Here's a diagram explaining why you shouldn't use narrow PVC pipe as a focusing mechanism. You will get dark corners from narrowing your FOV.

Here's some pics of how lumenlab users have cleared the focusing hurdle.

First is Ookpic's incredibly "why didn't I think of that" simple solution:

Here's Supermadmax's "box within a box" solution:

Of course, the "box within a box" doesn't have t be the size of the whole front panel, just large enough that it doesn't narrow the FOV. Here's what Slusher357 came up with:

I chose to make my front panel slide on drawer sliders from Lowe's:

And Clyde took my idea up a notch and used super-smooth keyboard drawer sliders:

Heres the mechanism in my projector. Very similar to the one on top.

EDIT by OKflyboy: Thanks for the post. Man that was a HUGE pic, I shrank it down a bit...

http://www.lumenlab.com/forums/index.php?showtopic=907&st=59


Sorry if the link didn't make sense earlier. They've been trimming off topic posts and it messed up the specific post I liked too. Somewhere on this post, (currently only a few entrys down), you will find a velcro lined box in a box design. The velcro keeps it both tight and smooth acting (using only the 'loop' of the velcro, the soft half).

I imagine other materials could be used, such as thick felt.

i was thinking of using something like this and it does not block the FOV....

it is threaded pvc 3" with flare the lens fits nicely, and i cut the white theaded part on table saw.

Cross between Ookpic's and Supermadmax's ideas.

Okay. So whats the simplest detailed way to build a focusing mechanism?

box inside of box would be the easiest.

And how exactly do I build that

The best explaination I've seen of this is Kjudki's BOX W/IN BOX. Once again excellent job Djudki.
Here is the link:
BOX W/IN BOX

correct me if im wrong, but most methods for focusing are sliding a lens forwards and back on a track of some sort.

just wondering has anyone setup there focus mechenism with gears?

so that on the out side you would have a small radio tuner type wheel thing, and when u spin it, the focus mechanism moves forwards and back

would this be a good thing to set-up?, to get the image more easily focused

Depends on what you classify as more easily?

I for one think that building a box within a box or using draw sliders has got to be way easier that putting together a gearing mechanism to move the focus.

For me the descision was based on how often I'd be moving the PJ and also on my ability and ideas (I went with drawer sliders). This is a DIY so it really is up to your own imagination. If you wanted to you could put an electric motor and IR receiver in and have electric focus from your lounge chair. It's all up to you!

Cheers,
Arkay.

water-pyro,

I thought the same thing

"correct me if im wrong, but most methods for focusing are sliding a lens forwards and back on a track of some sort. just wondering has anyone setup there focus mechenism with gears?"

To me it was the next logical step.

What I have is not actually a gear per say. Basically I'm using a box within a box design but, I'm taking it one step further. I have a worm gear, I think?. A long threaded rod, (Thread spacing is much different than a bolt) with a barrel attached to it that is threaded on the inside. As you spin the rod the barrel moves back and forth but the rod is stationary. Just connect the barrel to the box within a box on tracks and add your knob on the outside and wallah! Unfortunatly, I don't have any pics yet. When I get home tonight I'll scan it in and post it for all to see. It is actually quite simple. Although, I don't know where you can buy what I have. It came off of an old Radial arm saw that no longer worked. It adjusted the up and down height of the saw. Now the back and forth of my lenses!

Al_B

sounds cool, cant wait to see the pics

I thought of something similar to adapt, the focusing mechanism used on small telescopes. Basically a rack-and-pinion. Check garage sales etc., for a broken or unwanted telescope to cannibalize.

That's actually a really good idea, and simple, it sounds like. I see those in Thrift Stores all the time and have never thought anything of it, Hmm?

That's the beauty of this project, you can make it as simple or complex as you like.
For now, I'm planning on some kind of manual adjustment for keystone and focus, but only time will tell.

If budget and complexity were not a concern, however, you could easily rig up a small gear motor or linear actuator to move your focus box (and/or front fresnel) in and out. Then you could add a toggle switch (or separate in/out switches) and BAM, electric adjustment.

In case anyone feels like pursuing the above idea, here's a couple quick links:
Gear motors
Linear actuators

*edit* Found an even better site: Motors and actuators */edit*

*edit2* Whoa... this site doesn't really have much to do with motors and actuators (though they do have some manual rack & pinion stuff), but they do have a huge online catalog of lenses, mirrors, mounts, etc. Edmund Optics */edit2*

-Oloff

water-pyro,

Sorry I didn't get back to you last night. I don't have a camera but I was able to scan the parts with my scanner. So please pardon the pic quality and size.

The "L" bracket on the end will support the rod on the inside of the box.

The smooth part of the shaft at the other end by the knob will be resting in a hole I will drill through the box with the knob on the outside. A washer on the inside of this smooth part will keep the rod from going through the drilled hole in the box.

