Film-Tech Forum ARCHIVE: RealD XL filter constantly losing focus

This is topic RealD XL filter constantly losing focus in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Mark Strube (Member # 4190) on 01-08-2016, 10:43 PM:

In our big house we have a Barco DP4K-23B with a RealD XL filter. Before Star Wars, we hadn't run 3D in some time, and I noticed the image was a bit soft, so after confirming 2D focus was perfect, I tuned the X & Y axis on the XL by using the hex key.

We went to 2D for one week, so the filter was SLOWLY moved out of the way on the rails. Back to 3D starting on Friday, again, very slowly and carefully moved back into place. Lo and behold, it's slightly out of focus again, I'm going to have to run a test pattern at the end of the night to sharpen it up.

Any ideas what's going on here? I don't know the ins and outs of these filters, perhaps something else needs to be tightened up via a service call?

Posted by Steve Guttag (Member # 268) on 01-09-2016, 07:49 AM:

X/Y and focus are NOT the same thing. One is a convergence the other is focus. Now a misalignment of x-y can make it appear out of focus but again, that is just a misalignment. XL does have a magnification control too that can affect "focus". I generally put up a cross hatch pattern (as fine as possible...NEC's 8-bit cross pattern is very good for this) and align/set magnification as well as possible...hiding any misalignment uncorrectable in the upper corners. Note, on a curved screen, you'll never get a great alignment.