Hi,

Im still building my first projector and after lots of fiddling tonight I just happened to try using the fresnel after the lcd and with no focusing lens, the projected image was huge,.over 3m wide. (compared to maybe 40ish inches with the focusing lens - not sure if this the correct term for it )

The image quality is ok by me, maybe just a little out of focus if anything but the main drawback is i am not getting the whole image from my 6" widescreen tft..its nearly all there but the edges are a bit blurred. Im not sure of the specs of my fresnel as it was salvaged from an old OHP.

It may seem a bit odd but I think id rather use just the fresnel from what ive seen, Does anyone know how i can get the whole image projected? I noticed lumenlab sell a pro widescreen fresnel..would this help with focus etc?

P.S. I did notice that holding the fresnel one way round the image was distorted and curved but the over way it was fine

couldn't you just increase the distance from projector to screen? this would give you a larger image.

I cant go back much further and the image already fills my wall, its just not a complete image, if i move the fresnel from side to side it shos the missing parts..

This is what I am doing now with my 15". I was also getting blurry edges until I did this:
1. take a piece of cardboard the same size as the fresnel and cut a hole (experiment with different sizes) in its center
2. tape this piece of cardboard to the fresnel
3. project the same way you were but now with the cardboard - you will find that the image is a lot sharper (but a little dimmer).
4. Celebrate not having to get a projection lens lol

Now the entire image is sharp.

Seriously - If you can get it to your liking you may find you don't need a projection lens at all. By the way, I did this with an $11 page magnifier from staples

Hi Punisher,

Thanks for the advice ill give that a try now

Its great to here you have done the same thing, makes me feel better about trying it myself.

I cant think of many downsides yet, the image even seems to be in focus(ish) at a much closer distance than normally so ill be able to have a smaller enclosure too Just need a bigger room to fit my image in now

Ill let you know how i get on.

If the sides of your LCD are being cutt off in the projection then you have a design or implementation problem. Check to see if all light is reaching the triplet. You should see minimal light "splashing" around the triplet. Also, you might have something obstructing the field of vision of the triplet which could be blocking light. Conversely, you may not be passing light correctly through the LCD on its way to the triplet. If the fresnels are not at an acceptable distance fromt he LCD, and an acceptable size, they may not be illuminating the entire LCD.

Pun - Can you give me a couple rough distance measurements of your setup? 1. How far is your front fresnel from the lcd? 2. PJ to screen? 3. Screen size?

Thanks

Here's what I have right now - note that I'm not going to leave the projector where it is though -I will move it back a little further from the wall.

Distance from LCD to fresnel (not using one before LCD - have lightbulb array): 16.5"
Distance between projector and wall: 74"
Image size: 91" diagonal (may be off by an inch - tape kept falling lol)

Hope that helps

Oh Dell I forgot to mention that I have my fresnel set the way that produces an image that isn't distorted/curved.

Let me know if you get it working.

It does, thanks.
You say youre using an array as a light source? What type of bulbs are you using, and do they utilize any type of reflector?
Sorry for all the questions, I'm just always looking for new possibilities.

Maybe its because im using a 6" screen but I only have to have my fresnel about 5-6 inches from my lcd for it to focus.

My srceen distance (screen being the ceiling lol) is about 2.5m and im getting an image over 3m wide.

Am going through to test now so will post results soon.

It's ok I don't mind answering questions
I am using 26W compact fluorescents and I don't have any reflectors yet. It's nowhere near as bright as the metal halide pics look on this site but I think I can work with it since I will be using it in a completely dark room. Maybe with some reflectors it will be better. This type of light source is still in the experimental stages - I wanted to try something different instead of getting a metal halide bulb and ballast. I'll post more info as I make progress with it.

Dell you are right - it is probably your screen size - you are lucky! you can have a nice small projector enclosure.

Ok, ive given a try and dont seem to be having much luck

Any idea on size and shape of the hole? Ive tried a big and small square and a circle, not sure if its having much effect...

Did you notice straight away when you did it?

I initially tried a hole 3.5" in diameter (I have not tried a square) - I noticed the difference right away. I got the idea when I noticed the edges were blurry because 2 images of them were being projected over each other. When you move your hand across the lens does the image look clearer when certain parts are covered? Like one side or when both sides are covered?

