dracul
your calculations sound right.
i will open a new thread on how to calculate the additional lense... but for now here is a short discription:
1. go to this page http://www.opsci.com/index.asp?page...hCalc&exten=htm
fill in your specifications... then you will get and Maximum focal length of lens:
2. take the focal length (fl) of your existing lense in meters. then divide 1 by fl in meters
you'll get something like 3.xx (example)
3. take the Maximum focal length of lens in meters. then dive 1 by it
4. now take 2. - 3. and you'll get and negative number.
this is th edioptrin you need
5. in Europe they have 1/4 steps so take the dioptrin that is closest to your number (for example -0.8 --> -0.75)
in the US they have 1/8 steps same thing (for example -0.9 --> -0.875 )
that is all...
your calculations sound right.
i will open a new thread on how to calculate the additional lense... but for now here is a short discription:
1. go to this page http://www.opsci.com/index.asp?page...hCalc&exten=htm
fill in your specifications... then you will get and Maximum focal length of lens:
2. take the focal length (fl) of your existing lense in meters. then divide 1 by fl in meters
you'll get something like 3.xx (example)
3. take the Maximum focal length of lens in meters. then dive 1 by it
4. now take 2. - 3. and you'll get and negative number.
this is th edioptrin you need
5. in Europe they have 1/4 steps so take the dioptrin that is closest to your number (for example -0.8 --> -0.75)
in the US they have 1/8 steps same thing (for example -0.9 --> -0.875 )
that is all...
oops
4. now take 2. - 3. and you'll get and negative number.
Nope a positive number...
Slize in your earlier posts you have us subtract your existing lens from your ideal lens...
that means my adiotnal lens must have 2.6(ideal) - 3.45(existing) = - 0.85 dp
In you last post you have us subtract the ideal from the existing...
2. take the focal length (fl) of your existing lense in meters. then divide 1 by fl in meters you'll get something like 3.xx (example)
3. take the Maximum focal length of lens in meters. then dive 1 by it
4. now take 2(existing). - 3(ideal). and you'll get and negative number.
Number 4 should actually read "take 3 - 2 and you'll get a negative number."
Probably just a typo but confusing...
4. now take 2. - 3. and you'll get and negative number.
Nope a positive number...
Slize in your earlier posts you have us subtract your existing lens from your ideal lens...
that means my adiotnal lens must have 2.6(ideal) - 3.45(existing) = - 0.85 dp
In you last post you have us subtract the ideal from the existing...
2. take the focal length (fl) of your existing lense in meters. then divide 1 by fl in meters you'll get something like 3.xx (example)
3. take the Maximum focal length of lens in meters. then dive 1 by it
4. now take 2(existing). - 3(ideal). and you'll get and negative number.
Number 4 should actually read "take 3 - 2 and you'll get a negative number."
Probably just a typo but confusing...
dammit
i got the 508mm fl objectives i ordered, they do make the right size image where i want it, but the corners are messed up, i will need to play around with it over the weekend and see if i can get something going...
dammit...
the screen is the right size though, so you formulas DO work!!!
muahaha
aleksey
i got the 508mm fl objectives i ordered, they do make the right size image where i want it, but the corners are messed up, i will need to play around with it over the weekend and see if i can get something going...
dammit...
the screen is the right size though, so you formulas DO work!!!
muahaha
aleksey
so...
So I decided to try out this zoom thing. I did the calculations and came up with a number to put my projection on a different wall in my room, just for the hell of it. I figured I would need an eyeglass with -1.125 diopters. I called around, MalWart hung up on me, LensCrafters said they could do it with a prescription..hehe..I told them it was for a science experiment and they said 'OH...come on in it's free.' I get there and they're looking at me thinking, 'this guy is too old for highschool,' (I never mentioned school at all) but they begrudgingly give me the lens for free. 😉 They did grill me about what school I went to etc, I just told them the truth. I asked the guy how much it would cost if I wanted to buy it he said...'a lot..$60' heh.
I run home thinking I'll slap this thing on my lens triplet and watch my picture shrink...WRONG. All I get is a big blur..newsflash..you can't increase a len's focal length without moving that lens that much farther away from the object. So I grab my objective and put it 8"-10" farther out from the hole in my box, throw the eyeglass on and bingo, smaller picture, much smaller...and my calculations proved correct, my image was 9' horiz at a distance of 15'. Anyway, this led to a rash of questions about my fresnel, how I could even achieve a projection so far away from my collecting fresnel, why my projection was still oriented correctly, and how the hell I'm going to modify my box to include that extra distance. Man I figured I had a good handle on the theory of my optics, surprise. Guess who will be taking the MIT online optics course this week?
