If I'm right from some hours of research, the focal length should be the size of the lcd diagonal or slightly larger. That is wy we cannot use 35mm zoom lenses.
Here's all the data...
my projecor works great if:
distance from LCd to objective = 16"
distance from objective to the screen = 80" (this is where i can get a good focused 6' by 4.5' feet image ont he screen)
-------------------------------------------------------
this gives me a good focused 90" image 6.5 feet from the objective.
thanks guys
my projecor works great if:
distance from LCd to objective = 16"
distance from objective to the screen = 80" (this is where i can get a good focused 6' by 4.5' feet image ont he screen)
-------------------------------------------------------
this gives me a good focused 90" image 6.5 feet from the objective.
thanks guys
Update
I did a little research using a nice little program that you can find here http://www.opsci.com/index.asp?pagetitle=Calc/FocalLengthCalc&exten=htm
I decided that to have a perfect theater environment, i will need to have my screen 12 feet fromthe projector.
Here's what i got from my focal lenght and al the other stuff. Let me know if this is correct, and also where cal i got objectives with such focal length?
thanks
I did a little research using a nice little program that you can find here http://www.opsci.com/index.asp?pagetitle=Calc/FocalLengthCalc&exten=htm
I decided that to have a perfect theater environment, i will need to have my screen 12 feet fromthe projector.
Here's what i got from my focal lenght and al the other stuff. Let me know if this is correct, and also where cal i got objectives with such focal length?
thanks
Attachments
For projection purposes we would need zoom lenses with FL of about 350..500mm. Thus, we could possibly use some telephoto optics with 170..500 variable focal length, but new ones cost like hell. It's cheaper just to buy a set of lenses, with, say, 350mm, 400mm, 450mm fixed FL and change them in projector if needed.
Hey, look what I've found:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2946177925&category=3344
A super-telephoto zoom lens with 420..800mm FL for just $189.95. Incredible.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2946177925&category=3344
A super-telephoto zoom lens with 420..800mm FL for just $189.95. Incredible.
$189.99?!?!?! i do not think that ANYONE on this forum would be willing to pay that much money for the objective lens alone...
thanks guys
P.S.
is there a way that i can combine objecives with different focallengths to get the focal length that i need.
for example, have a 327mm objecive and add a 200mm objective, what will it give me? any ideas?
god luck
thanks guys
P.S.
is there a way that i can combine objecives with different focallengths to get the focal length that i need.
for example, have a 327mm objecive and add a 200mm objective, what will it give me? any ideas?
god luck
focal lengths
prjctr_builder:
I thought you were going for a 8'x6' (10' diagonal) screen at 15' away. Have you changed to trying for 6'x4.5' (7.5' diagonal) screen at 12'? Anyway, I think the ~520mm lens should work for the smaller, closer setup. (At least that value works in all of the formulas I've been using.)
As far as using your 327mm and 200mm objectives to get ~520mm, try using gunawan's spreadsheet for 2 lenses. Using those 2 focal lengths, if you placed the lenses 15-16" apart, you'd (in theory) get the equivalent of ~520mm. I don't know how well this actually works in real life, though. If you don't like the idea of that much space, try getting a couple of shorter focal length lenses. For example, (again, in theory) if you had 2 lenses with 100mm focal lengths, you could do it in about 7".
prjctr_builder:
I thought you were going for a 8'x6' (10' diagonal) screen at 15' away. Have you changed to trying for 6'x4.5' (7.5' diagonal) screen at 12'? Anyway, I think the ~520mm lens should work for the smaller, closer setup. (At least that value works in all of the formulas I've been using.)
As far as using your 327mm and 200mm objectives to get ~520mm, try using gunawan's spreadsheet for 2 lenses. Using those 2 focal lengths, if you placed the lenses 15-16" apart, you'd (in theory) get the equivalent of ~520mm. I don't know how well this actually works in real life, though. If you don't like the idea of that much space, try getting a couple of shorter focal length lenses. For example, (again, in theory) if you had 2 lenses with 100mm focal lengths, you could do it in about 7".
prjctr builder
here comes the dumb slize; may be you should ask genius ace for this...
anyways; here is a try to solve your problem...
the "maximum focal lenght of lense" means this is the maximum to get your picture projected in this way you want to have it.
