I want to catch and photograph both events, so I have collected some equipment and have put some effort into dry runs. For the solar eclipse, I want to be able to watch the moon take a bite out of the sun, and for the Venus transit, I want to be able to watch Venus crawl across the face of the sun. For the Venus transit I'll need some magnification and filtration, and for the solar eclipse I'll need at least some filtration. So I've decided that I'll use the same setup for both events. This will be my 120mm refractor telescope and my Nikon-D80 camera. And of course, a filter.
|Type-IIa glass on left, film on right|
I have two types of solar filters: a Type-IIa glass filter and a typical aluminized mylar filter. They both were purchased to match my telescope, so the filter frame fits over the glare shield of my telescope. (It is important that the excess light is rejected before it enters a telescope. An eyepiece filter will burn.)
I took a bunch of images with each of the filters, and here are representative images, one using each filter type. The first image is taken through the film filter. This looks pretty good. You can see the sunspots clearly and it is bright even at ISO500, 1ms exposure. It also has a distinct blue/purple tint to it. I wonder what I think about that.
|Sun using film filter|
|Sun using glass filter|
From the bunches of images, these two were typical from each filter. Both images use the same exposure settings, so the differences are entirely the differences between the filters. I'm looking for brightness and sharpness. Brightness might be an issue if I find I'm forced to take a long exposure, but both are bright enough (the images above were taken using 1ms exposure time) and neither filters seem to distort the image any, so those are not criteria for choosing one image over another.
Ultimately, I think this is going to be a matter of taste, and not science. Which looks better? To my eye, the glass filter looks better because the color looks more realistic. Technically, the blueish white image from the film filter may be more correct, in that the spectrum getting through is more uniform, but this is not going to be a scientific endeavor and we humans think of the sun (incorrectly!) as reddish yellow. So for the purposes of making pretty pictures that give the right impression, I think I'm going to go with the glass filter.
Of course, the moon (or Venus on the day of the transit) will be black so that's not an issue for either filter. I guess I'm ready to go. Now the planets need to do their part. And by the way, I'll be setting all this equipment up on the observatory deck at the Chabot Space and Science Center on the appointed days. Join us!