Testing Sharpness

[Elliotte Rusty Harold]

I've heard that various lenses, teleconverters, and such don't always have the best quality control. Sharpness can vary a lot from one unit to the next, even though they're ostensibly the same model. Are there any standard tests one can perform to check the quality of a particular lens, or to compare two lenses? When I pull a new lens out of the box, how should I test it?

[Roger Clark]

You can make your own standard, or follow someone else. For example, here is mine:
http://www.clarkvision.com/imagedeta...lens-sharpness

Any testing with a digital camera will be influenced by the camera (mainly the pixel spacing and blur filter) and you will get different results from different cameras. So do all your testing with one camera.

Another good test is stars. point your camera at the north or south celestial pole and take a 30 second exposure at high ISO. Check the stars for how round they are.

Roger

[Ed Erkes]

I would add the following points to Roger's reply. Use flash to light your resolution chart. It eliminates any camera vibration issues and allows better comparison of different apertures--say f4 vs f22 (since f22 would necesssarily involve a much slower shuter speed if using available light). Also, if your camera has Live View, zoom in to ensure precise focusing. Make sure your image magnification is identical for all shots. It is much harder to judge small resolution diffrences when corresponding line groupings are at different magnifications.