[ThatSummer]

I've been owning this lens for a few years now. I know it's a pretty sharp lens and gives great results for this focal length since I don't have a prime in this range to compare with. But I'm wondering if this is just my copy or other people having this issue or not - the color rendition looks unnatural to me, at least no close to my other lenses (mostly primes), such as DA 40mm, DA 70mm, FA 50mm 1.7, etc. To be more specific, on a overcast day, or in shadow, the color looks dull and it takes a great effort to increase the saturation to bring the color back. But in a sunny day the color could go the other direction - too deep and too contrasty and I will have to dial down the saturation and contrast to make it even. Sometimes after staring at the same image for a few minutes make my eyes sore so I had to give up. Does anybody have the same issue? Or how should I work around it? BTW I'm shooting mostly RAW.

[Adam]

Could the vignetting be to blame perhaps?

[ThatSummer]

I suspect vignetting is not the issue. I'm including two images here. The first one was taken with 12-24mm @18mm, and the second one with 31mm. Both at F11. So the colors are quite different. The second one is more natural to me.

[ABel]

EXIF says the auto white balance is used, it's quite possible the camera choose different WB settings for these shots.
Try to make two similar shots with a fixed custom WB.

[Na Horuk]

It could be white balance changes, particularly if you have AWB or CTE selected. It could also be jpeg mode or other custom modes, if you accidentally switched between shots (some buttons can be configured for these changes, and we had such cases before). Especially during sunsets (and sunrise), the WB of the scene is changing from second to second and AWB can struggle to 'keep up'. For those shots its usually best to have WB set to Daylight. You can still change the WB in PP if you shot raw, and compare the shots with the same WB values
Its also possible the Raw converter (Lightroom, SilkyPix, whatever you are using) is has some presets that get automatically applied. These presets can be dynamic (as in, they change from frame to frame) or can depend on things like Focal length.
Another thing that could affect the scene like that would be filters, like a polarizer. But you didn't mention you had one mounted, so that's probably not it.

One more thing to keep in mind is that UWA lenses do behave a little differently than telephoto lenses. Some of these differences are psychological, some are technical due to optics. From the sample photos you posted, your lens seems to be fine. There is just not way the glass inside a lens could so drastically change the colour of a photo without also experiencing major loss of image quality, sharpness.

Maybe you can just look at some online UWA tutorials, particularly regarding setup and PP, and they will give you a more consistent workflow

[BigMackCam]

It's almost certainly a white balance difference. I took your first photo as a JPEG into Lightroom, increased the colour temperature to +33 and reduced tint to -38 (and dropped the exposure a little) and it looks very, very similar to your first photo (see below the adjusted image).

When white balance accuracy is important at the time of capture - particularly where there's very little for the camera to pick as a reference - I'd suggest using an 18% gray card to set the white balance manually in advance.

[ScooterMaxi Jim]

I agree with the others regarding white balance. It does seem to me that getting natural coloration in UW lenses is difficult simply because a wide perspective often involves a variety of sources of light, as well as varying light angles that change color temperature. I have the Tokina 12-24 (same optical formula) in Canon mount, and find that it yields a somewhat dull and flat look despite its sharpness. The Pentax version seems warmer and fuller, though, undoubtedly related to the coatings - based on images posted.

[pacerr]

I believe this is an easily understood situation considering the TOTAL spectrum of the light conditions presented to the metering systems by UWA lenses. The more input, the more 'homogenizing'. Plan to fix it in PP to suit your taste.

[ThatSummer]

Thank you everyone! If I hadn't asked, this could remain as a myth to me for some more years! Back to the old days when I was shooting K-100D, I had to adjust white balance all the time so it's like a second nature to me then. But after upgrading to K-50 and now K-1 the auto white balance has been pretty accurate, which saves the hassle of forgetting to set white balance and getting a really weird picture, so I guess I was spoiled. Also none of my other lenses have this issue but just this one so I always thought there's something wrong with it ...