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Thread Index
• Aiden's Parabolic Projector.
• Test #1 - Bulb Horizonal
• Test #1 - Bulb Horizonal: Egg Yolk
• Test #2 - Bulb Vertical (mounted on Axis)
• Parabolic Projector Theoretical Working Design

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Hello everyone,

As many of you know Aiden has been trying out parabolic reflection with his projector you can view his log here. This was unknown to me when I placed my order, but non the less I want to go through some tests and post the results here for everyone to see.

First let me introduce you to my rough test setup:


#816:ISO Auto - As you can see, it is VERY EASY for me to move and reposition components. My whole projector will be built with this in mind, the case will be last.


#805:ISO Auto


TEST #1
[color=red]Please note, the oval shape of the light pattern or "hotspot" is due to the reflector not being square to the wall in these first pics. At least I think it is, my apologies for not double checking and overlooking this.

The first tests are with the bulb running horizontal, the next test will be with the bulb horizontal but with a mini reflector in front of the bulb. Unfortunately, I don't have time for this tonight. The S400DD is 72" from the wall and it is sitting directly square in the middle of the 4.5" focal point belonging to the 18" parabolic reflector.




#807:ISO Auto - This is the bulb warming up, room lights still on.

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#809:ISO Auto - This is the bulb almost full on, lights off

#810:ISO Auto - The horizontal measurement of the "HOT SPOT".


#812:ISO Auto - The verticle measurement of the "HOT SPOT".

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#816:ISO Auto - 330mm Fresnel placed 16" away from the bulb (sorry, should have had it 12")


#815:ISO Auto - REVERSED 330mm Fresnel placed 16" away from the bulb (sorry, should have had it 12")

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#818:ISO Auto - Adjusting the lamp position to place the uncut fresnel 330mm from the bulb, just for comparision.

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Now my lamp doesn't want to start? I gave it five minutes to cool down? I will try it again shortly.

Anyways, I plan on doing more tests with lots of pics, but this is now it for tonight. If there is anything you'd like to see me try, please post.

Who am I kidding? I had to stay up a little more.. this time the buld is 8" away from the focal point.


#819:ISO Auto - Bulb warming up, lights on.

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#821:ISO Auto - Bulb getting whiter, lights off.

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#822:ISO Auto - 48" diameter...

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#823:ISO Auto - 330mm Fresnel 330mm from the bulb, remember bulb is 8" away from reflector.


#824:ISO Auto - REVERSED 330mm Fresnel 330mm from the bulb, remember bulb is 8" away from reflector.

Ok, this is what I wanted to post earlier when I stopped and took pics of the bulb3.5" (8") out of focus with the reflector. This time, the bulb is at its 4.5" spot, the bulb is 72" from the wall, and the 330mm Fresnel is 330mm away from the lamp.



#827:ISO Auto - 330mm Fresnel 330mm from the bulb, bulb is 4.5" from the reflector. This is almost SEVEN feet tall!


#828:ISO Auto - REVERSED 330mm Fresnel 330mm from the bulb, bulb is 4.5" from the reflector.

I wish I had more time tonight.

why are you seeing the lamp projected?

mm, i would say if you have only 1 fresnell and the lamp is at its focal, you shouldn´t see the lamp on the wall.

what is your throw?

