What to check before buying an used Canon 24-70L?

Hi,

I will probably buy an used Canon 24-70mm 2.8L lens tomorrow.
The seller bought it last year and says it looks like brand new. I know it simple to look for scratches and flaws but what else should I check?

strap it onto your 40D and shoot at all apertures and focal lengths, and review the pictures before buying. remember that at f/2.8, DOF is pretty thin. check sharpness and check for chromatic abberation.

if you can, check the focusing at f/2.8 and 24mm, since some copies backfocus. the best way to test this is to place your camera on a table, focus on a single AA battery at minumum focusing distance while you are at 24mm and then take a picture. WITHOUT refocusing, place batteries at a diagonal in front and behind the original battery. retake the picture without refocusing. see if the batteries in front of and behind the battery are more sharp (they shouldn't be). if the farthest battery is sharper than the original batter, then the lens is backfocusing (focuses more clearly on things behind where it should be focusing) and you should avoid buying it.

We've had three of these - one got returned and of the other two one is noticeably better than the other .... though that's OK.

The issue I have seen with 2 of the 3 we've had is sharpness at f2.8 - I would check (bearing in mind how shallow f2.8 depth of field is) and make sure 'something' at or near where you think you focused is in sharp focus at f2.8.

Sharpness at f2.8 was the reason our first 24-70L went back and it is the same issue on the 2nd that made us have a good look at it to see if it really was OK. Canon tried sorting the sharpness twice but didn't make it much better and offered a new lens - even though they said it was 'within tolerances'.

FWIW at greater than f2.8 the lenses looked more or less the same image wise .... it's just that we bought it to use at f2.8 so looked to ensure it was OK at that aperture.

If the price is right, then BUY IT!!! Don't get wrapped up in scratches on the barrel, just make sure the glass is not messed up. A lens at the right price is worth a little back-focus, because even with repair at Canon it may be cheaper than buying new.

rabidcow: the price is 7400 SEK ($978 ), a brand new is 10945 SEK ($1447). 32,5% cheaper than a brand new.

the warranty card isn't signed so I guess I have to pay for the repair cost if it's needed.

...or I can have a brand new Canon 17-55mm 2.8 IS for almost the same price as a used 24-70L

blur07 wrote in post #6505305
rabidcow: the price is 7400 SEK ($978 ), a brand new is 10945 SEK ($1447). 32,5% cheaper than a brand new.

the warranty card isn't signed so I guess I have to pay for the repair cost if it's needed.

...or I can have a brand new Canon 17-55mm 2.8 IS for almost the same price as a used 24-70L

assuming you have a crop body?

I would go for the 17-55 in that case.

hania wrote in post #6505923
assuming you have a crop body?

yes, i do.

:: edit :: I'll use the lens mostly for indoor concerts. I've heard flare is big problem with the 17-55 IS :S