On Screen Troubleshooting: Difference between revisions

On Screen Troubleshooting (view source)

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 ==Focus Uniformity==
+Focus uniformity is the overall evenness of focus across the entire image. If examining focus uniformity using a test film, it is not uncommon for the far edges of the frame to be slightly softer than the center. More problematic is when one side or area of the image is less in focus than another.
+Uneven focus uniformity can be caused by anything in the optical chain being slightly out of alignment: if light from a poorly focused bulb is reflected onto a slightly out of alignment gate and magnified by a poor quality lens at an odd angle, the resulting image will almost certainly not focus evenly.
+If this is the case, it is usually best to start by checking [[lamp alignment]]. If [[lamp alignment]] is correct, check the gate for any debris, sticking rollers, or damaged parts. A small bit of dirt buildup is enough to cause one side of the image to be significantly out of focus, and a sticking [[lateral guide roller]] can pinch the film in the gate so that the top or bottom of the image is soft.
+In many installations, especially those with steep projection angles or short throws, it is not uncommon for the gate to be shimmed to be brought into alignment with the screen. This adjustment requires great care and patience.
+Focus uniformity can also be compromised by dirty lenses or port windows.
 =Jitter=