Sigma versus new 50D??

[groman]

Quick question for anyone and everyone. Set up in great spot for shuttle lift-off photos at night w/ new 50D and my old Sigma 170-500 from my film days. It was initially upgraded by Sigma for my 20D when I went digital. Has been working fine since then. I set up Friday night, took approx. 6 shots of the moon and began to get ready for the shuttle and my camera quit working. The info screen and light would come on and the sensor seemed to read the light, but it would not take a shot. Turned it off and on a few times to no avail, watched the beautiful launch and just shook my head. I could have had a great moon and shuttle photo, but no!! My wife convinced me to remove the battery and that seems to have corrected the problem for now. She has convinced me that the lens needs upgrading again. I will say that all of the moon shots were way overexposed, even when I under exposed 2 stops. Any ideas or recommendations.
I appreciate all ideas and interest.

Thanks
Mike

[tonylong]

Aside from your camera outright misbehaving, the most likely thing would be that your camera could not auto-focus -- when you are in one-shot AF the camera won't take a shot if it can't focus. You would have to set the lens to Manual Focus.

[61ache]

I believe (haven't played around with it) in the menu you can tell the 50D to shoot even if it can't find focus as well...but tonylong's guess seems like the possible reason.

[groman]

Aside from your camera outright misbehaving, the most likely thing would be that your camera could not auto-focus -- when you are in one-shot AF the camera won't take a shot if it can't focus. You would have to set the lens to Manual Focus.

Camera was in manual focus due to my uncertainty of auto-focus on the shuttle. Good idea though. Any others?

[tonylong]

Hang on, there -- the camera does not have an "auto-focus" setting -- that's a switch on the lens. What can throw you off is when your camera is set to the One Shot Auto Focus and if you can't get focus lock then your camera won't focus at all and won't take the shot.

[groman]

Hang on, there -- the camera does not have an "auto-focus" setting -- that's a switch on the lens. What can throw you off is when your camera is set to the One Shot Auto Focus and if you can't get focus lock then your camera won't focus at all and won't take the shot.

Sorry for the slip. Of course the AF is on the lens. It was set for manual focus. I have been doing this for quite a while, so I am familiar with this.
I plan to call/contact Sigma today if I can find time.
Thanks for your input.

[Mike]

If your wife suggests upgrading what are you waiting for?! ;)