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Exchanging a PJ's lens for more light

post #1 of 15
2/12/08 at 8:07am
Thread Starter 
Has anyone ever tried exchanging a projector's zoom lens for a high performance fixed focal length lens? It's the type of mod that immediately comes to my mind as a hobby photographer, since most projectors (actually all in the affordable price ranges) don't feature a lens with a wide aperture and thus waste a lot of light. Especially the zoom function is very "expensive" in terms of design and has a strong negative impact on all other properties of a lens. Even better would be a fixed focus lens, allows fantastically wide apertures (of course there's only one possible distance to the screen and screen size then).

With a "superfast" projection lens, we could have e.g. twice the amount of light (linear scale) at small zoom (short throw, wide angle) and 6x or more compared to the long end of the AE2000's built-in zoom.
Isn't the size of the panels rather similar to certain tubes? It could be possible to find fitting projection optics. Ideas anyone?
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post #2 of 15
2/12/08 at 8:15am
Optics have gotten a lot better in general to where most projectors have wat would be the equivelent of very high grade optics of just several years ago.

At max zoom, your at max light for most modern projectors, so I am not sure anything significant can be brought out from any given projector.

Your AE2000 has pretty amazing optics, as is in my opinion. I'm a serious astronomer and telescope builder / owner, so I understand high grade optics as well.
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post #3 of 15
2/12/08 at 8:43am
Thread Starter 
Most light should be at small zoom (=short focal length, max picture size). Does the video world really call widest angle "max zoom"?? That is very strange - max zoom should be smallest viewing angle = smallest picture, at least it is with photo lenses.

f/1.9 on the short end isn't too bad, sure. On the other hand, one stop (f/1.4 minus better t-stop value because of fewer elements) already yields a linear improvement to 200%.
And f/1.4 should be well possible with a fixed focal length, if not f/1.2. On the long end, the difference would be huge - long throw would be just as bright as short throw.
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post #4 of 15
2/12/08 at 8:59am
Shortest throw = max zoom for any given screen size.

Max zoom is the largest picture available for the throw distance of the projector.

This uses as much of the lens as possible and stresses the optics as far as CA and other edge optical distortions created by any given optics. The shutter is effectively as open as it can get if your attempting to equate it to photography. fastest (Old photographic term) / widest or greatest F/Stop if you will.
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post #5 of 15
2/12/08 at 9:21am
Thread Starter 
Yes but in photographic terms, the widest angle of view (short throw) would be minimum zoom because it's the shortest focal length. Max zoom is max focal length is smallest angle of view is maximum distance for a given projected area in photography. Is there an official definition of the term for Video anywhere, or are people just assuming "large=max"?

Also, it is not necessarily coupled to the f/stop, only cheaper zooms have a variable aperture. Think about pro zooms with constant f/2.8 (or even f/2.0, for Olympus 4/3) aperture. Are there any projectors with a constant aperture lens? It would be interesting to try to adapt them. Or maybe one of the interchangable ones from High-End PJs.
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post #6 of 15
2/12/08 at 9:40am
There are differences in the way this works from a recording device made to focus the light and record it to flim or digital sensor as opposed to a device made to throw images.

You almost have to go back to the prehistoric over head projector to get a better grasp of what is happening.

We have a large gap in between our knowledge here.

I come from the telecope world of gathering light and focusing it to a fine point.

You come from a background of using lenses both fixed and otherwise to record images on a sensor or film.

I guess what we really need in this thread is a person with a better background on optics pertaining to projected images.

I still assert that at closest throw, using max zoom, you not going to be able to get much if any more light out of a given projector. Now at longer throw distances than max zoom? I'd think your on to it. A fixed lens seems very beneficial to achieve the max light at any given throw distance for any given screen size.

Having no zoom on a projector would sure make installation tougher.
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post #7 of 15
2/12/08 at 9:40am
audiophobe,

I think you are completely correct especially at the long end of the lens. For a long throw projector, you would definitely get more light by using a wider aperature. According to the Panasonic literature the lens is a "(2x)/powered focus, F 1.9 - 3.2, f 22.4 mm-44.8 mm"

F1.9 is already pretty wide open and you won't likely find 22.4 mm lens any wider than that anyway. But the F3.2 at 44.8mm could definitely use some improvement. I can think of one good lens that might work and it is cheap. The Canon EF 50mm f/1.8 is an awesome lens and it is only $85. http://www.adorama.com/CA5018AFU.htm...0mm&item_no=17

In theory, with that lens you could get the 900+ lumens the AE2000 can do even at the telephoto position. On the wide angle side I don't see much room for improvement. Even if you did find lets say a F1.4 25mm lens, the incremental light output would probably not be worth the degraded optics associated with using an F1.4 lens (focusing would be very tricky and light fall off in the corners would likely be a real problem.)

Good luck. If you do switch out lenses, sell me your panasonic zoom lens. A 22.5-45mm F1.9-3.2 zoom lens sounds really good. It might work well on my canon camera .

-Mr. Wigggles
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post #8 of 15
2/12/08 at 10:44am
Thread Starter 
@Johndenver:
There shouldn't be a fundamental difference to photo lenses. In one case the panel throws an image onto a plane and in the other case the plane throws onto the panel. The only real difference is probably amount of light on each side.

