White balance and Iris descrepency

[James Ewen]

I have just got back from shooting commercial here, two HD100E cameras, diva lites with tungsten tubes, in a studio. Both cameras set up exactly the same. One camera had WB at 3700K the other read 3400K, there was also a full stop on the iris between the cameras. We tried them in all positions and still the same result.

Any ideas? I know that individual cameras can differ but this was just silly.

Is there something I have missed?

Thanks in advance,

James

[Tim Dashwood]

Were the scene files EXACTLY the same? Gain? Filters? ND? Shutter speed? frame rate? AE level?

When I shoot with two cameras, I setup one the way I want it for the scene, then save the Scene File to the SD card, put the SD card in the other camera and load it.

I then perform white balance on both (at the same time side-by-side) with an 18% gray card.

The white balance should read exactly the same. I'm not surprised that the F stops were reading differently though. There seems to be a wide range of tolerance with the stock lens. You should try manually setting exposure with zebras next time and see if the readings are the same.

[Steve Mullen]

Originally Posted by James Ewen

One camera had WB at 3700K the other read 3400K, there was also a full stop on the iris between the cameras.

I've found that the WB readout will change as the light goes from "too low" like when the iris is at OPEN to "OK" when light or gain is added so the iris opens to f/2.

So Tim's suggestion that there might be a difference that causes an exposure difference is a good place to start.

What where gain and iris?

And, did the video look different?

[Barry Green]

Originally Posted by James Ewen

was also a full stop on the iris between the cameras.

Were they at the same zoom setting? If one was at full telephoto and the other was at full wide angle, that would explain the iris differences. The lens loses easily at least one t-stop over the course of the zoom range, so if the telephoto camera was at f/1.4, it'd still be delivering a t-stop of no more than about t2 or t2.4, so a wide-angle camera would have to be stopped down a stop or so in order to compensate.

[Tim Dashwood]

That's a good point Barry. I didn't even think of that.

[James Ewen]

Tim, Barry, Steve,

Thanks for the input guys. The iris descrepency was also present at the WB, when we had both cameras in the same place with the card filling the frame.

Gain was at zero in both cases, Iris f4/5.6, no filters, same shutter blah blah. We do have another shoot this evening so I will try your trick with the SD cards Tim, if there is something different hidden in the menus then this will pick it up. I will also try a manual iris check.

Thanks again,

J