Diameter of the Moon in Pixels

[xpatUSA]

Having just bought a 400mm lens, I wondered how "big" the Moon would be in an image.

So I did a calculation assuming that the lens would be focused at virtually infinity - that is to say that the point of focus in the image plane would indeed be 400mm from the aperture (talking thin-lens).

The moon is said to be, on average, 31 arc-minutes (moa) "wide", seen from Earth. My G9 camera's pixel-pitch is about 3.32um. It's subtended angle with the 400mm lens is about 0.0285 moa **

Therefore, I would expect the moon to be 31 divided by about 0.0285 equals 1086px - about a fifth of the image width.

** = 2*invtan(pitch/(2*Flength))*60

Posted FWIW. Of course, I could have just gone out and shot it but it is daytime, the weather is atrocious and my tripod is a bit wobbly ...

[Panama Hat & Camera]

Ted,
Your reasoning is correct!
I do this calculation a little differently (I use one more step), but the result is the same.
Cheers,
Antonio.