DSLR Photometry Tutorial
Photometry by itself answers a single fundamental question: “How bright is it?” and if you do photometry over time you can answer another fundamental question: “How does brightness change with time?” These answers to these simple questions can be obtained from just visual inspection of a light curve, or through more advanced techniques, but the main reason why we do photometry is to gain additional insight to the behavior of various astronomical objects. In this tutorial we focus on stars, but the same approach we discuss here can be applied to planets, asteroids, comets, or even galaxies.
The AAVSO has already posted several documents discussing the importance of variable star work therefore we won't elaborate further here. Instead we wish to discuss a relatively new technique for observing variable stars that appears to be a middle-grounds in terms of ease and precision: DSLR photometry. (Even though our tutorials specifically say “DSLR” cameras, keep reading on. Your point-and-shoot camera may indeed be able to work with these techniques!) Unlike single-channel and CCD photometry which require expensive sensors and specialized astronomical filter sets (more on these later), DSLR photometry can produce high quality data in a fairly short period of time at modest cost. The DSLR Documentation and Reduction Team has created a series of tutorials to guide you through setting up your camera, imaging target and comparison stars, processing your data and submitting the results to the American Association of Variable Star Observers (AAVSO). Other tutorials on this website will walk you through analyzing your data to produce scientific results and publishing your results in scientific journals.
As you read through this tutorial you may find it to be out of sequence: we don't actually discuss taking images until the end of the tutorial. This is highly intentional as any experienced photometrist will tell you that frustration begins with bad data. Therefore we want you to work with known good data first so you can get a feel for the procedure as a whole before you take your first frame.
The tutorial is arranged into six major sections. We first introduce you to the broad concepts of how DSLR photometry works and what you will need if you decide to do it on your own. Then we give you an overview of the data reduction packages used to extract photometric magnitudes from images. Then we walk you through starting and finishing analysis and how and finally how to submit data to the AAVSO database for long-time archiving. After this is all complete we discuss the procedure for taking images and things you should check during and after the imaging process.
If you have questions as you go through this tutorial, please post them to the photometry forum as many of our team members regularly visit there.