long exposure question

October 27, 2007 7:49 PM

Emergency camera question: I'm staying at an astronomical observatory all night tonight and want to take some pictures of some really dark subjects. I borrowed a Canon Digital Rebel XTi from my school but don't have the manual...

Basically i want to take long exposure shots (30") but when it's really dark the shutter just won't go. I searched around the Canon knowledge base site but with no luck. Anyone have this camera or know it well enough to help me out? I'm completely clueless right now...

posted by Gankmore to media & arts (7 comments total)

You're probably encountering failure to autofocus, there's not enough light for the camera to do it for you. Switch to manual focus, focus by hand, and the shutter should fire freely.
posted by knave at 7:54 PM on October 27, 2007

I think what you are looking for is a "bulb" setting. That's the setting where the shutter will stay open while the button is pressed.

Perhaps there is the failure to autofocus, as knave suggested, but if you can find the bulb setting (if the camera has one; my only experience with bulb settings is the Pentax K1000) you should be able to get the shutter to open.
posted by jayder at 8:06 PM on October 27, 2007

This link says that the Xti has a bulb setting.
posted by jayder at 8:07 PM on October 27, 2007

1. Switch the top dial to "M" (manual).

2. Turn the wheel under your right index finger to the left until the screen says "BULB."

3. That's it!

Play with the aperture to get the exposure the way you want it (I have no experience w/ night shots like this so I can't help you with that). In manual mode you set the aperture by holding down the "AV+/-" button at the top-right of the rear screen and turning the index-finger dial.

Good luck!
posted by wemayfreeze at 8:26 PM on October 27, 2007

The bulb setting may be a useful tip, but it's certainly not his shutter speed setting that's causing problems firing.
posted by knave at 8:52 PM on October 27, 2007

switching from auto- to manual-focus fixed it. thanks guys!
posted by Gankmore at 9:02 PM on October 27, 2007

You also might want to set the custom function relating to the mirror flip-up. I forget exactly what menu it's in. This will allow the camera to flip up the mirror a little sooner than it begins reading sensor data, preventing any camera shake due to mirror flip from messing with your image data.
posted by odinsdream at 9:05 PM on October 27, 2007