We are upgrading the lenses in our projector project. We had our projector running as a simple ohp but now we are installing the following with a 15" LCD with a split fresnel.

220mm collimator lens
550mm collector lens
modified triplet lens from diyprojectorcompany

It focuses great but the centre of the screen is bright and the edges are dark.

What are we doing wrong?

Thanks,

Dave

you have a bad case of the munchies.. I mean vignetting. try increasing the distance from lamp to collimator fresnal 15-25mm and decreasing the distance from collector to triplet by the same. This should give you a more even image, but you'll take a hit in brightness.

We tried moving the collimator and collector lenses around a bit but this is the best we can get. The box is not sealed yet so there is some light coming around the edges.

Dave

When you say modified triplet, are you sure that the barrel isn't getting in
the way somehow? That's usually the common problem, from what I can
tell. Hope that helps, if not... anyone else?

Also make sure the fresnels are properly placed.

The grooves face the Lcd in a split design. The grooves face each other in an unsplit design.

well I meant to suggest altering the distance from light to collimator by moving the bulb while the fresnel remains stationary. Another good suggestion was to make sure the triplet's field of vision is not being blocked since it will inevitably be blocking lights coming from the edges of the LCD

duster,

Please post pics of the insides of your projector and the various distances between the lamp, fresnels, LCD, and triplet.

I plan on working on this thing some more today, thanks for the suggestions.

I cannot see how light would be blocked from getting to the triplet but I will double check. I am going to modify the light mount a bit and post some pics later today.

Dave