I haven't seen anyone mention the method I am using, I am using almost all the parts from my OHP to make an enclosed projector and will be re-using the focusing arm (geared) just as it was used on the OHP...except it will be horizontal instead of vertical

OHP

I've also thought about doing that...

I'd like to see pic's of your setup when you're all finished...and how well it works?...

Hey Haku, Great Idea! I think I may implement the salvaged CD-ROM drive concept for my PJ. Any idea what the voltage is on the motor to drive the CD case open and close?

I think that the best advantage to having an electric adjust is if it was controlled by a remote control(not cordless, as it is only needed when setting up. Basically you could set up the projector, then take the remote with a cord about as long as your throw and a switch for controlling focus movement, and stand next to the screen while focusing. I thought of this because I worked at a movie theater, and the biggest pain in the a** is trying to focus the screen from 350 feet back! This is a little more than the 10 feet that is normal for our projectors, but with a setup as fancy as an electric focus, I would want to be able to focus it pretty damn well!

i have been wanting for a while now to start my 2.0 pj now that i know more things about it and i know wut to do and wut not to do.

my plan is to get all my pj's critical parts and lenses on very fine gear track then use servos to move the gears with either a pulse button or a wireless remote/keypad interface, very slow thusly using the small fine tracks to get pinpoint focusing

Hey everyone!! Enjoying the ideas here. Had one of my own for a change. I was wandering HD for some metal brackets when I stumbled across a magnetic section. I opted to use magnetic cabinet clasps for the front perfect because I'm using gatorfoam for my next PJ again. I had the thought why can't I use a magnet for the focus mechanism. two semi-heavy duty magnets that run across a stip of metal on both sides I think will be enough So what are your thoughts?

I'm going this route too, as i just used the last of a stick... and, as a bonus, you can take the cap and place it over the bottom of the stick and use it as a cover to keep it from being adjusted accidentally...


Edit for grammar....

Hey guys,
I read through this thread and thought about it and came up with an idea, and drew a crappy picture of it....



To do this you would need to cut a piece of pipe diagonally, then find another pipe or connector that nests inside, or split the cut piece and wrap it partially over a pipe of the same size (I call this piece a ramp). Then attach the lense inside the ramp, more towards the back to retain a good FOV. Then there would be a nub attached to the body of the projector that rides inside the ramp, so that turning the ramp moves the lense in and out. Then you can make a fine adjustment by wrapping a belt or rubber band around the ramp and a smaller wheel. Then the whole thing can be motorized/automated by adding a motor/gear setup behind the fine adjustment knob. I like the idea of using LEGOs for that part. Also you would want to add a lockdown screw or spring to keep it from moving accidently....

Just an idea....

i've been thinking about adding a focusing mechanism to my projector that i will build and have a couple of questions.

1) is the only thing you have to move the triplet? since the triplet is supposed to be at the focal length of the fresnel wouldn't moving the triplet make the picture out of focus no matter how close/far the projector was to the screen? (does that make sense?)

2) ok, this may sound really really stupid, so keep in mind i'm just starting out and don't know a ton about projectors, but is the pro lens that lumenlab sells a good lens to use for focusing mechanisms? all of the projectors i've seen built that use it have not had a way to focus it, and i'm pretty sure i read something that said that if you used the lenses that lumen lab sells you can't have a focusing mechanism.

these questions may be pretty stupid, but i'm new, so bear with me.

I think you're confusing the two fresnels. For the rear fresnel, the lamp must be at or near the fresnel's focal length to work properly. For the front fresnel, you do not want the triplet exactly at the fresnel's FL because (as quoted from the wiki):

"Our projection lens may have a focal length of 320mm, but the if the lens were only placed at its focal length from the LCD panel we would be focused on infinity, so in practical usage we would place it around ~340mm from the LCD panel as represented by line Z (note this distance will vary with different screen sizes). "

To determine roughly where you want the lens, based on a given throw and screen size, use Dazzla's focal calculator



I think you are thinking of Beseler lenses instead of the pro triplet. Lenses without flanges (that slightly larger outer ring, with screw holes, that allows you to affix the lens to something) do make them a bit more difficult to work with, but people have made focus mechs with every lens imaginable. Without a focus mech, you projector will only be in focus at ONE given throw. Not the smartest way to go about building it, IMO.

What that is saying is that the triplet won’t be at its own FL from the LCD. For example a 320mmFL triplet will be around 360mm from the LCD. The fresnel’s FL should match this distance, 380mm for an un-split (20mm gap) and 340mm for split (20mm gap).

DJ

Whoops. I read his post too fast.
Looks like I'm the one who was confused... (runs and hids under my workbench)

here is my focusing mechanism =)





only haveto add a threaded rod and a knob on the front =)

Have you guys ever heard of using an overhead projector as the light source and using the fresnels and lenses already in it to bypass biulding a large box? Which one would promote better quality picture?

Yes that is done quite often.

But the image quality is SOOO much better building a diy projector with quality parts.

And this is a focus mechanism topic

My Toyota Camry is about to be hauled off to the junkyard, after several years of punishment. I wonder if the power window motors would be small enough to fit into a PC case design. Does anyone think something like power windows could be made to work in a focusing mechanism? (Maybe even sled position, keystone adjustment, lens sled and (varifocal) lens adjustment?) I may also have a power sunroof/moonroof and mirror to play with, provided I can bring myself to hack them all out of the car. (Not to mention some speakers.)

My thought was, as long as I could physically fit them into the case (I'm not honestly certain of their exact dimensions, without looking at them.), I should be able to figure out a way to retrofit them to control these focus mechanisms. I was planning on trying my luck with an HID headlight setup, so I planned on running all the electronics off a single (~600w) computer PSU. PSU's have 12v and 5v outputs, so I should be able to run them just like they were on a 12v car battery. However, worried that they might move to quickly/suddenly, could I possibly run them on the 5v line? Would they run slower or not at all?

If I could make it work, I would probably wire a panel with the window control levers to a 5-6ft cable so I could play with the various focus adjustments from the couch. (Hopefully using the original window controls from the car, for nostalgic value. This is all assuming I don't chicken out or run out of money completely.

Anywho, just a thought. Suppose it's in anyway feasible? I guess I could even move these ideas to a future project that takes place in a larger enclosure, if that were the only issue.

Will they fit? Sure. The motors for power windows aren't that large.

They are, however, power hungry little buggers. They're intended to move the windows, which is actually a fairly large load. They're also not REALLY made for fine adjustment, however, the speed, and therefore amount of adjustment will all have to do with your gearing (Or the threaded rod that you use.)

I have a couple of old power window motors from my own car that I am thinking of creative uses for.

Really though, there are cheaply available motors that are far more suited to this kind of work.

True, but the hidden message in that post was that I had to borrow money from my brother to get a new car. Now I'm poor beyond broke, so anything I can get for free will be a plus. Besides, it was my first car and I really liked the thing, so I don't want to get rid of it completely, you know?

Interesting though. This gives me a little hope. As long as I can wire it to a power supply, I can at least monkey with it for a while before shelving it.

How about turning the triplet in, the other way around??(After reversing the lensen in the triplet) Will this affect the image quality?

Would somethinng like this work well? Click the link on google

goooooood