An LED of a different thought

Lumens yes, but not lux (except for laser diodes). You need all those lumens to come from a very small point, or you can't focus the projected image.

Clifford Heath.

I won't address how focusing issues are handled with optical components, but not only 8mm home, but also full-size theatre projection light sources, are LEDs, one for each color. See the s.e.d. thread, "running LEDs to the max, 200A". See first post for links to OSRAM datasheet for the blue LED we used. There are several companies making high-power projection LEDs.

Wow. I knew of smaller LED projectors, but theatre-sized? Amazing, thanks.

If you accept similar life times as a real projector lamps, the issue is the phosphors at least in "white" LEDs. when exposed to very intense blue LED radiation. The light output drops very rapidly i this case.

Ah, ABLE1 is thinking of LEDs for film projectors. Haha, film, what a nostalgic thought of yesteryear.

Nowadays, for high-light-level digital projectors, we think of single-color LEDs, R G B, not white ones.

Thanks to all for their thoughts on the question. Be they on target or otherwise.

What started this thinking was that my brother has a bunch of our Dad's old 8mm movies and would like to try and digitize them. However, after pulling out the old projectors he found that the bulbs were blown. Trying to get a replacement antique bulb is not totally impossible, but, it is rather expen$ive. So the thoughts went to, would it be possible to use a LED to light the way, so to speak.

I am getting the drift that it may be more challenging than buying the expensive bulb and hope that it works.

And, yes we are aware that there are others out there that provide the service to convert to digital. At this point, since he is the pinch penny brother, all other courses of action need to be eliminated first.

Thanks for the assist.

Les

tell us what bulb type it uses, there are sometimes much cheaper replacements.

Last projector I used had carbon arcs.

NT

IMAX now has laser-illuminated 4K DLP micromirror arrays for theatre projection. By tuning the lasers precisely and using very narrow cutoff filters in the glasses they can improve the 3D experience. They don't use polarization in the new system and they did something fancy to get rid of laser speckle.

They had to do some fairly heroic things to get this to work, such as making some of the machined parts out of Invar. I saw this at their head office/test theatre last year, and it was pretty impressive (but that's what demos are supposed to be). Not sure it will convince that many more people to part with money for tickets (~20 quid in the UK). They were really careful about not letting any of the glasses leave with the visiting engineers.

--Spehro Pefhany

I'm not much of a 3-D movie fan, but if they are not using polarization, then do you have any idea what they are using? Alternating shutters?

George H.

What are you gonna do to acquire the image? You need very little light intensity to project into a camera.

Once you see a well-done and projected 3D movie, where you don't even realize it's 3D, but it's very real, then you'll become a 3D fan. But these conditions are tall orders.

I don't have the actual details on the bulbs in question but he said one projector had a 300 watt bulb and the other 150 watt.

I assume he was going to use a digital camera to record the picture. Actually right now he is not recording anything since he has no working bulb to make light.

ements.

It's likely they're halogens, which can often be easily replaced with much cheaper ones, lighting type bulbs for reflector units or car/truck halogens for 12/24v unhoused ones. The downside is lower light level, which may be fine for what you're doing.

Take the dead bulb to somewhere selling & compare, you need the same positi on for the element & similar reflector if fitted.

If you're dropping power a lot, if an LV lamp is run from an unregulated tr ansformer, as is usually the case, you might need to drop the voltage sligh tly to get decent lamp life with lighting type lamps. There are various way s to do that, some simple. Car lamps are less likely to need that. Check th e voltage on the lamp & switch off promptly if excessive.

NT

From what Speff says it might be two different reds, two greens, two blues (of matched apparent intensity) - and glasses that select one of each for each eye.

That would be *way* cool!

Clifford Heath

Background: I've been taking stereo snapshots since 1984, so while far from being an expert, I have picked up some amateur rules-of-thumb.

One of the dirty secrets of stereoscopic projection is that there is a "sweet spot" location in the audience.

Intuitively, sitting on the centre line is better than sitting on the periphery. But sit too far towards or away from the screen, and the Z dimension becomes distorted.

Another is that X-Y resolution is vitally important: film grain equates to Z axis quantisation.

Overall, when I have the choice between 70mm+60fps or stereoscopic, I'll choose 70mm+60fps. And that's true even though I love stereoscopic photos - and /know/ they ways in which they /can/ be really superiour to flattie photos.

OK that would work, so three series bandpass in each eye-piece. (Aren't there edge angle effects? the eye's see different colors?) I/we pay big bucks for a bandpass filter*. Well, I pay for the edge between 780 and 795 nm.

Band pass filters for ~$10? would be nice.

George H.

I've got (stole?) two pairs of 3-D glasses. One is linear (horizontal/ vertical) in each eye. The other is circular, right/ left.

George H.

It doesn't need to be lab standard though. Just a material that has the right properties (so yeah, that would be a big trade secret or patent) - then choose LEDs to suit. Very different market dynamic from scientific accessories.