[composr]

Has anyone here tried fitting 8" lenses on a 7" projector? Would it work, and if so, is it possible that it could help with corner focus?

 

[RoBro]

IMHO there are a lot of hd-8 on sony 1272.

depends if your tubes are spaced wide enough and if you can mod the mounting...

roland

 

[composr]

Oops, you're right about the 12xx models. I guess technically my ecp falls into the 5.5" category. Also, good point on the tube spacing. I bet even if you could manage to squeeze the 8" lenses onto the unit you still may have troubles with toe-in. Anyway, just trying to find a way to sharpen the corners!

 

[RoBro]

Try to find out dimensions of the HD-8.

I would also be interested...

Roland

P.S.:

Phosphor size of 12xx is like 8" tubes. Also phosphor of all the NECs from GP-3000 up, except GP5000 and PG10 which are 9"

 

[composr]

Roland, already done! The HD-6 lenses on my projector are 5.25 inches in diameter in the back where they mount into the crt bulkhead. The HD-8 lenses are, I believe, 5.75 inches so a modification to either the bulkhead or the back of the lenses would be necessary. I don't have a set of HD-8s or I'd try it, I just had someone measure them for me.

 

[composr]

I would also imagine that this could play havoc with throw distances.

 

[gn2]

Do you have an ECP with bad corner focus ? If so, you need to redo your sheimfluge. You should be able to get uniform focus on an ECP because it has scheimfluge adjustments. Try it some more. Bigger lenses don't work any differently, you'd still have unfocussed corners if your sheimfluge is not done correctly. If you'd like a scan of the manual page which explains how to do the scheimfluge, just email me and I'll pass it along.

If its a projector without scheimfluge adjustment, you can mimic scheimfluge by adding washers for spacers between the base of the lens and the lens mounting plate. A pain in the ass to do but effective.

 

[pcCinema]

Starting point for scheimflug on an ecp is exactly 1" between the metal plates all around.

 

[composr]

I have adjusted the scheimpflug and, don't get me wrong, the focus is not bad, it's just not as clean and sharp as the center. I guess I'm assuming that the limitation is the lens diameter since the tube face is perfectly focused. Also, it was my understanding that scheimpflug adjustments are for uneven focus top to bottom and left to right.

 

[gn2]

I'm not being coy but have you adjusted your front lens element for corner focus ?

Generally what happens when you dial in optical focus is you get center perfect, then get edge focus even. When it is even, you then defocus the center slightly and adjust scheimfluge till the top/bottom/sides are all exactly evenly defocussed. Now refocus the center exactly, then focus the edges exactly. IF you don't have good corner focus after this, I don't know what to tell you ?

I would check you are within the lenses focus range if you still have unfocussed corners.

 

[composr]

Paul, thanks for your input, I am going to try to dial those corners in a little better. I remember reading about the defocusing techniquie, I'll study up a little. But, on a more general scale, don't most of the ES focus pjs have less than perfect corner focus?

 

[gn2]

Yes they do, that would have been my last point.

The nature of the relationship between the electron gun and the tubeface is such that without electronic astig control the corners will necessarily be less well focussed than the center of the screen(ie. the beam travels farther to the corners than the center and strikes the tubeface at an angle instead of straight on). The shape of the beam will be an oblong radiating out from the center. One can minimize this with very careful setup, but it can't be totally eliminated. It is the whole reason why electromagnetic focus crt projectors were developed, for use in data applications where true edge to edge and corner to corner focus is a necessity.

 

[composr]

Ah, you answered my question. From a quick glance the tube face looks perfectly focused but that's probably because the size is small enough to mask the difference center to edge. Thank you!


Ray