what is wrong

[tweeky]

I brought a new sony a57 and also a sony a fitting 55 - 200 mm I went to the olympics and took my camera and I get test shots like this

they have these dark marks. they only happen when you focus to infinity. you can take a portrait photo at 50 or 60mm and its crystal clear but you try and take a photo like this boat scene and the edges go dark in all 4 corners



I just not sure why it does it

I am not sure if its the lens or the camera but with the default lens I dont get this.

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[Designer]

The effect is called "vignetting". It is caused by the lens being somewhat smaller than the sensor. The amount of light striking the sensor is reduced at the corners causing the corners to be darker.

[tweeky]

Would be a lens problem or camera because the sony a57 is supposed to have vignetting compensation or correction

[John B.]

I brought a new sony a57 and also a sony a fitting 55 - 200 mm I went to the olympics and took my camera and I get test shots like this

they have these dark marks. they only happen when you focus to infinity. you can take a portrait photo at 50 or 60mm and its crystal clear but you try and take a photo like this boat scene and the edges go dark in all 4 corners
I just not sure why it does it

I am not sure if its the lens or the camera but with the default lens I dont get this.

The fact that a shorter focal length does not produce the vignetting, shows that the lens is the problem. I doubt, though, that it's a faulty lens. Perhaps you was using a large aperture? Try a smaller aperture and see if it helps. Check this page where the causes of vignetting are explained. It's for Canon lenses but it would apply to other brands, too: Canon Lens Vignetting (Light Fall-off)