Here’s a test that you can try to see if this thing is going to fly. Set your arc at the FL of the reflector, Turn it on and check that the image on the screen is close to being the same size as the reflector and turn it off. Now you’ll need to make an aperture the same size as your LCD and place it either in front or behind the 330mm fresnel. I take it that you have a triplet lens. Place the triplet where it should be positioned for the throw you are using. Turn it on again and adjust the triplet’s position so you can see a nicely focused image of the LCD shaped aperture, if you want you could suspend some flat objects in the aperture to make it a bit easier to focus on or simply focus on the fresnel rings. Now you should have a rough model of a projector so you can see if the image on the screen has a nice even distribution of light. With the arc set so that the beam is collimated the distance to the fresnel should not be too important for the reflected light. But the direct light could be a problem. If you have the arc at 330mm from the fresnel what you will probably see is a bright circle of light in the centre of the screen. The bright spot is cause by the direct light becoming collimated by the fresnel. Because it is collimated, (parallel light rays), only the light that is perpendicular to the triplet will pass so that section of the lcd will have more light than the rest, reflected light plus the direct light see pic. With some careful adjustments you maybe able to even it out. You could possibly use a small disk about the size of the arc or smaller so that you can limit this direct light. Maybe the small disk could have some holes in it, like a colander, and be used as a mechanical dimmer. Another thing to consider is the direct may cause some problems in the front chamber of the projector. So you might have to use some sort of light baffle to stop this stray light from interfering with the image on the LCD and add a fan to vent excess heat.

DJ

DAZZZLA
Thanks, I hope to have a triplet today... I've been waiting

I have a 50mm diameter x 50mm FL mirror that I am going to try to put directly in front of the arc. I'm also thinking of trying a polished pop can as a cylindrical reflector and I might even sacrifice a soup ladel.

Did you notice that the light is PARALLEL? The measurement of the HOTSPOT is 18" on the vertical and 20+ on the horizontal (I think the larger number is due to the length of the arc).

I will built an LCD sized aperature. I just had to get going on something last night, I will also use a triplet when they arrrive. One thing though, do you think it would be worth it to set up a point light source, spherical reflector and 220mm collimating fresnel to offer some sort of comparison? (Still using no triplet), It's not really worth it is it? I notice the camera doesn't really capture all light in the same manner. Some of those pics look MUCH brighter in person. ACtually most of them.

From your pic, the blue and the yellow "waste" light should dissapper completely with a minor reflector in front of the lamp right?

Rox
All the measurements are in the thread describing each picture, if I missed something let me know! Every pic was taken with the BULB 72" away from the wall, I guess you can somewhat call that the throw.

mmm, I think it is the parabolic reflector that is focusing the lamp image. I mean, if you have just the lamp and the 330mm fresnell at its focal at 59" from the wall (72" from lamp to wall) (no parabolic reflector) you shouldn´t see the lamp image projected.

So I think the parabolic reflector is contributing to the lamp image projection on the wall.

Well, yes that makes sense as a lot of light is coming from the reflector through the lamp to the fresnel. Anyways, will do more tests this weekend, with lots of pics. Anyone else want to offer suggestions?

P.S. I am starting to think Ellipsoidal Reflectors are the truly best/ideal reflectors. But non the less I would like to show the pros and cons of parabolics here if I can.

No, Rox. It's the fresnel that's projecting the image of the lamp onto the wall. A parabolic reflector just isn't capable of doing such a thing.

Edit: The parabolic refector is doing one thing as far as the lamp image goes, however: It's providing more light to the lamp, to make the glass lamp casing more visible.

Lucky_me: What you should actually be trying to do is obtain as evenly lit a field of light as possible, as close as possible to the lamp position. In theory, you should be able to obtain a bright circle of light the approximate diameter of hte reflector on the wall. This is what you would then put through your LCD, and collect with the fresnel for projecting.

After all, it's not an image of the lamp that you want on the wall, it's the image from your LCD.

oooo, i am seing a long discussion here ;D.

Well, have FUN! I have to go to work now.

what diferencies are in a reflective parabolic "lens" with X focal and a

refractive "flat" lens with focal X?

Oh no, not again.

If we were dealig with a true point source light at the focal distance from a parabolic reflector, then what you would end up with is a SHADOW of something in between the light and the wall at a 1:1 size ratio. This is the same as what you'd expect from the same true point source light with a properly focused collimator lens. The same, in fact as when you get the shadow of an aircraft in the sunlight. The size of the shadow is roughly the same size as the object.

Since the lamp projection is clearly magnified, and is a projection of light, it is the artifact of a focusing lens.

