focus scales on lenses
Posted 09 November 2007 - 03:45 AM
i mean, if my lens has focus marks for 5 feet and 7 feet, will the 6 feet mark be in the middle or slightly more towards the 7 (considering the logarithmic progression of focus)?
is ther any trick to find these kind of intermediate marks?
thanks for your answers
Posted 09 November 2007 - 10:34 AM
Posted 09 November 2007 - 06:53 PM
Posted 09 November 2007 - 07:00 PM
2/3 is a good approximation, but it's not quite right on all lenses. See this photo of some master primes:
The 100mm on the right shows that the 11, 12, and 13 foot markings are almost equidistant. I usually just estimate a little farther than halfway on the barrel is halfway in realspace.
If you need something more accurate, a lot of ACs including myself make extra marks on the lens so we have those intermediate marks. Especially in the 5-20 foot range that is used a bunch, lenses are usually lacking in precise marks. During checkout I just measure out the distance I want (like 7 feet in this case), eye focus on a siemans star to be as precise as possible, and add the mark with some chart tape.