Full Version: Split Fresnels Behind lcd Separation ?
I am getting ready to build my frames for my large fresnels i got from 3dlens. They are 220mm FL and 330mm FL for a 17 inch lcd projector. I want to place both fresnels behind the lcd. I hear I should separate them a bit ? Why is this? If so how much so they be separated for 360mm objective lens?
The closer they are the more critical it is that they be PERFECTLY aligned. Gapping them is not deleterious aside from the fact that you "lose" that space so your total build must be a half inch longer or taller.
The trade-off is a much, much easier alignment for an extra half inch build size.
If they're not gapped and not PERFECTLY aligned you'll get projection artifacts. Not worth the hassle.
Recently, I'm being told - when they're gapped a centimeter or so - alignment is really not critical at all.
The trade-off is a much, much easier alignment for an extra half inch build size.
If they're not gapped and not PERFECTLY aligned you'll get projection artifacts. Not worth the hassle.
Recently, I'm being told - when they're gapped a centimeter or so - alignment is really not critical at all.
QUOTE (Durachko @ Apr 27 2006, 02:06 PM) 
The closer they are the more critical it is that they be PERFECTLY aligned. Gapping them is not deleterious aside from the fact that you "lose" that space so your total build must be a half inch longer or taller.
The trade-off is a much, much easier alignment for an extra half inch build size.
If they're not gapped and not PERFECTLY aligned you'll get projection artifacts. Not worth the hassle.
Recently, I'm being told - when they're gapped a centimeter or so - alignment is really not critical at all.
The trade-off is a much, much easier alignment for an extra half inch build size.
If they're not gapped and not PERFECTLY aligned you'll get projection artifacts. Not worth the hassle.
Recently, I'm being told - when they're gapped a centimeter or so - alignment is really not critical at all.
this is a good tip. But since they are not joined there is also the risk of warping faster and easier since its thinner.
QUOTE (dracul2006 @ Apr 27 2006, 06:56 PM)
this is a good tip. But since they are not joined there is also the risk of warping faster and easier since its thinner.
Sounds like you've made up your mind then?
QUOTE (dracul2006 @ Apr 27 2006, 05:56 PM)
this is a good tip. But since they are not joined there is also the risk of warping faster and easier since its thinner.
To add to this if you are using a heatshield in your build I wouldn't worry about warpage too much, I am running mine behind the lcd in a verticle build with no heatshield and I have no warping issues. If you run them unsplit and don't have them aligned you will get the glowies. I have mine framed in a piece of 1/2 in mdf on opposing sides and it works great.Leave a 15mm bap between the frensels and the lcd to keep the frensel rings away.
QUOTE (ChuckL @ Apr 29 2006, 03:37 PM)
To add to this if you are using a heatshield in your build I wouldn't worry about warpage too much, I am running mine behind the lcd in a verticle build with no heatshield and I have no warping issues. If you run them unsplit and don't have them aligned you will get the glowies. I have mine framed in a piece of 1/2 in mdf on opposing sides and it works great.Leave a 15mm bap between the frensels and the lcd to keep the frensel rings away.
What is your idea of a heatshield? you mean ir filter or just the lexan ? I am using just lexan at the moment.
My large Fresnels are new and I find they are already not perfectly flat. I can ofcourse sandwitch the back fresnel to the lexan but then im still left with the front fresnel to worry about or is the front fresnel not such a concern for being perfectly flat?
QUOTE (ChuckL @ Apr 29 2006, 03:37 PM)
To add to this if you are using a heatshield in your build I wouldn't worry about warpage too much, I am running mine behind the lcd in a verticle build with no heatshield and I have no warping issues. If you run them unsplit and don't have them aligned you will get the glowies. I have mine framed in a piece of 1/2 in mdf on opposing sides and it works great.Leave a 15mm bap between the frensels and the lcd to keep the frensel rings away.
How much are the fresnels overlapping your frame on the edges? I got about 8mm now.
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