What needs to be seen is how even the light can be at the position where the LCD would be. This is, after all, what we're intending to focus and project.

mm, I do not agree with you supra.

the fact is that there is a magnified lamp on the wall. the 330 focal fresnell won´t magnify the lamp so much (and not to talk about the lamp being at it's focal point, as well as the short throw)

let me work out the conbined focal of parabolic reflector + fresnell, wait some mins.

4.5" focal + 13" focal is =3.34" conbined focal

Click to view attachment
at this point i would assume somewhere 2 feet for the lamp size and 7 feet for the projected lamp size. this is 7/2=3,5 magnification

this magnification should work with this trhow;

1/3.34=1/T + 1/(T/3,5) = 1/T + 3,5/T = 4,5/T T=15" that is somehow close to

the trhow lucky has.

sorry roxy... the fresnel does it,,,, done several times as a tool to find sweet spot for lamp and reflector

same princple for aligning a slide projector lamp,, gotta have a lens

LOL
LOL
LOL
ROFL
ROFL
ROFL
LMFAO
LMFAO
LMFAO

Good Luck Supra,

Okay. I get your argument now. You're treating the parabolic reflector the same as a collimating lens.

In theory, it would be possible, however, there is still one important difference. In the case of a collimating lens, the direct light from the light source does not hit the second lens element, since it's all diffracted by the collimating lens. This is not the case with a parabolic reflector. I'd expect that even with the greater surface area of the reflector, the image would be swamped by this direct light, and show in AT BEST extemely poor contrast.

Also, the projected image would only be in focus at the second lens element's focal distance. This would work if the fresnel were about that distance FROM THE WALL, but not if it's that distance from the lamp.

If you want to see that kind of projection, place the second fresnel about the focal distance from the wall, but either much closer or much further from the parabolic reflector.

thanks for your input scuba,it is very constructive.

I know an easy way to conclude this last ROX's stupid teory;

lucky_me can do this test;

remove the parabolic reflector from his test where the lamp was at fresnell's focal and 72" was from lamp to wall, so he got this image;



If the lamp projection is there, it is the fresnell lens what is projecting the lamp,
If the lamp is gone, it is both the reflector and the fresnell lens conbination what is projecting the lamp.

Easy, only we can wish lucky to spend the needed time on complacing us (me).

Im not getting into a big big debate this time, mainly because Im not that informed on the optics side of things.

I dont proclaim to be a jack of all trades, when Im really a master of none.

BUT......

If the fresnel lens ISNT doing any of the magnification/projection. Then how do those slap a fresnel lens in front of a CRT TV, and wrap it in a cardboard box scams work?

Just cuirious

If it was the reflector doing the projection, then it would just be a SHADOW of the bulb reflected correct, the pictures LUCKY_ME posted clearly had detail to the insides of the bulb (the side facing the fresnel), which wouldnt even be the side facing the reflector.

Oh well, Im sure the answer is on a spec sheet somewhere

I am not either allknowing person. But i consider my optics aknowlegments enough to disscus this stuff, not to claim it is true, but enough to disscuss it.

I never said the fresnell isn´t doing anything. IF it was only the fresnell working, the distances are not correct to be a projection there. If you wish i can tell you where should be the things to have a projected image of the lamp when only the fresnell is working, i can tell you even the image size you would have.

what i am saing, is both the reflector and fresnell are working on the projection of the lamp. They can be considered as a conbined ideal singlet flat lens.

the only thing the reflector could be doing is adding light behind the bulb, so that appears more VIVID on the wall.

Again, Im not as informed as 1/2 the people on this forum about optics, I generally dont pay attention enough to discuss, and I just go with what the masses do.

I do however, have spent time playing with my fresnel lenses (I have 6 of them) 4 in my two projectors, and an extra dirty set from the original LL lens kit.

One time, playing around, I put the fresnel lense in front of the projection lens at night when the projector was projecting.

