What's wrong with this sketch. Working on the folded 15" without exterior 3rd mirror. A lot like the Lilliput design only for 15"

Dosn't an odd number of mirrors between the LCD and lens cause a backwards image? Or am I wrong on this?

Would this be workable? What would make it so?

Cheers, Seth

I think that has potential. The first mirror needs to be at 45º though.

If you use a transparency to test the optics first, you'll know which way round the LCD has to be, and so won't have to worry about getting it wrong.

Good call on the transparency. Thanks.

About the first mirror. Why dose it hav to be at a 45 degree on the bulb side of the LCD? I understand the other side of the LCD has to be at 45 degrees so the picture remains within propotional constraints...

Am I right in saying the an odd number of mirrors on the lens side of the LCD would result in a reversed image? Or do you then just flip the LCD?

Cheers,
Seth

The first mirror has to be 45 degrees because you show the light rays folding 90 degrees. When a light ray is reflected off a smooth surface the angle it leaves the surface is the same angle it came in but is reflected over a normal to the surface (a line 90 degrees to the mirror). The way you've drawn the first mirror and the light source, most of the light will be reflected towards the right side of the LCD if that is a top down drawing.

Ed

Oh, that makes sense. Thanks.

How about this? Problems? Is it better?

Have you ever thought about making just a test prototype on the cheap using cardboard box simple regular mirrors then using an incandescent lightbulb as light source and a transparency in place of the lcd... you may solve design flaws quicker that way. Just a suggestion.

Looks much better, but of course you still have to work out the light cones so you aren't blocking and part of the light source. You also have to make sure the focal lengths are correct.

3 mirrors will reverse the image the same as 1 mirror. Why do you want to have three mirrors? Each mirror will cause an estimated 8%(I think that is what I read hear) light loss.

Ed

Ed, I think I just figured out a couple things.

1. The image flips (horizontally) when it hits a mirror.
2. The image flips when it hits the triplet lens.
3. Only the flips between the LCD and lens count because the light dosn't "carry" the picture between the bulb and LCD, only after it penetrates the LCD and continues on to the lens side.
3. An even number of "flips" is required if the LCD is oriented to be read from front of projector.
4. If there is going to be an odd number of flips, then flip the LCD! No problem.

So it's really just a matter of flipping the LCD until what you read on the screen is correct.

Humm... I'm trying 3 mirrors so as to size down the dimentions of the box for my classroom. The Lilliput may be the way to go, but if so, this first folded 15" will become my personal projector for home.

Hummm... 8% that's 25% knock off just for 3 mirrors. How many ANSI lumens can one of these projectors produce without mirrors? (Never did figure that one out). Then I'll be able to tell if this degredation will be worth the trade-off in size.

Thanks for the feedback.
Seth

Might just make a bigger version of the Lilliput 7"

How do I get the focal length right?

Quicker? Cardboard? I'd wager that our brains are much quicker than I could be with cardboard. What's the saying, "Measure once, cut twice." Unless you cut it too short the first time... then your screwed.

After thinking through the designs, I'll start to play with real boxes.

Yeah I forgot to mention that to compensate for image reversals, just flip/invert the LCD panel. I was also incorrect about your layout, since you have only two mirrors after the LCD panel, your LCD should be put in the same as the basic design (I think ).

The 8% figure is something I think I remember reading in another thread, so don't hold me to that. I also seem to remember someone estimated that LumenLab PJs put out between 800 to 1400 lumens, but noone has actually measured it with a meter. This will vary with design of course.

I was just going to suggest a layout similar to Brains Lilliput design with 2 mirrors.

What I mean by keeping the focal length correct is if your fresnel's FL is 220mm, and you fold the light path, the segments should add up to 220mm. The focal length is determined by the properties of the lens.

Ed

Cardboard? Hmmmm.
Kinda like this.
I'm Anal. I can't help it.

Remdaddy,

That's hilarious! Looks great, just don't use a candle as your light source.

Just has thought, you could market that as a Flintstone's projector!

Ed

FIRE FIRE

Measure once, cut twice?? Seems like I am not the olny one who's anal about prototyping while I think through the design b4 to get hand on the "real" box... ;P

Prototype looks interesting Remdaddy, why the oddly (curved) shaped back?

Any guesses as to what Brian had in mind for the folded 15" without the third mirror? It is an attractive project in my mind because the 15" LCD is cheapest and most readily available, and the folded 15" is a good use of space.

I was trying to find a way to keep the light path pependicular to the front of the projector without the exterior 3rd mirror. Still working on 2 dimensions however--eventually I think we will find solutions with mirrors change the light path in 3 dimensions and thus we'll get smaller, more boxy projectors.

Just my blabbering. I may try a cardboard model this weekend.

Cheers,

Seth

Wow gotta give credit to RiCoda for starting a nice wood/steel working tips thread. He's real sharp with its tools and came up with a kickass PJ enclosure: RiCoda PJ

...Yo RemDaddy! One of the tips are to make a cardboard prototype b4 to put hands on power tools! We're not alone! check it out

Keep up the good job Seth!

PS: will the PJ look something like this?:

Actually, no, I was thinking of the diagram being the top view/footprint.

Cool animation though. I'm quite ready to begin with prototypes. I've just got to check on focal lengths. It will be a couple weeks until I have something working, as I've a few other projects that take precidence.

Cheers,
Seth

Seth,

I think that the third external mirror in Brain's 15" design is for keystone correction, kinda like on an overhead projector.

Ed

Prototyping is a must for me.
I get rather tweaked if I screw something up.
My cardboard mockup is basically a rectangular box with 2 back corners trimmed off to save on weight and space. I have been cutting and taping some more to reduce the project to as small a footprint a possible.
I did this mockup so I could nail down the design and cut angles. Easy to make changes in cardboard or poster board than in the middle of a build.
Many designs look good on paper only to later be hard as heck to implement in the "real world".
I have also used the prototype to look at placement in my viewing room. I have already decided to move my placement and change some design charteristics due to observations. You can't do that on paper. The ever proverbial saying that seeing is believing always rings true

Every watch American Chopper? They use the same concepts with poster board and trace it to steel


R

Your design looks great! Once you get the focal lengths and overall dimensions of the box and component placement, please post them for all to see!

I will be intereseted to know if, or how much, the mirrors decrease the brightness and quality of hte picture. If anyone has any ideas, please let me know.

The only figure that I have seen is an 8% reduction and I believe that figure is for a front surface mirror.