Evaluating Sharpness

[KeithB]

Bob:
I just bought my new Sigma 150-500 and so far seems to be pretty good.

Do you have any tips for evaluating sharpness on screen?  I know your lens evaluation article says "don't do that", but...

Are most of your sample shots (especially of the Sigma 50-500) taken with a tripod or handheld?

[Bob Atkins]

Unless I'm testing stabilization systems, most of my lens review shots are taken using a tripod. A tripod is the only way of being certain that camera movement isn't affecting sharpness.

Maybe the easierst way to test sharpness is to compare images with a lens you know to be really sharp, for example a 50/1.8 or an 85/1.8 stopped down to f4 or 5.6. With a long lens you have to back away from your target of course but if you have a flat target and fill the same amount of the frame with it using each lens (or each different focal length for a zoom), you can get a good idea of relative sharpness.

[KeithB]

Thanks, do you have any procedure for evaluating the sharpness on your monitor? 

[Bob Atkins]

Just the eyeball test. If it looks sharper it is sharper. The best target is one that has fine detail down to a level that isn't resolved.

However if a 100% blowup of a digital image looks sharp, it is sharp. It's generally not hard to spot a soft image.

I presume you've seen this article - http://www.bobatkins.com/photography/technical/lens_sharpness.html

and these examples http://www.bobatkins.com/photography/technical/lens_test_samples.html

[KeithB]

Yes, I have, thanks, I even have the peg board ready to go.  Unfortunately, I just moved to Albuquerque, so I do not have that many overcast days to play with.  It was nice in Southern California, you could count on many overcast mornings!

Now I just need a new tripod, I have a lightweight travelling one that is not going to work at all with the 150-500!