4 rules
first rule:
imager distance twice the focal (2xf) lenght then picture wide has the same size in the same focal lenght (2xf) on the other side of the lense
second rule:
imager distance is bigger than 2xf then picture wide is smaller
third rule:
imager distance lies between focal length and 2xf then the picture is magnified
fourth a rule:
imager distance is smaller focal lenght the picture won't never become sharp
now to your problem:
i guess you are using an ohp lense (guessing from your lense focal length)
my ohp lense has a focal length of 30cm that is 1/f = 0,033 dioptrin
in my case i'll need a lense with maximum of 54cm = 0,0185 dioptrin
ok that means i'll need an additional lense that has -0,0145 dioprtin
0.033-0.0145=0.0185
tomorrow i'll go to the optiker a gonna buy an eyeglasses with -0,0145 dioptrin...
as i see your parameters are quite the same as mine... hope that helps everyone...
BTW nice program you discovered there...
i don't know if this works but i am confidently it will because i tried to build a 2 lense system with eyeglasses; it worked ok; better then the fresnel lenses but worse than the ohp 3 lense systems...; but if you combine the 3 lense system and the single eyeglass may be that makes a clear sharp picture with the size you want...
hope that helps everyone; i will try it in about 2 weeks
slize
here comes the dumb slize; may be you should ask genius ace for this...
anyways; here is a try to solve your problem...
the "maximum focal lenght of lense" means this is the maximum to get your picture projected in this way you want to have it.
4 rules
first rule:
imager distance twice the focal (2xf) lenght then picture wide has the same size in the same focal lenght (2xf) on the other side of the lense
second rule:
imager distance is bigger than 2xf then picture wide is smaller
third rule:
imager distance lies between focal length and 2xf then the picture is magnified
fourth a rule:
imager distance is smaller focal lenght the picture won't never become sharp
now to your problem:
i guess you are using an ohp lense (guessing from your lense focal length)
my ohp lense has a focal length of 30cm that is 1/f = 0,033 dioptrin
in my case i'll need a lense with maximum of 54cm = 0,0185 dioptrin
ok that means i'll need an additional lense that has -0,0145 dioprtin
0.033-0.0145=0.0185
tomorrow i'll go to the optiker a gonna buy an eyeglasses with -0,0145 dioptrin...
as i see your parameters are quite the same as mine... hope that helps everyone...
BTW nice program you discovered there...
i don't know if this works but i am confidently it will because i tried to build a 2 lense system with eyeglasses; it worked ok; better then the fresnel lenses but worse than the ohp 3 lense systems...; but if you combine the 3 lense system and the single eyeglass may be that makes a clear sharp picture with the size you want...
hope that helps everyone; i will try it in about 2 weeks
slize
and LOL 190 bucks for a lense we don't know how/IF it works, that is WAY to much...
🙂)))))))))))))))))))))))))))))
in my opinion it won't work, because the imager wide has to be the same as a camera film; and an lcd of this size with good resolution would be great for all of us...
with oph lenses it is different, they are constructed for din A4 sheets, in wide near to our LCDs...
slize
🙂)))))))))))))))))))))))))))))
in my opinion it won't work, because the imager wide has to be the same as a camera film; and an lcd of this size with good resolution would be great for all of us...
with oph lenses it is different, they are constructed for din A4 sheets, in wide near to our LCDs...
slize
slize, wait!!!
so what lens will i need to purchase in addition to my 327mm objective so that my max focal length would be about 521mm?
thanks slize
so what lens will i need to purchase in addition to my 327mm objective so that my max focal length would be about 521mm?
thanks slize
Sounds like you could use the two lens focal length calcualtion tool.
you can download it here
peace
you can download it here
peace
focal length attrib
so you need a -610mm focal length at 100mm from your 327 to give you 520.81mm total focal length. I guess that means you use a convex lense but I'm totally new to optics.
so you need a -610mm focal length at 100mm from your 327 to give you 520.81mm total focal length. I guess that means you use a convex lense but I'm totally new to optics.
Grrrrrrr
all this S%*T is confusing... i cannot seem to find the right way that i can solve my problem.
theoretically, using slize's way of solving for the dioptrin, i will need a lens with -0.011391 dioptrin. please correct me if i am wrong, slize.
but at the same time, having my 327mm objective and adding to it a 200mm lens 400mm away... will give me about the same 521mm final focal length.
Can sone one who's good at this tell me if i am on the right track or am i just getting deeper and deeper in the forest of confusion.
thanks guys
all this S%*T is confusing... i cannot seem to find the right way that i can solve my problem.
theoretically, using slize's way of solving for the dioptrin, i will need a lens with -0.011391 dioptrin. please correct me if i am wrong, slize.
but at the same time, having my 327mm objective and adding to it a 200mm lens 400mm away... will give me about the same 521mm final focal length.