I was able to move the fresnel, and tilt it an angle to project a PERFECTLY focused image of my LCD onto the ceiling.

I dont see why the same thing couldnt be happening here. The parabolic reflector is reflecting light, not perfectled, so its illuminating the area behind the bulb, and the fresnel is magnifying/projecting it.

It's close enough to get a projection. Not a SHARP projection, but a projection.

I noticed that the first "projection" pictures were done with the fresnel 16" away from the lamp. 16" IS pretty close to correct, and at that distance, the image of the lamp was quite sharp and clear.

At 330mm, the image was blured and indistinct.

Time to do a bit of experimentation with my lamp, reflector and fresnel.

Add to the fact the manufacturing tolerances, and that most have found about a 2-4% error in the measured focal points, from the rated focal point.

Makes sense to me

what i am suggesting is not contradicting all you are saiyng. I have some fresnells as well, and have projected tv lot of times as well. But this case, the distances of lucky are not compatible with fresnell lens based projection.

disscussing this further is pointless, let's see what lucky can do for us. Would you accept the test result posibilities to conclude the theory validity? (if lamp goes, teory is fine, if lamp still there stupid wrong teory)

FWIW, I've often noticed that when the projector is on, if I remove the triplet, I get an image of the bulb on the screen. (I think. I'll need to verify that.)

The only way the projection could be caused by the reflector, I believe, is if we are farther then the focal point (to far away from the reflector). When we're at the focal point we are focused on infinity and the light is collimated. If we move too far inside the reflector, closer then the focal length, the light will spread out as it moves forward and will have a negative focal length. So if the parabolic reflector is indeed causing the projection, its probably too far out of the reflector.

That said, if your parabollic reflector and bulb are alligned properly, and you placed your collector in front (grooves facing the reflector) IF you place the collector at the focal length of your collector, or closer, then theirs absolutely no doubt the projection is coming from the reflected bulb, not the bulb itself. But this doesn't mean the reflector is making the projected image. Its most likely the two working together. The reflector collimating and the collector forming the projection.

But really, I don't think we should be worrying about that. How many of us have really looked at whats projected by our fresnels without the triplet? I don't know but I'm going to go take a look right now.

Meanwhile, Lucky Me, I'd say first measure the diameter of your parabolic reflector, don't use the collector, and project it onto a wall, then slowly adjust the bulb (or reflector) untill the spot of light on the wall is the exact same size of your reflector. That will mean the light is perfectly collimated. Collimated light is all we need coming into the collector. Don't worry if the collector projects an image if you put it in front, what matters is what the triplet will do. Ignore the image on the wall and put your hand, or a piece of paper at the focal length of your collector to see how well the light is concentrated. IF you get an intensly bright spot at the focal length, thats all you need.

I'm really interested in this project, I'd love to see what kind of improvement a parabollic reflector would make. Where did you get yours, Lucky Me? How much did it cost? Does it have a mirror surface or just polished metal?

Noooo! You can’t give up that easily can you?

DJ

Lets see if Lucky wakes up first... I am so tired! I finally have parts to play with and all I want to do is SLEEP! I just woke up from a 3 hour nap... I'm sorry everyone but I've been shorting myself on sleep the last week or two, it's finally caught up to me.

P.S. Still no triplets today!

Im wondering if an off axis parabolic would work beter as far as getting the lamp out of the way?
http://www.optiforms.com/3000products/3133...rabolicGEO.html

Coffee... Mmmm good... I'm not going to be able to sleep tonight. Why are these sites popping up now? I looked and looked before buying this reflector! Those offset parabolics are too small, you need a reflector that covers the ENTIRE LCD panel for its use to be practical. I don't know if they readily exist, but I think they will be big bucks!

EDIT: There are some really neat things on that site pjgibbs!

EDIT2: Wow, I just noticed those prices $400+!!!!

OK, BACK ON TOPIC, sort of....

