The Northcoast Photographer

Some samples with the 20-40:
23mm f.3.2


30mm f11


40mm f4


40mm f8

[DWS1]

Depends on the landscape. For me it mostly the 16-85. However, my most used lens on a trip to Yellowstone was the 55-300plm. There the landscape is so huge you have to zoom in to get any detail at all.

[carlb]

I have both of them and they're fine lenses. I think I'd go for the 16-85 just for that extra versatility at both ends of the focal length range.

[tranq78]

Go 16-85. You are going to find 20mm isn't wide enough sometimes and 40mm isn't long enough sometimes.

[MadBill]

To paraphrase Ansel Adams, the best lens for landscape photography is the heaviest (and most expense) one you are willing to carry.

[Alex Zhang]

I chose the 20-40 for three reasons:
1. It's more compact and light.
2. Rendering is more prime like.
3. With rear baffle modified, it can be use on my K1 as an 21-40mm zoom.

It all comes down to personal preferences.

[Ronald Oakes]

Since I have both lenses I'm going to make this a lot easier for you!
Buy either one as they're both excellent lenses. One thing that stands out in my mind is the 16-85 is actually a quite large lens compared with the 20-40 limited.
However if I could only have one it would be the 20-40 limited.....No wait....maybe the 16-85 ?No....for sure the 20-40 .... unless...well....hmmm.
Hope this helps.

[Gopersuel]

In this case, I would prefer to use the 16-85 mm, as it is more versatile, it would give you more play for landscape, portrait etc.

[Bertrand3000]

I know I already answered on this thread, advising the 16-85, but I thought about two other things :

1) Usually the 20-40 is somewhat more costly than the 16-85, economically, getting the former would be a better deal
2) The 20-40 is light, perfectly paired with the KP while the 16-85 is bulky ; you will need the L grip for the KP

That said, if you have to choose only one, I still stand for the 16-85 with the KP, like I did when I was in your place two months ago. It's the most versatile lens, and sharpness is comparable. Besides, ability to zoom up to 5 times is invaluable when outdoors. I really love the wide part (16mm), but I wish I could zoom even further than 85mm, even if it is enough most of the times. 18-135 could have been an option for me, but it's not as wide, and perhaps a bit less sharp.

[aslyfox]

To paraphrase Ansel Adams, the best lens for landscape photography is the heaviest (and most expense) one you are willing to carry.

or have carried by your pack animal if you have one

I've always been told, you bought it, you carry it

_____________________________


seriously, I'm a traditionalist

a Pentax Limited lens will always be a prime

yes I am narrow minded as well as dumb

I also like my 16-85 zoom

[jddwoods]

I can't speak for the 20-40 Limited but I have the SMC 15, 21, 35 macro, 70 and HD 40 Limiteds. I also have the 16-85. For landscape photography I would definitely lean to the 16-85. Based on my 21 limited I would find 20 - 40 a bit too restricted on the wide end. If I had the 20 - 40 I would certainly see the need for also having the 15 Limited too. I acquired the 16 -85 well after I completed my collection of Limited primes. Had I had the 16-85 first, I would not have needed or bought the 15 limited. Regarding sharpness, I cannot see any situation where the 16 - 85 is less sharp than the primes on my 4K iMac computer, even with cropping. I definitely see the limiteds as a better choice for urban street shooting due to their compactness, and when traveling light is a priority, but I find myself using the 16 - 85 as my go to lens for outdoor & landscape photography.

[3by2]

If I had the 20 - 40 I would certainly see the need for also having the 15 Limited too

This is exactly what I've done but I'm happy with that. I think the post Des made above sums up why you might choose the Ltd over the 16-85. With the Ltd's you're buying into a certain form, philosophy and style and for me that's part of the appeal. If you're more practically minded then the 16-85 is probably the better choice. Not that you can't have a foot in both camps mind.

The 20-40 will do landscapes though. Or seascapes

[sergysergy]

16mm vs 20mm makes a bit difference if you want to go wide.

[northcoastgreg]

What he says about the 21 is broadly applicable to the 20-40.

If that is true, if the DA 20-40 performs pretty much like the DA 21 (particularly at apertures generally used in landscape photography), then I'd expect it to be slightly better than the DA 16-85. I'm not talking here about "sharpness," which is probably a wash (or perhaps better toward the edges and corners with the DA 16-85). What the limiteds give you is slightly richer color, a bit more contrast and clarity, and perhaps slightly more realistic rendering of detail (i.e., the "smooth but precise" rendering). But the DA 16-85, especially in the 20 to 40 range, really is quite good in those respects as well, so these differences are subtle, and won't necessarily be obvious. I bought both the DA 21 and DA 35 Ltds after I had the DA 16-85, and I did so to get little extra image quality, which is all they provide. They are also a little easier to work with because of their smaller size, but the downside is you lose focal range variety. The DA 20-40 gives you more versatility, but not as much, obviously, as the DA 16-85. If you already have one of the wide angle zooms, along with the DA 55-300 PLM, you can get away with the DA 20-40 as your standard zoom for landscapes. If however you're looking for a one lens solution, the DA 16-85 is the obvious choice.

Here are a few images with the DA 16-85: