Hi guys, working my way through the parts to use, got my LCD and now I've got access to a lens...
and I dont know much about optics
has 5.6/180 on the side, which I assume is the Fstop and the focal length?
is this at all useful? and if so any guesses as to upto what Panel size?
wondering if it's worth building a test bench with this or track down another lens first?
thanks for any input!
and I dont know much about optics
has 5.6/180 on the side, which I assume is the Fstop and the focal length?
is this at all useful? and if so any guesses as to upto what Panel size?
wondering if it's worth building a test bench with this or track down another lens first?
thanks for any input!
lens
The clear aperature of that lens would be 180mm / 5.6 = 32 mm
That is probably not wide enough to be useful for a DIY video projector. When you use a MH lamp with a 24 mm arc length, you would get a arc image at the projection lens that is 24 mm times the ratio of the condensor and field fresnels. Say you use a pair of 200 mm fresnels, then you would get a 24 mm arc image. Some of the light would get through the lens, but a lot of it wouldn't (because of the steep angles of light from the corners) unless you used a very small LCD. Liike maybe a 5" PS1 display.
You can actually get lenses better suited for small LCD DIY projection at surplusShed.com for about $6! Look for copy lenses. But I recommend that you think about using something more standard for a first projector. for example, lumenlab.com has a lens kit that has a much wider triplet and fresnels that match.
You did not say how large your LCD is! Or the image size you need, or the throw distances you can use. Those are all needed to calculate the optical design.
As for putting together a testbench: Yes, absolutely. This is the essential first step for any new projector design, unless you are buying complete plans and a lens kit.
The clear aperature of that lens would be 180mm / 5.6 = 32 mm
That is probably not wide enough to be useful for a DIY video projector. When you use a MH lamp with a 24 mm arc length, you would get a arc image at the projection lens that is 24 mm times the ratio of the condensor and field fresnels. Say you use a pair of 200 mm fresnels, then you would get a 24 mm arc image. Some of the light would get through the lens, but a lot of it wouldn't (because of the steep angles of light from the corners) unless you used a very small LCD. Liike maybe a 5" PS1 display.
You can actually get lenses better suited for small LCD DIY projection at surplusShed.com for about $6! Look for copy lenses. But I recommend that you think about using something more standard for a first projector. for example, lumenlab.com has a lens kit that has a much wider triplet and fresnels that match.
You did not say how large your LCD is! Or the image size you need, or the throw distances you can use. Those are all needed to calculate the optical design.
As for putting together a testbench: Yes, absolutely. This is the essential first step for any new projector design, unless you are buying complete plans and a lens kit.
Hi Guy Grotke, thanks for the info
it's not sounding doable with that lens from the looks of things
this will be with a 15 inch LCD for the moment, which I've dismantled and put in a frame for the testing phase
looking for around a 2 metre image, throw distance (again for the moment) would be around... well anything upto 3.2 metres
first build will just be a proof of concept and fiddletime
after that I'll be making something more permanent with what I've learnt.
maybe even something with a much shorter throw and some MAJOR keystone correction to project upish from the ground. though that might take 3-4 practice builds!
I've wandered through surplus shed a couple of times, will email them for an estimate of shipping to Australia
once again, thanks for the help. I feel a bit more confident about what I need to get there
it's not sounding doable with that lens from the looks of things
this will be with a 15 inch LCD for the moment, which I've dismantled and put in a frame for the testing phase
looking for around a 2 metre image, throw distance (again for the moment) would be around... well anything upto 3.2 metres
first build will just be a proof of concept and fiddletime
after that I'll be making something more permanent with what I've learnt.
maybe even something with a much shorter throw and some MAJOR keystone correction to project upish from the ground. though that might take 3-4 practice builds!
I've wandered through surplus shed a couple of times, will email them for an estimate of shipping to Australia
once again, thanks for the help. I feel a bit more confident about what I need to get there
bigger than you think
15" LCD-based projectors are pretty big. Most short-throw designs use 300 mm fl projection lenses with 220 mm fl and 330 mm fl fresnels. That is at least 550 mm from the lamp arc to the center of the projection lens, probably more like 650 with a reflector, etc. So a lot of builders include a front-surface mirror so the box can send the light up through the LCD and fresnels, bend 90 degrees in the mirror, and then hit the lens on the front of the box.
My point is, that you don't have to make a projector that lays on the floor and then does extreme keystone correction. You can build a box that puts the lens high enough off the floor, so you don't need so much keystone correction.
Or even better: With a 15" LCD, an 18" focal length opaque projector lens (the most common fl), and a throw distance of 2.9 meters, you would get a 2.036 meter image. Then you can leave the projector at the back of the room, high enough so you don't need any keystone correction.
There are lots of designs possible, but the easy ones for large LCDs use standard lens/fresnel combinations that work together. (Like 300 mm lens with 220/330 mm fl fresnels, or a 450 mm lens with 220/550 mm fl fresnels.)
15" LCD-based projectors are pretty big. Most short-throw designs use 300 mm fl projection lenses with 220 mm fl and 330 mm fl fresnels. That is at least 550 mm from the lamp arc to the center of the projection lens, probably more like 650 with a reflector, etc. So a lot of builders include a front-surface mirror so the box can send the light up through the LCD and fresnels, bend 90 degrees in the mirror, and then hit the lens on the front of the box.
