New Lens Scale: How To Convert Milliseconds To Standard Camera Fractions?

[Doremus Scudder]

Andy,

There are a range of shutter speeds; some of them are off more than others, e.g., some are 2/3 stop too slow, some only 1/3 stop too slow. If you can get your head around my method, I'll do the other work for you. Here's the list of your shutter speed indications and the actual shutter speeds from the sheet you posted in your first post (with note about how much too slow they are that you could also use as factors).

Just remember, the + and - signs refer to the numbers, so end up being the opposite of what you might think. E.g., 1/4+ is something like 1/5 or 1/6, so is less exposure than 1/4. Plus is less exposure, minus is more.

1 sec. = 1.35 sec. (1/3 stop slow)
1/2 sec. = 1- sec. (2/3 stop slow)
1/4 sec. = 1/2+ sec. (2/3 stop slow)
1/8 sec. = 1/4+ sec. (2/3 stop slow)
1/15 sec. = 1/8+ sec. (2/3 stop slow)
1/30 sec. = 1/15+ sec. (2/3 stop slow)
1/60 sec. = 1/30+ sec. (2/3 stop slow)
1/125 sec. = 1/125- sec. (1/3 stop slow)
1/250 sec. = 1/125+ sec. (2/3 stop slow)
1/400 sec. = 1/250 sec. (2/3+ stop slow)

You could just print these out, paste them on your lens board and use the plus and minus signs as factors. Minus means More exposure, so give less at the aperture by stopping down the appropriate amount. Plus means Less exposure, so give more with the aperture by opening the appropriate amount.

Example: your meter wants 1/15th at f/22. You don't have a true 1/15 available, the closest is 1/15+ that you get when you set your shutter to the 1/30 mark, So do that, note the "+" sign, which means the shutter is giving you 1/3 stop less exposure than 1/15 and close your aperture to (correction!) f/22 minus (1/3 stop more exposure) to compensate.

Note that if there's a "+" on the shutter speed, you compensate with a "-" at the aperture and vice-versa. It's really easy once you get used to it.

Alternately, in this particular case, you could just underexpose everything 2/3 stop from the actual setting, which would only be about 1/3 stop off in the worst case. Still, that's not as precise nor does it really allow finding optimum shutter-speed/aperture combinations.

Best,

Doremus