What to watch out for w/used lenses?

[P3 Photography]

I am going to look at a Canon EF 24-105 f/L USM lens. When I test it out on my camera (Canon xsi) what would be the best thing to take a picture of to see if there are flaws?

 

[scorpion_tyr]

I'm not pro, or expert, but I've been looking at buying some used glass myself so I've given it lots of thought. Anyone else can feel free to correct me if I'm wrong, but here's what I've been looking at:

1. A DETAILED visual inspection. Check the glass at different angles and lighting for cracks and scratches.

2. Manually turn the zoom and focus rings all the way to the stops a few times to feel for anything out of the norm like dirt buildup or binding. Also turn the focus ring in both auto and manual. Should have free movement in manual, but some resistance in auto.

3. When on your camera take at least one shot in every mode. For the Aperature priority mode, start at one end and working your way down take a shot at ever f stop to ensure the camera and the lense are communicating good. Do this at different focal lengths as well.

4. While you're doing this test out the auto focus and take different shots of colorful stuff and very detailed stuff to ensure a sharp image.

To really answer your question I would try to take some shots of a face. I'd focus on the eyes and make sure the lens worked as expected. I'd also try to shoot some type of cloth to test the minimum focus length and the dept of field at different aperatures.

Anyone else have any good advice? I'm also in the market for some good used glass so I'm curious as well.

 

[P3 Photography]

Good points! I did not think of some of these. Thanks.
I was going to bring a white cloth to test for dust or imperfections. I have never seen what dust on a lens looks like, would white be the best color choice? I'm just a little nervous about buying used.

 

[scorpion_tyr]

Just from the limited test I've done, dust on/in the lens doesn't really show up in the image unless it's really bad, or a layer of it will throw off your focus.

I do know that dust spots on the sensor show up better against a light blue sky type background than white for some reason. Maybe that's just with my camera though? So I would guess the same would go with dust or imperfections on the lens. If you really want to test out the lens I would go with white, red, yellow, and blue paper or cloth.

I don't blame you for being nervous. At least in my area the prices of used are just a little less than that of new equipment, so when I run across a good deal I want to REALLY test it out to make sure the seller isn't trying to hide anything.