Projection TV Lenses: Super Tightening the Optical Focus

There are six things that need to be focused on a projection TV: 3 lenses and 3 CRT faces. When focused properly, considering your set is properly calibrated otherwise, you will have a dazzling picture. To achieve the tightest optical focusing possible, whether on a Front- or Rear-Projection TV, I use a procedure called the Cantilever Technique. Examples of just two projection TV manufacturers this information applies to are Pioneer and Mitsubishi.

 

 

Projection TV Troubleshooting Advice

Three of the six lenses on a Projection TV point to a mirror. The image bounces off the mirror and hits the screen. In the past, we would loosen things up and then we would change this position so it would go out or in and make the image look as crisp as we could.

What if out of the box the image is already perfect on your projection TV? As soon as you loosen lenses and move them you mess it up. There is a way around that – of focusing everything on a projection TV and double- checking that focus – without altering the focus in the process. I call it the Cantilever technique.

What you do on the set pictured (Mitsubishi WS 83517 rear projection TV), is undo it at the bottom so you can pull it out a bit and you can cantilever it at the top. Pull it out 3 or 4 inches. What we’re looking for is the spaces between the scan lines, and we have a grid up here that is 480i or 480p. Those little shadow areas between the scan lines- you can’t see them in high definition. You can in 480 (i or p), so that’s what we focus with. When you pull it out, let’s say it goes out of focus a little bit. You can tell it’s going out of focus if you push it in with a pillow and it goes out of focus a little bit. Okay, you can see that, but what happens if, when it looks good here at rest, you pull it out? The focus gets sharper, and you push it in, it loses its sharpness and you know that lens is out of focus. It could be the red, green or blue lens. You go in, alter the focus, do what you need to do, and then repeat the process: You pull it out, you push it in.

When it’s in focus, it’s going to be at its absolute crispest when it’s at rest. So you pull it out a little bit, it goes out of focus a little bit. You push it in a little bit, it goes out of focus a little bit. When you leave it at rest and it’s better than either of those, then you know you’ve got it. It’s a balance between pulling it out and pushing it in. When the focus is as sharp when it’s pulled out as it is when it’s pulled in you know at rest its going to be adjusted properly.

 

The only other focus we need to worry about is the electronic focusing at the CRT faces themselves, at the focus block. There are 6 trim spots, or gain controls, and 3 of those are for focusing. Make sure not to touch the other 3. Those are called Screen Controls and they govern how much energy gets to each gun. That’s a precision adjustment and you don’t want to alter it. Put tape over them if you think you might accidentally turn something.

 

 

 

For more information about all things Big Screen search “AVSforum Mr Bob”. For videos see Youtube channel MrBobBigScreen. 

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Robert Jones is a Professional LEVEL II ISF Calibrator. His special talent lies in using the Image Perfection protocol as the final and most crucial step in the ultrafine tuning of High-Definition Home Theater and Front and Rear Projection TV systems. He optimizes and extends the working life of Projection TVs to 20 years and beyond.  Though Bob specializes in Pioneer and Mitsubishi projection TV’s, he repairs and maintains Flat Screen and Flat Panel systems made by most manufacturers. Bob started the popular “Don’t Dump Your CRT-RPTV!” thread in 2006. It has over 13,000 posts spanning more than 400 pages and it is still going strong. These posts can be found at www.AVSForum.com  under the handle “Mr Bob”. Informational videos can be found at Youtube channel MrBobBigScreen. You can reach Bob directly at 510-278-4247 or bob@imageperfection.com.

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