Take the lens off the Camera, rotate the aperture to the largest hole f2.8 or f3.5 or whatever is your biggest hole, then look through the lens towards a strong lightsource, you will soon see if there is any mould or imperfections...
There is something else you should look for. When releasing the pin that opens the aperture the aperture should close swiftly. Some old lenses have sticking aperture blades because the lubricant is old. A possible cause for this is being left in a hot car on a sunny day...
Where is that pin Karet? I should test that if I can as the lenses haven't been used for ages..
I guess you haven't taken off the rear lens cap as the pin is blindingly obvious. Just push it in gently and the aperture blades should shut down - but set the thing to f/16 first as it won't work when wide open. BTW I thought the lenses had a little bit sticking out of a curved slot around the edge of the rear plate. In which case rotate it gently along the slot, etc, as above..
The acid test for lenses is a torch (flashlight to our American friends) and a dark room or corner of a room. But you'll be shocked how many lenses that work perfectly well look dreadfull when you check them like this. (All of mine: new and old, as zooms work like pistons and suck in dust... ).
Scratches on the front and rear elements are what you should also check for and the smooth turning of the focus ring. Fungus and haze are pretty obvious. Also look for what might just be the lens components coming un-glued at the edges. Again something people can live with (or not even know about)..
Almost any lens fault can be cured, btw, but costs a lot. But I wouldn't worry too much if the fault is blindingly obvious then it won't affect the pictures much that will be noticed in real life..
Thanks David, yes I have taken off the rear lens cap to check the lens and have tried to slide the metal part along in it's groove (no pin to push in). This had no effect on the aperture size which is the reason for my original question. I'm guessing this means it is faulty?.
I set the aperture size on the camera and it let me so I took a few test shots but won't know if they are ok until the film comes back. If the aperture won't move manually, is it possible that it could still be set by the camera? Common sense tells me no but......