End-to-End Testing for Neutrality – Vectorscope Testing
Rhodium FSND Testing
Camera rental facilities do not have access to a spectrophotometer nor the time
it takes to determine an ND’s level of neutrality.
A quick and easy way to determine a filter’s neutrality is by testing the sample
on the very cameras on which the filters will be used. The output of the camera
can be piped out to a “Vectorscope.”
“Vectorscope” testing is very effective because it is a test of the image through
the filter→lens→sensor→electronics→monitor. This method is be*er known as:
End-to-End testing.
Here is an example of a vectorscope display:
There are 6 sectors of the 360 degree
display, each one representing either a primary or secondary color. Below is an
image showing the colors:
The camera is focused on an optical target that represents a neutral gray.
With no filter in front of the lens, the vectorscope will display a burst in the
center of the display – the center is considered perfectly neutral as it represents
an equal response from all 6 colors.
With a filter in front of the lens, the center burst should remain in the center.
A shift into any of the six sectors indicates a color shift of that sector.
Note: The relationship between the magnitude of the shift and whether that
shift would actually be noticed in a real image on camera, is difficult to quantify.
However, as empirically tested, if the vectorscope is set for 5X (times five)
range, a small shift (nudge) of the center burst within the square boundary can
be considered a fine neutral where the color shift will not be noticeable.