The drum in the middle is what moves back and forth as you turn the knob. Just screw it to the side of the box within a box on tracks and you now have your focusing mechinism.

I hope you like my idea. It is as simple as you can get without getting to complicated.

You could use this as a base design if you wanted to make one with a long bolt and nuts but, the movement would be less with the turn of the knob.

When I build my box I will submit pictures for you to see it set up.

Al_B

Hey Joe, I really like the PVC idea. I think it would work great but I seem to be having trouble with the threading. It seems to me that the threads (both male and female) are slightly conical in shape so that they get unmovabley tight before they can be fully screwed together. Did you run into this problem? In case I'm not being clear: I got myself a 3" male and female PVC adapter. I chopped the female at about 3/4" so I'm using just the threads. The male part threads seem to be a tad bit thicker towards the flare such that it gets really tight after about 4 full turns and won't go any further. This unfourtunately gives me only 1" of travel on my focusing mechanism rather than the hoped for 2" . I saw you used the same type of pieces I'm using a page back and was wondering if you encountered this problem. Thanks.

I put this together at work today. Thought I might try it as a focusing mechanism. Still need to figure how I will attach it to the focus lense.

The motor is 12vdc with 10:1 gear reduction from globe motors. Original invoice for the motor shows $14.95. Not sur it thats us or can funds. Will post more pics as it comes together.

sfg

really simple and dumb focusing mechanism.



Focusing panel mounted on keyboard slides. so its like a L with the horizontal board attached to the slides. The slidea re mounted at the bottom of the box so the board is about 3/4 of an inch off the bottom of the box. (i mounted all my stuff aka tv tuner and lcd controller on the horzontal board, but if you have ffcs i guess you wont be able to.) I have a threaded rod (with two lock nuts) attched to the bottom of the box then running under the board and into a nut glued to the focusing panel.. then the threaded rod jsut goes out the box and to a knob..

<inside projector


attaching a motor (Stepper probably) would probably be a really good idea, or just using a liner actuator instead of the threaded rod

cons, even though i used threaded rod it still takes a ton of turns to focus if i move the box, (i just took the knob off and used a drill when i had to move it really far) so maybe a really cheap handheld driver permanatly mounted would work well in this situation...

When I get my thread up and have pics, this will be easier to explain, but I used a simple 4" to 3" PVC Schedule 40 adapter.

The lens drops in to the 3" side and is prevented from falling through by a lip in the middle of the adapter. The lens flange is just barely smaller than the inside diameter of the adapter. I used a 1" slice of 3" pipe slid into the adapter tight to the backside of the lens flange to secure it, and then packed felt weatherstripping around the lens barrel.

You should probably thicken up the front of the projector box with another piece of 3/4" material to make an 1 1/2" thick surface to slide in and line hole with felt.

The rear of the lens is only a 1/4" recessed into the 3" portion of the adapter, and the 4" dia. of the adapter in the front makes for a nice look and no FOV issues.

A pic is worth a thousand words-I'll get some up soon.

Got an idea for Focusing Mechanism. I got the idea after going to bed last night, so I have not had chance to test anything, but I think it should work..

If I take a pvc/plastic pipe big enough to not interfear with the FOV, and slice 4 paralell "slots" in it (one on each "side" of the pipe) with the right angle and length, and mount this pipe in a hole in the front of the projector by putting one screw in each of the slots. Then I should be able to focus just by turning the pipe as this would cause it to slide in and out of the box..

I currently don't have any sort of cad program, so I just made a quick (and horrible) sketch by hand..

Have anyone tried anything like this??

I just like to add.. The pipe would off course be much shorter than on the sketch.
The sketch does not show any dimensions, it's just to explain the idea..


The Edge

Please excuse my ignorance, but is ther a top/bottom to the triplet, the old or new, that will require it to be installed a certain way, or does it not matter whether it is one way or another??
My reasoning is that if it doesn't matter, then you could make a threaded channel, and turn the lense itself to tighten (shorten) or loosen (elongate) the throw with a threaded mechanism. in other words, if I turn the focusing mechanism to adjust the focus, and that makes the lense turn on it's horizontal axis, would the picture turn with it, and then be sideways, or will it always be rightside up, no matter what you do with the lense????
I hope this makes sense..................

Ryan

It doesn't matter, as long as it stays perpendicular to the incoming light. Rotating the lense will have no effect on the projected image.

That's effectively the same as what's shown in the design above suggested by The Edge. That solution is basically using a very coarse "thread pitch" so that a small rotation will result in a forward/back motion that's much larger than what you'd get with a typical threaded connector.

Hope this helps,
Phil.

That's how it is done with CRT projectors.
You could also use a larger diameter tube on the outside of this one with the same slots using nuts&bolts connecting them together at the right tension for easy adjusting.

