[panoguy]

If focus accuracy, size, Wr and Pentax character are important to you get the Da 20-40. If you shoot starry skies get the 18-35, its exhibits the lowest aberration and coma of the modern lenses.

I always assume the lens designers at Pentax and Sigma know more about the compromises they are making than I do, so I'm sure the differences are as simple as you state it. What may be pushing me over to the 20-40 (aside from Blackcloudbrew's lenspr0n) is the size and weight. The Sigma is a hefty lens!

Thins one's actually easy. You already have the 18-35, although on a different system. If you get the urge to shoot with that lens, just shoot the Foveon. Get the 20-40 so at least you have something new and different.

You've never shot with a Sigma camera, have you? The reason I'm getting into this focal range for Pentax is because the SD1 Merrill produces wonderful shots of brightly lit, totally static objects, and takes 15 seconds to recover after each shutter press. A rather zen experience, but the K-3 is much more fluid and forgiving.

[klh]

I wish I had the Sigma to compare with the DA 20-40 but I don't. However, I'm loving my new DA 20-40 (in silver to match my K3).

That is pretty! But please stop tempting me.

[percy]

The DA 20-40 although slower has a higher t-stop value (than conventional lenses) meaning you can bump the ISO higher before noise becomes an issue. For all practical purposes its a constant f2.8 lens

I'll have to read up a bit more on t-stops . . . . . . something I'm aware of without ever having gone into it in much detail

Pentax glass has the notoriety because they don't skimp on quality, and although the Sigma Art series lenses have improved dramatically I feel they're still shy of the Pentax products. The HD coating alone is worth the price of admission IMO.

Without a doubt the Pentax Limited lenses really do feel like (and are) a well engineered and quality item . . . . . . a pleasure to use.

[Dice]

Lots of good thoughts already. I bought my DA ltd zoom in 2013. The main things that kept me from waiting for the 18-35 to come out in PK were size, weight and lack of WR. Like you I had the the limiteds that cover the DA ltd. zoom range and was tired of switching back and forth + concerns about taking them out in the rain/elements. I held onto the 35 ltd. for about a month or so after I bought the zoom because I didn't expect the ltd. zoom to be able to produce images in comparison. In the end, I let the 35 ltd. go and haven't looked back. I think only you can decide which features and limitations will help or hold you back respectively. In the end, I've seen excellent images from both so I don't think you can go wrong.

[panoguy]

Ugh! No camera stores, in this, the largest city in Canada, have the 20-40 stocked at any of their locations to even be able to judge its size next to my SA 18-35. And the usual spring photo expo is cancelled this year, so no heading to the Pentax booth!

Anyone in Toronto have this lens?

[Stavri]

Ugh! No camera stores, in this, the largest city in Canada, have the 20-40 stocked at any of their locations to even be able to judge its size next to my SA 18-35. And the usual spring photo expo is cancelled this year, so no heading to the Pentax booth!

Anyone in Toronto have this lens?

I take it all back, the DA 20-40 sucks, just buy my Art 18-35/f1.8

[panoguy]

I take it all back, the DA 20-40 sucks, just buy my Art 18-35/f1.8

Unless you want a K-3 II in trade, I might make you an offer. At least I know what I'll be getting in the box!

[rrstuff]

My heart says 20-40 and the head says 18-35. If you have a chance, pick up the 18-35 and play with it a little. It's a bit of a heavy lens.

[yorik]

Ugh! No camera stores, in this, the largest city in Canada, have the 20-40 stocked at any of their locations to even be able to judge its size next to my SA 18-35. And the usual spring photo expo is cancelled this year, so no heading to the Pentax booth!

I'm not in Toronto and don't have the lens... and apparently neither do the nice people at "camerasize.com". But, for what it's worth here is a picture of the K3+18-35 next to the K3+FA31. The 31 is the same length as the 20-40, a little bit svelter, but heavier....

Signed: `living vicariously through people who are actually buying the lenses I covet'

[Stagnant]

I don't have 20 - 40, but I own Sigma 18-35 and since the pruchase last July it is my most used lens. I don't give a damn about the size and weight of the gear as long as it performs well.

Pros of Sigma 18 - 35

* Constant f1.8
* Wider than the Limited zoom at 18 mm
* Uniform sharpness across the frame at all focal lengths.
* Very sharp starting from f1.8
* Well built
* Excelllent sharpness paired with K-3's sensor allow for some extreme cropping.

Cons.

* The focusing can be quirky. Strangely enough at this point the lens focusing is almost perfect as opposed to the moment of purchase.

[ClickMe!]

Easy peasy, the DA 20-40. Positively Pentax!

[bdery]

The question would be better answered by yourself, I think

You already own the 18-35 on another mount. Do you want to duplicate the performances it gives you in Pentax mount? Is it important to you?

Do you value more aperture or size and WR? for traveling I'd say the choice is pretty obvious, for walking around your hometown less so.

I'd strongly favor the 20-40 myself (and would own it if it produced starbursts like the DA21 does) but my own reasons are not yours.

either way you'll get good images.

I'll have to read up a bit more on t-stops

Here

https://www.pentaxforums.com/articles/photo-articles/t-stop-vs-f-stop-in-a-camera-lens.html

[yorik]

Here

T-stop vs. F-stop In a Camera Lens - Articles and Tips | PentaxForums.com

Do you know of a reliable resource that provides the T-stops of existing lenses?

[Stavri]

DxO measures transmission of its lenses, don't have a comprehensive list but will let you compare specs between lenses on a given sensor including transmission (in stops) I couldn't get the comparison tool to work so I put the lenses in columns (sigma is third as measured on the Canon sensor, the only available) The Da 20-40 is a vari-focal lens thus making it harder to estimate the t-stop as opposed to a fixed focal zoom. The DA* 55 has a loss of 0.3 (t-stop minus f-stop), From this graph it looks like the Sigma Art 18-35 has a perfect transmittance (t-stop = f-stop) with no loss of light which is a theoretically impossible but hey...maybe it's so good is negligible.

[yorik]

Thanks!