[BigDave]

Just some background info. I'm an photo enthusiast, not a pro or semi-pro. I take picture for the enjoyment of the process and outcome, I don't make prints of my photo's. I shoot with a Pentax K=5iis and will migrate to a K-3ii sometime in the future. I have a ancient film KX if I ever want to shoot full frame and have several nice ff lenses. I enjoy shooting manual lenses but I also shoot af, typically at longer focal length. My current widest lenses are the FA 28-105mm, K 30 and M 35-70mm. I shoot primariily landscape, portrait and wildlife. I'm finding my current lot of lenses are not wode enough in many situations. Finally, I like nice lenses.

So, the question is: What wide angle should I acquire? I'm considering the following:

1. Sigma 17-50mm f2.8
2. Pentax HD 20-40mm f2.8-4 lmited
3. HD Pentax-DA 21mm F3.2 Limited

Which one should I add and why? Am I missing anything?

You mention 3 lenses, but two are wide to normal even telephoto on the K-5 and K-3 (17-55 and 20-40). If you are looking for W/A, then maybe stay there. Sagitta's recommendation of the Sigma 10-20 3.5 is a good one. I have this lens and LOVE it! The constant aperture is a must and the lens is very sharp. It is a rectilinear W/A too, so it distorts much less than a curvilinear (fisheye) or not at all, great for landscapes and architecture. An added benefit, I bought it for my K-7 and after getting the K-1 tried it, and it works great from 20 to about 15mm! FYI, Borrowlens.com has some of the Pentax wide angle lenses you can rent for a decent price. Play before you pay!

[chrisfer]

My best lens for landscape are the 20-40mm and the 15mm, superb rendering, very pleasant to use.

I have had a 17-50, 12-24 but I really prefer 15 and 20-40mm, principaly for size and construction quality.

I have tryed three 20-40mm before I have one without issue...

[kh1234567890]

So, the question is: What wide angle should I acquire? I'm considering the following:

1. Sigma 17-50mm f2.8
2. Pentax HD 20-40mm f2.8-4 lmited
3. HD Pentax-DA 21mm F3.2 Limited

Which one should I add and why? Am I missing anything?

I can comment only on the DA21 - I find it an excellent little allrounder lens - Flickriver: kh1234567890's photos tagged with da21. The DA15 is a bit more of an acquired taste, as is a fisheye.

As for zooms, I have the DA16-45 - Flickriver: kh1234567890's photos tagged with smcpda1645mmf40edal and I'm very happy with it.

15 or 16mm is about as wide as I'd want to go with APS-C, even at that focal length the corner distortion of the rectilinears becomes quite noticeable and annoying after a while, IMO. And you don't really need very wide aperture with ultra-wides, especially for landscape shots.

[Sandy Hancock]

I'm a big fan of the DA21. It is tiny and sharp, and produces lovely colours with flare resistance and starbursts comparable to the DA15. It is one of very few crop lenses I will never part with.
It's more of a landscape lens though - the barrel distortion is not ideal for architecture.

My copy of the HD20-40 was very poor at the wider focal lengths, but others have had more positive experiences.

I have owned a Sigma 17-50/2.8, and before that a 17-70/2.8-4. Both were fine lenses, but they won't give you the magic a limited prime can produce.

[WPRESTO]

Today (Oct 8) there are two Sigma 10~20mm for sale in the Marketplace - one for $325, the other for $239. This is an excellent ultra-wide zoom at a bargain price. I would strongly recommend you pop for one of them.

[onlineflyer]

Today (Oct 8) there are two Sigma 10~20mm for sale in the Marketplace - one for $325, the other for $239. This is an excellent ultra-wide zoom at a bargain price. I would strongly recommend you pop for one of them.

Good pricing but I'm looking to get something faster than f4.5.

[UncleVanya]

Good pricing but I'm looking to get something faster than f4.5.

Typically wide angles are used at f8 for landscapes. What is the reason for the fast aperture in your use case?

[cali92rs]

I personally rarely use ultrawides (15mm and wider in APS-C) for landscapes, i use them to exaggerate perspective, and in this case it can be useful to have a fast aperture for shooting in less than optimal light, like indoors.

[UncleVanya]

I personally rarely use ultrawides (15mm and wider in APS-C) for landscapes, i use them to exaggerate perspective, and in this case it can be useful to have a fast aperture for shooting in less than optimal light, like indoors.

Ahhhh!

[SpecialK]

The Pentax 12-24 will fit nicely, covering the range below 28-105. Also it's really better optically vs the other zooms in the range at least.

Yep. The 12-24 is very versatile, and the other lenses mentioned by the OP are not particularly wide.

[Sagitta]

Good pricing but I'm looking to get something faster than f4.5.

One thing to remember about when you go ultrawide is the need for faster apertures drops.

The only reason to pop for a fast UWA (and the selection is very limited) would be for something like astrophotography or perhaps action shots (in which case an UWA seems a bit of an odd choice).

All of these were shot with the Sigma 10-20 f/3.5 constant aperture lens. I bought it for astrophotography mostly, but I've wound up using it for much, much more.

Handheld, 1/6 of a second@ISO6400


Handheld - not sure the speed, but it was slow.


Handheld, 1/20 of a second

[onlineflyer]

For some reason, I had it in my head the Sigma is a f4.5, although it was shown as a f3.5 by several contribuors to this thread. Guess my reading comprehension is wanting. I'll have to do more research on the Sigma 10-20mm f3.5. Looks like it might be a good recomendation.

[UncleVanya]

Two different but similar lenses. The large lens with HSM silent focus is a constant f3.5

Sigma 10-20mm F3.5 EX DC HSM Lens Reviews - Sigma Lenses - Pentax Lens Review Database



The smaller lens which is supposedly sharper is f4-5.6 and smaller.

Sigma 10-20mm F4-5.6 EX DC J Lens Reviews - Sigma Lenses - Pentax Lens Review Database

My understanding is that the smaller screwdrive lens is the only one still made but that could be hearsay.

[KC0PET]

Two different but similar lenses. The large lens with HSM silent focus is a constant f3.5

Sigma 10-20mm F3.5 EX DC HSM Lens Reviews - Sigma Lenses - Pentax Lens Review Database

The smaller lens which is supposedly sharper is f4-5.6 and smaller.

Sigma 10-20mm F4-5.6 EX DC J Lens Reviews - Sigma Lenses - Pentax Lens Review Database

My understanding is that the smaller screwdrive lens is the only one still made but that could be hearsay.

The f/3.5 HSM lens can still be bought new. Here is an offering from B & H. Sigma 10-20mm f/3.5 EX DC HSM Autofocus Zoom Lens 202109 B&H

[Cthulhugan]

Ultra-wides are specialist lenses. As others have noted they are less useful for landscape, and are best suited for perspective exaggeration and "close quarters" shooting, where you can't back up, and can't stitch due to motion or parralax issues. If that is what you need, then the Sigma 10-20/3.5 is an excellent choice, especially if you shoot in bad light. I have the 8-16, and find myself wishing for that extra stop when shooting indoors.