PROJECTION LENS question

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I am planning on making a projector soon. I have the 15" Samsung LCD, and a 250 metal halide lamp/ballast (bigger type). I am looking on getting 2 fresnel lenses but i dont know what size to get or if i need split fresnels or does it matter? And i need a projection lens. Im not sure what lens to get but i dont want to spend so much money and buy the ones from lumenlab or diybuildersgroup and all those sites who are charging an arm and a leg. Also, i am from Canada so it would cost me a hell of alot more. About the projection lens, i dont know what focal length to get. Im thinking i want about 4 meters from the lens to the screen because i want the projector to be behind me. But if it is that far away, will i lose alot of light? Lastly, are there any good plans out there that dont cost any money? Even if somebody could help me out and send one of there plans, i would greatly appreciate it.
 
they are too small for a 15" LCD. get 12.5"x 12.5" fresnel and triplet projection lens (~~300mm FL) from the website posted earlier in the thread.
Gizmotech said:
Try the fresnels from officemax and triplets from surplus shed. Any copy lens should do. If using folded optics design, them automotive side mirror glass will do. I think thats the cheapest I've found. Let us know if there are cheaper possibilities.
 
Im probably not going to do the folded design, just a simple one. Knocking off a few inches from the box doesnt make much difference.

About the 12.5" fresnels, arent those too small ? And about the 300mm lens, will that let me have the projector about 3-4 meters or 12 feet ish back from the screen? And will i lose alot of light if i have it that far back?


18WHEELER, didd you use these lenses and fresnels for your projector? If so, whats your setup like and how far is your projector from the screen?
 

cbm5

Member
2005-03-14 12:47 am
Arkansas
A common misconception with DIY LCD projectors is that they are easy to throw together from common components, and are practically free.

In reality, it will cost on average $300 to get satisfying results.

The Lumenlabs & other's lenses and fresnels aren't even ideal for this application, but they really are the best quality for the cheapest price. Same goes for the electronic metal halide ballasts and bulbs, though I ended up piecing together my own 400W magnetic ballast system.

Then you have to add in a lot of essentials like building materials, the cost of mistakes, electrical parts, cooling fans, paint, spherical reflector, switches, thermometers, everything that eventually becomes part of the system. And good luck if your airflow path is sufficient on your first try. And good luck safely handling a bare LCD.

It's not a simple project, and it's not a cheap one. For those who are able to build one, it is a rewarding project and it is cost-effective compared to buying a new projector and replacing the bulbs. But unless you find all the parts in garbage dumpsters, you must plan to spend money. If you can't justify spending $300 on a piece of A/V equipment, then you probably shouldn't attempt to build a projector.
 
cbm5 said:
A common misconception with DIY LCD projectors is that they are easy to throw together from common components, and are practically free.


It's not a simple project, and it's not a cheap one. For those who are able to build one, it is a rewarding project and it is cost-effective compared to buying a new projector and replacing the bulbs. .



I already have the ballast and LCD and a few fans from scrap parts. I know theres alot of things to buy and it requires patience and time, thats why i have been researching for the past year or so . The reason i am asking so many questions is because i want to do it right, get the right parts... I plan on getting lens that are good not just, ok, but not the best either because those will cost too much. I nee input here and i know other people do who reas this and other posts.
 
juice_e said:
About the 12.5" fresnels, arent those too small ? And about the 300mm lens, will that let me have the projector about 3-4 meters or 12 feet ish back from the screen? And will i lose alot of light if i have it that far back?

15" LCD is 12" wide X 9" high, so 12.5" x 12.5" is large enough

the lenses are about 330mm FL. idealy you want longer FL in order to place the projector farther behind you without having a too big / dim projection, but it is hard to find a matching fresnel and a projection lens at a reasonable price. 12 feet back you probably get a reasonable sized image

18WHEELER, didd you use these lenses and fresnels for your projector? If so, whats your setup like and how far is your projector from the screen? [/B]

I didn't use their lenses. but mine was similar ( 300mm fresnel, 290-320mm FL varifocal lens). If I remembered correctly, I got about 90" from 10 feet with a 12" LCD.
 
18wheeler said:


mine was similar ( 300mm fresnel, 290-320mm FL varifocal lens). If I remembered correctly, I got about 90" from 10 feet with a 12" LCD.


Ok, thanks alot for the info. Should i get the Fresnels from www.diyprojectorcompany.com/ ?

EITHER:
2x 330 mm focal length fresnel lenses

OR

1 x330 mm focal length fresnel lens and 1 220 mm focal length fresnel lens

Also, will the 80mm projection lens be good quality or should i look elsewhere for a better quality one? By the way, i thought about it and i guess i dont really need the projector to be behind me, id rather it be a brighter image so ill just put it on a table in front of me. If i put the projector on a low table, what kind of angle can i put it at? Do you know at all? Because i dont want it to high that it gets in the way of the view of the screen. Hopefully you know what i mean :)
 

cbm5

Member
2005-03-14 12:47 am
Arkansas
Those lenses are both a bit small in diameter; a bigger lens will probably get you a brighter image. There is of course a limit to how much improvement you get with progressively bigger lenses.

More importantly, the focal lengths are pretty short. You probably couldn't get away with using either for a 15" display. The angle would be too great and you wouldn't be able to see the corners. A 7" display is a better bet, especially for the second lens.

The 80mm triplet lens is good. It's sharp and projects color evenly. The focal length is shorter than ideal, but it works.

Guy Grotke has done some good work with long focal length duplets made out of eyeglass lens blanks. With a long focal length, distortion at the edges of the screen isn't as much of an issue. However the problem then becomes finding a matching fresnel.
 
___________________________________________

* Expexted image of 75"

* LCD 15"

75 / 15 = 5

* Projector lens to screen (throw) of 6 Feet


-------------------------------

Calc. 6 feet (1828.8 mm) / 5 +1 = 304.80 mm


I NEED A 304.80 mm Projector Lens


(so the 80mm triplet with 320 mm FL ffrom www.diyprojectorcompany.com is perfect... ?)

Only if the calculation i did is right?
 

Rox

Member
2004-07-25 10:06 pm
?
yes it is correct;

you would like to have 30cm focal but even if there are some available, you would have easier to buy one of 32cm focal.

the image will be something smaller than if you had 30cm focal.
71" diagonal instead your desired 75". I guess there is no problem with this issue.
 
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