Calculating exposure
So you've shot a test roll or two, but you may be wondering why some pictures haven't come out properly. Chances are you haven't exposed the film properly: either too little or too much light on film. But don't worry, all you need to do is read through Fred Parker's excellent Ultimate Exposure Counter, and you'll be soon taking perfectly exposed pictures.
I did want to include an edited version of the table, relavant for Holga users, but unfortunately it is copyright and I cannot afford Freds $3500 asking price for redistribution. You are on your own I'm afraid. Here are some general rules when using your Holga in normal mode (1/100 shutter speed):
- Use 100 ISO in very bright sunshine, or use a flash
- Use 200 ISO in bright sunshine, or slightly cloudy conditions
- Use 400 ISO in overcast conditions, where there are no shadows
- Use 800 ISO for sunsets or brightly lit indoor scenes
- Use 1600 ISO indoors in reasonably well lit conditions
- Use 3200 ISO in pubs/clubs/museums where light is lower and flash is prohibited
Note: these are general rules. If you live in tropical countries you will want to reduce the speed even further. E.g. use 100 or 200 ISO instead of 400 ISO (thanks Vick the Viking). Or if you live in Northern latitudes (Scotland, North Canada, Scandinavia, etc), you'll want to increase the speed. E.g. use 400 or 800 ISO instead of 200 ISO (thanks matt).
Reciprocity failure
Reciprocity failure is where the sensitivity of a film changes over time. Basically this means when shooting long exposures, you need to allow more time than a light meter would tell you. Each manufacturer tells you how much extra time to allow in their data sheets for their film. If you don't know and need to guess, add about 10% more time for exposures longer than 2 minutes, or about 25% more for exposures longer than 30 minutes.
You can read more about reciprocity on Wikipedia or on PhotoNotes.org. You can see data for Kodak black and white films here, and data for slide films at photo.net.
