I used this to mark off changes in f/stops from 0.0 [infinity] to 4.0 in 0.5 increments.
But if you want a 1 stop change, you get 135mm, and that should be a 0 stop change. Or am I missing something?
For a 135mm lens I calculate a 1 stop difference at 191mm, 2 stops at 234mm, and 3 stops at 270mm.
Last edited by johnnywalker; 11-13-2010 at 06:29 PM. Click to view previous post history.
If I had been present at the creation, I would have given some useful hints for the better arrangement of the Universe.
Alfonso the Wise, 1221-1284
Math makes my head hurt. I learned the algebra in the '60's at a photo school. I always had a headache. Then I found out about the f/stop/inches method that Steve Sherman describes. I've been pain free ever since.
I keep half a dressmakers tape in my bags and studio roller cabinet, that lets me hit my exposures within a third of an f/stop. But even using the guesstimate in your head method it puts you in the half an f/stop range. Then you just go over for negs and under for trans.
I crunched the numbers backward to find length and marked a small retractable metal measuring tape accordingly for each lens (3) in a different color permanent ink. It is attached with a key ring to the strap of a spotmeter. Its a no-brainer -- just measure from the lensboard to the film plane and see which exposure factor is the closest .
The only time Salzberger's "Quick Disk" has failed me is the time I left it in the middle of a frame... nicely focused and perfectly exposed.
I agree. What can be easier than using a focusing target and measuring the exposure modification off the screen with a ruler. It may not work in all and every situations, but it works in most cases and does so without math.