[Content moved from http://photographingtransitofvenus.wordpress.com/]
The last time I pointed my camera towards the Sun to photograph the 2009 Total Solar Eclipse, which is also a “once in a lifetime experience,” I had used a piece of a $9.00 Mylar Thermal Blanket instead of a proper solar filter in front of my lens. Well, that was not by choice but by chance as I was carrying a Mylar thermal blanket with me. Mylar blankets, which are made by vacuum depositing a very precise amount of pure aluminum vapor onto a very thin film substrate (Mylar), reflects upto 97% of radiated heat. This makes them very effective for preventing body heat from escaping. They are commonly used by campers as “thermal blankets” and also used in a lot of solar projects.
The transit of Venus is one of the rarest predictable celestial event, and most likely I will not be around the next time Venus decides (predictably) to show up in between the Earth and the Sun. While I don’t have any extreme gear, such as a telescope or a extreme-telephoto lens, I have lately become a little obsessed with the “RESOLUTION” thing! This is nothing more than a professional hazard I guess; nevertheless, it is a damn “unignorable” one!
I decided to order a $88.00 “Baader AstroSolar(TM)” Foto film (Optical Density=3.8) from ASTRO-PHYSICS.COM for making a solar filter for my lens. A solar filter must (highly recommended) be placed IN-FRONT of the lens while pointing an optical system directly towards the Sun. If you don’t, then you will potentially roast not only your precious equipment but also your retina if you look through the viewfinder. The Baader AstroSolar film is manufactured by Baader Planetarium (GmbH) in Germany and certified by the German Republic Bureau of Standards. According to the technical specifications, the Baader AstroSolar filter boast the following properties:
- It is streak- and blister-free, 0.012 mm thick foil, providing very good contrast and neutrality.
- It attains the optical performance of high quality diffraction-limited (optical aberration-free) plane-parallel glass filters.
- The base material is TurboFilm and not “Mylar” plastic. TurboFilm, which has a highly uniform molecular structure, was a result of research in nuclear and elementary particle physics.
- The AstroSolar film has a Strehl ratio of 94.1% compared to the Mylar that has a Strehl ratio of only 57.2%. This means that in an independent comparison of the two, AstroSolar film should produce almost 2 times the resolution of Mylar films. [More on Sterhl ratio and comparison of their resolution will be a topic of another blog post!]
[This content was originally posted by me at http://photographingtransitofvenus.wordpress.com/, a blog dedicated to the 2012 transit of Venus]