New Projector Build

JavaDog

Member
2005-08-11 8:10 pm
Hello all,
I've been wanting to do a DIY Projector build for some time now and have been pouring over the massive amount of information on this site. Finally decided to get moving on it...

I thinking of using the USHIO UHI-S400DD lamp and S51 Ballast with the E39 Socket for the light source.

I already have a BUHL Lens, with power zoom and focus - which I will be wiring up so I can use them. The lens is a BUHL 743MCL012, 30.5 mm wide angle lens F2.8. I'm really hoping I will be able to use this lens (it is a beauty) - check it out:

[IMGHTTPDEAD]http://users.adelphia.net/~javamoose/Lens/2.jpg[/IMGHTTPDEAD]

[IMGHTTPDEAD]http://users.adelphia.net/~javamoose/Lens/4.jpg[/IMGHTTPDEAD]

Now, as far as the LCD - I haven't picked out a model yet. However, I am planning to use a 15in LCD. I know I can use smaller, but the quality you guys are getting from the 15in screens is excellent!

I am looking to have this finished in about 1-2 months time, and this will be a full build-log with pictures every step of the way.

The problems I am having is trying to find out (and I have searched!) what Fresnal lenses I will need - in addition to condenser lenses?
 
I already have a BUHL Lens, with power zoom and focus - which I will be wiring up so I can use them. The lens is a BUHL 743MCL012, 30.5 mm wide angle lens F2.8. I'm really hoping I will be able to use this lens (it is a beauty)

That is a beautiful lens, but I don't think it will work for a DIY projector. The problem is the diameter of the lens, 30.5mm. That's REALLY small for this kind of project. Even as a wide angle lens, it might not "see" the whole 15" LCD. The other thing that others have brought to my attention is the projection lens has to be able to "see" the entire arc (in the bulb) in order to get a bright picture. Most arcs are in the 20mm - 30mm range (that I've seen). Even the slightest magnification (which happens when you use fresnel lenses with different focal lengths) will make the arc bigger than your lens.

To make use of this lens you would need a bulb with a VERY small arc length (5mm? -> EXPENSIVE) and a small enough LCD so that your projection lens can "see" the whole LCD screen.

I am not an expert at optics. Just taking my experiences and what more informed people have told me.

To figure out lenses, first you need to know the focal length of the projection lens, the throw (distance from the projection lens to the screen), and the size of the screen (diagonally).

[IMGDEAD]http://www.diyprojectorcompany.com/images/theory/equations_for_focal_length.gif[/IMGDEAD]

1 / (projector lens focal length) = 1 / (distance from LCD to projection lens) + 1 / (throw)

These are great equations. Generally, in an unsplit design, you want to place the field fresnel about 20mm behind the LCD. In a split design, you want to place the field fresnel about 20mm in front of the LCD.

A shorter FL for the back fresnel will give you a brighter image.

Do a search on this site and you will find all this information I have told you in more detail.

I hate to give news like this, but it's better to hear now than get most of the project built and find out.
 

JavaDog

Member
2005-08-11 8:10 pm
superdaveumo said:
That is a beautiful lens, but I don't think it will work for a DIY projector...I hate to give news like this, but it's better to hear now than get most of the project built and find out.

Hmm, that is rather depressing. Would it work with a smaller lcd, or is there just no way around it? I had looked at the lenses that DIYPC sells, but their varifocal is so boring - and is $60 to boot. This BUHL lens only cost me $35 (although, it is a $2,500 lens).

cbm5 said:
You could probably get enough money for that lens on ebay to finance a good portion of a DIY projector using components everyone knows will work.

Kinda sucks just to use the same kit everyone else uses...
 

JavaDog

Member
2005-08-11 8:10 pm
cbm5 said:
Well, try it then. Build a projector so that if the Buhl lens doesn't work, you can buy the normal triplet and use that. Only loss is waiting for the new lens so you can use your projector.

Oh, I wasn't trying to be contrary... If the math says it won't work - then I trust that it won't work. ;)

I was just lamenting the fact that we all seem to use the same hardware and are all building the same projector...and I like to innovate. Maybe I'll save the innovation for version-2! :D

Superdave mentioned the arc on the lamp. Unless I am missing something, I didn't see that spec. listed on the USHIO lamp I am looking to use. What exactly is 'arc' in a lamp? Any info on what the arc of the USHIO is?
 
