Yesterday I spent the day at the MidAmerican Regional Astrophysics Conference. This year this roaming astronomy meeting was held just outside St Louis at St Charles Community College. I have to say I was really impressed with the quality of the presentations and the staff took care of me extraordinarily well. One of the ones that particularly caught my attention was on the use of didymium filters to minimize the effects of sodium light on astroimages. Here are some examples:
In this presentation by Doug Kniffen, I learned that these photographic “enhancement” filters are fairly effective at blocking light the color emitted by sodium (and thus emitted in sodium lights). While not designed for telescopes, when employed for off label uses, these filters allow astroimagers to take aesthetically pleasing pictures from sites that otherwise can’t support deep sky photography.
If you look closely at the images above, you’ll notice there are actually more stars near the horizon in the After image than in the before. Specifically, look above and to the right of the house in the center. There are two stars in the image on the right that just aren’t in the image on the left.
From what Kniffen said, you can’t get these filters in standard – screw onto your eyepiece or insert into your filter wheel – sizes, but they do exist in many camera size, perfect for the piggy backed camera. I did a bit of research, and found them here at very reasonable prices (mind you, in grad school I managed to destroy a $1500 filter, so, well… I have weird scales for these things). Now that our house has roof top access (we are resurrecting a widows walk), I may have to get one and try doing some city-based astrophotography. It has been a long time since by happy little SLR (yes, film) camera saw starlight, and a new filter just might be the kick in the butt I need to get going again.