Re: exposure outdoors using meter

----- Original Message -----
From: <heyseus@xtra.co.nz>

> With your info i got off your website, the sunny16 + iso exposure rule, when using a meter do you use the meter reading and the iso=shutterspeed to calculate your exposure?

Did you mean "iso+shutterspeed"? if so, here is the answer (BTW, I may overexplain, my excuses in advance for doing that):

When I use a meter, I set it for the ISO of the emulsion in use, then I take a reading and obtain a "pair of exposure values", f/stop+shutter_speed, that is. Then I translate that pair of exposure values to an equivalent pair for when the f/stop is the one of my pinhole camera. For instance: My pinhole camera is f/512, a meter reading gives me f/45 @ 1/30, there are 7 stops between f/45 and f/512 (45 -> 64,90,128,180,256,360,512), therefore the equivalent pair of exposures values f/45@1/30 for my pinhole camera would be f/512 @ (1/30 +7stops). 1/30 +7 stops is equal to doubling the time 7 times 1/30 -> 1/15, 1/8, 1/4, 1/2, 1, 2, 4secs, my pinhole camera exposure should then be f/512@4 seconds plus any reciprocity correction needed for the emulsion in use.

> I used it to teach a class but had varying results, although i have suspitions that the cameras were dodgy.
> I just need a little clarification on this.
> But the ones that did turn out on my camera and one other were as near perfect as i could have hoped.
>

The only way to get consistent results from many cameras is if you have measured the pinholes of all the cameras in a relatively accurate way, which in turn allow you to know the f/stop of your cameras. Obviously, pinhole of all the cameras should be clean, free of burrs and obstructions.
 
> Also if you have any info on Pinhole under studio flash conditions i would really appretiate it, i had a formula worked out which worked well for my camera but had limited success with the others.
> I used
> exposure = difference of stops from meter reading to camera aperture x 1.5
> If you have any suggestions to improve this, that would be great.

Here is what the Laws of physics MANDATE: you should give a number of flash "pops" equal to 2 multiplied by itself a number of times equal to the difference of stops. For instance, stops of difference = 5, number of "pops"= 2x2x2x2x2 = 32 pops
And then you will have to give few pops more to compensate for INTERMITTENCY (sp) EFFECT which for the above example would state: an exposure of 32 pops of low power flashes (flash-A) is less effective that one single pop of a flash-B with a power equal 5 times the power of flash-A.
  
If shooting negative material, you may obtain printable results for up to 4 stops of difference when using your formula, but for the more stops of difference the more unlikely you will.

Hope it helps,

Guillermo
Received on Wed Jul 18 08:23:22 2001