My longest lens is an old T-mount 500mm f8; I also test T-mount lenses fairly often, since I buy and sell them on eBay. One of the problems with them is that my D50 doesn't meter or confirm focus unless the lens has a chip, which really slows things down if I'm trying to get a picture of a bird or something.
Various vendors offer T-mounts with the chip, but they look a bit fragile and home-made; I'm a little worried that the chip might break off and damage the camera. I'm also unclear as to how the chips actually work - do they have to be programmed for the individual lens, or is it more a generic "this is a manual lens, just return a speed for the light that's coming in and don't worry about anything else" sort of thing?
Has anyone tried them, and what were the results like? Can you recommend a particular supplier?
I'm also looking at getting a chipped adapter for using M42 screw lenses, since I probably sell more of them than any other fitting and it would be useful for testing them. Again, has anyone tried them?