Originally posted by fourfivesix A friend has just given me a box of camera bits, some pentax flash units, filters, tamron adapter, screw mount adapters, lens caps etc there is also a photax paragon 135 lens. Would it be useful to keep? What kind of images would it be good for?
Ita also has a slider switch with an A and M, what is this for?
Def. don't use those flashes - they will fry your camera. You can use them with remote triggers, though, or with a high voltage adapter... but don't use them for now.
Don't know anything about the quality of the lens itself, but fast 135mm lenses (usually f2.8) were THE classic portrait lens. They have some other uses as well - get creative! It will be closer to a 200mm equivalent on a crop camera, though - good for any short-tele stuff.
To explain the A/M switch - On a modern lens, the aperture stays all the way open until the second you press the shutter switch. This lets a lot of light in, and makes composition and focusing easier, since its easier to see. It also makes focusing with a split ring or prism easier, since those go black if the light gets low. In modern lenses, there's a little arm that swings over and pushes a little arm on the back of the lens, actuating the aperture. It also means you need to use a Depth of Field Preview if you want to see how the focus will actually look. This will close the aperture blades but still show you the view through the finder.
On the oldest lenses, though, aperture was pre-set. You move the ring, and the aperture blades closed. There was an intermediate step on M42 lenses, before bayonet mounts became popular - the auto aperture system. There is a pin sticking out the back of that lens. On old m42 cameras, when the shutter was pressed, a lever would flip forward and hit that pin, which would stop down the blades. Only the most expensive cameras did that, though, so the lenses could work either way. In A mode, the blades don't close until that pin gets pressed. In M mode, the blades stop down like the older pre-set lenses.
Modern SLR's don't have the lever to actuate that pin - they use a different lever arrangement that is more reliable and durable. This means you have to use M mode, otherwise you will always be shooting wide open.