So I decided to try out this zoom thing. I did the calculations and came up with a number to put my projection on a different wall in my room, just for the hell of it. I figured I would need an eyeglass with -1.125 diopters. I called around, MalWart hung up on me, LensCrafters said they could do it with a prescription..hehe..I told them it was for a science experiment and they said 'OH...come on in it's free.' I get there and they're looking at me thinking, 'this guy is too old for highschool,' (I never mentioned school at all) but they begrudgingly give me the lens for free. 😉 They did grill me about what school I went to etc, I just told them the truth. I asked the guy how much it would cost if I wanted to buy it he said...'a lot..$60' heh.
I run home thinking I'll slap this thing on my lens triplet and watch my picture shrink...WRONG. All I get is a big blur..newsflash..you can't increase a len's focal length without moving that lens that much farther away from the object. So I grab my objective and put it 8"-10" farther out from the hole in my box, throw the eyeglass on and bingo, smaller picture, much smaller...and my calculations proved correct, my image was 9' horiz at a distance of 15'. Anyway, this led to a rash of questions about my fresnel, how I could even achieve a projection so far away from my collecting fresnel, why my projection was still oriented correctly, and how the hell I'm going to modify my box to include that extra distance. Man I figured I had a good handle on the theory of my optics, surprise. Guess who will be taking the MIT online optics course this week?
damnit
same thing with my eyeglasses projctr_builder... must to have something to do with the fresnel lense; i'll check that out in the next days...
same thing with my eyeglasses projctr_builder... must to have something to do with the fresnel lense; i'll check that out in the next days...
brainchild
what focal length does your fresnel etc have? because my picture is smaller, but the edges or not bright enough... do you use a 15" tft or smaller? hmm... i feel i am on the right way but for now i didn't find the perfect solution for me... just as i said, the fresnel has something to do with it i just didn't figure out yet...
what focal length does your fresnel etc have? because my picture is smaller, but the edges or not bright enough... do you use a 15" tft or smaller? hmm... i feel i am on the right way but for now i didn't find the perfect solution for me... just as i said, the fresnel has something to do with it i just didn't figure out yet...
Re: oops
yes you are right...
it was late when i posted that 🙂 so 3. - 2. is correct
brainchild said:
yes you are right...
it was late when i posted that 🙂 so 3. - 2. is correctnew idea
i have a new idea; what are these plastic things behind the lcd called?
everyone who has taken apart an PC monitor TFT has to find such a thing. May we can use it??? i thought instead of this cfls with a "low" light lever, we could use our MH, HQI, HRI or whatever bulbs and build a thing that we backlight our tft s... that would solve the probs with the fresnel lense and may be then we can use our optics with the adoppted focal length??? as i stoped building my second projectorm because i want to make it compact i will try this solution. let me know what you think of that.
this idea comes from the basics of this 100" seller things, because there u can project a (dark, not sharp) picture, but without a fresnel... maybe that would solve our probs with the size of our projectors....
i have a new idea; what are these plastic things behind the lcd called?
everyone who has taken apart an PC monitor TFT has to find such a thing. May we can use it??? i thought instead of this cfls with a "low" light lever, we could use our MH, HQI, HRI or whatever bulbs and build a thing that we backlight our tft s... that would solve the probs with the fresnel lense and may be then we can use our optics with the adoppted focal length??? as i stoped building my second projectorm because i want to make it compact i will try this solution. let me know what you think of that.
this idea comes from the basics of this 100" seller things, because there u can project a (dark, not sharp) picture, but without a fresnel... maybe that would solve our probs with the size of our projectors....
YES
it has defently something to do with the fl of the fresnel lense (i took an older fresnel from an old project which is splitted and i got more picture at the right size; but still not the full...) i will search for a way to calculate the right fl of the fresnel for our new lenses and i am sure then it will work. i will think about it for the week end...
it has defently something to do with the fl of the fresnel lense (i took an older fresnel from an old project which is splitted and i got more picture at the right size; but still not the full...) i will search for a way to calculate the right fl of the fresnel for our new lenses and i am sure then it will work. i will think about it for the week end...
as i read from other threads this two sided fresnels have to different focal points. one for the bulb one for the optic. i looked for it at the splitted fresnel and damn it was right. the one had 330mm which was the dictance for the bulb i had and the other had 280mm which was the distance for the optic i used, as my optic has a fl of 290mm. that would mean i have to turn around the fresnel move the light closer to it and give it another try with the additional lense...
