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What you will need

The camera itself
While these tutorials focus on DSLR cameras, any digital camera will do as long as it meets the following criteria:

  1. Produces images in a RAW data format.

  2. Focuses semi-manually.

  3. Can manually select a shutter speed/exposure time of several seconds.

  4. Has a wide enough field of view to get a variable star and comparison star in the image. A typical 50-90 mm lens will do just fine.

For reference, several Cannon point-and-shoot cameras meet this criterion. Although you can do this type of photometry using JPEG images, we don't recommend it. JPEG images offer a very small dynamic range (256 levels) whereas most DSLR cameras offer several times that (4096 or more levels is typical). Such a low dynamic range makes it difficult to observe the small change in brightness that is typical in variable stars.

Something to hold your camera
A simple photo tripod will do. Even a pocket tripod will work, as long as it can support the weight of your camera. Our tutorials focus on bright stars for which exposure times are typically less than 10 seconds and a little star trailing actually helps. For our tutorials, you do not need a telescope or expensive motorized mount, but as your skill grows and you start to do photometry on faint stars, a better mounting scheme will probably be required.

Two other items that will make imaging much easier are a cable release and right angle viewer. The viewer makes locating your stars in the viewfinder a much more comfortable exercise.

A photometric analysis software package
After you snap a few images with your camera, you need to extract the information from the images. In our tutorials we discuss free (IRIS), entry level (AIP4WIN), and high-end (MAXIMDL) reduction packages. We’ll show you how to use each of these suites to reduce the data. A few of our first-time participants have found Richard Berry's AIP4WIN book plus software suite to be helpful for answering fundamental questions about image processing, theory, and practice.

A Computer Capable of running the software
Almost all of the analysis suites run in Windows, but some can be made to run on Macs and Linux machines. You will need to check that your computer meets the requirement of whichever suite you decide to use. Although not explicitly required, we also ask that you submit our data to the AAVSO electronically over the Internet (instead of by mail) to help reduce transcription errors.

An unobstructed view
Although you don't need a fully unobstructed view of the sky, you do need to be able to see the variable star and at least one comparison star. Having a good "dark sky" spot out in the country is not necessary. Successful photometry can be done from a backyard with typical suburban light pollution. Darker skies will make the analysis easier, especially when targeting dimmer variables. Light pollution in a city sky will make faint star photometry nearly impossible, but you can still do meaningful bright star photometry with a DSLR camera.

AAVSO 49 Bay State Rd. Cambridge, MA 02138 617-354-0484