| Author | Message | ||
     Donnie_strickland Tinkerer Username: Donnie_strickland Post Number: 144 Registered: 09-2006 Rating: N/A |
I don't know either Glenn. People keep trying to make this more difficult than it should be. I think Rick Oleson says it best: "The lens only has one absolute position in terms of a specific distance, that's infinity - at all other distances you'd have to compare the engraved distance scale against a tape measure reading or something similar and I wouldn't trust that. Equally or possibly more significant is that the infinity setting can be produced by a collimator so that you have a standard instrument with which to set the infinity point to ensure that it's optically correct and not just a "that light pole looks sharp" approximation. True, a collimator can be adjusted to set a different distance than infinity, but this is not generally what they are made for: they are made to deliver a collimated beam, which is the optical equivalent of infinity. If you have such an instrument, then it's much easier to correct at infinity than to pace off distances and worry over whether the engraving on the lens barrel is correct... Also, the lens generally has a stop at infinity. If it is correct there, and incorrect at closer distances, it's still perfectly usable as long as it matches the viewing system (RF or groundglass). But if you correct it at a close distance and it's off at infinity, you may never be able to attain correct infinity focus because you may hit the stop before you get there." |