Sigma 201927

Free flash

good clear pictures at 20mm

vigneting at 10mm

Build quality and finish are second to none. Manual focus ring is perfectly weighted. Centre focus is excellent.

Some chromatic aberration Soft corners when wide open Slight fringing.

Very good lens. Value for money.

Not as good as a Canon wide angle. Otherwise would recommend.

Easy to use and gives good view with good quality of picture. Fits on the GSr and the camera case like a standard ense so no need for a different case when it is fitted. I bought it for wide sceen (scotland) views and it did what I wanted.

As with any dedicated lense it exposes the camera to dust when fitting it. Not the choice if you want to have a variety of types of shjots.

Great price and great results.

At that price.... none!

Excellent build, as wide as you can go with a cropped sensor, excellent centre sharpness, good even at the corners except when wide open. Distortion well handled and easily corrected except at the extreme edges of the frame at the wide end.

Tendency to vignette, especially at wider apertures and although well handled, chromatic aberration seems to be highest around the lens' sharpest aperture of f/8... still, not too tricky to correct with software so not a major blemish. Certainly better...

Good focal range with very little barreling. Excellent ultra wide angle for the money

Towards the edge of the picture it does start to come out of focus. Aperture still a little too small at F4 and with a polarizer filter you need a tripod more often than not when using ISO 100.

good value lense, good quality pictures, comes with a nice case.

you need to take shots in the daylight, well lit room or get a flash, otherwise you'll find out how lacking your built in flash is ;)

As with any wide-angle zoom there is considerable barrel distortion that can be easily treated in post-processing. There is a degree of CA that can easily be dealt with. Light weight, sharp and contrasty this lens is easy to live with.