In this article I will advice you how you can buy old lenses with maximum safety. You should know only some important thing and you will not disappointed in any way. To use manual focus lenses more than just for fun, you can at very low cost enter into professional level photography.
Where to buy
Bring with yourself into the shop air-blower and flash light. Blow the dust on both side of lens with air-blower and light through from both end. You should see any problem in strong light. If the item is mint condition and high priced, you expect crystal clear lenses without cleaning marks (light circular scratches), scratches, dust inside, fungus etc. Strong light show you all if there are any of them.
For lower price you can accept cleaning marks, small scratches, little dust inside because they don't impact optical quality at all, just make them hard to sell if you don't want to use them anymore.
For real bargain price you can accept almost every problems on glasses except fungus. Even if lenses are little damaged, it's optical quality is usually great, you can't see anything from the damages on the pictures!
!!!FUNGUS!!! always risky business !
Your never know how fast fungus eats your lens coating and cover of the the lens, and not only just current one's, it can attack others lenses too.
Check carefully every function: focusing must be able to turn smoothly to the end and back, but depending on the price, hard focusing can be ok for cheap price.
Set the aperture at least into maximum and minimum position and look through the lens, to check is it working properly or not.
If the lens has it, look at the auto-manual switch, if you planning to use it on DSLR, you must use it in manual mode. In auto mode is the right working stage very important on analog camera body. Try it always with camera body if possible.
Finally about fungus: if you get lens with fungus and you want to keep it, store it in a separate dry box, don't mixed with other healthy lenses.
Buy from the internet:
If you can't test personally, you must trust in the seller. Ask the seller in advance every important thing. If it is not described, you also need to ask in advance the safe postage cost /insured, signed-for/.
Don't buy from this kind of sellers:
"I have not much clue about photography, I just got from my friends" - this means: the item has a defect, mostly fungus or other serious problem.
"Sold as no return":the same than above, but not in every case. If you are enough brave to risk a few money sometimes you can make a good deal, sometimes you don't.
Anyway many good lens are available only on Ebay, so take some risk and you should get valuable pieces.