Can sone one who's good at this tell me if i am on the right track or am i just getting deeper and deeper in the forest of confusion.
thanks guys
prjctr_builder
your dioptrin sounds right...
1. divide 1 / "focal length of your existing lense" and you'll get the dioptrin
2. then divide 1 / "max focal length you'll need"
now "1." - "2." = something negative, that is your dioptrin of the additional lense
you'll need a konvex konkav eyeglass...
because a bi konkav eyeglass is very expensive and will paralell the rays, so you won't never get a sharp picture.
just ask for eyeglasses for farsightedly people, they have to be cheap at this low dioptrin...
important: in my conclusions, you'll need to add the additional lense as close to your ohp lense as possible, that means NO distance just put it right in front of it. Becaue if you have more lenses fixed togehter closely you count it as one. but if you have distances between it, you'll need to count every single lense and that is too much work 🙂 (at least for me)
your dioptrin sounds right...
1. divide 1 / "focal length of your existing lense" and you'll get the dioptrin
2. then divide 1 / "max focal length you'll need"
now "1." - "2." = something negative, that is your dioptrin of the additional lense
you'll need a konvex konkav eyeglass...
because a bi konkav eyeglass is very expensive and will paralell the rays, so you won't never get a sharp picture.
just ask for eyeglasses for farsightedly people, they have to be cheap at this low dioptrin...
important: in my conclusions, you'll need to add the additional lense as close to your ohp lense as possible, that means NO distance just put it right in front of it. Becaue if you have more lenses fixed togehter closely you count it as one. but if you have distances between it, you'll need to count every single lense and that is too much work 🙂 (at least for me)
verbose
thx verbose,
great programm too...
@prjctr_builder:
you can try your results with the program of verbose mustafa and you'll see; if you leave the distance at 0 the focal length will come out just as youwant it...
thx verbose,
great programm too...
@prjctr_builder:
you can try your results with the program of verbose mustafa and you'll see; if you leave the distance at 0 the focal length will come out just as youwant it...
prjctr_builder
A few pages ago, you mentioned you made a pretty decent reflector from a sheet of steel. How/what did you do? I've got the same bulb as you, and am thinking of just bending a length of sheetmetal into a semi-circle, so that the bulb runs the length of the metal. Kind of like this:
(o
( is the reflector, o is the bulb. Both are running into the screen.
If that's not enough for me, I'm thinking of adding a couple of other pieces of metal to the ends, to try to focus more of the light back in.
Is this similar to what you did? Or what worked for you?
A few pages ago, you mentioned you made a pretty decent reflector from a sheet of steel. How/what did you do? I've got the same bulb as you, and am thinking of just bending a length of sheetmetal into a semi-circle, so that the bulb runs the length of the metal. Kind of like this:
(o
( is the reflector, o is the bulb. Both are running into the screen.
If that's not enough for me, I'm thinking of adding a couple of other pieces of metal to the ends, to try to focus more of the light back in.
Is this similar to what you did? Or what worked for you?
HUI this site prjctr_builder discoverd is FANTASTIC!!! I found out that i can zoom in and out the projected picture by reducing and increasing the distance between my ohp lense and this additonal eyeglass... i'll go tomorrow and buy that eyeglasses with the right dioptrin after some more calculations tonight...
if the sharpness is good that would be a great solution...
if the sharpness is good that would be a great solution...
THROW DISTANCE
Slize:
I consider the "throw distance" to be the biggest issue with our DIY projectors.......There's alot of people doing math and saying this or that SHOULD work, but I've yet to see a DIY 15" LCD/OHP projector that projects a small enough picture. My box is probably only 8 foot from the screen and the picture is like 12 foot diagonal......
IF ANYONE OUT THERE CAN SOLVE THIS....PREFERABLY WITH AN ADD ON LENS, I'D PAY GOOD MONEY FOR IT...AND I'LL BET MOST OTHER DIY'S WOULD TOO!!!
PLEASE KEEP US POSTED ON YOUR EXPERIMENTS!!!
Slize:
I consider the "throw distance" to be the biggest issue with our DIY projectors.......There's alot of people doing math and saying this or that SHOULD work, but I've yet to see a DIY 15" LCD/OHP projector that projects a small enough picture. My box is probably only 8 foot from the screen and the picture is like 12 foot diagonal......
IF ANYONE OUT THERE CAN SOLVE THIS....PREFERABLY WITH AN ADD ON LENS, I'D PAY GOOD MONEY FOR IT...AND I'LL BET MOST OTHER DIY'S WOULD TOO!!!
PLEASE KEEP US POSTED ON YOUR EXPERIMENTS!!!