The "Download Now" link directs you to the iTunes App Store, where you must continue the download process. You must have iTunes installed in order to open the link, and you must have an active iTunes account to download the application. This download may not be available in some countries.
From The Ilex Press Ltd.:
The Ilex PhotoTool is a 4-in-1 tool for digital photographers trying to get the best out of their cameras. Building on Ilex's heritage as a leading publisher of photography books, the PhotoTool offers quick and convenient access to everything the photographer needs to get the perfect shot, straight from their pocket. It includes advice on shooting in a variety of situations, all of which help you develop as a photographer rather than fall back on auto modes, and a complete glossary of digital photography terminology, many with illustrations. Better still, all the content is stored on your phone, so you can still get all the info you need fast, wherever you are, even with no network connection. As well as top-quality editorial content from experienced contributors, the App includes a pro-level focus calculator, which you can use to calculate the depth of field, near and far limits, and hyperfocal distance for any given focal length, aperture, and crop factor. This versatile, yet easy-to-use tool will help you control your creativity precisely, leaving nothing to chance (Settings allows you to switch between metric or imperial measurements, and choose your crop factor manually or from a list of camera types). The Reciprocity and Exposure Value calculator is also a valuable tool for photographers getting to grips with their camera's manual functions. With one easy-to-use screen you're able to see the effect changing any of the core exposure functions aperture, shutter speed, or ISO has on the other. You can also calculate the Exposure Value (EV) for any given set of values. Finally, if you're in a network area, you can see the latest news from Ilex Press. Future editions (free upgrade) will include video clips.