My take on the projected lamp issue is that BOTH the fresnel and the reflector play a complimenting role. But from these pics, you will clearly see that Rox is NOT wrong.

The lamp is 32" away from the wall and smack in the middle of the 4.5" focal point. It is actually a little too far inside the reflector as the hotspot measures 16" x 16". In the pictures you will clearly see the outline of the lamp, three pics as I have been fooling with the ISO settings on the camera.


#829:ISO 400 - lamp 32" from wall, sitting at 4.5" focal point.


#830:ISO 200 - lamp 32" from wall, sitting at 4.5" focal point.


#831:ISO 100 - lamp 32" from wall, sitting at 4.5" focal point.

EDIT: P.S. Just so you guys know, it actually HURTS to look at that HOTSPOT! It's too bad teh camera doesn't do it justice.

What I see there looks to me like the shadow of the lamp glass. Since the glass bends light, there will be some artifacts from the lamp acting as a shadow. Take that lamp outside in the bright sunlight, and hold it up, and you'll get a similar effect, even it it's turned on.

This is one way in which a light can cast a shadow of itself.

#834:ISO 100 - Well, these were taken with NO reflector - lamp 32" from wall.


#835:ISO 100 - 330mm Fresnel, 330mm from lamp - lamp 32" from wall


#836:ISO 100 - REVERSED 330mm Fresnel, 330mm from lamp - lamp 32" from wall


#837:ISO 100 - 330mm Fresnel, 330mm from lamp - lamp 72" from wall


#838: ISO 100 - REVERSED 330mm Fresnel, 330mm from lamp - lamp 72" from wall

I should note that the lamp was not fully warmed up, but I think it is irrelevant.

I still think Supra is correct, and here is why. You can test this with another light source

In the shot with the fresnel lense gone, you are seeing the shadow cast from the bulb behind it.

Since your bulb isnt a true POINT source of light, it cant sit perfectly at the focal point of the reflector, What happens is that reflector starts reflecting light off axis, and sort of works a little like a BACKLIGHT behind the bulb.

When the fresnel is in place, its literally projects everything behind it. So the reflector having off axis lightings illuminates the area behind the bulb, and this illumination gets projected by the fresnel. This is why we paint the front chamber of our PJs black. Because extra lighting can cause other things to be projected. The only thing that should be ILLUMINATED are the things you want to show up in the projection

Get a lamp or something, take the shade off of it, and put it behind the S400DD. With the S400DD OFF, put the fresnel in place, and I Bet you get a the outline of the bulb on the wall again. Im not sure how far you would have to place the lamp behind the S400DD, cause it obviously is MUCH brighter and creates more light than the reflector was throwing off axis.

Give that a try.

Then try it with the S400DD.

If all else fails, its a learning experience. I hope I was able to illustrate myself clearly above.

Which if I am correct, than that means everyone here was correct.

After thinking about it again, I think ROXs language barrier is at fault.

He said the reflector is AIDING in the bulb being projected. In which It is. Im saying the same thing. I think the rest of us just cross-confused terms with technicalities.

The fresnel physically is the only thing projecting.

But because the parabolic reflector is adding light to the area BEHIND the bulb, then its also at reason why the bulb is being projected on the wall.

Is that what you meant ROX. Im sure your know the reflector itself couldnt project anything.

I think we all may be like dogs chasing our tails on this one.

Yeah... it's both components.

I was looking for a spherical reflector here, but... turns out I don't have one (at least that I have found). Does this problem, the projection of the lamp - does it happen with a spherical reflector and a fresnel? anyone?

One of the things to do later is to widen the hole on that parabolic reflector to accept the S400DD axially, instead of illuminating the parabola across horizontally like am doing. However, if it turns out that I get better lighting this way, I'll regret widening that hole.

I tried taking a pop can and cutting the curved aluminum from it. I placed this in front of the arc and it difused the light in a messy way before falling off its mount. It was glued with a hot glue gun, but... hehe, the heat from the light just melted the glue. Glad I didn't use my over-priced 50mm x 50mm Fl curved glass mirror.

