Brightness trouble...

dewil · 11th June 2004, 08:26 AM

Hi ppl ! I'm trying to find some answer. Can you try projecting onto wall without any panel, I mean just the fresnels ? I've tried it yesterday. And I cannot get 100% brightness uniformity. The center portion is more bright than the sides. But not too bright to say that there is something wrong though (I guess ??? ). It's about 100% on the center and reduces to 85% on the sides.. Is this normal ? Remember, it's on the sides not only the corners. I put the lamp at 8.5" to condenser fres., 2" from condenser fres to LCD, 2" from LCD to field lens. Anyone experiencing this too ? Any way out Thanks people.....

mccamp82 · 11th June 2004, 03:32 PM

have you tried moving the triplet around to achieve beter brightness? I am pretty sure that you may not have your triplet mounted in the right position. It is probably a litle off. Also, how far away from the field fresnel did you mount the triplet?
Dont worry too much, you'll get it firgured out.
Take care.

doughboy · 12th June 2004, 04:12 AM

Make sure your fresnel rings(rough side) are facing each other. I had a much more severe version of your lighting problem because I had a fresnel backwards.
Are u using bare bulb, reflector, or condenser?

dewil · 14th June 2004, 06:39 AM

Yes, I've tried moving the triplet closer to the LCD, but when I do that, the Image from the LCD will become kinda streched on the corners only. And yes, the grooves are facing each other. Mccamp82, can you tell me the distance between your condenser fresnel to LCD and from LCD to field lens, also from field to triplet ? I think 2" from LCD to field lens in my setup is too far. I'm also using CMV1515 like you. I can't get the field lens closer to the LCD because the PCB board will get in the way.

dewil · 14th June 2004, 10:37 AM

Yes, I've tried moving the triplet closer to the LCD, but when I do that, the Image from the LCD will become kinda streched on the corners only. And yes, the grooves are facing each other. Mccamp82, can you tell me the distance between your condenser fresnel to LCD and from LCD to field lens, also from field to triplet ? I think 2" from LCD to field lens in my setup is too far. I'm also using CMV1515 like you. I can't get the field lens closer to the LCD because the PCB board will get in the way.

mccamp82 · 14th June 2004, 04:41 PM

my condensor fres is about 1.3 inches from my LCD, and the field fres is about 2 inches from my LCD. The Triplet is about 12 inches from my field fres. The main thing i am talking about here is that the triplet is aligned (centered) on the light source. Distance doesnt really matter right now, only that the triplet is perfectly aligned and centered.

dewil · 15th June 2004, 05:50 AM

Hi Mccamp82, using that distance, can u get full focused and even projection image of your LCD ?
And yes....I think my triplet is aligned with the LCD. I could get a nice square image but like I said before, there's about 15% reduction of brightness on the sides of the image.

mccamp82 · 15th June 2004, 01:03 PM

i get full projected image. it is hard to tell the exact distance of my triplet. As you may know, my projector is adjustable. I just have it adjusted to where it was focused the best. It is between 12 and 13 inches.
If the triplet is a little mis-aligned, you will still get a square image, but the light will be dimmer in certain areas.
Have you tried it with the lcd on yet? is it still noticable. I think all projectors to a certain extent are a little brighter in the center than on the edges.

The_Mazta · 16th June 2004, 09:53 PM

Hi, before you put anything together you need to find out the focal points of your optics, eg

My copy lens is a fuji 240mm, which means it needs to be 240mm from my source to work corectly, also find out the focal point of your first fresnal, mine is 210mm, so from the bulb to the frez its that,

hope this helped

dewil · 17th June 2004, 06:51 AM

As a matter of fact, I'm thinking about what Mccamp said, which is : "I think all projectors to a certain extent are a little brighter in the center than on the edges"
And that's what I'm thinking too. I've got my fresnels and triplet from Tony Dean. The FL is 330 and 220 mm. Anyone has an exact and easy way how to check the FL of the fresnels ? Have anyone of you ever tried the calculation from diygroupbuilder.com ? It said that if you put a space between the fresnels, the FL will differ. Any comment ?

11th June 2004, 08:26 AM	#1
dewil diyAudio Member Join Date: Mar 2004 Location: Jakarta	Brightness trouble... Hi ppl ! I'm trying to find some answer. Can you try projecting onto wall without any panel, I mean just the fresnels ? I've tried it yesterday. And I cannot get 100% brightness uniformity. The center portion is more bright than the sides. But not too bright to say that there is something wrong though (I guess ??? ). It's about 100% on the center and reduces to 85% on the sides.. Is this normal ? Remember, it's on the sides not only the corners. I put the lamp at 8.5" to condenser fres., 2" from condenser fres to LCD, 2" from LCD to field lens. Anyone experiencing this too ? Any way out Thanks people.....

