i'm wondering, why have lumenlab matched the focal length of the triplet to the fresnel, surely if it was a shorter focal length by about 30mm you could get the whole arc on the lens. where i have it now for a 10" image the light goes to a point about 30 mm before the triplet which seems a waste?
arc image location
That is only true if you make the light through the LCD perfectly parallel. You can easily adjust the location of the arc image by changing the distance between the lamp arc and the condensor fresnel. If you make that distance a few mm shorter than the condensor fresnel's focal length, then the light will slightly diverge through the LCD. Then the field fresnel will focus it at a longer distance.
That is only true if you make the light through the LCD perfectly parallel. You can easily adjust the location of the arc image by changing the distance between the lamp arc and the condensor fresnel. If you make that distance a few mm shorter than the condensor fresnel's focal length, then the light will slightly diverge through the LCD. Then the field fresnel will focus it at a longer distance.
yeah that makes sense, thanks for the answer. I focused the condensor fresnel by removing the LCD panel and field fresnel and locating the bulb so an image of the centre of the arc was focussed on the projection wall. So after doing that I figure the light is as parallel through the LCD panel as it's going to get.
Prior to doing this I had the lamp about 30mm closer (placed at the theoretical focal length) to the condensor fresnel and I found my corners were dim. I'll try moving a little closer and see how the results turn out.
My little bro just got a XGA 1200 lumen LCD projector off ebay, the bulb has 1000 hours on it and the image is still slightly brighter than mine. I don't have a reflector yet so my efficiency is dire, he's got a 150W bulb with 3 0.7" LCDs and with my 400W metal halide it's still dimmer but watchable!
I think the next time i build one i'm going to make it small, it's too hard to get good reflectors for grow lamps and the arc is huge..
Prior to doing this I had the lamp about 30mm closer (placed at the theoretical focal length) to the condensor fresnel and I found my corners were dim. I'll try moving a little closer and see how the results turn out.
My little bro just got a XGA 1200 lumen LCD projector off ebay, the bulb has 1000 hours on it and the image is still slightly brighter than mine. I don't have a reflector yet so my efficiency is dire, he's got a 150W bulb with 3 0.7" LCDs and with my 400W metal halide it's still dimmer but watchable!
I think the next time i build one i'm going to make it small, it's too hard to get good reflectors for grow lamps and the arc is huge..
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