NBTV Projection

[Colin-JB]

Hi everyone,

Haven't been around for several months as between the business I run, the business a group of us are setting up and my p/t job, I have had no time spare at all. However things are settling down now and my thoughts once again turn to NBTV. I have suspended my experiments with editing audio at the moment for something a bit more practical. I want to project an NBTV film on the big (well bigger) screen.

I figured that in theory the principles are similar, both involve a light source to illuminate the image, and the light source passes through the image in film or holes in the disk or drum for NBTV. I suppose that's where the similarity currently ends, but what if you could project nbtv on to the wall?

I know I will need a good projection lens, and there are many available on E-bay, and a brighter light source. The dull red LED just doesn't quite cut it! I've picked up a lens which I hope will do the job, there is only one way to find out, but now I need a brighter light source.

Now I am not expecting the brilliance of a 20ft screen with this experiment, but If I can fill a post card, or even an 8'x10' I will be happy. I know the answer is in bright white LED's, but my electronics experiences are the best part of none.

Firstly, can anyone tell me what are the brightest LED's available, how many is recommended and where to get them? Also a budget version as my money fluctuates in typical self employed fashion so I may not be able to afford the best right now. I also imagine that these will need to be encased to prevent light leakage (and to protect the observers eyes) and possibly reflected back towards the disk?

The next thing I will need help with is how to line them up. I don't have the understanding yet on how to link them up into a working circuit. Do they even have a + and a -? Then I imagine there will be power issues. Will I need a greater power source than the two AA's provided with the televisor kit and if so what?

Once those questions are answered I can remove the guts of the beast and place it in a new housing, one capable of supporting the lens and then see how well she focuses. If I get a success at this stage I can move on to address the expected reverse image problem!

Colin-JB

PS, the plastic disk has warped. Any ideas on how I can straighten it? Or should I be in the jumble sales looking for a 45 to replace it?

[gary]

With the paraphrase: "that's not a LED, THIS is a LED" you might want to have a look at the range of Phlatlight LEDs as shown, somewhat flippantly, in the video shown here:

http://hackedgadgets.com/2010/07/14/sup ... hlatlight/

You might also want to look at a variation (PWM modulation, etc) of this simple laser projector:

[Klaas Robers]

At the convention of 2001 Colin Hopper demonstrated a laser writing a green NBTV picture on the wall. The laser had sufficient power to write a picture of about half, or a quarter of a postcard on the wall. The light beam was sweeped with electronically steered mirrors and modulated in intensity by a Kerr cell or a Pockels cell. On NBTV CD number 3 you may see the result. However this was not something that a beginner in that field will do.

The problem of the Nipkow disc is that only 0.1% of the light is left through the tiny hole of the disc. So you should have 1000x the amount of light available that you should have in a normal slide projector for the same brightness on the screen.

A second problem is that you will see the 32 lines very clearly on the screen if you enlarge them to a larger picture. Or if this is not the case, the picture will appear very unsharp. Gary might confirm you that the "Big Picture" should be watched at quite some distance for a good view.

[gary]

A second problem is that you will see the 32 lines very clearly on the screen if you enlarge them to a larger picture. Or if this is not the case, the picture will appear very unsharp. Gary might confirm you that the "Big Picture" should be watched at quite some distance for a good view.

Indeed that is true, on the other hand I would expect anyone looking at projection would be doing so to allow "viewing at a distance" and thus the effective size of the picture would be the same or similar to that on a normal monitor. In the case of TBP if you view it in "full screen mode" from across a large room it looks the same as if you were sitting in front of the computer with it in "normal mode".

On the other hand again, even though the "full screen mode" is useful if, for instance, you were giving a demonstration to a group of people, it is not the reason TBP (The Big Picture!) was developed - it came about because Les Robotham requested it due to his deteriorating vision making it difficult for him to see the picture on the old NBTV player (he was so kind to me on my last visit to the UK I could hardly refuse could I?).

I guess for vision impaired people ANY picture is better than no picture at all so line structure is a moot point.

But yes, if Colin-JB was expecting HD quality he is definitely going to be disappointed.

BTW - I developed a computer based NBTV player to give me a benchmark against which I could compare my mechanical monitor results (at that time people seemed to be getting much better results than I was from what I could tell from the Newsletter etc.) - you could stretch a point and say that TBP's "full screen mode" is a benchmark for NBTV projectors - especially if you had an AV output on your video card or capture card - or used TBP's AVI creation feature to make a DVD - and displayed the results on a large screen television set - or, dare I say it?, your home theatre projection TV!

[Panrock]

You could do this with a lens drum or lens disc... lots of little lightweight plastic lenses. Each would act as a projection lens for one line. I suggested a 120 line scheme based on this principle in a recent NBTVA article, but somehow I don't think you would want to go this far...

Steve_O

[gary]

You could do this with a lens drum or lens disc... lots of little lightweight plastic lenses. Each would act as a projection lens for one line. I suggested a 120 line scheme based on this principle in a recent NBTVA article, but somehow I don't think you would want to go this far...

Steve_O

Yes, I should have mentioned that, even with just one high brightness white LED through my bead disk, I can project a discernible image onto a piece of white paper. Goodness knows how a 3 watt Luxeon LED or, heaven forbid, a phlatlight (probably melt the beads) would go.

I must get around to trying it one day - I am pretty sure I would need additional optics though.

[Colin-JB]

gary;

http://hackedgadgets.com/2010/07/14/super-high-power-led-pt54-phlatlight/

Wow! Possibly a bit too powerful for this project - my disk would probably burn!
Klaas Robers;

The problem of the Nipkow disc is that only 0.1% of the light is left through the tiny hole of the disc.

That's why I don't expect to be able to project very far, but need a huge amount of light.

A second problem is that you will see the 32 lines very clearly on the screen if you enlarge them to a larger picture

True, When using TBP on full screen, you have difficulty seeing it a close distance, but it looks fine from way back on the sofa! If I can get that sort of clarity at that distance ( or similar in smaller distance) then I shall be very happy.
Panrock;

You could do this with a lens drum or lens disc... lots of little lightweight plastic lenses.

I did ponder some time back about the viability of contact lenses? If I get this working I may look further into this. Has anyone else tried them (for Televisor)?
gary;

even with just one high brightness white LED through my bead disk

Bead disk? Tell me more...

Colin-JB

[gary]

Bead disk? Tell me more...

Colin-JB

A bead disk is a nipkow disk that has the apertures replaced by small optical quality glass or acrylic spherical beads.

Here is a very bad quality (I have no means of taking good quality photographs) picture of my first version - I have it leaned over in order for the beads to take the light.

Here is how I made it:

http://www.taswegian.com/NBTV/forum/dow ... hp?id=1887

and here is a VERY bad video of my first tests with it - I show this because it shows how it looks in daylight and it looks around the disk at the single high brightness LED.

The results look much better than this in reality - the glare and flaring seen in the video is not present to the naked eye. It is very hard to video.