I'm not sure if the same size hole would work for you too. I've attached a pic of mine - the cardboard is on the inside. (Note The hole in the pic is bigger than 3.5")
Click to view attachment

Thanks Punisher

I'll go and try again now, i had the card on top oof the fresnel..will that make a difference? Ill go and try underneath anyway..brb

I don't think it makes a difference. When you tried it before you didn't see any change? How big was the hole you used? Maybe try a smaller one.

I didnt notice much no, maybe a tiny bit but the sides were def still blurred..its was 5-6 inches big..

Try some smaller holes - the difference between our LCD sizes could be the reason 5-6 inches is not working for yours. Keep trying different sizes until you notice a change - for me anything larger than 6" makes the edges blur from a doubled image. You just need to find the maximum hole size for yours.

I think the hole has to be smaller than the LCD.

Ok thanks for all this advice. Not had chance to test yet..waiting for it to get dark.

Im starting with an inch and will work from there

using a round hole is either 1) going to cut off the corners if its too small, or 2) going to let unwanted light pass through around the edges. You will get one of the two results, there is no way around it. For best results, all light gates should be rectangular since the light 'cone' you want passing through the LCD is rectangular. basically you're trying to get a rectangular pyramid of light to pass through the LCD and block all other light.

Ok thanks for the tip Ill try it rectangular holes too. Its starting to go dark now so will try it soon.

That is a good point you make! I think I'll try some rectangular holes as well.

I just tried the rectangular hole as you suggested and it produced terrible results. It did not improve the image enough to make it a better option than a circular hole.

Only part of the fresnel is projecting a useful image - that part is a circle of a certain diameter at the centre of the lens. Not a rectangle. Placing a rectangle over this would prevent some of the useful projected image from being projected OR cause some of the counter-productive image to be projected (the projection that is making your edges blurry - you are essentially getting two images projected on each other). In my opinion the circular hole is the way to go and not the rectangular.

Dell, that doesn't mean you shouldn't experiment with rectangular holes - I just don't think they will allow you to produce the sharpest AND brightest image possible. It will either be sharp and dim (rectangle that restricts too much light) or bright and blurry (rectangle that doesn't restrict enough).

Im glad to find you had bad results too punisher... i was starting to think there was something fundamently wrong with my setup

I just tried a rectangle hole all the way up to the same size as my tft and it may be a tiny bit sharper but i still have very blurred edges (mainly the left and rigtht)

If you have better results with a circle i may try that.

The circle is what I have decided to use - it works well for me. I dunno why it's not working for you though. Might be the differences between our lenses? The rectangular hole will not work - just doesn't provide a good enough balance between brightness and sharpness. I will try to post some pics of my projection without the cardboard with the circular hole and some with the cardboard so you can see how much of an improvement the circle does.

Im not having much luck with a circle either Maybe my fresnel is just wrong..?

My image is distorted/blurry on the left and right side and in focus in the middle..if i move it either way that side then comes in focus, any size circle or rectangle ive tried seems to do little

Ive attched an image to try and show my problem, although the quality is a bit bad so im not sure if you can tell..



Looking forward to seeing your pics to compare

Ok let me first say that my digital camera is crap in the dark and the images look grainy but I think you can see what I'm saying. Remember that I'm not using a metal halide bulb so the images are quite dim on camera.

PROJECTION WITH ONLY THE FRESNEL LENS:
***Notice that the small boxes are blurry in the left of the image.***

Click to view attachment

PROJECTION WITH FRESNEL AND CARDBOARD WITH CIRCLE: - see next post - can't attach it for some reason.

PROJECTION WITH FRESNEL AND CARDBOARD WITH CIRCLE:
***Now the small boxes are sharper but the image is dimmer - my camera barely picked anything up. The grainyness makes it look like the boxes are blurry but they are actually clearer in person. Also, the image looks yellowish but it is really blue in person just like the photo I posted before with only the fresnel***

Click to view attachment

Thanks for the pics Punisher, do you think looking at mine I have a similar edge problem to you?

Would our images be clearer and sharper if the light source was brighter? Im using an array of 144 leds.

Thanks for taking the time to do this.

I know this is going to sound nuts, but have you tried curving the fresnel?

What effect would this have?

I think you guys will have better results if you use large diameter plain old magnifying glass rather than a fresnel.

Ive just been looking at these at Maplin What would you class as large? Ive seen a nice looking 3" and a 3.9"...

I'm thinking he meant something like 6".

