Hi,
Here is my problem: three precondensor lenses already cracked in my projector, because of the extreme heat of a 400W bulb. It's a vertical design, so the lens is above the bulb. I was pretty sure at least one of these lens were designed to work with a high power lamp, and cracked anyway. So far I use one of the broken lens, I just attached the pieces together, wrapping a strip of aluminium foil around the whole edge. But these cracks cast visible shadows on the screen. I also have a small, too short FL precondensor lens, that is truly heat resistant, can work with my bulb, but it does not lit the whole LCD, just makes a big bright circle in the center. So my idea is to "spread" this tight beam, using a negative lens, something like "wide angle" lens for rear car window. I would attach it to the glass, that is about 10cm above the bulb, and adjust this distance if necessary. There is a good cooling there, so I'm not afraid it would melt. But does this idea make any sense? I don't know much of the theory, is that true, that putting "positive" and "negative" lens one after another makes an equivalent of something like an average of both of them?
Regards
Here is my problem: three precondensor lenses already cracked in my projector, because of the extreme heat of a 400W bulb. It's a vertical design, so the lens is above the bulb. I was pretty sure at least one of these lens were designed to work with a high power lamp, and cracked anyway. So far I use one of the broken lens, I just attached the pieces together, wrapping a strip of aluminium foil around the whole edge. But these cracks cast visible shadows on the screen. I also have a small, too short FL precondensor lens, that is truly heat resistant, can work with my bulb, but it does not lit the whole LCD, just makes a big bright circle in the center. So my idea is to "spread" this tight beam, using a negative lens, something like "wide angle" lens for rear car window. I would attach it to the glass, that is about 10cm above the bulb, and adjust this distance if necessary. There is a good cooling there, so I'm not afraid it would melt. But does this idea make any sense? I don't know much of the theory, is that true, that putting "positive" and "negative" lens one after another makes an equivalent of something like an average of both of them?
Regards
to calculate the focal of multi lens assembly you could use gunawan's tools on is web site here
however I'm not sure this will be efficient for a precondensor since when you assemble some lens together you increase the thicness of your lens and loose a lot of light on the side.
another solution is to do like in slide projector a very short focal lens for the fisrt condenser concentrate the lens and then another precondensor lens to set the angle of the light to the fresnel.
the precondensor from slide projector are heat resistant but they are a little bit small.
however I'm not sure this will be efficient for a precondensor since when you assemble some lens together you increase the thicness of your lens and loose a lot of light on the side.
another solution is to do like in slide projector a very short focal lens for the fisrt condenser concentrate the lens and then another precondensor lens to set the angle of the light to the fresnel.
the precondensor from slide projector are heat resistant but they are a little bit small.
I read on another post that someone turned their condeser over and it projected a bigger image on the lcd. Maybe try that with the one's that are heat resistant?
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