RE: exposure calculation with paper negatives

Hi Earl,

Recently I've been working a lot with Ilford MG IV Fiber Matte paper. I did
a series of tests and determined that, for a 7 inch (178 mm) focal length
camera with a .4 mm aperture, the proper exposure in full sun is 70 seconds.
You're using a slightly longer focal length, but also a slighly larger
aperture, so I'd guess that your exposure should also be about 70 seconds in
bright sun. This is assuming that the emulsion on pearl and matte surface
papers are similar (and this is a BIG assumption). You might try the
70-second BDE rule-of-thumb and see if it helps.

I also read Chuck Flagg's response that he has his students do in-camera
test strips. This is an excellent idea and might be something to try, too.
I've found that papers vary widely in sensitivity to light: in one camera
that I use a lot, Kodak P-Max Art RC has an exposure of 8 seconds in bright
sun, whereas Cachet RC warm-tone matte needs 45 seconds (about 2 1/2 more
stops).

Hope this helps.

Tom

> -----Original Message-----
> From: owner-pinhole-discussion@spitbite.org
> [mailto:owner-pinhole-discussion@spitbite.org]On Behalf Of Earl and
> Patty Johnson
> Sent: Tuesday, March 16, 2004 9:08 PM
> To: pinhole-discussion@spitbite.org
> Subject: [pinhole-discussion] exposure calculation with paper
> negatives
>
>
> Hello, all of you friendly folks:
>
> I am new to this discussion, and I have enjoyed reading your posts and
> looking at many of your websites. The pinhole world includes many very
> talented and dedicated artists.
>
> I recently re-kindled a long dormant interest in photography by
> constructing several pinhole cameras. I read as many of the internet
> instruction sites as I could digest, and went forth into the world to
> make pictures. I used Guillermo Penate's suggestion of ASA 6 for RC
> paper, and taped a copy of his reciprocity failure chart to my copy
> paper box camera. Most of my attempts have turned out over-exposed. I
> am using Ilford MG IV pearl paper. This morning I exposed a sheet in
> bright, early-morning sunlight. My meter (set at ASA 6) said 1/4 sec
> at f16. My aperture is .508 mm with 205 mm focal length, for f404. My
> little cheat sheet says double the reading nine times, then apply
> reciprocity factor. I exposed for 2 minutes (which does not include
> any reciprocity allowance), and got a very dark negative - it will be
> printable, but it will be a challenge for my rusty chops.
>
> My camera is light-tight, and I am pretty sure of the accuracy of my
> pinholes. Is the effective ASA of the paper higher than 6? I love the
> few images that I have been able to print, but it is a struggle. I
> would like to graduate to film, but I want to be more sure of my
> exposures before I start burning up the expensive stuff.
>
> Any suggestions would be appreciated.
>
> Earl Johnson
> Inver Grove Heights, MN
> earlj@comcast.net
>
>
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Received on Tue Mar 16 21:34:58 2004