I have a 400w tube metal halide bulb Philips. Its arc is 35mm in length. Its mounted diagnolly in a vertical build. After i realized i was getting vignetting i decided to check the arc on the back and sure enough its one big blur slightly larger then the 65mm clear diameter of the triplet. Yes i removed the lcd and i get the same issue. I remember when bulding another projector with 150hqi the arc was very sharp on the triplet.
Ofcourse the 400 is a stronger punch but should i not get a reasonable shape of the arc without the lcd in place. I have a double OHP unsplit fresnel that is 330/330 from a buhl overhead projector.
At first i thought the fresnel was causing the vignetting but now i know its the triplet not letting in the entire arc.
Can i improve this if i position the lamp vertically or horizontally?
Full Version: I Cant Get Arc To Be Sharp On Back Of Fresnel
I don't think rotating the arc from diagonal to horizontal or vertical will make a HUGE difference but it will make SOME difference. I also don't think you'd want to fine tune your light engine with the 400W lamp. Maybe trying this method outlined by SupraGuy would be wiser?
Edit: Note that in general I'm quite certain a smaller & "weaker" arc will be easier to resolve into a nice, sharp virtual image on the back of the triplet than will a huge 400W arc. I've not done much fiddling with sharpening up my arc at the back of the triplet but what I see with my 400W sounds just like what you see - a "blur". When I look at my 400W arc with a welding helmet it's - guess what? - a blur.
Nature of the beast? I have a ceramic to try and I look forward to someday seeing if I can get a nice, cylindrical (well - rectangular) looking arc image at the back of my triplet instead of a fuzzy blur using my standard MH arc chamber bulb.
Edit: Note that in general I'm quite certain a smaller & "weaker" arc will be easier to resolve into a nice, sharp virtual image on the back of the triplet than will a huge 400W arc. I've not done much fiddling with sharpening up my arc at the back of the triplet but what I see with my 400W sounds just like what you see - a "blur". When I look at my 400W arc with a welding helmet it's - guess what? - a blur.
Nature of the beast? I have a ceramic to try and I look forward to someday seeing if I can get a nice, cylindrical (well - rectangular) looking arc image at the back of my triplet instead of a fuzzy blur using my standard MH arc chamber bulb.
QUOTE (Durachko @ Jul 9 2007, 06:22 PM) 
I don't think rotating the arc from diagonal to horizontal or vertical will make a HUGE difference but it will make SOME difference. I also don't think you'd want to fine tune your light engine with the 400W lamp. Maybe trying this method outlined by SupraGuy would be wiser?
Edit: Note that in general I'm quite certain a smaller & "weaker" arc will be easier to resolve into a nice, sharp virtual image on the back of the triplet than will a huge 400W arc. I've not done much fiddling with sharpening up my arc at the back of the triplet but what I see with my 400W sounds just like what you see - a "blur". When I look at my 400W arc with a welding helmet it's - guess what? - a blur. Nature of the beast? I have a ceramic to try and I look forward to someday seeing if I can get a nice, cylindrical (well - rectangular) looking arc image at the back of my triplet instead of a fuzzy blur using my standard MH arc chamber bulb.
Edit: Note that in general I'm quite certain a smaller & "weaker" arc will be easier to resolve into a nice, sharp virtual image on the back of the triplet than will a huge 400W arc. I've not done much fiddling with sharpening up my arc at the back of the triplet but what I see with my 400W sounds just like what you see - a "blur". When I look at my 400W arc with a welding helmet it's - guess what? - a blur.
Nature of the beast? I have a ceramic to try and I look forward to someday seeing if I can get a nice, cylindrical (well - rectangular) looking arc image at the back of my triplet instead of a fuzzy blur using my standard MH arc chamber bulb.Ok. Thanks for confirming this.
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