Ouch...
I -finally- found a shop in Belgium where I can order a MH bulb + ballast, but it seems rather expensive, especially compared to prices in the US:
250Watt bulb: 61€
400Watt bulb: 90€
250Watt ballast: 150€
400Watt ballast: i didn't want to know anymore
(€ is about the same value as $ for the moment)
-sigh- i wanted to get a 400watt setup but our prices seem to be like 3 or 4 times higher than US prices 🙁
are there any people from belgium or the netherlands on this forum who know about cheaper shops?
I -finally- found a shop in Belgium where I can order a MH bulb + ballast, but it seems rather expensive, especially compared to prices in the US:
250Watt bulb: 61€
400Watt bulb: 90€
250Watt ballast: 150€
400Watt ballast: i didn't want to know anymore
(€ is about the same value as $ for the moment)
-sigh- i wanted to get a 400watt setup but our prices seem to be like 3 or 4 times higher than US prices 🙁
are there any people from belgium or the netherlands on this forum who know about cheaper shops?
declined said:
may be MH bulbs are so expensive because they are imported from the us. here in germany/europe we usally use "hqi" "hri" "hmi" and so on. they are equal to mh-bulbs...
may be you should look for that in belgium... i got my complete set for 59€ plus shipping... a brand new bulb costs 65€ but on ebay i got it for 25€...
diylabs said:
nope it's not; i made my calculations and i made 'em good as my test shows because it works...
here is a short sketch and a link to a program that proofs it http://www.mathe-online.at/materialien/karlheinz.haas/files/Strahlenoptik/Strahlenoptik.htm
go on "Sammellinse" to see what i mean
Attachments
so first of all: a fresnel has ALWAYS two focal points one on each site at the SAME distance no matter if it is made out of two glued together and each at a different focal point. the new focal point is then 1/focal length of first in meters + 1/focal/lenght of second in meters = 1/new focal point ===>> reciprocal value and you have the new focal point...
now to the problem with the additional lense: the reason we only see a small point and not the whole picture lies in the fact that our optic has now a new focal length and lies behind the second focal point (i know it is not right but ii call it like that because it is easier, you can see in the sketch what i mean...)
to see the full picture this above must be and the bulb must be behind the second focal point on the other side of the fresnel; you can take a look at the programm i linked then you can see what i mean: go to "sammellinse" and you'll see what i mean
so we need a fresnel lense that has the specs like the last sketch, that means twice the focal point must be longer than the focal lenght of our new optic and the bulb must be placed behind that. i got that by splitting my existing fresnel lense. one had 13.78" focal length and the other 12.6" (that's why 6.5 before). so i got one. and the distance will be solved by mirrors...
now to the problem with the additional lense: the reason we only see a small point and not the whole picture lies in the fact that our optic has now a new focal length and lies behind the second focal point (i know it is not right but ii call it like that because it is easier, you can see in the sketch what i mean...)
to see the full picture this above must be and the bulb must be behind the second focal point on the other side of the fresnel; you can take a look at the programm i linked then you can see what i mean: go to "sammellinse" and you'll see what i mean
so we need a fresnel lense that has the specs like the last sketch, that means twice the focal point must be longer than the focal lenght of our new optic and the bulb must be placed behind that. i got that by splitting my existing fresnel lense. one had 13.78" focal length and the other 12.6" (that's why 6.5 before). so i got one. and the distance will be solved by mirrors...
Yeah - I can sell you a complete 250 watt HQI kit with sockets for $150 in USD ... shipping (4-10 day airmail with USPS) would cost $24. That makes it a little cheaper than buying it locally, but you'd still have to wire it since I don't know what type of plugs you use in Belgium (the ballast can be 220v though). I have a person in France who buys some of my lenses in larger numbers to sell in bulk to other people in France - that saves everyone on shipping big time! If anyone wants to do the same for the ballasts, then just let me know. I can usually get quantities of 10 ballasts within about 1 week of ordering them (I don't keep that many in stock usually). Email me at diylabs@hotmail.com if you want to talk about doing something like that with any of the parts I carry. It would be very nice if we could get this going in multiple countries because I know that shipping 10 units all at once is a lot cheaper per unit than shipping 1 at a time, although shipping to the Netherlands is actually not too expensive!