Sigma 18-50mm F2.8 vs. Pentax Kit

camperguy01 · 08-17-2007, 07:42 PM

I’ve owned the K100D, kit lens, DA 50-200 and the FA 50 1.4 for about a year now. The 50-200 does well when I need something with a little bit of reach and the 50 1.4 does great for portrait-type shots but I wanted to upgrade from the kit lens to a lens that would give me a little bit sharper images.

After doing quite a bit of research, I decided on picking up the Sigma 18-50mm F2.8 EX DC Macro. My expectation was that I would see a noticeable difference between the Pentax kit lens and the Sigma. But after taking a good number of pics with both lenses at the same settings, environment, etc…I’m not really seeing the difference in sharpness I was hoping to see. I do see a very slight difference with the Sigma but it’s almost not noticeable and in my opinion definitely not worth the $410 I paid for it.

I guess I’m looking for advice. Are my expectations too high? Any advice on how I can perform a more thorough test on each lens to determine the difference in sharpness? Could I have received a bad copy? Unless I can see a noticeable improvement with the Sigma, I’m really considering sending it back.

A few samples listed below. Not great compositions but the purpose is to show the difference between the 2 lenses.

Any help would be much appreciated…….

Pentax Kit Lens 50mm/f9

Sigma 18-50 50mm/f9

Pentax 35mm/f5.6

Sigma 35mm/f5.6

Pentax

Sigma

Pentax

Sigma

Pentax

Sigma

Pentax

Sigma

FotoPete · 08-17-2007, 07:57 PM

The price premium is almost all in the versatility of the F2.8 constant vs. 3.5 to 5.6.

Thanks for the comparison. It certainly is informative!

camperguy01 · 08-17-2007, 08:11 PM

Originally Posted by FotoPete

The price premium is almost all in the versatility of the F2.8 constant vs. 3.5 to 5.6.

Thanks for the comparison. It certainly is informative!

Thanks for the reply.

I've heard some very good things about this Sigma, one of them being that the lens is very sharp. The kit is a decent lens but I don't think most put the kit in the category of "tack sharp".

If the only significant difference is the constant f/2.8, I'm not sure it it's worth it to me to hang on to it. F/2.8, especially for a wide angle is not that important. (for me)....

FotoPete · 08-17-2007, 08:22 PM

You should try out the Tamron 17-50mm/2.8 or the longer 28-75/2.8. They should be able to deliver the resolution kick you were hoping for.

Yea I was really wondering about Sigma lenses. Their MTF charts are really high for all their lenses. Perhaps its the sensors they use to test their lenses.

camperguy01 · 08-17-2007, 08:30 PM

Originally Posted by FotoPete

You should try out the Tamron 17-50mm/2.8 or the longer 28-75/2.8. They should be able to deliver the resolution kick you were hoping for.

Yea I was really wondering about Sigma lenses. Their MTF charts are really high for all their lenses. Perhaps its the sensors they use to test their lenses.

Thanks again Pete.

Yea, sad thing is, I was trying to decide between this Sigma and the Tammy 28-75. May end up swapping in the Sigma.

I'd love the Tamron 17-50mm but I don't think they make it in a Pentax mount.....

Kguru · 08-17-2007, 09:52 PM

You should compare them at f/4 wide end, f/5.6 long end, using a tripod and controlled lighting. Otherwise you've negated the paid-for advantages of the Sigma.

sbmitschke · 08-17-2007, 10:07 PM

Originally Posted by camperguy01

Thanks for the reply.

I've heard some very good things about this Sigma, one of them being that the lens is very sharp. The kit is a decent lens but I don't think most put the kit in the category of "tack sharp".

If the only significant difference is the constant f/2.8, I'm not sure it it's worth it to me to hang on to it. F/2.8, especially for a wide angle is not that important. (for me)....

This was exactly the type of post I was looking for.

Reading the review at photozone.de shows the kit lens to be pretty good at 35-55, even opened up. And, you photos show this.

I'm also looking at getting the lens, but my needs are more for the lower light/indoor photography.

Would it be possible if you could take a few pictures at 18mm at 2.8 (Sigma only) and then 3.5 (Pentax & Sigma) I suspect this is where a difference will be seen.

