Camera support
Mar 1, 2008 12:00 PM, David Hart
Camera maintenance has changed. During the days of the tube camera, much more needed to be done to maintain the overall quality of the camera. With CCD cameras and now digital cameras, maintenance requirements have changed and are, overall, easier. However, just because the requirements are easier doesn't mean you still don't need the proper tools to set up and align cameras to maintain a consistent quality. The need for correct tools is one requirement that has not changed.
Color temperature
Your alignment flow and lighting and test charts must be the same for all cameras to maintain consistency.
What's most important is to have a consistent and correct color temperature lighting source. My Sony PTB 500 light box, for example, has sensors that vary the voltage to the lamp as the lamp deteriorates so it will maintain a consistent output and color temp. My Minolta color meter rates the light box at 3180K, which is close to the ideal 3200K.
If your lighting is not exactly 3200K but very close, it's probably fine. The issue is not necessarily having the exact color temperature of 3200K, but having a consistent color temperature.
Having a chart on the wall with the proper lighting to cover it evenly is also a fine setup for aligning cameras. However, you should measure the color temperature daily to be sure that it is consistent, as tungsten lights deteriorate in temperature with time.
Reference lenses
It is advisable to have a reference lens for calibrating your cameras. The optimum sweet spot for the lenses I use has been 60mm to 70mm. That puts me in the middle of the zoom range on most normal 15- or 18-to-1 lenses. I try to be 6ft to 7ft away from my charts or light box.
With the advent of digital cinematography, you may want to consider some of the prime lenses for the test area instead of a zoom lens as the primes are used most often in movie creation. Again, being consistent and using the same lens for all the setups will provide consistent results. Consistency is the key to success.
Camera setup
As for the cameras, almost all have the same basic type of setup. In older analog cameras, the user would verify an output level from the CCD block green channel using the lens iris and then balance the output of the first stage or video amplifier board to be a nominal value for red, green and blue. In the case of most Sony cameras, it was 0.5V on the output. On some cameras, you would also need to balance the test signal outputs to 0.5V for each channel. Then, assuming the rest of the camera (i.e. the encoder) works correctly, you can use that same test signal to adjust the rest of the signal path through the camera.
The analog camera is out, and we are in the digital camera age. These cameras are easier to adjust. In essence, all that is needed is to set the output of the CCD block either in the first stage, the video amplifier board in Sony cameras, or directly on the CCD block itself.
Several cameras now have either a video amplifier board directly on the CCD block or the initial output is set on the preamplifier board on the CCD block. Next, set the test signals, and balance the output of the video amplifier card using the test signals. After doing this, the camera is set. There are, of course, separate issues of black and white shading that need to be checked and adjusted to match your lenses.
Alignment
To give an example of how to align an HD camera, let's look at Sony cameras. Most cameras will use a similar process.
Because of the dual output on these HD cameras, the levels of each of the two outputs for each channel, RGB, need to be balanced. The balance should be checked and adjusted for both black and white — black with the lens capped, and white using a grey scale. Balancing the outputs assures you that there will not be any abnormalities in the final output of the camera.
Next, the lens needs to be adjusted to the recommended f-stop. I recommend using a remote control or master setup unit to set the lens iris. The readout on either of these is much more accurate than trying to line up the markings on the iris ring on the lens.
Once you have the proper iris level, the outputs of each channel should be adjusted on the CCD block preamplifier board. The levels are normally given in the service manual.
Not all cameras have the same output level. However, most of them do have the same adjustments. You can also use the remote control or master setup panel to set the test output levels. This is done by setting the individual levels of each channel for 100 percent on the HD waveform and then storing the information in your reference file.
Finally, the output level of the CCD block signal on the video amplifier board is set to 100 percent, also using the controls on the video amplifier board. When this is completed, both the test signals and the analog video signals should be 100 percent.
Many of the new cameras are almost alignment free. For example, Sony's HDC1500, F23 and HDWF900R normally do not need any of the alignments the older HD cameras required. They are set at the factory to exacting standards for the output of the CCD blocks. And even though the CCD is an analog device, the output through the camera will remain the same over the entire life of the unit.
In cameras with lens files, a white offset for individual lenses can be stored. This is a great advantage if you use several different manufacturers' lenses. It allows you to adjust the red and blue balances to correct for any difference in color transmission between lenses. You can also store white shading data in that same lens file.
Lighting
Any camera, including the latest generation of HD cameras, needs a consistent light source for the charts and a standard lens for the tests. Without them, you can never be sure that any of your cameras — analog, SD or HD — are set correctly. But with consistent lighting for charts and a standard lens for the cameras, all your cameras will give you the same look every time.
David Hart is 37-year veteran of the video, HD and digital cinema camera field, specializing in Sony cameras.
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