CurtPalme.com Home Theater Forum

[deronmoped]

Here is something very interesting when using expanded phosphor areas.

For years I could not figure out how to get my linearity correct, I figured it had something to do with phase or some component on one of my boards. Well all this talk about lenses has me messing with mine, trying the three different sets I have to see what they will do. I'm running the GT26's, they are best for my screen size, I tried the GT17's and the 300's out of a Barco.

When I started to mess with the different lenses I used a convergence pattern instead of a focus pattern and I had left the green and red on at the same time. I found out real quick that adjusting the corner focus was changing my convergence. This would effect the linearity on the sides to about a quarter of the way in, Woe, this should not be happening. Well at least I'm pretty sure I have figured out why I can not get my linearity perfect. I'm going to do some adjusting and testing of my GT26's to see if I can get this problem fixed.

I posted this on the lense thread, but I felt it was important enough to start a new thread and point this out to people having convergence problems.

Deron.

[ecrabb]

This has been discussed a bit here and there before, albeit piecemeal. If you push raster usage too far, corner focus, convergence, linearity, and uniformity will all suffer to some degree. It's all about compromise. No free lunches!!!

SC

[deronmoped]

Maybe I did hear about the problems with running to the outer limits of the phosphor and just did not pay much attention to how it effects the lens system till I tried fixing the convergence problems using the lenses.

Well I can tell you with these GT26's I would have to be running a real small image on the face of the tube to get it in the sweet spot where I would encounter no problems with convergence.

I tried the GT17's as I was close (a little over) to the upper limit for screen size for these and wanted to see what they would do. Still had the same convergence problems, center focus was more consistent and just a touch better, corner focus was not as good.

I went back to the GT26's as they had good center and corner focus, tried different combinations of them on the tubes (swapped them from tube to tube) that did not seem to help. I put the sharpest one for center focus on the green and tried rotating the whole lens, that seemed to help a little. Right now convergence is pretty dam close. I wish these lenses had a touch better center focus though.

I think these lenses can be good if you hand picked the best ones as they seem to vary in how good they are. Not sure if this is a defect or if they are just not adjusted perfectly from the factory.

Deron.