Sunspots on the sun come and go. Count them for many years and you’ll soon find out that there is an 11 year periodic cycle when the solar magnetic activity peaks. We are presently in Solar Cycle 24 and on the tail end of the double peak of 2011 and 2014. So why would I want a solar filter when the Sun is heading into a quiet period?
Number of sunspots observed and predicted for 1995 to 2020
Well, just because the number of sunspots goes down doesn’t mean that there’s not good some great observing opportunities. Sunspot 2529 provided that perfect occasion to finally try out my new solar filter.
Sunspot 2529 (April 10, 2016) – Benoit Guertin
The above image was captured on April 10th, 2016 with on my Skywatcher 80ED with Canon 400D at ISO 200 and 1/500s. 19 frames were processed with Registax6. Sunspot 2529 is still visible today and may be there for another week as readings indicate that it’s quite stable.
There are various types of solar filter out there. They all essentially do the same thing which is to permit only a small percentage (roughly 0.001%) of the white light to pass through. Solar filters are not designed to allow observation of prominence and flares, special hydrogen-alpha narrow-band pass filters are required for that, but they do allow a view of sunspots and granulation if you happen to have sufficient focal length. By blocking out most of the sunlight, you can then safely observer or photograph the sun. Remember not to install your finderscope, and move the telescope away from the sun before removing the solar filter. Your telescope is a MIGHTY strong magnifying glass.
Shopping around there are generally two types of solar filter: glass and film. While the glass are more durable, the films offer just as good optical performance at a lower price, especially for larger aperture.
Thousand Oaks Optical R-G Solar Filter
Normally for anything in the optical path, especially filters, backyard astronomers are always looking for the smoothest and most parallel surfaces, but for solar film, it appears that the ripples from the loose film have no effect on the image quality.
The filter that I selected is the R-G Solar Filter from Thousand Oaks Optical. It provides a light yellow pleasant view of the sun, and works very well both visually and with the DSLR. I enhanced the yellow in the photo of the sun above, but it’s quite close to what can be seen and photographed.
Mark your calendars for May 9th 14:57UT, Mercury will transit in front of the Sun. The last time that happened was 2006.