I can't wait to get started on my 7" lillput projector but I have a few questions about the lenses.
The only thing that I know is that I need to build my projector so that it is 14 foot from the screen, and have a screen size of 6' x 4'. Besides that I'm lost on how to figure out what size of lens, ferensel, and condenser I need to build the smallest projector I can and still get the screen size and distance I need.
I have search for this info but all I can find is equasions that I don't understand. I know that you all probably think I am retarded but can you please help me with the equasions to figure out what lens, frenzel, and condenser I need.
I also need the equasions to figure out the distances between the bulb and condenser, condenser to frenzel, ETC.
PLEASE HELP 😕
Thanks Dave
The only thing that I know is that I need to build my projector so that it is 14 foot from the screen, and have a screen size of 6' x 4'. Besides that I'm lost on how to figure out what size of lens, ferensel, and condenser I need to build the smallest projector I can and still get the screen size and distance I need.
I have search for this info but all I can find is equasions that I don't understand. I know that you all probably think I am retarded but can you please help me with the equasions to figure out what lens, frenzel, and condenser I need.
I also need the equasions to figure out the distances between the bulb and condenser, condenser to frenzel, ETC.
PLEASE HELP 😕
Thanks Dave
Hi Dave,
Here is the equation you need, image curtesy of dpc:
(Distance" refers to the distance between the front of your projector and the wall or projection surface - FL refers to the projection lens effective focal length).
Pop some numbers in there and see how you do. The image size/throw distance is reliant entirely on your LCD size and projection lens focal length - With your LCD size being fixed at 7" it'd be nice to be able to choose a perfect focal length projection lens but this just isn't an option. Common focal lengths used by us range from ~300 to 450mm.
Here is the equation you need, image curtesy of dpc:
An externally hosted image should be here but it was not working when we last tested it.
(Distance" refers to the distance between the front of your projector and the wall or projection surface - FL refers to the projection lens effective focal length).
Pop some numbers in there and see how you do. The image size/throw distance is reliant entirely on your LCD size and projection lens focal length - With your LCD size being fixed at 7" it'd be nice to be able to choose a perfect focal length projection lens but this just isn't an option. Common focal lengths used by us range from ~300 to 450mm.
Provided I've done the maths right, you'll be looking at about a 7' diagonal screen from 14' throw distance when using the 330mm FL projection lens. I've gotta go out, someone else can help with the fresnel/condenser selection 🙂
Thanks Quin
I now know what projector lens I need, now I need to find out if there's any equations to figure out what lenses I have to have to build the inside of my projector to make it as small as possible.
I now know what projector lens I need, now I need to find out if there's any equations to figure out what lenses I have to have to build the inside of my projector to make it as small as possible.
Hi
I started a Project same as you, with a 400w, what type of layer are you going for?
Upright
Flat one
Straing
Hope they make sence there the 3 main ones
But heat is going to be a BIG problem as a 400w pumps the heat out, going to need an ir filter or cold mirror
Quin has covered the size, as for internal focal lengths that depends on the optics
I started a Project same as you, with a 400w, what type of layer are you going for?
Upright
Flat one
Straing
Hope they make sence there the 3 main ones
But heat is going to be a BIG problem as a 400w pumps the heat out, going to need an ir filter or cold mirror
Quin has covered the size, as for internal focal lengths that depends on the optics
If I were you I'd go for a 250w lamp, I use one + simple reflector on a 15" pannel and have a superb bright image at 100". I can't see why you'd need 400w unless you want to be able to use it in daylight, especially with a 7" pannel. Trying to control the heat as Nick said is also a big factor on a small box setup.
As for fresnels, the common choice for a setup like this is 220mm FL rear fresnel, 330mm FL front fresnel. Get them just large enough to cover the LCD fully - Buying larger (in size, not FL!) and cutting them down isn't a problem with the acrylic ones.
As for fresnels, the common choice for a setup like this is 220mm FL rear fresnel, 330mm FL front fresnel. Get them just large enough to cover the LCD fully - Buying larger (in size, not FL!) and cutting them down isn't a problem with the acrylic ones.
nick[1x]
I'm not for sure what kind I am going to build yet, i am in between an upright or a flat projector. I will have to draw up some plans of for each one and figure out witch one makes the smallest projector. It seems like the strait designs will be to big for me. That is my goal to make the smallest projector that I can.