It's going to be a fair bit of work setting up what I call the "minor" reflector. It has to take HEAT and be aligned just right. I personally always switch the light off and let the bulb cool before any movements because I don't want that thing exploding in my face.

Lucky Me,

So glad you are working on parabolics.
Very interested in your progress.

I think that it's the light bulb that's causing us problems.
The reflector is very straightforward -

-it will columnate a point source of light if placed at the focal point, period.

But we don't have a point source, and we have - what - about 3 inches of interfering material in the way? (extra glass beyond the light source)

If I had a smaller lamp, with less material beyond the light source, I think I'd have a smaller dark spot in the final image.
(Also wouldn't have to widen the hole in the Parabolic.)

Just think what pattern you and I would be getting
if we could just supernaturally hang a point light source
at the focal point of our parabolic reflector -
-a perfect, very bright light pattern.

Wondering about alternative bulbs...

Thanks for thinking and working and experiementing -
-helps to have others slogging along with me.

By the way - I am going to send this problem to Edmund Optics -
-and you could too.
They have engineers there that will help us for free,
because we bought the parabolic from them.
Perhaps would help even a prospective customer?


Aiden.

I take your bet scuba ;D. Tell me how much $ are we talking about .

NO, allthough my english barrier (what does it mean?) i would say is still horrible, I think I spressed right this time. I think the reflector could project the lamp with no fresnell there if correct distances are used.

Now, I know the fresnell lens can project the lamp, but as i said before, The DISTANCES lucky has are not compatible with a fresnell based projection. Not even the magnification introduced to the lamp is compatible with the expected magnification by the 330 focal fresnell. I think the projection "thing" is shorther focal than the 330 fresnell because of 2 things; magnification is larger and trhow/distances are shorter.

I did some math on some post back, where i stimated roughly the equivalent ideal flat lens for the reflector+fresnell. This ideal lens is projecting the lamp.

Just a note, there are telescopes with the primary lens being a refractive lens on the input of the telescope. But as you know, there are "primary lenses" that are parabolic reflexive lenses on the botton of the telescope. The effect is the same we can both remplace for a ideal flat lens.

I hold my not so stupid teory.

edit; sorry i forgot to thank lucky for his loosed sleep ours ;D, but have to scold him because he did not have the lamp at 72" from the wall as his test1 with the parabolic reflector there

some more math;

Assume fresnell only projection for lucky's test 1;

72-13=59" this is the throw.

he said 7 foot lamp on the image (glass I guess) and the glass on the lamp is 9 inch. (this is from ushio's pdf stimation, sorry my previous 2 feet stimation, inches... why the hell would you still use this unit ?, i did a big mistake there. Sorry about it.

SO;

84 inch lamp on the projection/9 inch real lamp=9.3 magnification.

9.3 magnification and 59" throw are FACTS (assuming fresnell based only projection of course as you are sugesting).

this facts being true, we can work out the fresnell's focal lengh;

1/F=1/59 + 1/(59/9.3)= => F= 5,7" focal of the fresnell.

Wasn´t the fresnell 13" focal?

more math II;

let's see what should the distances be, assuming we want to project 7 feet lamp with a 330mm fresnell;

magnification is 9.3 as before.

1/F=1/T + 1/(T/9.3) (T=throw unknown, F=13" fresnells focal)

1/13=10.3/T ==> T=11 feet. lamp to lens=11'/9.3=14.4"


So a ushio lamp at 14.4" from a 330mm focal fresnell should project a 7 feet lamp at 11 feet throw. If someone could test it ;D.

I think he meant the spot of light was almost 7 feet tall, not the bulb itself.

Those pictures were also NOT in focus, so your math isnt going to conclude correct numbers.

In his second set of pics last night, he took pictures without the fresnel, and there was no projection on the wall. If your saying the parabola is the cause of the projection then why wouldnt the bulb be on the wall.

