..Mike Del Vecchio Said: "f-stops, I learned from old timers, is a ratio of aperture to lens size"
Yes
This is the Era I started in and this is what we were told. All my experience is in Motion Picture Lenses but maybe some of it applies to still camera Lenses. If the F Stops are a mathematical number arrived at by aperture diameter to focal length. Then other things affect the light passing through at a given F stop, If you have different lenses and they have more or less elements than others the ones with more elements pass less light than a lens with less elements. Therefore the lens with more elements will make a lighter exposer on your film than the one with fewer elements.
I have seen lenses with another mark on them along with the F stop, There was a T, these were called T Stop lenses. "True Transmission of light". With these Lenses you could use any lens and at the same T Stop you got the same exposure with any lens. You could look at these lenses and see the deferences in the positions of the F Stops and T Stops.
In those days we used a Kodak film called ECO it was a color Reversal Film 25 ASA in 3200 K. Light. With a 85 Filter it was 16 ASA in sun light. The nature of Reversal film was if you were off a 1/8 of a stop you were getting in trouble.
The other day I Saw a Kodak ad.for a movie film stock and they said 5 stops latitude.
Mike Del Vecchio "Said"
"Lenses around the edges are less than perfect parabolas, causing the
light rays to not be exactly on the focal point. That's why wide open lenses
look funny compared to the same lens at f-8;"
Yes!
I am from the old school and I believe the sharp part of a Lens is 2 stops closed down from wide open. "Do Not confuse me with facts as my mind is all ready make up" there fore I do all I can to get the lens into that range when filming (Video). Take a lens that is off a camera and look through it wide open, close the F Stop 1 Click you can see you have lost 1/2 of the aperture hole. Close down 1 more F Stop click and you have lost 1/2 of that aperture hole. Enouf Said.
Back To Lenses
The lenses were all set to go past Infinity. Therefore when the lenses were cold they would go past Infinity. But when the barrels of the lenses got hot and expanded and got long you could still get back to Infinity.
Zoom Lenses, We are always checking and setting the Back Focus. When the back focus is right you can zoom in tight, Focus and zoom Back to wide and it will stay in Focus or any were in between if not get lens fixed.
Enouf For Now
DANA
_______________________________________
Dana Fuller
Dana Fuller Company
PO Box 70282, Richmond, CA 94807-0282
Voice 510-620-0330 * Fax 510-620-1839
URL: http://www.trainsonvideo.com
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