The Holga's Aperture
What the fudge is an aperture? An aperture is the opening where light comes through into your camera. Aperture numbers can be calculated by using the following formula: N = ƒ/D. Where N is your aperture number, ƒ is the focal length and D is the diameter of the aperture.
The smaller the aperture number gets, the wider the aperture is. For example, an aperture of f/2 is much wider than f/16, and therefore lets in more light. The trade-off of using a wider aperture is shallow depth of field. Depth of field is the portion of a scene which has acceptable focus. A shallow depth of field would mean that very little in front or behind your subject is in focus.
What is the Holga's aperture?
The Holga's lens comes with a stock aperture of f/13 (thanks Nicolai). On older models, the sunny/cloudy switch does absolutely nothing as the larger aperture is placed behind the smaller aperture. This is like putting a window in front of a spy-hole in your door; it doesn't matter how large the window is, it will never let more light through the tiny spy-hole.
Old cloudy setting (f/13)
Old sunny setting (still f/13)
New cloudy setting (f/13)
New sunny setting (f/20)
If you bought your Holga in 2009 or later, chances are that it came with working apertures. The new stock apertures are: f/13 cloudy and f/20 sunny. This is only really 1 + 1/3 stop difference, but its better than nothing.
Can you change the stock apertures?
Yes you can, you can bust open your Holga and create your own custom apertures, or buy a pre-modified Holga from Holgamods with apertures of f/8, and f/11.