[NeilGratton]

I was looking through the images from my most recent wedding shoot, I took the group shots with the Sigma 17-70mm f/2.8-4. In a large group sharpness is important, to keep the details in the all of the faces when looking closely. At 17mm and f/5.6, I was a bit disappointed with the shots from my siggy zoom.

I've pretty much discounted an upgrade to the Pentax 16-50mm f/2.8 as an alternative - there are too many scare stories of autofocus failures and quality control issues among the amazon reviews and elsewhere.

So, what are the other options?

I'm considering:
Sigma 17-50mm f/2.8 (DXO mark show this as being quite a bit sharper than my 17-70mm)
Pentax 21mm f/3.2 (although - which version to go for? And I hear the distortion is noticeable?)
Sigma 20mm f/1.8
Sigma 18-35mm f/1.8

Any opinions on these - thinking particularly of cross-frame sharpness? Any other suggestions?

---------- Post added 12-10-15 at 09:52 AM ----------

Anyone know if/when the new Sigma 20mm f/1.4 will arrive in Pentax mount?

[Sandy Hancock]

I would use my DA*16-50, with bounced flash if required. The DA21 would be a close second - for this sort of shot it wouldn't matter SMC vs HD.

[Reed]

Check out Samyang/Vivitar/Rokinon/Falcon 14mm/2.8, its manual, but hey-with that angle,set it to F4, and ring to around 1,5m and you have everything from 80cm to infinity in focus. Tack sharp.

[Digitalis]

The Sigma 17-50mm f/2.8 is your best ticket, it is reliable and covers a very useful focal length range, the 21mm f/3.2 would also be a good choice, I would avoid the Sigma 20mm f/1.8 - it's an older lens and a bit long in the tooth for modern Dslrs.

As for the Sigma 18-35mm f/1.8 ART - there are many things I can say about it, Optically it offers performance that is almost unrivaled among APS-C format lenses, it has a small but useful focal length range coupled with a wide aperture that allows for shooting under low light conditions with ease. But that is about as positive as I can be about this lens in all honesty. Ethically I can't recommend it at all, because there are serious issues with this lens - notably its poor AF accuracy. I still have my copy, and I rarely use it, even after the painstaking AF calibrations with the Sigma lens dock hasn't eliminated the problems.

DXO mark show this as being quite a bit sharper than my 17-70mm

My intention is not to be rude, but I would ignore anything DXO says about lenses. Klaus at Photozone, and Roger Cicala at lensrentals offer good quality data and balanced opinions regarding lens performance. Hell, even the folks at fredmiranda have more accurate and balanced views on lenses.

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Last edited by Digitalis; 12-10-2015 at 04:09 AM.

[mikeSF]

you can't go wrong with the DA21 as it is sharp and has good coatings. Either version should be fine (I have the v1).
There is some barrel distortion on this lens but very easily correctable if you are shooting architecture or panos. Otherwise, i leave it alone and hardly notice.

[Sandy Hancock]

P.S. I had the Sigma 17-50/2.8 for a while before I got my DA*16-50. After a spell comparing the two I decided to keep the latter and sell the former, with no regrets despite having to convert the DA* to screw drive.

[jawsy]

despite having to convert the DA* to screw drive.

DA's out of the running then.

[JohnX]

The SDM issues with the 16-50 still get reported, but I'm not sure whether this affects recently manufactured lenses? Unfortunately bad reputation's stick.

Also, just how many people report 'there's nothing wrong. with my...?

The issue also applied to the 50-135. Mine continues to be faultless, which might be due to (a) luck, or (b) the fact that I run each of my SDM lenses for a few minutes once a fortnight, focussing back and forth, whether they've been used in the interim or not, as one common theme with the SDM failures appeared to be failures occurring after periods of non-use.

Also, buy from a Pentax Pro dealer - SRS in Watford for example.

[Alnjpn]

What aperture do you usually shoot at? I have both the Sigma 17-50 2.8 and the Pentax da21 3.2. At wider apertures the Sigma is noticeably sharper than the DA21. At 2.8 the Sigma is really great. The Pentax gets better at around F4-5.6, but any lower than this and you will be disappointed with the sharpness. If size and weight aren't an issue I would go with the Sigma (it is heavy), overall the picture quality and sharpness surpass the Pentax.

If it is just sharpness you are after the Samyang 14mm 2.8 is cheap, wide and very sharp (at 5.6) but it may not be suitable for weddings. It is extremely prone to flair and there is a lot of distortion (it can be corrected). Plus it is manual focus.

[NeilGratton]

What aperture do you usually shoot at? I have both the Sigma 17-50 2.8 and the Pentax da21 3.2. At wider apertures the Sigma is noticeably sharper than the DA21. At 2.8 the Sigma is really great. The Pentax gets better at around F4-5.6, but any lower than this and you will be disappointed with the sharpness. If size and weight aren't an issue I would go with the Sigma (it is heavy), overall the picture quality and sharpness surpass the Pentax.

If it is just sharpness you are after the Samyang 14mm 2.8 is cheap, wide and very sharp (at 5.6) but it may not be suitable for weddings. It is extremely prone to flair and there is a lot of distortion (it can be corrected). Plus it is manual focus.

For the group shots I'm typically at around f/5.6 or f/8 (depending on the set up) to make sure everyone is in focus.

A Sigma 17-50 would replace my 17-70 and would be used at the whole range of apertures. A 21mm would be an additional purchase, though, so it wouldn't have to do everything. 14mm is too wide.

Size and weight can be an issue, as I'm carrying my cameras for up to 10 hours, sometimes longer - usually two bodies at once.

[TER-OR]

I've found the DA21 is quite sharp. Distortion is not bad, it looks "right" for this FL. Lightroom can remove the distortion if you want. It's a fun little lens. It has plenty of contrast and is great for walking around scenic areas.

If you want something super-wide, the Sigma 8-16 is great. At 8mm of course you'll have a lot of distortion, but it's really interesting. Closer to the 16mm end it's more of just an ultra-wide lens. It is a very specialized lens, but you'll probably enjoy it.

[Digitalis]

the Sigma 8-16 is great

Especially when you want to get images like this:

[TER-OR]

Outstanding. that's where the vast panoramic view really pays off.
I presume this is bulb mode?

[Digitalis]

I presume this is bulb mode?

Nope, I'm a bit lazy. I used 30s in manual mode. With bulb mode you often have to stop down too much the lightning isn't bright enough to overcome the constantly shining city lights. Unless the lightning manages to take out every light in the area and become the dominant light source - then bulb should work fine.

[wissink]

I agree about reputation. The 16-50 can be a fantastic lens. The 50-135 the same. I'd say the same applies to the Sigma 18-35. Enough bad apples spoils the name perhaps, but it doesn't mean that there are enough of them out there that live up to its design. I for one haven't had a problem and its been my most used lens for the past few months since I got it.

Sample variation and quality control are certainly factors. There was an article posted here this past week that describes it well. Unfortunately certain lenses fall victim to this in higher percentages despite the ART or DA* or L etc. label indicating that the manufacturer should have been more careful.