Cool idea.


peace

Found this box at Bed, Bath, and Beyond. Think I'll try it for my focusing box. $5.00

6x6...2.25 inches deep.


Forgot to reduce..

i used a type of "rack and pinion" a dowel out the side of the box with string wrapped around it and tied to front and back of the focus box, turning the dowel causes the box to move in or out ..... backlash free.

scuse the 'poor' photo

[Edited by OKflyboy. Please don't curse, we're a family site. Thanks!]

Why not just mount the lens on a large threaded PVC Tube and then glue a threaded collar into the box? the lens would simply screw in and out for focusing.

Eric

joe2000chevy and The Edge already suggested this idea. ^^


peace

Has that threaded PVC tube idea been used, I was looking at the different options and that one seems best to fit my style, but just want to make sure that I won't be cutting out any of the picture using the pvc idea.

PVC will work but you must use a large diameter, 4" at the least. If there's any doubt about whether it will cut into your light cone, check it. You can do this by tracing yourlight cone on the bottom and side of your box with a pencil, or jsut even using a piece of string to visualize it.

Here is my idea for a focusing mechanism for the lens.

Edit: Won't work, PVC pipe has Tapered Pipe Threads, they tighten as they are screwed together.

Those are good graphics, but that is almost exactly what I bought from the home depot yesterday. I am worried about the FOV or whatever and don't want to cut the incoming/outgoing light so I am going to cut down the pvc. I should have my projector done by next wednesday and I am going to try and implement this idea, and will let you know if it works.

You will run into trouble with the threaded PVC design as pipe threads are tapered and will get tighter as they are screwed in deeper. You will be able to get a little bit of travel, but probably not as much as you would like.

What area of the threads are tapered?
Is there anyway to cut out the tapered area so it will screw all the way in?

I looked at some Schedule 40 (Thin Wall), the threaded area is about half
that of Schedule 80. It screws all the way in but it has tapered threads
as well (NPT).

Tried to glue a piece of pipe to the Flush Plug, it didn't work well.
The Flush Plug needs to be grooved so the pipe has more to adhere to.

What looked promising was the 2" Grey PVC Coupler, it has Standard Threads.
They make it in 4" but I think the price might be prohibitive.

What are the dimensions of the Standard Lens?

http://www.lumenlab.com/forums/index.php?showtopic=3085&hl=

8th post down.

Just a thought I had, do you think it would be possible to use the top of a travel mug for a focusing mechanism? Assuming it is the threaded type and has a moderately large diameter?

I am about to start construction on my box and was trying to design some sort of focusing mechanism. These are the requirements I set and am trying to come up with an idea. Maybe you all can provide suggestions.

Requirements
1. Triplet enclosed in PVC *a lot better looking than box in box*---> A 3-4 in coupler or a straight 3 in coupler with some cut off not to restrict field-of-view and lens must be secured so it wont fall out
2. Lens Must move in and out 2 in for focusing
3. Must tilt up and down with the pivot point at center of lens *Hard part*---> I will have extreme keystoning so I need the triplet tilt to focus the picture and if the lens is to move in and out, the pivot point will have to move to stay centered with the lens
4. Front wall of box fixed in place
5. Minimal holes/slots for light leakage

Tell me if I am trying to make this too complicated. This is the first and only idea I have so far. You can screw the top and bottom knobs independent to move the PVC/lens in and out and tilt. The lense will be secured in the PVC by wedging a wooden ring inside the pvc.

If someone could add improvements to this design or come up with a better it would be appreciated. A mechanism with the knobs coming out of the box out of any orrientation is fine. I would least like the knobs where I currently have them though because I want the height of the front to be as minimal as possible.

I hope all of this makes sense. Thanks.

This is haas_man's (see his plog) adjustable lens assemby.
It uses a 3-4 PVC reducer, I believe it requires some machining on a lathe.
I read in someones PLOG, ?, they used a 3" PVC cap and fit it inside a 4" PVC pipe.

Looks like a good idea.
How about springs on the adjustment screws for tension?

I had thought about the springs and Haas_Man also suggested that. His 3-4in reducer idea is what inspired me to go this route. I dont have easy access to a lathe so I am trying to accomplish this without. I figured I wouldn't need the outer sheath since the bolts would be holding the 3-4in reducer in place.

Anyone else have thoughts on how to improve on this or even an entirely different approach?

From my understanding, the Projection Lens focuses on the LCD.
If you angle your Projections Lens you will need to angle the LCD also, to keep it in focus.

In the keystoning thread about 11th post down they talk about this. They never say that the LCD needs tilted.

Is this going to work?....if not, let us modify this

I dont think it is going to. I did some thinking and found some flaws. First off, the PVC is heavy and with that wooden ring on the back of it there will be a lot of weight on the back off the bottom bolt. Second, even with big springs I dont think it will keep it from moving side to side. I am working on a new design that should be finished this week. I will draw it up real quick and post it.