Well it was one of my most popular posts, so I'm back with more advise for you crazy pinholers out there. Either to create images or view Solar events :)
In the last post talked about making a better pinhole and some basic ideas on how to make the box better. This time I'm going to go a little more into the mechanics of the camera. For simplicity's sake I'm pretty much going to focus on Pinholes using Black and white media, you can do it with Colour but it's much trickier to do and the result will vary much more.
The Pinhole: As noted last time you will get the best results the rounder the pinhole is, this means using a thicker material to create the lens plate. (see my last post) To stop refraction it is good to paint the plate black but if the interior of the box is light tight and painted black as well this is not always necessary. The plate should be slightly larger than the hole cut in the camera body (box or whatever) and afixed to the inside to prevent light leak. I have found black gaffer tape to be a pinhole camera builders best friend in this regard, it's black and will block most light.
The Pinhole should also be as small as is practicable, a smaller hole will extend exposure but give you a sharper image and greater depth of field.
The Camera Body: This can be anything you want but it is best that the focal plane (the back of the box where the image projects) and the lens plate are on a flat surface parallel to one another. (You can do things with curved focal plains etc but I'm dealing with making the best image possible from the pinhole camera) As mentioned in my previous post; almost anything can be the Camera body so long as it's light proof. I Built a Pinhole Camera once that mounted the paper in a 4"x5" darkslide which I could take in and out of the back of the box, the entry way was suitably padded with gaffer tape to keep light out. This allowed me to effectively reload the camera in the field without using a dark bag or anything like that. (Each darkslide also held two plates so two shots per slide) I have also seen people make panoramic pinholes with multiple holes that they open at the same time...
The Shutter: The other important part of a Pinhole camera is the shutter. Traditionally this is just a light blocking piece of paper that is moved in front of the pinhole when it is not exposing. Depending on the exposures you are working with; Camera movement when opening and closing the shutter may or may not be an issue. I have found this is often more to do with the weight of the Camera body, lighter cameras tend to move more when you flip open the shutter. The most important thing is that your shutter needs to be securely closed when the Camera is loaded and not in use, even small amounts of light over time will fog paper or film and lead to a poor image.
The Light Sensitive Medium: You have a number of options here; Photographic paper is the most common as it is easy and quick to develop making it good for trial and error. It also is not very light sensitive so it is more forgiving with exposure length and fogging. It has some issues, long exposures are usually necessary for example. The biggest is conversion to a final image, remember that the image you will get on your Photographic paper will be a negative so you will need to "print" it to get a positive image. The only real way to do this with a paper negative gives quite low resolution images as you have to expose the print through another piece of paper. Film gives better results but requires you to be a little more careful handling and loading/unloading the camera. Film will give you a negative that can be enlarged and printed like any analogue image and it is also available in a variety of ISO speeds and generally will be more light sensitive than paper. (ie shorter exposures) By far the best results come from the larger film formats, 4"x5" or 8"x10" film can create glorious pin hole images with very high resolutions.
Next couple of times in this infrequent series will deal with Focal length and Pinhole cameras and calculating exposure. (Yes you can do it without trial and error!)
Oh and here is a great page about building a Pinhole, very easy and quite a good one