How many stops of light does the earth's atmosphere filter?

Question: How many stops of light does the earth's atmosphere filter!?
Best Answer - Chosen by Asker:

If you can find out the exposures and ISO settings used for the lunar landings and then compare them to midday images taken at the equator on a sunny day you'd have your answer!.

Obviously it will be more the further you are from the equator as the sun will have to penetrate more atmosphere to hit the polar regions too!.

I've written to NASA and asked - it's an intriguing question!.!. one of the most interesting I've seen here!. My guess is a stop or so!.Www@QuestionHome@Com

I do not believe that there is any type of scale in photography to measure the intensity of sunlight!. The light meter simply records it internally and matches an aperature opening (f-stop) and a shutter speed to match it based on the film speed or ISO or ASA rating!.

There are other factors to consider also!. They include the amount of cloud cover, dust, smog and even location on the Earth!.Www@QuestionHome@Com

That is hard to answer!. Many variables are involved!.

Altitude would play a big part as would the weather!.Www@QuestionHome@Com

I think it's multi-coated, too, hopefully T*!.Www@QuestionHome@Com