What you can do is find the viewing circle of the lens. You can do this by taking an 8.5x11 sheet of paper and making marks (using actual measurements like cm, inches, mm, etc) edge to edge. Then shine a bright light behind it and put your lens in front of it. Find a wall to shine the whole thing onto and look at how much of the sheet the lens can "see". Be sure the image is focused first. Here's a picture to help:

[IMGDEAD]http://img400.imageshack.us/img400/7166/viewingcircle9xv.jpg[/IMGDEAD]

Using the markings from the sheet of paper, find the diameter of the viewing circle. Your LCD's diagonal can't be any bigger than this. If you have clear plastic to used (ziplock, transparancies, etc) those would work better than the 8.5x11 paper. Make the lines on the paper dark. Helps to see on the wall. Concentric circles as your markings on the paper might work better as well. Good luck with the project!

What exactly is 'arc' in a lamp? Any info on what the arc of the USHIO is?

In gas bulbs (like the metal halides used for DIY projectors), there are two points (electrodes; not touching) with gas inbetween them. Electricity is passed to the electrodes and an arc jumps across the gap, igniting the gas in between. The gap is where all the light comes from. Smaller the gap = better light source = more expensive bulb.
 

JavaDog

Member
2005-08-11 8:10 pm
superdaveumo said:
What you can do is find the viewing circle of the lens. You can do this by taking an 8.5x11 sheet of paper and making marks (using actual measurements like cm, inches, mm, etc) edge to edge. Then shine a bright light behind it and put your lens in front of it. Find a wall to shine the whole thing onto and look at how much of the sheet the lens can "see". Be sure the image is focused first. Here's a picture to help:

http://img400.imageshack.us/img400/7166/viewingcircle9xv.jpg

Using the markings from the sheet of paper, find the diameter of the viewing circle. Your LCD's diagonal can't be any bigger than this. If you have clear plastic to used (ziplock, transparancies, etc) those would work better than the 8.5x11 paper. Make the lines on the paper dark. Helps to see on the wall. Concentric circles as your markings on the paper might work better as well. Good luck with the project!

Cool tip, I will try that tonight and post the results. Thanks! :D

Nice lens, let us know if you got it to work :)

Thanks, hopefully - otherwise it will make a very pretty paper-weight. I'm hoping I can rig something - because having power zoom and focus on a DIY rig would be sweet...
 

cbm5

Member
2005-03-14 12:47 am
Arkansas
hanks, hopefully - otherwise it will make a very pretty paper-weight. I'm hoping I can rig something - because having power zoom and focus on a DIY rig would be sweet...


Nah, because a 15" DIY projector is usually so big and heavy, you put it somewhere and leave it there. The exception being some of those builds done by the guys with too much time on their hands, with nifty projector/PC carts and stuff.
 

JavaDog

Member
2005-08-11 8:10 pm
Well, I decided to just use one of the "normal" lenses from DIYProjector, since it seems those are the best option I can find.

After doing the math, for my room and panel size (15") it looks like I would need a 500mm FL to get the screen size I want (around 120" diag). However, looking at the kits DIY-PC lists, their long-throw kit is the closest with a total FL of 450mm. So, I guess this looks to be the best way to go?

I was also looking at the F550 fresnel from 3dLens.com instead of the kit fresnels from DIY-PC - but I am not sure if a 550mm fl fresnel would work with any of the DIY-PC lenses, or if I would need two of the 3DLens fresnels or just one?
 
Well, using the numbers you gave (120" screen, 500mm lens, 15" screen), you have a throw of about 177" or 14.75ft. If this is so, you have a couple options. One is to use the 500mm projection lens from lumen labs (the pro lens, $199).

Just remember this equation:

1 / (projector lens focal length) = 1 / (distance from LCD to projection lens) + 1 / (throw)

So in your case:

1 / 500 = 1 / (distance from LCD to projection lens) + 1 / 4496

Distance from LCD to Projection Lens = 562mm

So the 550mm fresnel lens would work great for a split design. The other solution is to use a 450mm lens and either increase the size of your screen (to about 134") or move the projector closer to the screen.

You could also use a 22" FL (558mm) opaque projector lens. Good luck!