Hello all,

Its been a while since I posted. Ive had my 15" PJ working well for quite some time but havent had time to tweak it out. Well now Im unemployed and I have some time while I look for another job to do some tweaks to make my PJ better. I already replaced the sheet that I was using as a screen with engineering bond paper.. world of difference. Im going to do a better screen later but this is an improvement over what I had.

the question im asking now is what are some methods to make the image lighting more even. i mean its really good but the center is a little brighter than the corners. my lens holder/focusing mechanism isnt blocking light fyi. thanks

Brian

Beyond insuring that all your components are aligned properly, realistically your corners will usually be bit darker than the center. This should not be visible during normal viewing though, so if that's case, you've got some adjustments to make. Darker corners are the nature of the beast for the state of our DIY projects, though.

Not necessarily, I have been looking at some diffusers, and I have an idea for putting in a holographic diffuser that will spread out the light I think it could be sandwiched between the LCD and second fresnels. Just an idea, check this stuff out http://www.edmundoptics.com/onlinecatalog/...?productid=1363
A tad exspensive though....

no matter what you do, with the current fresnels and implentation design the dark corners and sides are always gonna be there. Its the nature of the optics, the lamp arc is dead in center and loses intensity as it spreads out to the sides and corners. However, when I switched to the Venture PS bulb, i noticed much less uneven lighting than with the ushio and reflector, but the color temp on the venture is just a tad bit yellow. If you want complete even lighting, you're gonna have to find a way to get a bowed fresnel to where it loses intensity in the center to where it matches the corners, but that will make for a very dark projection.

The lamp arc to rear fresnel distance has the biggest effect on corner brightness. 210mm is the common distance but tweaking can make huge improvements.

thanks Brain, I thought that was going to be the case. Im going to be taking the PJ apart soon to try some new tweaks (reducing the howl that the PCAC's make or replacing them with a totally different setup, fixing some light leaks around the LCD with black silicone, better filtration etc...) and when I do that, I'll make a setup that makes it easier to reposition the lamp center from outside the case. when I make the box originally, I made it a little too narrow for the ushio and the base so I had to take a wide wood bit and countersink an area so the base was centered. ill rethink that soon.

thanks guys.

Brian