What kind are you going to try to build?
I'm not for sure what kind I am going to build yet, i am in between an upright or a flat projector. I will have to draw up some plans of for each one and figure out witch one makes the smallest projector. It seems like the strait designs will be to big for me. That is my goal to make the smallest projector that I can.
What kind are you going to try to build?
Quin
I already have a 400 watt bulb & ballast that I have bought so I am going to go ahead and use it. I have thought up a sweet design for a light box that I hope will give me plenty of air flow to keep it cool. A 250 watt does sound like a better idea but I have to try with what I got, anyway it would be awsome to be able to watch it during the day in a sun filled room.
If the front fersnel has a focal length of 330mm, does that mean that I will have to have 330mm between the fersnel and the projection lens? If so, if I use a mirror am I able to cut that in half to were I will have to have a distance of 115mm from the frensel to the mirror, then 115mm from the mirror to the lens?
Sorry for the hundred questions but I have one more that maybe you can help me out with and that is the condenser. I'm gessing that 80mm to 100mm diamiter would be big enough to catch most of the light but what about the focal lenght. If I get a condeser with a shorter focal lenght than I won't have as far distance from the condenser to the fernsel witch makes for a smaller projector. But is there a certain focal lenght that is best to get all of the light to the frensel?
Thanks again for your help
Dave
I already have a 400 watt bulb & ballast that I have bought so I am going to go ahead and use it. I have thought up a sweet design for a light box that I hope will give me plenty of air flow to keep it cool. A 250 watt does sound like a better idea but I have to try with what I got, anyway it would be awsome to be able to watch it during the day in a sun filled room.
If the front fersnel has a focal length of 330mm, does that mean that I will have to have 330mm between the fersnel and the projection lens? If so, if I use a mirror am I able to cut that in half to were I will have to have a distance of 115mm from the frensel to the mirror, then 115mm from the mirror to the lens?
Sorry for the hundred questions but I have one more that maybe you can help me out with and that is the condenser. I'm gessing that 80mm to 100mm diamiter would be big enough to catch most of the light but what about the focal lenght. If I get a condeser with a shorter focal lenght than I won't have as far distance from the condenser to the fernsel witch makes for a smaller projector. But is there a certain focal lenght that is best to get all of the light to the frensel?
Thanks again for your help
Dave
Hi Dave,
Correct, or there abouts. The distance from fresnel to projection lens will change in order to focus the image - The larger the image on the wall, the smaller the distance. If memory serves me correctly you'd place it at 330mm if you had infinte image size? Or maybe the other way round
Yep, bearing in mind the slight alterations needed to focus it - Unless you have a varifocal lens.
As for the condensor lens, it's an area I don't want to speak much about as I'm not 100% clear on them 😉 80mm-100mm diametre sounds sensible, I'd assume you would want to try and match it to your reflector diametre and then place the bulb inside the reflector to get a torch-like beam of light going into the condensor lens. In terms of image definition I don't think this is preferable (reflected light isn't parallel with direct etc), but it certainly improves brightness in my setup compared to when the lamp is at the reflectors FL instead of inside. I forget the focal length of my condensor, but I expect you'd want something shorter seeing as you will be using a 7" not a 15" screen with the 220ml rear fresnel.
Hope I've not confused you/myself too much there
EDIT: Forgot to mention, you might want to consider putting your 'bend' on the lamp side of the box - This way you could use a coldmirror and hopefully kill off some of that nasty heat!
Correct, or there abouts. The distance from fresnel to projection lens will change in order to focus the image - The larger the image on the wall, the smaller the distance. If memory serves me correctly you'd place it at 330mm if you had infinte image size? Or maybe the other way round
Yep, bearing in mind the slight alterations needed to focus it - Unless you have a varifocal lens.
