Hugo Poon , Feb 27, 2010; 05:15 a.m.
Firstly, it's a 1000D, not D1000 :)
If you're using a tripod, why use ISO 800? Are there moving subjects? If it's all "still", I'd say use ISO 100, and get it right in the camera, especially if you're shooting JPEG. Post-process exposure editing will only bring the noise levels up, and at ISO 800, it could give quite a bit of noise (it's good if you're aiming to get that look; otherwise just shoot at the lowest ISO possible).
Also, if you're on a tripod, the only causes for motion blur I can think of are:
You shake the apparatus when pressing the shutter (solution: use a cable release/self timer/remote)
The church/hall's near a railway where a train regularly passes, or where there're heavy vehicles(?) (solution: time your shots)
The mirror's slapping so hard that the apparatus becomes unsteady? (solution: make sure everything on the tripod's as tight as possible (but not so tight that you hurt your fingers unscrewing))
Shoot full manual; it gives you so much more control over your exposure.
Assuming that your current Manual settings have the "right" exposure (whether it's "right" or not is your decision to make), at ISO 100 (base ISO for most Canon dSLRs), you would be shooting at 4.5 and (taking 1/80th to the nearest full stop of 1/125th) 1/15th.
However, shooting wide open doesn't give you a lot of DOF; it's also often not the lens' sweet spot.
So do a series of tests at ISO 100:
Beyond that the photos will likely look "soft" due to diffraction. A wild guess is that your lens' sweet spot will be f/11.
When viewing the results of this test, use the self timer (preferably 10 seconds) or a cable release; have your tripod at its tightest settings and make sure everything around you is still.
It might also help to step back a bit from the tripod after pressing "the button", just to make sure your feet don't hit the tripod (this is something I always do, especially with exposures under 1/30th on an SLR)
Obviously, trying to compare sharpness on the camera's screen won't be easy. Nor will it be accurate. Get the photos on your computer, view them at 100% (and 100% only); anything above or below won't be a fair test.
Personally, I stay away from all auto modes on cameras. Actually, 2 of my 3 (properly working) cameras don't have auto. 1 of the 3 (Kiev 4a) doesn't have a meter (I specifically bought the 4a because I didn't want a meter); the Nikon FM has a meter but no auto mode (I just took the batteries out because I hate distractions in the viewfinder), and my D50 has auto-everything (but I still use my incident meter and manual mode).
Manual's brilliant once you get used to it. Especially easy on most negative films (can afford errors of up to 4 stops either way).
Especially if you're shooting in light that doesn't change really quickly (and you don't have a decisive moment to catch), you should have all the time you need (especially indoors, unless you count the window light); use manual mode.
I find that when shooting indoors, a lot of the time, auto WB just doesn't do it - set WB yourself (saves time on the computer).