RE: Re: exposure outdoors using meter

Ah Gill...Since he's from New Zealand, he speaks "English".....You speak
"American" (& pretty well, I might add)...It's kind of like Castilian & all
the rest of spoken Spanish.....
have a good day all!
andy

-----Original Message-----
From: pinhole-discussion-admin@pinhole.com
[mailto:pinhole-discussion-admin@pinhole.com]On Behalf Of Guillermo
Sent: Thursday, July 19, 2001 12:31 AM
To: pinhole-discussion@pinhole.com
Subject: Re: Re: [pinhole-discussion] exposure outdoors using meter

I am sorry my incipient English didn't convey the ideas well enough.

----- Original Message -----
From: <heyseus@xtra.co.nz>
To: <pinhole-discussion@pinhole.com>

> Thanks for that Guillermo,
> so as understand it it doesn't matter what the shutterspeed is for you
meter reading its the f-stop that counts as it will be converted recipricly
anyway.

Of course it matters, you have to double the exposure your meter gives you
as many times as f/stops there are between your meter reading f/stop and the
one of your pinhole camera.

> i was using paper for this exercise and thought that you set the shutter
speed to the iso of the neg material used, and make a light reading from
there.

That's exactly what you should do (if possible). You should also get a
reading of the exposure time needed for the nearest f/stop to your pinhole
f/stop, your meter is capable of (this so the numbers of doubling is
reduced, IOW less multiplications by 2).
Mine for instance, is capable of ISO6 (perfect for Ilford Paper rating) and
f/128 (good enough for all my zoneplate stuff and at least 1 very wide angle
35mm format camera).

Regards,

Guillermo

> >
> > 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
> >
> >
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>
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Received on Thu Jul 19 10:04:24 2001