How do you 'test' a lens?

[kyzen]

I found a 28-210mm lens from "Cosina" for a whopping $40, and figured that at that price, I could risk having a lens that produced painfully blurry pictures. The lens is labled f/4.2-f/6.5, but my Rebel XSi is showing f/4.5 at the 28mm end, and f/6.3 at the 210mm end. Don't know which one is right

The lens itself is pretty hefty, and pretty large - a whopping 72mm. However, so far, to my amateur eye, the few pictures I've taken have been pretty good. My tripod broke last week, so I haven't taken any outdoor shots yet though.

Anyways, I'd like to see how it compares to the few other lenses I have (18-55mm IS kit lens, 28-90mm, f/1.8 50mm, but am not sure the best way to go about it. Would it really be as simple as taking shots of the same scene a couple of times with each lens, at the same focal length? Is there anything in particular I should take pictures of for a good comparison?

Feedback would be great, and I'll definitely post the results

 

[corkyg]

We used to do resolution testing for CCD cameras on a government contract. There are standard resolution charts available that you can down load. Hoe testing would involve a tripod (table top is good) and a well lighted wall to put the chart on. Then you set the camera at a specific constant distance and you can compare the results of different lenses. The government standard was expressed in line pairs per millimeter. This is a good tutorial and has links to useful charts.

Test

And this is a downloadable copy of the type of chart we used for such tests:

Chart

 

[ivan2]

Originally posted by: corkyg
We used to do resolution testing for CCD cameras on a government contract. There are standard resolution charts available that you can down load. Hoe testing would involve a tripod (table top is good) and a well lighted wall to put the chart on. Then you set the camera at a specific constant distance and you can compare the results of different lenses. The government standard was expressed in line pairs per millimeter. This is a good tutorial and has links to useful charts.

Test

And this is a downloadable copy of the type of chart we used for such tests:

Chart

My own hoe testing will include on the field usage as well.

 

[Kirby64]

Resolution charts will tell you how sharp the image is. The chart linked above is good. Depending on the mpxl of your camera, take the same pictures from the same space at the same mm setting and that'll tell you how sharp the lens is at the given aperature.

Keep in mind, resolution will greatly increase for cheaper lenses as the aperature approaches the optimal length. This varies from lenses to lense, but as a general rule, you'll probably see fairly close to optimal sharpness between F8-F11.

This is why people pay hundreds of dollars for L quality lenses. In addition to the larger aperatures, they generally are much sharper wide open than lower quality lenses.

 

[ElFenix]

the rebel can't display anything between 4 and 4.5, so it'll show 4.5 even at 4.3.

i like to use something that i can definitely tell what it should look like to the naked eye, such as text.

not sure how to make sure the sensor plane is parallel to the wall.

 

[corkyg]

Originally posted by: ElFenix
not sure how to make sure the sensor plane is parallel to the wall.

Use a tripod with a centering bubble or twin axes bubbles. On a SLR, lock up the mirror and use the self timer or a cable release to avoid moving the camera.