@MrWiggles:
I thought the AE2000's lens was f/3.5 at the long end.. sheesh, that's why my calculations didn't correspond to the measured lumen output.
A normal photo lens would very likely not work though. Their working distance should be far shorter than a projector lens' (<5 cm).
Distortion free f/1.4 is possible but might not be cheap. On the other hand, giving up zoom typically yields at least a one stop gain of brightness by design. The large working distance of PJ lenses gives them an advantage in this regard anyway because the light doesn't travel in steep angles.

I'm not going to dissect my AE2000 . I was just wondering if anyone had tried something like this.
Without the lens present, the firmware will prolly refuse to work so the electronics need to be ripped out and remain connected. And one would need to find a PJ lens with a fitting registration distance (equal to or larger than the original one).

p.s. I was astounded to find the f-numbers for my old Z3's lens to be f/2 to f/2.5. Only about half a stop difference.
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post #9 of 15
2/12/08 at 10:56am
[quote=audiophobe;13089667]@Johndenver:
There shouldn't be a fundamental difference to photo lenses. In one case the panel throws an image onto a plane and in the other case the plane throws onto the panel. The only real difference is probably amount of light on each side.QUOTE]


Fundamentals do remain some what the same. But it still requires thinking of it from a different direction.

I think your onto it for longer throws... I always 100% of the time do my best to install at the shortest throw / max zoom anymore, my only point was? That if your always mounting at the shortest throw possible for the desired screen size, I still don't think your going to eek out any significant additonal light from it.
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post #10 of 15
2/12/08 at 4:26pm
Quote:
Originally Posted by audiophobe View Post

I thought the AE2000's lens was f/3.5 at the long end.. sheesh, that's why my calculations didn't correspond to the measured lumen output.
A normal photo lens would very likely not work though. Their working distance should be far shorter than a projector lens' (<5 cm).
Distortion free f/1.4 is possible but might not be cheap. On the other hand, giving up zoom typically yields at least a one stop gain of brightness by design. The large working distance of PJ lenses gives them an advantage in this regard anyway because the light doesn't travel in steep angles.

I'm not going to dissect my AE2000 . I was just wondering if anyone had tried something like this.
Without the lens present, the firmware will prolly refuse to work so the electronics need to be ripped out and remain connected. And one would need to find a PJ lens with a fitting registration distance (equal to or larger than the original one).

I seriously doubt the projector will refuse to work without the factory lens present. I doubt there is any feedback to the projector to let it know if the lens is there or not.

As far as "registration distance" is concerned, You would have to play around with things to find the what the Flange Focal Distance is. For the Canon EF lens, the FFD is 44mm. So "optically" the 1080p imagers need to be less than 44mm away from the closest lens mount location. I doubt the imagers are physically less than 44mm away but with all of the prism blocks etc. in the light path, they might be "optically" less than that far away. It either will work or it won't but there is nothing mythical about a projector lens - the Canon will be as good or better (it just won't have the zoom feature). In the past I have put a Plus UP-1100 projector lens on a different projector with success. It worked pretty well.

There is a company that makes aftermarket lens called Navitar. http://presentation.navitar.com/apps/lenssearch/. This company used to be know as Buhl. As you can see from there search most of there lens are in the F3 range not lower than F2.

Anyway, for a guy who was the starter of this thread, it sounds like you are wussing out on us.

-Mr. Wigggles
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post #11 of 15
2/12/08 at 5:14pm
I did some research on the Navitar site and they have a bunch of lens for other Panasonic models (primarily installation projectors.) The Back Focal Length (effectively the same thing as FFD) for those lens ranged from as low as 53mm. If the AE2000 was less than 53mm there is a good chance that a standard camera lens could work on it.

Now it would probably recess deeply in the case and there might be some cutting involved.

-Mr. Wigggles
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post #12 of 15
2/13/08 at 1:06am
"Does the video world really call widest angle "max zoom"??"

I think that's because the light is going in the opposite direction for cameras and pj's.
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post #13 of 15
2/13/08 at 1:42am
Thread Starter 
Quote:
Originally Posted by MrWigggles View Post

You would have to play around with things to find the what the Flange Focal Distance is. For the Canon EF lens, the FFD is 44mm.

This is not quite the number we need, because it only defines the distance to the lens mount but not how far the rear element can reach back for mirror clearance. That's why there's some M42 lenses that don't work on certain cameras.
I looked at images of disassembled LCD PJs and it looks like the distance is a lot larger.

Quote:


Anyway, for a guy who was the starter of this thread, it sounds like you are wussing out on us.

Hehe. Remember, I only asked if it has been done.
I might try if I had a defective device to play with, but with a new AE2000, nah.

Quote:
Originally Posted by noah katz View Post

think that's because the light is going in the opposite direction for cameras and pj's.

But that doesn't change anything about the geometry of the whole thing. Smallest viewing angle is still largest focal length and (usually) smallest aperture..
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post #14 of 15
2/13/08 at 8:38am
Quote:
Originally Posted by audiophobe View Post

This is not quite the number we need, because it only defines the distance to the lens mount but not how far the rear element can reach back for mirror clearance. That's why there's some M42 lenses that don't work on certain cameras.
I looked at images of disassembled LCD PJs and it looks like the distance is a lot larger.

For Canon EF lenses the FFD is the same as the BFL because the flange is at the very end of the lens. The EF-S lenses have a protrusion so the FFD is larger than the BFL (it's probably about 25mm)

-Mr. Wigggles
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post #15 of 15
2/13/08 at 11:15am
"But that doesn't change anything about the geometry of the whole thing."

But it changes the relativity of the effects.

I think it makes sense to call a pj zoomed in when it makes the image seem bigger /closer.
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