Pentax 18-50 replacement

ahelg · Mar 6, 2009

I'm thinking about replacing the kit lens that I got with my Pentax K200D. Unfortunately the shop mixed up the lenses and gave me a 18-50 instead of the 18-50 II lens. Not really sure if there is all that much difference but it is a bit annoying. They went bust so I can't really do anything about it anymore.

Anyway, I've been looking around and I like the look of the Sigma 18-50 f/2.8 lens. I've even seen a comparison between this lens and the Pentax 16-50 f/2.8 which costs almost twice as much as the Sigma, and the reviewer thought the Sigma outperformed the Pentax lens, despite the price difference. Does anyone have this lens. Any comments on it. Most reviews seem to be to hung up on lab tests without actually taking it out for real world tests.

Johnboy2978 · Mar 6, 2009

you might also look at the sigma ex 24-70mm. It's about $430 new, but a pretty decent lens. I have one and use it alot. I also really enjoy the 50mm prime lens f/1.4 at around $200. While you don't have the zoom feature, it's a helluva nice lens for the price.

Tolyk · Mar 6, 2009

I've used the 16-50 2.8 Pentax glass and I have to say, it's amazing. No way the Sigma is better. Not only is the Pentax one 100% sealed, it's Pentax glass!!! It's awesome stuff. I've not used the Sigma, but I'll try it out when I'm at work tomorrow and let you know for sure, but pretty damn sure the 16-50 is significantly better.

ahelg · Mar 7, 2009

Just a minor correction. The lens that I want to replace is 18-55 not 18-50.

[Edit] I've just had my camera on a tripod in the backyard taking the same picture at f/5.6, f/8, f/11, f/16, f/22 and f/38. The camera was at 55mm and focused at infinity at an object aprox 100 m away. The first thing I noticed was that the image was no where near sharp at f/16, f/22 and f/38. The others though were nice and sharp, the best being at f/11.

Now this is one of the reasons I want to get a better lens than the kit lens. I would appreciate more consistent sharpness than this, and at the same time f/2.8 would be awesome. My lens is a 3.5-5.6 lens. The ability to use f/2.8 throughout the lens would be a great plus as I often have to boost the ISO up to 400 to be able to cope in these gray winters we have in Oslo. Also, the K200D isn't the best camera for high ISO. Even at ISO 400 the grain becomes very evident. I would love to have a K20D, but I don't want to upgrade yet. I'd rather invest in some good lenses at this time. I'll probably wait for the K40D which I expect we'll see in about 3 years time.

Here is a link to the lens I am considering. Even if the Pentax is better, this is still a much nicer price

http://www.sigma-photo.co.jp/english/news/18_50_28_dc_macro.htm

RyanLilly · Mar 7, 2009

It's not the lens causing the the lack of sharpness at smaller apertures, it actually diffraction, and it will be same same will all lenses. Now the pentax 16-50 2.8 and the sigma 18-50, are certainly much higher quality lenses, but the lack of sharpness will still remain similar at small apertures. The big advantage to these lenses comes from being faster and also very sharp wide open.

Also consider the Tamron 17-50 2.8, I ended up going for the Tamron over the Sigma, but they each have their slight advantages.

Tolyk · Mar 7, 2009

I didn't get the chance to test out the 18-50 sigma today, was crazy busy. However, seems you're pretty set on the Sigma anyway, so won't bother.

ahelg · Mar 7, 2009

Not completely set on the Sigma, but the Pentax one that we've been talking about it just to expensive for me.

I'm also tempted by the limited lenses, more specifically the 40mm limited lens. Heard great things about it and the price is something I'd be able to live with.

While browsing reviews of the sigma I've now come accross a few negative ones that seem to mention things that weren't brought up in the other reviews I've read, so I'll have to look more into it now. It's still three weeks until the army pays me, so plenty of time to look around.

ahelg · Mar 7, 2009

RyanLilly said:
It's not the lens causing the the lack of sharpness at smaller apertures, it actually diffraction, and it will be same same will all lenses. Now the pentax 16-50 2.8 and the sigma 18-50, are certainly much higher quality lenses, but the lack of sharpness will still remain similar at small apertures. The big advantage to these lenses comes from being faster and also very sharp wide open.

Also consider the Tamron 17-50 2.8, I ended up going for the Tamron over the Sigma, but they each have their slight advantages.

That's good to know. I was under the impression that more of the image would be sharp if I used small apertures. As far as I can tell from the pictures I've been looking at, f/11 seems to be giving the best result. So I guess if I'm photographing and I want a long exposure, I should consider an ND filter if the aperture gets much smaller than f/11 if I want to keep it as sharp as possible?