aus74cjl said:
I found that if the triplet is modified, that the front lens has to be closer to the middle one than the rear one. I have not had time to do much experimenting with the 220/550mm with the 135 mm triplet, but my setup has 9' throw. The space between the front lens to the middle is 0.5" and the space between the middle and the rear triplet lens is 1.25", the rear triplet lens is 24" from the transparency (LCD).
I do not know if this wil help or not, but I thought I would mention it.
I tried readjusting the lens spacing to be closer to what rl suggested, but still the image is not very sharp. We need to make the lens assembly more adjustable to come to any conclusions though.
I moved the 550mm lens behind the LCD instead of the original split design. This has decreased the field angle to the triplet and as a consequence the image is much better focussed at the sides. It also makes the projected image a little smaller of course.
We also tried putting an aperture on the triplet at the light entry side. This improved the focus immensley, and was almost good enough to do a full 1280 x 1027 on the 17" display. Only problem was very dim corners. I moved the lamp forward and this helped a little.
On 1280 widescreen, with the fresnels behind the LCD, the corners are only just out of focus.
I moved the 550mm lens behind the LCD instead of the original split design. This has decreased the field angle to the triplet and as a consequence the image is much better focussed at the sides. It also makes the projected image a little smaller of course.
We also tried putting an aperture on the triplet at the light entry side. This improved the focus immensley, and was almost good enough to do a full 1280 x 1027 on the 17" display. Only problem was very dim corners. I moved the lamp forward and this helped a little.
On 1280 widescreen, with the fresnels behind the LCD, the corners are only just out of focus.
aus74cjl said:
Can you explain this aperture for me? I am doing a VERY similar set up and am interested in any forward progress with a 17" LCD screen. Thanks for the info.
Speaking of lighting, has anyone thought of using two lights? Maybe two 250W Halides? One spaced 1/3 of the total width and the other 2/3 of the total width. Then have a giant reflector behind the whole thing. That might give more light to the edges?
aperature
I suspect that adding an aperature just before the middle lens might work better than one at the first lens.
Making the lens aperature smaller usually sharpens the focus by discarding light that would go through the parts of the lens far from the central axis. This is where the aberration is usually the worst. The price you pay may be less light on the screen. You can make up for that by adjusting the fresnels just right, so most of the light goes through the aperature.
I suspect that adding an aperature just before the middle lens might work better than one at the first lens.
Making the lens aperature smaller usually sharpens the focus by discarding light that would go through the parts of the lens far from the central axis. This is where the aberration is usually the worst. The price you pay may be less light on the screen. You can make up for that by adjusting the fresnels just right, so most of the light goes through the aperature.
Re: new triplet
I don't know much about it, but Lumenlabs is indeed working on a new triplet. I think they have the design ready and are just waiting on (or looking for) the manufacturer. Again, I don't know much about the process of creating a new triplet, so I'm not clear how far they are in the lens' production. Below is a quote by Brainchild of Lumenlabs (from a news post made July 15th of this year):
Not sure how much use this is to you, but I thought I'd try to clarify.
Guy Grotke said:
I don't know much about it, but Lumenlabs is indeed working on a new triplet. I think they have the design ready and are just waiting on (or looking for) the manufacturer. Again, I don't know much about the process of creating a new triplet, so I'm not clear how far they are in the lens' production. Below is a quote by Brainchild of Lumenlabs (from a news post made July 15th of this year):
Not sure how much use this is to you, but I thought I'd try to clarify.
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