[jayman_1975]

I just recently aquired a couple of lenses the 16-50 being one of them. I have noticed very quickly that at 16mm vignetting is noticeable. Upon doing an Internet search it seems this is a normal thing with this lens. I don't get it, why does this happen and who would be cool with a lens that makes the corners all dark. I never had this with my 18-135 but that could be due to the 2mm difference on the wide end? Is there a way to correct this? If I need a lesson please feel free to guide me somewhere I can be better informed

[Na Horuk]

Vignetting depends on the specific lens design, not just focal length (though it is true that wide angles often have more obvious vignetting than telephoto). Some lenses will have vignetting, others practically none. Just keep in mind that if you are taking a photo of an illuminated wall, the part closest to the camera (middle of frame) will be more intensely illuminated because the light travels a shorter distance. So taking photos of walls can give false impressions of vignetting. In practice, vignetting will not be noticeable in most photos you take, and sometimes you will actually want some vignetting, for added contrast and subject isolation.
Now on to remedies: Some modern Pentax cameras have a vignetting reduction feature (make sure you are using the latest firmware update). This only works for jpegs. If you shoot raw, most raw developing software will have features that let you reduce vignetting manually, or even use a lens profile for that specific lens and camera combination. So vignetting can be reduced quite effectively.

Then there are the mechanical parts. Vignetting can be caused if the lens hood is too tight, especially with wide angle lenses. You can try removing the lens hood when you zoom wider than 20mm. The other factor is aperture. Wide open usually has more vignetting than the lens slightly stopped down. Using f5.6-f11 should help with that.

[yusuf]

are you shooting wide-open? I have read some posts about 16-50 vignetting wide-open at all the focal length, maybe be try stopping down and see if it helps (though it defeats the purpose of having a f2.8 lens)

[jayman_1975]

It occurs on the wide and of the zoom at wide open even f4 and 5.6 it is noticable. It seems I can turn on "in camera lens correction" and it clears it all up, as to what compromise of image quality I dont know until i do some more tests.

[Na Horuk]

as to what compromise of image quality I dont know until i do some more tests.

Vignetting correction is usually very good, with very little negative effect. It might increase the amount of noise in the edges, but this is only noticeable at very high ISO, I think.