[Edgar_in_Indy]

Outside it seems to underexpose while wide open judging by the light meter if the sky is in the shot, other than that yeah, where it is darker I get overexposure. I can compensate for it pretty easily though. I simply have to learn the lens.

Could the vignetting have anything to do with it? What type of metering are you using?

[VoiceOfReason]

Could the vignetting have anything to do with it? What type of metering are you using?

I'm only using the in camera metering. I didn't think to check on on vignetting. I didn't notice much if any of that.

One other thing I really like about it is how fast it is to focus, and it doesn't seem to hunt, even on my K5. It will lock on to things I don't want it to, but that's just the K5 classic way of doing things, so I always know to refocus. Another thing I like is that the lens stays exactly the same size no matter where you have it zoomed to.

It has to have the tightest lens hood ever, which is why they put the grippy surface on it.

My only thing is I definitely need a slight focus adjustment on it. I need to look up a tutorial on how to do it.

[Edgar_in_Indy]

I'm only using the in camera metering. I didn't think to check on on vignetting. I didn't notice much if any of that.

Most cameras offer three basic metering modes. 1) Matrix-metering, where it looks at the entire frame to judge exposures, 2) Center-weighted, where it still looks at the entire frame, but gives more weight to the center of the frame, and 3) Spot-metering, where exposure is set based on a single spot.

If you use any automatic exposure modes (Auto, Aperture priority, Shutter priority, etc), then it's important to understand how the various metering modes work and effect your pictures. Here's a short video that is supposed to explain it well (though I haven't actually watched it):

You Tube

You Tube

It has been reported that there is significant vignetting at f1.8 with this lens. If that's the case, then that means that the edges of your frame could be 1 to 2 stops darker (or more) than the center. If the camera is using matrix metering to average exposure across the whole frame, then the vignetting could result in some unpredictable exposures. I usually keep my camera set to center-weighted, and only change it if a specific situation calls for it.

[Rich M]

In an ill lit room I have to apply (-) 1 EC

[VoiceOfReason]

Most cameras offer three basic metering modes. 1) Matrix-metering, where it looks at the entire frame to judge exposures, 2) Center-weighted, where it still looks at the entire frame, but gives more weight to the center of the frame, and 3) Spot-metering, where exposure is set based on a single spot.

If you use any automatic exposure modes (Auto, Aperture priority, Shutter priority, etc), then it's important to understand how the various metering modes work and effect your pictures. Here's a short video that is supposed to explain it well (though I haven't actually watched it):

Understanding camera metering modes (Matrix, Centre-weighted & Spot metering) - YouTube

It has been reported that there is significant vignetting at f1.8 with this lens. If that's the case, then that means that the edges of your frame could be 1 to 2 stops darker (or more) than the center. If the camera is using matrix metering to average exposure across the whole frame, then the vignetting could result in some unpredictable exposures. I usually keep my camera set to center-weighted, and only change it if a specific situation calls for it.

I use manual mode and center weighted metering, or at least that is where I had it set but have not checked in a while since I let someone else borrow it.

I don't think that there's really much of a problem with vignetting, nowhere near what my DA18-135 does. Here's a link to some of my sample pics that I posted on FB, reduced in size with the loss of resolution and detail you'd expect, but it still shows the lens does well https://www.facebook.com/media/set/?set=a.10204473613940059.1073741850.12234...1

[y0chang]

Someone correct me if I'm wrong but I think ff a lens has significant vignetting wide open, the camera will meter wrong. I think first party pentax lenses have correction factors in the camera firmware.

[rawr]

a lens has significant vignetting wide open, the camera will meter wrong

It will depend on the metering scheme (matrix, centre-weighted, spot), and the camera metering technology.

The K-3, using matrix metering and its 86,000 pixel RGB metering sensor, is unlikely to be confused by a bit of lens vignetting. Pic related.

[Digitalis]

The K-3, using matrix metering and its 86,000 pixel RGB metering sensor, is unlikely to be confused by a bit of lens vignetting

this lens has more than a bit of vignetting.

[rawr]

this lens has more than a bit of vignetting.

I see what you mean. Wide-open, and nearby, there does seem to be a fair amount:


Sigma A 18-35 mm f/1.8 DC HSM review - Vignetting - Lenstip.com

But I still think this wouldn't cause the K-3 metering system too much trouble, given it's fine granularity, and its ability to use some scene detection intelligence.

Since I don't have the lens, however, I am just speculating.

[MadMathMind]

Took this lens into Mammoth Cave today. Shot it at f/2 and f/1.8 almost exclusively. Even with that, still needed ISO3200, 4000, and 5000 with shutter speeds around 1/15. The results are a bit blurry due to camera shake, obviously, but wow...this lens can do impressive things. The vignetting at the corners can be seen to a degree, but given how dark it was anyway, it's not an issue.

What was amusing were all the people taking photos with their iPhones. They got nothing but black. At one point, I took the same photo as another tourist in front of me. My wife and I saw the result on her screen and I said, "Her photo looks like that. Mine looks like this."

If you're looking for corner-to-corner sharpness below f/2,8...why? The issue is obviously present but in practice, it's unlikely to affect your photos in ways that you really care.

[Digitalis]

Make no mistake - this lens is a beast.



I'm going to be out of town for the next few days on a photography trip - I should have a full review and comparison between lenses of similar focal length complete within a few days.

[TrueFocus]

Agreed, especially for Pentax users it is large. It is a bit offset by the fact that it replaces 3 primes, though.

[Edgar_in_Indy]

The funny thing is, people will probably think you have a massive telephoto on your camera when they see the 18-35mm.

[y0chang]

Agreed, especially for Pentax users it is large. It is a bit offset by the fact that it replaces 3 primes, though.

I do wonder if one sigma is the same weight as a 20mm, 31mm, and a 35mm

[Edgar_in_Indy]

I do wonder if one sigma is the same weight as a 20mm, 31mm, and a 35mm

I'm not sure exactly what 20mm and 35mm f1.8 lenses you're talking about (Sigma 20mm 1.8?), but I'm guessing that the 18-35mm would weigh less, and cost way less than those three lenses. Not to mention the convenience of not having to change lenses, and having f1.8 from 18 to 35mm. For some people, this lens will just make a lot of sense, despite the size.

FYI, The Sigma 20mm 1.8 by itself weighs 520 grams (vs 810g for the 18-35mm), and costs about $600. Not to mention that the difference between 20mm and 18mm is not insignificant. (I think on APS-C 18mm is about 7-8 degrees wider than 20mm).