Guy Grotke please share your wisdom master

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Hey guy, I've read through many of your post and your are extremely helpful. I almost feel obliged to give you a million dollars (wish i had it :)). I have a very similar predicament as tawamiami posted in his 'Please guide me through my setup' post. I have began the ever so famous box design for my projector using my lil ole Apollo Horizon II light source (360w, 2000 lumens or so) until i manage to get some free cash. I have a 10.4" lcd, the lens kit from lumenlab (220mm focal length, 317 mm focal length fresnels, lens triplet 320mm FL). Also some UV filter. Where the heck am I to place all these things if I want the max projected image to be than 84" in diam (because of room size). Could you also recommend a condenser, cause the single lens objective from the apollo overhead doesn't look like its gonna work (295mm FL).
An externally hosted image should be here but it was not working when we last tested it.
??:bigeyes: :confused: :confused: :bigeyes: ??

hmmmm well maybe, but you shoudn't direct your question at one person on a forum... thats a good way not to get it answered lol :D

Actually, this "master" only knows a tiny bit of optics, a few equations anybody could lookup, and mostly DIY projector stuff gleaned from other people's posts. I just read a lot of them!

Now, if you want to know something about verifying a big chip design before taping it out, or about growing avocados, then I really do know some stuff.

So let's see here:

I hope you meant 20000 lumens. 2000 will give you a night light.

I guess you want an 84" diagonal image? With a 10.5" diagonal LCD, that gives you a magnification (M) of 84/10.5 = 8.

We know your projection lens has a 320 mm fl. Looking in my handy little "Popular Optics" by Edmund Scientific (available from Surplus Shed) :D that should take the mystery out of my great optics knowledge :D, I see that:

B = (M + 1) * F where B is the throw distance
B = (8 + 1) * 320 mm = 2880 mm ( 9.45 feet)

I also know that:

M = B / A where A is the LCD to lens distance, so
A = B / M = 360 mm

A 330 mm fl field fresnel 30 mm after the LCD (in a split design) would make parallel light going through the LCD focus an image of the lamp arc right at the center of the triplet. But since you have a 317 mm fl field fresnel, you will have to make the light diverge slightly as it travels from the condensor fresnel to the field fresnel. No big deal: You just start with the lamp arc 220 mm from the condensor fresnel and then adjust that distance to be shorter in tiny increments, until the two fresnels send most of the light into the triplet. (This is easier to see with the LCD removed and a piece of white paper where the center of the triplet will go.)

One thing you have going for you, is that you got the fresnels and triplet together in a set. So they will be about right either way you build it. For a split design that can do keystone correction, put the condensor fresnel (220) about 20 mm before the LCD, and the field fresnel (317) about 30 mm after the LCD. Fire it up and adjust the triplet position to focus the image at your actual throw distance. (about 360 mm from LCD?). Start with the lamp about 220 mm from the condensor fresnel and adjust for bright & even image.

For a non-split design, put the field fresnel right against the condensor fresnel about 20 mm before the LCD. Light up, focus image, and play with lamp to condensor fresnel distance.

I made a thread about finding a good pre-condensor lens, a while back. Search for it. You probably need more like a 100 mm diameter 200 mm fl heat resistant glass PCX.

Fun Fact: My icon is an untouched photo of one of my yellow labs. He just loves being photographed!
Yea, i cracked the 10.4" lcd. It was vga only and came out of an Nview z210 so if anyone needs the control boards for that let me know. I decided it was time to strip my Gateway FPD1520 15" monitor. I did so with much ease, except that the connectors to the screen are a little inconvient. I keep getting dark edges, and cannot figure it out. I am using the same lenses as mentioned before.


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