In any event, he took the second set of pictures, and both items were needed to recreate the projection on the wall.

Your approaching this from the other side, Your using his rough approximationg of a 7 foot projection, and assuming he meant the bulb exactly, even if he did mean the bulb he said about 7 feet. Dont know the actual measurment.

Your seeing that as not working out mathematically, and just assuming the reflector to be at fault.

Disregard the math on the fresnel for a second, and thing about the reflector alone, how can it PROJECT by itself. If we took the bulb out and placed an LCD there (ignoring the fact of no light for the LCD), could the LCDs image be projected on the wall to by the parabolic reflector. What about the transparency films that teachers in high school used to write on with on the OHP. Would the parabolic reflect project that to??

Of course it wont, the parabolic reflector cant PROJECT anything, it can cast a SHADOW. and depending on the distance between the reflector and the wall that shadow will be LARGER or SMALLER.

This would be the same thing as holding a S400DD in there, placing a flashlight behind it, and looking at the shadow on the wall. Would you say the flashlight is projecting the bulb on the wall?? Or would you say its shadow is casted on the wall?

Thread HighJackers... they are EVERYWHERE! lol

Look, it takes BOTH components to project the lamp image, END OF STORY. There are pics with the reflector and no fresnel, then there are pics with fresnel and no reflector, there is also pics with just a bulb, and pics with reflector and fresnel. The lamp is only clearly projected with BOTH COMPONENTS. Again, END of story.

P.S. The lamp image being seven feet tall, I meant the whole light circle in that pic, not the bulb itself.


ON TOPIC

Does a spherical reflector and a collimating fresnel do the same thing (no triplet)? Somebody here must know?

I never said the reflector is the only projecting element, but i said like 3 times it is both the reflector+fresnell system the lamp projecting "engine".

I said as well, the reflector could itself project the lamp IF proper distances are used. Removing the fresnell does change the conbined focal lengh it is why there was not the lamp projected when same distances where used when no fresnell was there. I could work out the distances for the reflector only projection, but I am not soo shure about it.

You are right on the 7 feet assumtion (i thought he was talking about the lamp)

I see the shadow concept supra told us about, but wouln´d the shadow be same image size as real lamp?

what about the bet?

Thank you, I knew I wasnt crazy....

Yes a spherical reflector can possibly do it, but shouldnt in theory.

Since our bulbs arent a point source of light, the relectors can have some off axis light, and anytime light is behind the bulb, as in this case above, it will show.

It shouldnt matter in your projection though, because the LCD stops any projection from that point. So it wont make it into the final projection on the wall.

No, because the spot on the wall isnt the same size.

if the parabola is 10 diameter, and it reflects a spot on the wall that is 40 inches in diameter, then you have a gain of 4.

In which case the shadow of the bulb would also be roughly 4 times bigger casted on the wall.

In any effect, I guess you can conclude that the math on the fresnel lens works out now, huh Rox?

This is why I said your approaching it from the wrong side, and assuming variables. Use logic and approach it from its possibilities.

A reflector can only CAST SHADOW, it cant PROJECT

Well, unfortunately I haven't yet been able to get perfectly collimated light (using the setup PIC#829-831). If I place an object between the assembly and the wall, it's shadow is only sharp near the wall. The closer I bring the object to the light engine the fuzzier the shadow gets. this tells me the light is not perfectly collimated.

However the lamp is roughly the same size.

scubasteve2365

The parabolic reflector is 18" in diameter and it's focal point is 4.5".

I was just using an example, of a reflected light source casting a shadow. wasnt trying to coorelate with your exact reflector

do you understand how reflective telescopes work scuba?

sorry, lucky but i think we need again your time on new test, are you disposed? I can tell you about my stimated relfector only distances to see if there is any porjection on the lamp.

mmm, i agree with scuba on the assumtion error, what was the lamp glass size on the wall?