CurtPalme.com Home Theater Forum

[pm]

My excitement at the imminent arrival of new tubes is still being tempered by my ongoing inability to get focus down the left side as good as elsewhere on the screen.

Scouring the net, I found an opinion that said that, although the lenses have a quoted range of suitable sizes, they are at their best in the middle of the range and can be distinctly softer at the margins..... My screen is 80in at the moment with the HD120 lenses..... i.e. right at the bottom end of their range. Could this be a factor???

I know that theory should probably dictate that the right side should be softer as well possibly.... I'm really clutching at straws at the moment. I thought I'd found a discrepancy in the physical alignment of screen and PJ but, although there was a small misalignment, in turned into a false dawn...

Cheers,

Paul

[Curt Palme]

try this:

Using the main focus adjustment of your lenses, defocus the center, and concentrate on the left side.

By defocusing the middle, can you get the left side in focus?

Also, didn't we talk in another thread about you having modded tubes? Once you pull the LC chambers apart, you'll most likely find a shim that tilts the tubes very slightly. that's what's causing your poor left focus.

[Curt Palme]

try this:

Using the main focus adjustment of your lenses, defocus the center, and concentrate on the left side.

By defocusing the middle, can you get the left side in focus?

Also, didn't we talk in another thread about you having modded tubes? Once you pull the LC chambers apart, you'll most likely find a shim that tilts the tubes very slightly. that's what's causing your poor left focus.

[pm]

[opv]

Do you have enough scheimpflug range?
I have an 80" with HD120 lens, and I had to add washers to get the picture focused all over the screen.
Look here:
https://www.curtpalme.com/forum_archived/viewtopic.php@t=32491.html

[pm]

Thanks opv,

That's almost spooky.... I was about to post something along those lines as a follow up to Curt's suggestion earlier.

I tried de-focusing the centre to see if I could get better focus in the corners and in particularly down the left side, without much success.

With the Scheimpflug, I didn't run out of range but observed that the best result was somewhere in the middle, it's just that the result wasn't very good! Still blurry by comparison to the centre. What I did notice however, was that the optical outer focus on the blue tube ran out of range going full deflection. That, as well as the orientation of the "raw" pattern on the blue tube are quite different to the red and green. This seems to tie in with Curt's suggestion that my blue tube might be shimmed from a previous installation. I have to admit, I don't understand the geometry of why only one tube might be shimmed.

Since I have a watchable picture at the moment, I might as well wait for my replacement tubes to arrive and start again with a ground up rebuild. Especially as it will also be going on the ceiling and getting a bigger screen.

Thanks for the inputs,

Paul

[km987654]

This sounds like "does my bum look big in this"

Sorry in advance.