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A tripod is going to be essential for this and it needs to be on a solid surface for long exposures. If the legs are on grass, mud or sand, they can sink enough in a 30 second exposure to blur the photo.
The next thing to think about is the exposure time. If you need a basic primer in photography there are plenty of good sites out there.
You need to know the F stop of your camera. This depends on the distance from the pinhole to the film (focal length) and the pinhole diameter (aperture).
Divide the focal length in mm by the pinhole size, eg. my camera has a focal length of 36mm and the pinhole is 0.2mm diameter.
36/0.2 = F180

You can make a viewfinder or simply draw lines on the top and side of the camera to show the cameras field of view. You can then look along the lines to see what will be in the shot.

You can use a lot of normal cameras as a lightmeter for pinhole cameras. If you can set the ISO of the camera to the same as the film that you are using that simplifies things. Then set the camera to F22 and get the shutter speed.
As an example, if the shutter speed is 1/60 second and I then need convert that to a shutter speed for F180:
The sequence of whole F stops is as below:
1 1.4 2 2.8 4 5.6 8 11 16 22 32 45 64 90 128 180 256 360 512 etc
Each whole F stop lets in half as much light as the one before it. Notice that each number is double the number 2 to the left of itself.
F180 is 6 stops smaller than F22 so we need to half the exposure time 6 times to get the correct shutter speed:
1/60 1/30 1/15 1/8 1/4 1/2 1
This gives us a shutter speed of 1 second which would be common for a bright day and ISO100 film.
You could also use a modification of the "Sunny 16 rule", which I use most of the time. It saves time and gives fairly accurate results. The sunny 16 rule says that on a bright sunny day you should use a shutter speed the same as the film ISO rating at F16, ie. using ISO 100 film you would use a shutter speed of 1/125 (the closest standard shutter speed) at F16.
For my camera I just add 7 stops which gives 1 second.
If there is a slight haze which gives shadows a soft edge, then add one stop to give 2 seconds.
If it is overcast which makes shadows hard to make out then add two stops to give 4 seconds.
If it is heavily overcast and no shadows are visible add three stops to give 8 seconds.

If your subject is in shadow add another 3 stops.

If you thought it was all getting a bit complicated then you won't like this next bit. Unfortunately film doesn't work quite as expected at long expoures. It takes a bit longer to correctly expose the film as the shutter speed gets slower which is called reciprocity failure. Even worse this varies with different film types. Fortunately film manufacturers publish tables which tell you how much to compensate. Search for the datasheet for the film type you are using.
This is the compensation required for Fuji Velvia RVP ISO 50 film.
I have extended this from the Fuji datasheet which only goes up to 32 seconds. However I have tested it up to the 200 second meter reading and all appears fine. There will be some colour shifts at the longer exposures.
Meter reading         Required exposure time
4                     5
8                     11
10                    15
12                    19
16                    28
20                    37
25                    49
32                    1min07
40                    1min28
50                    1min56
64                    2min37
100                   4min16
128                   5min45
200                   9min22
256                   12min30
400                   20min20
512                   27min03


With my camera which uses 120 film and a 6x6 cm image size I wind on 9 and a half turns to start the film. This will vary with the design of your camera. I then wind one and a half turns for the first 6 shots and one and a quarter turns for the next 4 shots. I usually only get 10 shots instead of the 12 that it is possible to get on a 120 film.

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