I hope I post this the right place.

I have a problem. I was shooting the moon using auto-focus and it focused so the image looked good in the finder, but the slides where not sharp. I noticed later that my lens wasn't focusing at infinity when it focused on the moon, and that is weird. I have done a manual focus shot at the moon, but are waiting for the film to be developed. The image in finder was then blurred. I wonder what the slide will be like.
Why is my camera being fooled by this? It normally focuses perfectly.

Can any of you give me advice on moon focus? And perhaps on exposure. I shot the moon with an exposure calculated from the following:

Shutterspeed = 1 / film speed (I use 90 and 125 with Fuji Sensia 100)
Aperture = 8 or 11
(or a faster speed and a wider aperture)

Is my calculation right?

Greetings Morten