As a newbie, i am interested to buy - APO 70-200mm F2.8 EX DG HSM.
However, got no extra $$$$ to get a new set.
Can anyone advise me how do i ensure that the lense condition is good.
How do i check the lense?
Here's a general checklist from off the top off my head (do a search, there have been many prior threads regarding this):
1. Check the optics for any dust, fungus, cracks, scratches etc. Take off both front and rear caps and look in from both sides, towards a bright light source. Fungus should appear as a spidery white stain on the lens.
2. Test the zoom ring and manual focus rings of the lens, make sure they are not too tight or stiff.
3. Mount the lens on your cam and test the AF. For the Sigma, it should be quite smooth and silent, and quite fast. Look out for weird noises or unable to lock on when during AF. Shoot some test shots at wide open (f/2.8) and stopped down. Shoot wide open at a subject, say a battery on a table, this is to check for front/back focusing. If you have a laptop, all the better to download the shots on the spots and view at 100% to check.
Thats all I can think of, perhaps some of the fellow CS-ers here can add more! Hope this helps.