Any comments on the handling?

-Stephen

raider · 08-17-2007, 10:28 PM

I also debated last time which one to get, whether the sigma 18-50/f2.8 or the tamron 28-75/f2.8. In the end, I decided to get the Tammy since there are so many people who praise the lens for its sharpness and quality. The lens is now on its way and it should be here in 2 weeks or so.

camperguy01 · 08-18-2007, 03:59 AM

Originally Posted by sbmitschke

This was exactly the type of post I was looking for.

Reading the review at photozone.de shows the kit lens to be pretty good at 35-55, even opened up. And, you photos show this.

I'm also looking at getting the lens, but my needs are more for the lower light/indoor photography.

Would it be possible if you could take a few pictures at 18mm at 2.8 (Sigma only) and then 3.5 (Pentax & Sigma) I suspect this is where a difference will be seen.

Any comments on the handling?

-Stephen

Just on my way out the door and will be gone until tomorrow, but when I get back I'll display a few at these settings.

Very nice looking lens. Look, feel, handling is all superb just wish IQ was up there a bit.

camperguy01 · 08-18-2007, 04:03 AM

Originally Posted by raider

I also debated last time which one to get, whether the sigma 18-50/f2.8 or the tamron 28-75/f2.8. In the end, I decided to get the Tammy since there are so many people who praise the lens for its sharpness and quality. The lens is now on its way and it should be here in 2 weeks or so.

From the info. I was gathering, I read the Sigma was similar to the Tamron except with a wider reach, that's why I'm wondering if I have a slightly softer copy. Regardless, IQ is more important to me than the extra width, so there's a pretty good chance I'll be swapping it out for the Tammy.

Hope you enjoy you're new lens. Let us know how it goes.

ChrisA · 08-18-2007, 05:08 AM

Originally Posted by camperguy01

Any advice on how I can perform a more thorough test on each lens to determine the difference in sharpness?

Even assuming that each pair of shots is identically framed and exposed, which in some cases they clearly are not, it's impossible to distinguish anything other than the grossest differences between the sharpness of pictures if you start with a 3000-pixel wide image and reproduce it on a computer monitor at only 800 pixels wide.

If you want to be able to distinguish differences on a computer screen, the differences have to be large compared with the size of a screen pixel. Anything else is a waste of time.

So at the very least, you need to crop identical pieces of the pictures and display them at full size, so that any differences in detail resolution have the best chance of being seen.

camperguy01 · 08-19-2007, 08:36 AM

Originally Posted by sbmitschke

This was exactly the type of post I was looking for.

Reading the review at photozone.de shows the kit lens to be pretty good at 35-55, even opened up. And, you photos show this.

I'm also looking at getting the lens, but my needs are more for the lower light/indoor photography.

Would it be possible if you could take a few pictures at 18mm at 2.8 (Sigma only) and then 3.5 (Pentax & Sigma) I suspect this is where a difference will be seen.

Any comments on the handling?

-Stephen

Focus is in the center of the small red coffee can.

Hope this helps -

Sigma - f/2.8 @ 18mm

Sigma - f/3.5 @ 18mm

Pentax Kit - f/3.5 @ 18mm

sbmitschke · 08-19-2007, 12:07 PM

Originally Posted by camperguy01

Focus is in the center of the small red coffee can.

Hope this helps -

Thanks for the postings. Can you send me the original "hi-rez" jpgs from the camera. I PM'd you with my personal email address.

Also, how did the focusing speed compare in lower light compared to the kit?

-Stephen

Chako · 08-19-2007, 12:25 PM

Sigma's are well known to have a cooler colour cast to their lenses. Your photos show this quite nicely.

to be honest, I much prefer the warmer tones of the Pentax glass. Mind you, you can warm up the Sigma photos quite nicely in post processing.

camperguy01 · 08-19-2007, 02:22 PM

Originally Posted by sbmitschke

Thanks for the postings. Can you send me the original "hi-rez" jpgs from the camera. I PM'd you with my personal email address.

Also, how did the focusing speed compare in lower light compared to the kit?

-Stephen

Sure, jpegs on the way....

Focusing speed is very good. Faster than any other lens I own.