My point is, that you don't have to make a projector that lays on the floor and then does extreme keystone correction. You can build a box that puts the lens high enough off the floor, so you don't need so much keystone correction.
Or even better: With a 15" LCD, an 18" focal length opaque projector lens (the most common fl), and a throw distance of 2.9 meters, you would get a 2.036 meter image. Then you can leave the projector at the back of the room, high enough so you don't need any keystone correction.
There are lots of designs possible, but the easy ones for large LCDs use standard lens/fresnel combinations that work together. (Like 300 mm lens with 220/330 mm fl fresnels, or a 450 mm lens with 220/550 mm fl fresnels.)
first off
BIG thanks for all the info Guy, nice and understandable too
This projector is likely to go through 3 phases - Test bed, setup and working (but ugly bare MDF) and finally tweaked and prettier to look at
the former phase would be all horizontal and the last 2 phases I'm thinking a vertical set up with a mirror at the top to send the image to a wall
I noticed you said bend the 90 degrees then hit the lens, would it be feasible to hit the lens then hit a mirror? there shouldn't be much more to this than to factor that distance into the throw distance and flip the image?
the extreme keystone correction stuff is just hypotheticals. If I build a projector with a short throw, short enough that it has to be in front of the viewers I'd rather it not be raised so it's as unobtrusive as possible, which means ceiling or floor mounted and keystone correction? this is just hypothetical at this stage
one other random thought that occured to me
I saw somewhere a succesful light source using a LED array, it looked effective though I imagine in a lit room things might be a bit difficult. I'm likely to stick with MH lamps...
this is another fairly random thought, but could your replace one say 400W lamp with 2 175W or 2 250W lamps? this would also mean 2 condensor fresnels (condensor fresnels are the fresnels BEFORE the LCD in a split design?) one covering half of the screen each? I'm sure this would complicate things no end but it might have some advantages? better heat distribution perhaps? or reduce the distance needed from lamps to condensors?
once again, big thanks Guy!
BIG thanks for all the info Guy, nice and understandable too
This projector is likely to go through 3 phases - Test bed, setup and working (but ugly bare MDF) and finally tweaked and prettier to look at
the former phase would be all horizontal and the last 2 phases I'm thinking a vertical set up with a mirror at the top to send the image to a wall
I noticed you said bend the 90 degrees then hit the lens, would it be feasible to hit the lens then hit a mirror? there shouldn't be much more to this than to factor that distance into the throw distance and flip the image?
the extreme keystone correction stuff is just hypotheticals. If I build a projector with a short throw, short enough that it has to be in front of the viewers I'd rather it not be raised so it's as unobtrusive as possible, which means ceiling or floor mounted and keystone correction? this is just hypothetical at this stage
one other random thought that occured to me
I saw somewhere a succesful light source using a LED array, it looked effective though I imagine in a lit room things might be a bit difficult. I'm likely to stick with MH lamps...
this is another fairly random thought, but could your replace one say 400W lamp with 2 175W or 2 250W lamps? this would also mean 2 condensor fresnels (condensor fresnels are the fresnels BEFORE the LCD in a split design?) one covering half of the screen each? I'm sure this would complicate things no end but it might have some advantages? better heat distribution perhaps? or reduce the distance needed from lamps to condensors?
once again, big thanks Guy!
Sure, you can put a mirror anywhere you like. The reason to put it near the projection lens is that front-surface mirrors are expensive. The further it is from the lens, the bigger it has to be.
A little bit of optical keystone correction can be done by tilting the field fresnel in a split-fresnel design. A lot of keystone correction would be very difficult to get right. You can try it, but I bet you end up doing something less extreme.
LEDs are still orders of magnitude more expensive to buy compared to the cost of MH lamps on a per lumen basis. They also are much less efficient than MH lamps in lumens per Watt of power consumed. So they cost more to run, and make more heat than a MH lamp. The people who are fixated on LEDs as "cool low-power" devices are only thinking about individual 10-30 milliwatt LEDs. The very few LED-powered projectors you can buy make tiny images that are difficult to see with any ambient light.
There are no advantages to using 2 MH lamps. The point-source lamp, spherical reflector, and fresnels all work together to send the light to a relatively small projection lens. Using two light sources would mean you need a very large lens or two small lenses with screen image alignment issues. Other designs are certainly possible, just much more difficult and expensive.
A little bit of optical keystone correction can be done by tilting the field fresnel in a split-fresnel design. A lot of keystone correction would be very difficult to get right. You can try it, but I bet you end up doing something less extreme.
LEDs are still orders of magnitude more expensive to buy compared to the cost of MH lamps on a per lumen basis. They also are much less efficient than MH lamps in lumens per Watt of power consumed. So they cost more to run, and make more heat than a MH lamp. The people who are fixated on LEDs as "cool low-power" devices are only thinking about individual 10-30 milliwatt LEDs. The very few LED-powered projectors you can buy make tiny images that are difficult to see with any ambient light.
There are no advantages to using 2 MH lamps. The point-source lamp, spherical reflector, and fresnels all work together to send the light to a relatively small projection lens. Using two light sources would mean you need a very large lens or two small lenses with screen image alignment issues. Other designs are certainly possible, just much more difficult and expensive.
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