Thanks for the wonderful response! I must ask, how do you determine what iso and f-stop I used? Can you tell by just looking at it? Next time I see the moon, I hope to use your tips!
I missed this reply when you posted it (sorry -- didn't mean to ignore this.)
When I take a photo of the moon I _always_ start with the assumption of a "daylight" photo. There's an old rule (which is _very_ handy to know because there are lots of occasions to use the rule) from the days in which cameras didn't have built-in meters. It's the "Sunny 16" rule - it describes a baseline exposure whenever you're taking a photo of something in full/direct sunlight.
The rule says that you can set the f-stop to 16, and then set the shutter speed to the "inverse" of the ISO. Since full-sun is quite bright, you don't need an increased ISO... the base ISO 100 is totally adequate. So that would give you an exposure of f/16, ISO 100, and 1/100th of a second. But that's just a "baseline". You don't really need to use f/16.
The _reason_ it's called the Sunny 16 rule and not the Sunny 11 rule or the Sunny 5.6 rule is because at f/16 (and only at f/16) the shutter speed will coincidentally work out to always be the "inverse" of the ISO. If you were at ISO 400, then shutter would be 1/400th. If, on the other hand, you were at f/11, then the shutter would no longer be the inverse of the ISO... it would be 2x the inverse of the ISO. So they call it the "Sunny 16" rule because it's _easy_ to remember the baseline exposure.
The rules of the exposure triangle are that once you know any valid exposure, you can play with it by trading off a stop of exposure in one part of the triangle for a stop of exposure in another part of the triangle). The triangle is ISO, shutter, and aperture. So if I'm using a telescope (let's just assume I have an f/8 telescope because f/6 is a fractional stop), then f/8 is TWO full stops more light than f/16 (f/16 -> f/11 -> f/8 are all "whole" stops... they are based on powers of the square root of 2 and remember that photographers and cameras always round these values). That means I can decrease light by 2 full stops ... either in ISO or in shutter speed. If I was at ISO 100, I probably cannot reduce the ISO any more (most cameras have a base ISO of 100... some can go down to 50). So likely I'll have to speed up the shutter to decrease the amount of light collected... instead of 1/100, I'll use 1/400 (1/100 -> 1/200 -> 1/400 -- each time you double the speed, you collect half the light.)
So we've established the moon is in full sun and we're using a Sunny-16 equivalent exposure, and in my example it's ISO 100, f/8, and 1/400th.
It turns out, the atmosphere of Earth does eat up some of the moonlight and I find that it tends to be "about a stop" (there's a factor that astronomer's measure in the atmosphere called "transparency") That means rather than actually using ISO 100, f/8, and 1/400th, I might increase the exposure by 1 stop -- usually by just slowing down the shutter speed ... so I'd use ISO 100, f/8, and 1/200th (rather than 1/400th).
Since I don't necessarily know what the actual transparency will be on a given night, I'll have to take a few test shots and adjust. Keep in mind you're trying to get nice contrast and that typically means you don't want the moon to appear too bright.
Also notice that in this whole discussion, I never brought up the topic of taking a meter reading with a light meter. That's because I wouldn't expect the meter to be accurate. All that black sky will tend to make the meter want to bump up the exposure and result in a blown-out moon. I have not attempted to take a "spot" meter reading off the moon, but that might work -- the moon might qualify as a nice "middle gray" target, but I'm speculating... usually I do the base Sunny-16 rule and "salt to taste" on my exposure.