Paul C. Buff, Inc. Technical Forum

There's something that's been bothering me when using my Alien Bee lights with the Cyber Commander.

I've followed the instructions carefully and set my CC so that I have my three Alien Bee lights (1 x AB800 and 2 x AB400's) configured and ready for a shoot.

The Cyber Commander is set at ISO100 and 1/125, so I have my Canon EOS 5D Mk2 set at the same using the Manual settings.

I set the lights individually at first at f8.0 and tested their output with the built-in light metre on the CC. Each was spot-on. Once I set the lights to ALL, the light metre showed a much higher reading, but this is to be expected. I then lowered the lights whilst still in the ALL setting until the overall output was f8.0.

After following the manual, I assumed that if I had my camera set up with the same settings of ISO 100, 1/125, and f8.0, then my shots would be perfectly exposed.

They weren't.

In fact , the shots all came out marginally underexposed. The model looked like she was sitting in the dark.

I had to turn the lights up to f16 (using ALL setting) before I managed to get photos with a desirable exposer.

Can anyone tell me what happened? Why did the reading not correspond with the expected exposure?

What do I need to do to fix this problem in future so that it's not all guess work?

Thanks.

Are you tethered? (did you download the photos onto a calibrated computer monitor to check?)
And do you have another light meter to verify calibration on the CC?

Not tethered. I downloaded the photos and they are indeed under exposed. My monitors are calibrated regularly. I don't have another light meter to check against, nor am I able to source one.

Sounds like the CC is probably out of calibration.
Do you have any local photography or Meetup groups? Someone there probably has light meter you can test with. Or post your location and someone here might help.

First, I assume you do not have a polarizing or ND or other filter on your camera lens?

Second, did the meter say f/8.0'0? or was it, say, f/8.0'8 or f/8.0'9? That is improtant, as that is almost a full stop difference.

Third, you are metering from the subjects position with the meter dome aimed back at the camera?

Fourth, use your right joystick to scroll to the right and enter the SETUP screen. Then use the right joystick up/down to toggle to FLASHMETER, and press in with the same button. In the upper right hand corner, you will see the letters CAL. What is underneath that? It should typically say -0.0f. If not, use the right joystick up/down to adjust.

Fifth, if the above checks out OK, from the SETUP screen, use the right joystick to scroll down to ADVANCED CONFIGURATION and press in. Then scroll to FACTORY CALIBRATION. Then use the left joystick to click left or right to "REVERT" the calibration to factory specs.

You can now try again you tests you laid out earlier.

You can somewhat verify meter accuracy (certainly within a stop) on a sunny day. With the settings you have set, aim the dome directly at the sun and meter. You should get pretty darn close to f/16.

.
Thanks for the detailed reply. I can answer some of your questions now.


I have a Pro UV filter, but that's all. It shouldn't make any difference (hopefully) like a polarizing filter would.



f/8.0'0. I'm aware of the full stop difference (mainly because you emphasized it in the manual several times to ensure that us dummies would know the difference).



I stood where the model was going to stand and put the CC just below my chin with the dome pointing toward the lights.



I'll get back to you regarding these steps. I'll be away tomorrow, so will set up the lights and CC on the weekend and try your suggestions.

That's not how you meter - point at the camera. That will clear up your 'problem'.

Respectfully, that is not how you meter, light dome angled to the light source, this is incident metering.

If your intent in metering is to determine the camera exposure, you should point any incident meter toward the camera, not the light(s). Consider a light that is at a steep angle to one side of the subject. Pointing the meter at the light is going to indicate a much higher f stop than the camera is going to actually see, and the shot will be underexposed.