Archived posting to the Leica Users Group, 1997/12/17
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]>It never actually reaches 0, but mathematically speaking you would say that >the limit of y as x approaches infinity is 0. > =20 > Thus, it is possible to be focused on "infinity" even though there is= =20 > no number that actually represents this distance. --Marc Turner >-------------------------------------------------------------- >Marc, > >The next inevitable question is: When a lens is focused to the infinity >symbol, what distance is it really mechanically focused on? An actual lens >isn't a formula. It must be focused to a particular point in space.=20 Bob: I believe this statement is based upon a false premise. There is a specific= distance measured between a lens and the focal plane (focal length) where= the lens is focused at infinity; when the lens is racked out beyond this= point it is focused at a finite point, when the lens is racked closer it is= not focused on anything (ie set beyond inf.). Becuase soem lens materials= are sensitive to temperture change, the true infinity setting will vary,= hence some lenses focus "past" inf. Ths may not seem intuitive but mathematically there are some wierd things. I= recall in Calculus class that we were able to integrate between two= infinite lines and able to come up with a finite area - this was a long= time ago for me - back in the early 70s. Hope this helps Tom That is >the ultimate question as it concerns photographers. > >For example, we would like to know at what distance the lens designer invok= es >infinity; after, say for a 50mm lens does infinity begin at 500', a 1000', >etc. I would like to know that number. But nobody who should know tells me >what is is. Why? Is it the last number before Infinity marked on the focusi= ng >collar? Or is it an undisclosed number that is arbitrarily assigned the >Infinity symbol? > >Once and for all, let's nail this thing to the wall. > >Bob