Manual Canon 50mm FD lense will not focus!?
In that case the linkage between the movable parts of the lens group and the focussing ring has failed.
What follows applies to most lenses; I have a Canon 50mm FD to hand but as it works perfectly I've not needed to dismantle it so far but have repaired many others.
When you turn the focus ring there are usually two pegs which engage into helical slots cut into the focussing ring, these are hidden within the lens and you won't see them unless the lens is dismantled. The pegs are usually rounded to make the passage along the helical slot even smoother and each one is fixed to the inner lens barrel by a screw. On older lenses, the grease inside can dry out a bit, especially if the lens remains unused, when this happens the pegs may either shear off or simply become unscrewed and drop off. The gummy grease may hold them so you won't always hear a rattling part inside.
To fix it, you carefully dismantle the lens to the minimum extent you can get away with. You'll need good light, patience and a set of good quality crosshead precision screwdrivers. Normally you start with the screws on the mounting flange and watch out for small springs and detent balls which tend to escape to freedom never to be seen again. Some of the screws are usually hidden beneath the rubber grip on the focussing ring, and you remove this to check by carefully lifting an edge and then rolling it back over itself. It may need re-gluing afterwards. Clean out dried grease as you go and apply a small amount of thick grease to replace it on reassembly: less is far better than too much! Some of the screws may need thread lock applied to them when they go back in, but you're better off leaving this as your first time lens repair usually has to come apart again due to an error in reassembly.
Be prepared to ruin this lens as it's your first lens repair. The good news is that auction websites have plenty of other cheaply and in full working order, just make sure to ask if the iris (aperture) works smoothly and snappily and that the lens does not have the dreaded lens fungus on the glass elements (a patchy white haze). You can also usually get these lenses for free on Yahoo FreeCycle and a camera body and other goodies normally come as part of the offer. FreeCycle is how I've collected various Nikons, Canons and Pentax SLRs and lenses over the last year to add to my existing Olympus gear.
I hope that I've helped you, if so please return the favour by rating my answer.
Jul 08, 2009 |