I though it would be an excellent idea to use a pre-condenser lens (fresnell or other) between the lamp and collimating fresnell. If the lamp is 14" from the fresnell the fresnel will gather only a small partion of the light the lamp is emitting. Using a pre-condenser you can actually increase the intensity of the light from that lamp. So how to calculate the FL and optimum distance from the lamp for the pre-condenser, and where to get such fresnell? I guess the total FL is calculated from 1/FLtot = 1/FLpre + 1/FLcoll, but how to select the first two (FLtot and FLpre) and where to put the pre-condencer fresnell? I know some people use regular lenses placed as close to the lamp as possible, but is it actually a better way to go, will the small lens gather enough ligh?
Obviously a fresnell close to the lamp is not a good thing, it needs at least an e-glass between and it simply doesn't work well if the angle of beams to fresnell surface is too big. Any ideas?
Obviously a fresnell close to the lamp is not a good thing, it needs at least an e-glass between and it simply doesn't work well if the angle of beams to fresnell surface is too big. Any ideas?
BUMP
Recommedations for the conderser lens, please? Type, FL, size, distance from bulp etc? Why would the fresnell condencer be bad (or good), anybody tried it yet?
Recommedations for the conderser lens, please? Type, FL, size, distance from bulp etc? Why would the fresnell condencer be bad (or good), anybody tried it yet?
some OHPs have condensor lens right in front of the bulb. Like 3m 9550 I have, the lens is pretty thick. the side toward the bulb is slightly curved in; the other side is really curved out. you need to put it really close to the bulb, so it has to be glass.
Is this condenser len OK? Or is
this aspheric condencer lens (75mm) any better?
Found the one ywh uses (in old threads), the lens is concave-convex (one side is concave and the other is convex).
One problem with fresnells is that they can't stand heat. Also the glass condenser lens blocks some UV and heat, too.
this aspheric condencer lens (75mm) any better?
Found the one ywh uses (in old threads), the lens is concave-convex (one side is concave and the other is convex).
One problem with fresnells is that they can't stand heat. Also the glass condenser lens blocks some UV and heat, too.
Wow, it is expensive! Ask YWH if he can get you a cheap one. Even better, ask mikekniner, since he just bought a box of 3m optics, there ought to be some condensor lenses among them.
The lenses in 2nd link are too small. but you can use it if you have a reflector like the one listed in
this website. the reflector actually collect all lights to a smal point near the condensor lens.
The lenses in 2nd link are too small. but you can use it if you have a reflector like the one listed in
this website. the reflector actually collect all lights to a smal point near the condensor lens.
I think $45 isn't too big investment regarding the benefits (more light, less electric power is consumed). Too bad the postage to EU is expensive. Also it's almost unpossible to find ~ $100 OHP's here.
Actually they called me from Edmund optics UK this morning, the condenser lens would cost me £62, that's about $95. Needless to say that I didn't order it...
try anchor optical. better than the surplus shed and you know what you will get in therms of focal lengths and so on. good prices too.
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