In the dark

[sharlet]

I do portrait photography in studio in my home. Mainly as a hobby. I am a true blue film user attempting to enter the digital world. I have a Canon Rebel XT EOS and I use a Canon Speedlite 420EX flash unit. I use an umbrella for main and fill, a medium softbox for accent and a background light. I use manual setting with a shutterspeed of 100 and adjust my aperture to accomadate a nice print. My question is why is it that one photo is perfect and then I repeat the same photo (absolutely nothing changed) and get underexposed results? I just don't understand. I know there is variability in light but is there a way I can avoid this? It is very frustrating and I am trying to resist the urge to grab my film camera.
And another thing that may or not be related is that one of my umbrella strobes keeps blowing a fuse. Please help.

[Medley]

Are you shooting in RAW or JPEG format?

-Joe U.

[Canuck935]

Are you allowing enough time for the flash to fully charge up after each shot? How bad is the underexposure? Not sure about the fuse blowing problem, but it is an issue since that shouldn't be happening all the time.

[cyberlord]

I assume the speedlight is on camera. Is it set to P-TTL (CLS in Canon I think)? You mention manual setting, but is that the camera or the flash?

You want your flash in manual mode too, P-TTL or CLS will fire your slave strobes too soon and they won't light the frame when the shutter is open. All that will be lighting the frame is the on camera flash and if you are bouncing it just to fire the slaves then the photo will be dark.

What setting was your film camera flash set to when you were using that? It maybe had TTL setting and that does not fire a pre flash that prematurely triggers the strobes so it was not affecting the light.

Other than what Canuck said, make sure the ready lights are lit on the slave flashes.

I'm not sure on the fuse blowing, usually that means there is something wrong where too much current is being used. U can take that strobe out of the equation by not using it and shoot some test shots. You key light should expose properly when you have everything setup right. Then add the suspect strobe as fill and see what happens. If it keeps blowing fuses, it's time to have it checked out as something is not right with it.

Tim

[sharlet]

I am shooting in JPEG format. My Canon Rebel XT has the E-TTL feature which I have disabled by setting it to "average" instead of "evaluative". This to disable the preflash evaluative metering which triggers my strobes to early. My flash unit is not set on manual however it is my understanding from the manual book that the camera AND the flash unit must be E-TTL ready before this feature can act. So by disabling the camera I assume I have disable the feature. It is possible that I am not allowing the flash or strobes one to recharge as I hadn't thought of that aspect but will definitely try that.
I sometimes use my Canon Rebel film camera (which has no E-TTL feature) on Manual mode SS 100 and aperture 11 on high key white and 18 on low key black and get good results. I thought that digital would make my life easier. But again, I will try to allow more recharge time.
Thanks to all for your help.