hav@dual.UUCP (Helen Anne Vigneau) (01/26/85)
<*munch*> I am looking for help in determining how to compensate for a film speed that is not available on the ASA setting on my camera. My camera is a Pentax ME Super. I generally operate it in the automatic mode, because I'm fairly camera-illiterate. It looks, though, as if I'm going to have to do a little more learning. Last weekend as I was excitedly putting my first roll of 1000 ASA film into my camera (hoping to see how well the film works) I discovered, *much* to my chagrin, that the camera's ASA settings in the range I need go straight from 800 to 1600. Obviously, I set the ASA meter to 800, which is closest to what I need, but I'm afraid that I'll still get overexposed photographs from this. My question is this: Does anyone out there have any experience in compensating for this type of discrepancy? I assume I'll have to go to manual mode, but I'd like to know a little more specifically what's needed and what experiences (and luck!) others have had with such shenanigans. Please respond soon; I probably won't be using the film until I find out something. Helen Anne
kenw@lcuxc.UUCP (K Wolman) (01/28/85)
If the Pentax is anything like the Minolta (. . . it has a lens, a shutter, a body . . .), there probably are small dots or markings of some kind between 800 and 1600 on the ASA setting dial. This is what they indicate: . 800 ASA . 1000 ASA . 1250 ASA . 1600 ASA That is, one mark past the 800 setting should set your meter to handle ASA 1000 film. Have fun. -- Ken Wolman Bell Communications Research @ Livingston, NJ lcuxc!kenw (201) 740-4565 . . . not Philip Roth . . .
briand@tekig1.UUCP (Brian Diehm) (01/30/85)
> I am looking for help in determining how to compensate for a film speed that > is not available on the ASA setting on my camera. My camera is a Pentax ME > Super. I generally operate it in the automatic mode, because I'm fairly > camera-illiterate. It looks, though, as if I'm going to have to do a little > more learning. > > Last weekend as I was excitedly putting my first roll of 1000 ASA film into > my camera (hoping to see how well the film works) I discovered, *much* to my > chagrin, that the camera's ASA settings in the range I need go straight from > 800 to 1600. Obviously, I set the ASA meter to 800, which is closest to what > I need, but I'm afraid that I'll still get overexposed photographs from this. > > My question is this: Does anyone out there have any experience in > compensating for this type of discrepancy? I assume I'll have to go to > manual mode, but I'd like to know a little more specifically what's needed > and what experiences (and luck!) others have had with such shenanigans. > > Please respond soon; I probably won't be using the film until I find out > something. > > Helen Anne OK, here goes with a quick lesson. ASA is a logarithmic scale. Each doubling (or halving) is equivalent to requiring one less (or one more) f-stop to get the same "exposure" on the film. Equivalently, one could halve (or double) the shutter speed to get the same "result." Anyway, it is easiest to take the base2 log of the ASA numbers you wish to compare (log(b) of n = log(x) of n / log(x) of b, where x can be any base you wish). So. log2 of 800 = 9.6438562, and log2 of 1600 = 10.6438562 . By definition of logarithmic scales, the difference is one, which means they are one f-stop apart in the use of the ASA scale. Now, log2 of 1000 = 9.9657843, and (log2 of 1000) - (log2 of 800) = 0.3219281 . The result? 1000 is almost exactly 1/3 f-stop faster than 800. Now, this was more than you really needed, because the industry has standardized on 1/3 stop increments for ASA and for light meter readings. Probably your ASA dial has intermediate clicks at 1/3 intervals. If not, you'll have to go to manual and adjust a smaller aperture (larger number) by 1/3 stop. UNFORTUNATELY, the industry has standardized on 1/2 stop increments for aperture, so you'll probably be 1/6th stop off this way! However, all this probably doesn't matter, as 1/3 stop for all but critical work is "pretty close", and if you're shooting color prints, the automated printing machines screw up by much more than 1/3 stop. -Brian Diehm Tektronix, Inc. (Need I say this is not an official Tektronix pronouncement?)