Glad you could make it back! Here’s the exposure guide I promised. It’s not the last word on exposure by a long shot, but it’ll get most people going right off the bat with reasonable exposures.
There are other ways to gage exposure, I like this one. But then again I’ve always liked flying by the seat of my pants…
The ‘Seat-O-the-Pants’ Guide to pinhole exposures
First a little bit about the size of your pinhole relative to the size of your camera. I usually go with the rule of thumb that says that is your camera has a focal length of 6″ then your pinhole should be .5mm in diameter. This is a rough measure, but it gets you into the right area. The table below explains the other rules of thumb that you might want to try.
When you make the pinhole use a ‘drilling’ motion to get the pin through the tin or brass sheet. This avoids making a big, messy, rough hole…(not that every pinhole has to be perfect) but until you get the hang of making cameras it might be a good idea to make things as “normal” (what ever that is) as possible.
I use aluminum baking sheets from the grocery store for my pinhole material. It’s cheaper and just as good as brass…up to you really.
ATTENTION!…ok, now that I’ve got your attention…
Larry Fratkin has created a really useful tool for calculating the focal length and pinhole diameter of your camera…try it! And once you try it let Larry know what you think of it!
Camera Length
|
Needle Size
|
Diameter
|
Relative
|
|
8″ |
8 |
.023″ |
f/350 |
|
6.5″ |
9 |
.020″ |
f/300 |
|
5″ |
10 |
.018″ |
f/280 |
|
4″ |
12 |
.016 |
f/250 |
|
2.5″ |
13 |
.013 |
f/190 |
or you could use this formula…
dia/focal length
or…
the optimum pinhole = the sq.root of 0.0016
multiplied by the pinhole to film distance…
(or you can wing it…)
Making exposures?…Start here
Weather Conditions
|
f/stop
|
Photo
|
ASA
|
ASA
|
| Bright or hazy sun. A scene with light sand or on snow. |
250 300 350 |
17 seconds 29 seconds 44 seconds |
1 second 1.6 seconds 2.5 seconds |
1/4 second 1/3 seconds 1/2 second |
| Bright or bright-hazy sun. The shadows are distinct (sharp) Your typical nice, sunny type day. |
250 300 350 |
49 seconds 1.3 minutes 2.1 minutes |
2.8 second 4.6 seconds 7.1 seconds |
1 second 1.25 seconds 1.5 seconds |
| Weak or hazy sun. The shadows aren’t distinct (soft) An OK type day. |
250 300 350 |
2 minutes 3.3 minutes 5.1 minutes |
6.7 seconds 11 seconds 17 seconds |
1.3 seconds 2.2 seconds 3.4 seconds |
| Cloudy. But bright! No shadows No sun. No rain. |
250 300 350 |
5.4 minutes 9 minutes 14 minutes |
18 seconds 31 seconds 47 seconds |
3.6 seconds 6 seconds 9.2 seconds |
| Open Shade or heavily overcast No shadows Either a grey day or in the shadow of a tall building |
250 300 350 |
14 minutes 23 minutes 36 minutes |
47 seconds 1.3 minutes 2.0 minutes |
9.2 seconds 15 seconds 24 seconds |
| Dawn or Dusk Dark out here… Like it says. Early morning or early evening |
250 300 350 |
38 minutes 1 hour 1.6 hours |
2.1 minutes 3.5 minutes 5.4 minutes |
25 seconds 42 seconds 1 minute |
Ok. Keep in mind that all these times are just starting points. As you make more exposures and get better at making guesses that work you’ll make your own exposure chart.
When you make an exposure that is just way too dark as a print then double the exposure you gave the neg. If your print is just too light then halve the exposure. It might sound like the long way around but by splitting the differences each time you can arrive at a pretty good exposure in a your first few attempts.
Another great idea is to keep a notebook of all your exposures, the weather conditions, the film or paper etc.