12th June 2004, 04:12 AM	#3
doughboy diyAudio Member Join Date: May 2003 Location: NE	Make sure your fresnel rings(rough side) are facing each other. I had a much more severe version of your lighting problem because I had a fresnel backwards. Are u using bare bulb, reflector, or condenser? __________________ Benq 557s, Split 12.2 fresnel, 250W Ushio, S50 ballast, beer can reflector soon to be oneida stainless ladle

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11th June 2004, 03:32 PM	#2
mccamp82 diyAudio Member Join Date: Jan 2004 Location: Lubbock, TX	have you tried moving the triplet around to achieve beter brightness? I am pretty sure that you may not have your triplet mounted in the right position. It is probably a litle off. Also, how far away from the field fresnel did you mount the triplet? Dont worry too much, you'll get it firgured out. Take care.

14th June 2004, 06:39 AM	#4
dewil diyAudio Member Join Date: Mar 2004 Location: Jakarta	Yes, I've tried moving the triplet closer to the LCD, but when I do that, the Image from the LCD will become kinda streched on the corners only. And yes, the grooves are facing each other. Mccamp82, can you tell me the distance between your condenser fresnel to LCD and from LCD to field lens, also from field to triplet ? I think 2" from LCD to field lens in my setup is too far. I'm also using CMV1515 like you. I can't get the field lens closer to the LCD because the PCB board will get in the way.

14th June 2004, 10:37 AM	#5
dewil diyAudio Member Join Date: Mar 2004 Location: Jakarta	Yes, I've tried moving the triplet closer to the LCD, but when I do that, the Image from the LCD will become kinda streched on the corners only. And yes, the grooves are facing each other. Mccamp82, can you tell me the distance between your condenser fresnel to LCD and from LCD to field lens, also from field to triplet ? I think 2" from LCD to field lens in my setup is too far. I'm also using CMV1515 like you. I can't get the field lens closer to the LCD because the PCB board will get in the way.

14th June 2004, 04:41 PM	#6
mccamp82 diyAudio Member Join Date: Jan 2004 Location: Lubbock, TX	my condensor fres is about 1.3 inches from my LCD, and the field fres is about 2 inches from my LCD. The Triplet is about 12 inches from my field fres. The main thing i am talking about here is that the triplet is aligned (centered) on the light source. Distance doesnt really matter right now, only that the triplet is perfectly aligned and centered.

15th June 2004, 05:50 AM	#7
dewil diyAudio Member Join Date: Mar 2004 Location: Jakarta	Hi Mccamp82, using that distance, can u get full focused and even projection image of your LCD ? And yes....I think my triplet is aligned with the LCD. I could get a nice square image but like I said before, there's about 15% reduction of brightness on the sides of the image.

15th June 2004, 01:03 PM	#8
mccamp82 diyAudio Member Join Date: Jan 2004 Location: Lubbock, TX	i get full projected image. it is hard to tell the exact distance of my triplet. As you may know, my projector is adjustable. I just have it adjusted to where it was focused the best. It is between 12 and 13 inches. If the triplet is a little mis-aligned, you will still get a square image, but the light will be dimmer in certain areas. Have you tried it with the lcd on yet? is it still noticable. I think all projectors to a certain extent are a little brighter in the center than on the edges.

16th June 2004, 09:53 PM	#9
The_Mazta diyAudio Member Join Date: May 2004 Location: Uk	Hi, before you put anything together you need to find out the focal points of your optics, eg My copy lens is a fuji 240mm, which means it needs to be 240mm from my source to work corectly, also find out the focal point of your first fresnal, mine is 210mm, so from the bulb to the frez its that, hope this helped

17th June 2004, 06:51 AM	#10
dewil diyAudio Member Join Date: Mar 2004 Location: Jakarta	As a matter of fact, I'm thinking about what Mccamp said, which is : "I think all projectors to a certain extent are a little brighter in the center than on the edges" And that's what I'm thinking too. I've got my fresnels and triplet from Tony Dean. The FL is 330 and 220 mm. Anyone has an exact and easy way how to check the FL of the fresnels ? Have anyone of you ever tried the calculation from diygroupbuilder.com ? It said that if you put a space between the fresnels, the FL will differ. Any comment ?

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