Testing a lens sharpness

[chim_knee]

Hi,

Does anyone know of a tutorial on how to test the accuracy/focus etc. of a lens. I seem to remember that there is a grid you can print off and photograph and that will tell you.

I've just bought a Sigma 10-20mm lens for my D70 and when it arrived the box was quite bashed. I'd like to check whether the lens is OK and send it back if it isn't. Does anyone have any suggestions on how to test this?

I also bought a 50mm prime at the same time. I was wondering about putting the camera on a tripod and taking a shot with one lens and then with another and, objectively, comparing the two shots (obviously the shot will look different, but presumably there should be at least comparable sharpness or lack of bokhe(?).

As always, advice gratefully received if there's a better/more sensible way of telling whether a lens is soft because of damage or design/price compromise.

Thanks,
Phil.

[_dobbo_]

www.focustestchart.com/chart.html

Not sure you will get any decent measurable results with this though, because with a 10-20 the DOF is quite large even at 20mm wide open.

[robdickinson]

I tested mine fine, focusing close (the sigma 10-20 focuses at 24cm I think) will reduce the DOF to acceptably small results.

Use a tripod & test a range of fstops from wide open at 45degrees to the test chart.

[Parrot of Doom]

Flange Focus chart, might be of use. Its particularly good on video cameras for testing the ability of the lens to refract different colours (red/green are the most obvious).