Aw, man, I got this… this… coding problem. I keep finding myself writing things that only I would have a use for. So on my iPad, I found this App called “Emerald Observatory”, and I was so, so impressed. First, it’s pretty. Really pretty. Second, it’s full of astronomical data, useful stuff. And I thought to myself, wow… I really like some of this.
Then (oh, no…) I began to think about what parts of it I would like to use, that is, have directly available to me. So I wrote those nice folks, complementing them sincerely on what a nice App they had come up with (check it out, you won’t regret it), and suggesting they write what I had in mind, because actually, they sort of had the data in the app already, it was just a matter of organizing it differently. I got a nice reply, thanking me for the suggestion, but allowing as to how they had a lot to do, and so it would be “on their list.”
Trying to figure out if there is an aurora, and if it can be photographed, really requires looking at some different kinds of data. One is the earth’s magnetosphere; how disturbed is it? That’s what causes auroras. That information has to be obtained from the GOES satellites, or magnetometers on the ground (I find the satellites to be a better indicator.) Another is the weather – if it’s cloudy, give up now. Then visibility comes into play – fog will kill the opportunity just as quickly as clouds. You can get that from NOAA (or whoever is your local weather provider if you’re not in the US.) But what if the moon is above the horizon? That’ll kill it too, at least, if the moon is showing any significant crescent. And of course, along those same lines, the sun has to be below the horizon. The moon and sun information can be calculated.
Generally speaking, the 
is a great lens. The bokeh is fine. The lens is pretty fast. f/2.8 to f/22 is useful as a creative range. The optics are sharp and the all-time focusing is a boon. So what’s not to like? Well, here’s the thing. The Canon EOS50D, which I use, has the ability to use the viewfinder in “live preview” mode, and when doing so, will allow you to zoom in on your focus point (or anywhere else, but that’s irrelevant to my point here) such that you can see extremely fine detail. At which point you can manually focus the lens so that it is exactly right. Marvelous, right? 
is a very heavy (1025 grams or 2.25 lbs), very well built lens. It comes packaged with the appropriate hood, the Canon ES-7911. You get both a lens cap and a mount cap, all packed inside tight conformal foam to protect the lens during shipping. There’s also a very brief manual and the usual warranty paperwork. 
