Datacolor User to User Support Group.

On Feb 3, 2009, at 1:08 PM, Nathan Gutman wrote:

> Using Spyder2Pro. I wonder how the distance from projector to the  
> screen affects the calibration. When calibrating the projector the  
> screen to projector distance is limited by length of the Spyder cord  
> which is about eight feet so there is a lots of light reaching the  
> screen.
> In actual use the projector to screen distance is much greater so  
> consequently less light reaches the screen.
> How does this affect the projector calibration?

The length of the Spyder USB cable is not the limiting factor, its the  
location of the various elements, how you have them configured... and  
how long a projector cable and USB extension cable you happen to own.  
In most situations getting a 10 foot USB extension will ease things  
considerably.

The goal is to have the Spyder close to the screen. Especially with  
the Spyder2, it reads a very broad angle of the screen, so it needs to  
be within a couple of feet of it, to capture maximum light. Closer  
than a foot makes its own 'shadow' large, and reduces light, being  
farther back means its reading the whole screen, plus lots of  
'nonscreen' area, reducing captured light again. More light from the  
projector reflected back from the screen into the Spyder makes for  
more effective reading.

Moving the projector closer to the screen (the phenomenon you seem to  
be referring to) in order to have the assorted cables reach, makes the  
screen more intensely illuminated, which is a good thing, though there  
is a point where the screen area is small and the Spyder shadow is  
big, so there is probably a reversal, and a reduction in total light  
gathered.

But any configuration that allows a generous amount of screen  
reflected light, and NO OTHER light sources to be sampled will do the  
trick (yes. that red EXIT sign right next to the screen must be  
avoided for an accurate measurement). Its all relative, so more or  
less luminance does not really effect color measurements (little x and  
little y) only total luminance (cap Y), so for a projector profile,  
its all the same beyond getting enough light to take accurate  
measurements.

C. David Tobie
Global Product Technology Manager
Digital Imaging & Home Theater
CDTobie@...