As for the condensor lens, it's an area I don't want to speak much about as I'm not 100% clear on them 😉 80mm-100mm diametre sounds sensible, I'd assume you would want to try and match it to your reflector diametre and then place the bulb inside the reflector to get a torch-like beam of light going into the condensor lens. In terms of image definition I don't think this is preferable (reflected light isn't parallel with direct etc), but it certainly improves brightness in my setup compared to when the lamp is at the reflectors FL instead of inside. I forget the focal length of my condensor, but I expect you'd want something shorter seeing as you will be using a 7" not a 15" screen with the 220ml rear fresnel.
Hope I've not confused you/myself too much there
EDIT: Forgot to mention, you might want to consider putting your 'bend' on the lamp side of the box - This way you could use a coldmirror and hopefully kill off some of that nasty heat!
Quin
You diden't confuse me I understand what you are saying.
About the coldmirror, is it like UV filter glass?
Does it ubsorb much light?
Or would it be best to have a cold mirror and have UV filter glass. I don't want the uv rays to ruin my lcd panel. If I put the coldmirror in front of the lcd then will need to have a condenser with a longer FL that if the light was going straight from the condenser to the first frensel? It seems like it would be a further distance if the light is going from the conderser, to the mirror, to the first frensel.
That also means that I will have almost 13 inches[330mm]from the back frensel to the lens, unless I use a first surface mirror on the back side to. I would think that it would loose alot of light if you use two mirrors. What do you think?
Dave
You diden't confuse me I understand what you are saying.
About the coldmirror, is it like UV filter glass?
Does it ubsorb much light?
Or would it be best to have a cold mirror and have UV filter glass. I don't want the uv rays to ruin my lcd panel. If I put the coldmirror in front of the lcd then will need to have a condenser with a longer FL that if the light was going straight from the condenser to the first frensel? It seems like it would be a further distance if the light is going from the conderser, to the mirror, to the first frensel.
That also means that I will have almost 13 inches[330mm]from the back frensel to the lens, unless I use a first surface mirror on the back side to. I would think that it would loose alot of light if you use two mirrors. What do you think?
Dave
Hi Dave,
A cold mirror simply passes IR but reflects normal light like a mirror - You'd still want to use a UV filter if your bulb doesn't have a built in stop. I haven't got any experience using mirrors, but they don't seem to present any serious brightness issues. Using a front surface secondary mirror as you suggest is a good idea to reduce ghosting.
Here's a nice double folded design I like that seems to suit your plans: http://www.allinbox.com/beberbox/beberbox.htm
A cold mirror simply passes IR but reflects normal light like a mirror - You'd still want to use a UV filter if your bulb doesn't have a built in stop. I haven't got any experience using mirrors, but they don't seem to present any serious brightness issues. Using a front surface secondary mirror as you suggest is a good idea to reduce ghosting.
Here's a nice double folded design I like that seems to suit your plans: http://www.allinbox.com/beberbox/beberbox.htm
I think that I will try useing a coldmirror + uv filter + first surface mirror in my first design, if it dosen't work very good or I just don't like it I will start over with another idea.
Allinbox has a lot of good designs and looks like it would be a cool forum if I could read the language. I like pictures but I would also like to read what evryone is saying. Is there any way for me to get my computer to translate the forum?
I like the design of that projector, do you know the demensions of the box. It looks a little big for what I want, but maybe it is just the picture adding on a few inches. I'm not for sure if I will make a upright or a flat projector. I will design plans for both then see witch one will be smaller.
Thanks
Dave
Allinbox has a lot of good designs and looks like it would be a cool forum if I could read the language. I like pictures but I would also like to read what evryone is saying. Is there any way for me to get my computer to translate the forum?
I like the design of that projector, do you know the demensions of the box. It looks a little big for what I want, but maybe it is just the picture adding on a few inches. I'm not for sure if I will make a upright or a flat projector. I will design plans for both then see witch one will be smaller.
Thanks
Dave
Does anyone know the dimensions of a 400 watt double ended bulb? I had one but when I went in my room to get it and get the dimensions of it to start my light box design it wasen't there. I had a grill out yesterday with probebley 20 people, I don't know if someone picked it up on the way to the bathroom or what, what ever happened it really f****n pisses me off that I can't find it. So I was wondering if anyone knows the dimensions of a 400 watt double ended bulb so I can design my light box.
Thanks
Dave
Thanks
Dave
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