Really... I don't know. I was just thinking that you could test what effect it
would have.

Ok well ive been and bought 2 magnifying lens, cant try them yet as the proj is in a very bright room at the mo.



Ill give this a try too once it goes dark

I'd like to clear up some misinformation presented here.

The shape of the hole isn't important. What matters is the quality and consistency of the lens in that area. You are thinking that the LCD image will somehow be a focused image at the projection triplet. It is not. The LCD image is scattered. Each and every pixel can be thought to hit the entire surface of the lens. What matters after that is how well the lens then recollects those pixels and redirects them to their proper places at the screen. This is why we have to FOCUS the projector on the screen.

It therefore does not matter what shape the hole is, only that it is of adequate size to catch the light that you want to project. You will notice for example that projection lenses tend to be round, regardless of the shape of the final projection.

If anything, provided that you are using a pair of fresnels as per a standard projector design, the lens opening would then be ideally shaped like your light source.

Ok ive been and bought 2 magnifying lens, neither of them are up to the job Nevermind. They show even less image than the fresnel.

I did find a small old magnifying glass in the house..this gives by far the sharpest most detailed image so far..but only a very small portion of it at once

Just as a side note, my girlfriend lovingly made me a new box and covered the inside with tin foil - this gave a noticable improvement in brightness I was surpprised to see that with leds but im not complaining

Hi Supraguy,

Thanks for the info, are my blurred edges simply due to me using the wrong lens then? One with an incrroect fl?

I have no rear fresnel as im using leds so have nothing to match the focus lens too...ive tried with the fresnel i have behind anyway out of interest and it just makes my image much darker..i asume because a lot of the light is then mising my focus/objective lens..

It looks pretty much the same as what mine looks like without the hole.

vonneuton - the lens was already slightly curved when I got it - unfortunately it has lost some of it now lol.

And for what SupraGuy said: "What matters after that is how well the lens then recollects those pixels and redirects them to their proper places at the screen."
- the area of the lens that the I have the cardboard covering does not properly place the pixels - in fact the entire left and right parts of the fresnel are what is causing the edges to blur in my projection. Passing my hand across the lens while projecting an image (without the cardboard) clearly shows that two images are being projected on each other. I don't know if this applies to all fresnels - maybe its just the page magnifiers.

ok that shut me up

Dell can you post a pic of your led set up? I'm always interested in alternative light sources.

Oh Dell you could get a page magnifier from Staples or somewhere and try projecting with the hole - just make sure you open it nice and carefully so you can return it if it doesn't work LOLLLL

Yep, ill get some taken tonight Im still tweaking them but they hardly get hot at all so can be put nice and close to the lcd.

I did go to staples but couldnt see any page magnifiers Oh well..cant think of a high street store that sells these types of things.

When I did a search (link below) for "page magnifier" on the staples website it found it under furniture for some reason lol

http://www.staples.com/webapp/wcs/stores/s...aplesZipCodeAdd

When I went to the store around here it was in the crafts section

The problem with a page magnifier is that it's a crappy lens. Being that it's not a great lens to begin with, it never properly focuses the light to all points on the lens. If it's bent that's even worse.

Even the LL fresnels (Which are very high quality -- for a fresnel) aren't great projection lenses, they're not MEANT to be projction lenses, though.

Well said! Covering part of the page magnifier made the projection sharper with my 15" LCD (good enough to watch a movie but not suitable for reading very small text) but I'm sure its quality is no where near what can be achieved with a projection lens (Will know for sure when I get mine in a few days ).

Dell, I am only using the page magnifier while I am waiting for my projection lens to arrive - Sorry I forgot to mention that - but you did say you would prefer to use a fresnel so I was just letting you know what I came up with for using one. Sorry it didn't work on your OHP lens.

Ok, here are the images of my led array..






This is with the room lights on.


This is with them off.


This is the image we are getting so far (approx 100" wide) with the fresnel and a round hole. You can see the left and right sides are darker..this may be because the array is on cardboard and has curved. We are building another array on wood to make sure they are all parallel.

Its only using a total of 20watts including the tft

Also, have measured the tft and it is 7" even though it says 6" on the box

What are the specs for the LEDs you used? I like the results you are getting with them!

Hi to do a better config,,, find something called veroboard,, it has pararrell copper tracks with holes,, they are mostly used for prototying circuits,,, that way you can solder you leds,, and only have a few wires for power off each end of veroboard