W
willie
Here's a new alternative lens for those who are using the 7" VGA's (Lilliput's) and didn't get one of those 240mm copy lens. This one is 210mm but it should work on screens up to 8.25". I don't have one (I have one of the 240's) but the specs seem pretty much the same (except the focal length). Anyway, it's only $10.00, so get one before there gone. 😉
http://www.surplusshed.com/pages/item/l3233.html
http://www.surplusshed.com/pages/item/l3233.html
W
willie
The size of the focal length is the size of the lcd it will work up to with. To convert mm to inches, divide by 25.4
So lets see a 320mm fl triplet / 25.4 = lcd up to 12.59 '
Yet their used with 15' lcds
Im confused do you mean the width of the lcd?
Yet their used with 15' lcds
Im confused do you mean the width of the lcd?
W
willie
From what I've heard, what I've said is true, but I could be mistaken. If someone else here know's otherwise, then feel free to correct me. But I think the lens I mentioned would still work for the Lilliput.
The FL of the objective should be bigger than the diagonal of the object being projected.However viewing angle of an objective lens is a spec that nobody seems to look for!!!
Viewing angle is mesured in degrees.The bigger viewing angle
the sharper edges but less light gain.The smaller the viewing angle,unfocus edges but more light gain.The best objective is the one that has bigger diameter than the diameter of the object being projected and is a not wide viewing angle.This way,parallel
light that comes out of the lcd passes threw the objective consalting in a very focused,bright and crisp image.Thats how comersial projectors work.
Using a 320mm ohp triplet will never give a fully focus image with a 15" lcd and if there is someone that thinks dfferent please let us know.Also 320mm on 15" panel will produse a very big image if you place the projector something like 3 meters away and will also produce geometrical aberations!!
Did anyone ever thought why there is a nice image with desktop
still image and when video is projected something does not go right?It is another spec that everyone ignores that objective lenses have and it is called speed.
Yes the abilitty of an objective lens to trap light between collor transitions is called speed of the objective.The higher the better,the lower image looks a liitle out of focus when collor transition are very often.
Believe me,OHP triplets are not made for video projection so they
luck of these caracteristics!Only pressision multi coated,(realy multi coated not just coated),triplets can do the job.
Anyway who cares?Everyone here gets any triplet,places it on a wooden box and expects it will do the job!!!
Many people have build same projectors with different objectives having totally different results.Nobody said anything about the triplets,they were just messing around with everything else.
Bigger FL than object diagonal,proper effective viewing angle and high speed is what you want guys.
Viewing angle is mesured in degrees.The bigger viewing angle
the sharper edges but less light gain.The smaller the viewing angle,unfocus edges but more light gain.The best objective is the one that has bigger diameter than the diameter of the object being projected and is a not wide viewing angle.This way,parallel
light that comes out of the lcd passes threw the objective consalting in a very focused,bright and crisp image.Thats how comersial projectors work.
Using a 320mm ohp triplet will never give a fully focus image with a 15" lcd and if there is someone that thinks dfferent please let us know.Also 320mm on 15" panel will produse a very big image if you place the projector something like 3 meters away and will also produce geometrical aberations!!
Did anyone ever thought why there is a nice image with desktop
still image and when video is projected something does not go right?It is another spec that everyone ignores that objective lenses have and it is called speed.
Yes the abilitty of an objective lens to trap light between collor transitions is called speed of the objective.The higher the better,the lower image looks a liitle out of focus when collor transition are very often.
Believe me,OHP triplets are not made for video projection so they
luck of these caracteristics!Only pressision multi coated,(realy multi coated not just coated),triplets can do the job.
Anyway who cares?Everyone here gets any triplet,places it on a wooden box and expects it will do the job!!!
Many people have build same projectors with different objectives having totally different results.Nobody said anything about the triplets,they were just messing around with everything else.
Bigger FL than object diagonal,proper effective viewing angle and high speed is what you want guys.
WMT said:
WMT , yeah, u're so right.
the 210mm will work with the 7 incher cos the diagonal of the 7" will fit in this viewing angle plus extra, which avoid blurred edges.
i often told it .your explanation is superb buddy.
but i do not agree in your "bigger diameter" theory. the light is forced through the objective by a proper fresnel. when the light spot fits the diameter of the objective 100% of the available light will pass through. sometimes we cannot find the proper fresnel, so then it'll be better to have a bigger diameter of the objective to catch all the light.
multi coated triplets are expensive and not available. so i take what i can get. that's the compromise i've to accept and the results are satisfactorily.
ief
Hello I_eat_flowers,
This is exactly how comercial projectors work with their little lcds that are no bigger than 1" anymore.
I agree that you can force the light threw the objective with the proper fresnel FL but there are some more issues to take in mind.
When a 65mm objective is analyzing a 15" panel with 390mm FL combining with the right fresnel,the image will be without geometrical distorsions,it will be focused well but it will not be 100% because of 2 reasons.
One reason is the lens map diagram which is something like this and shows the strenth of the lens according to the object being projected on the screen.I know that you will say that this is fixed long time ago with the new lenses but not with the ones we use!!
The second reason is the power output which is bigger in the middle just because the diastance compared to the sides is shorter.I know we can not get a 15" triplet 🙂 but thats how hotspots and staff would be eliminated.
Parellel light threw the objective is excellent.
Last year i tried making the light parallel after the field fresnel with a system of lenses and project it threw a 70mm fl 55mm diameter triplet that i got from a comercial projector.The hole project did not get out well and costed me money🙁 .
The proplem was that i was now projecting a virtual image of the subject consulting in low brightness and heavy goasting!!!
The OHP design we use has limitasions and only very expensive gear will do,something that is not worth it.
Anyway i agree that the results we get to the money we pay are awesome but if you want to go deaper many surprises are waitting 🙂.
One thing is for sure,smaller lcds is the key if you want top image.
Oh and something else,big optics waste a lot more light.
The only reason i would bother in building another projector now is if i find a true 1920X1080 15" panel!!!If this happens then interest will go way high!!
At the moment i built two identical 10" toshiba projectors with different polarization (after replacing the one lcd polarizers) for 3d viewing but again i have stuck because i must invert the polarity to the one controler and have not done it yet.After replacing with S polarizers the image is like the negative films!!!
Anyway it will be a linear polarized 3d system driven with my dual head nvidia that you will not be able to move your head a lot 🙁 .
Sorry for the long post guys but remember there are many more things we can do with our projectors.
This is exactly how comercial projectors work with their little lcds that are no bigger than 1" anymore.
I agree that you can force the light threw the objective with the proper fresnel FL but there are some more issues to take in mind.
When a 65mm objective is analyzing a 15" panel with 390mm FL combining with the right fresnel,the image will be without geometrical distorsions,it will be focused well but it will not be 100% because of 2 reasons.
One reason is the lens map diagram which is something like this and shows the strenth of the lens according to the object being projected on the screen.I know that you will say that this is fixed long time ago with the new lenses but not with the ones we use!!
The second reason is the power output which is bigger in the middle just because the diastance compared to the sides is shorter.I know we can not get a 15" triplet 🙂 but thats how hotspots and staff would be eliminated.
Parellel light threw the objective is excellent.
Last year i tried making the light parallel after the field fresnel with a system of lenses and project it threw a 70mm fl 55mm diameter triplet that i got from a comercial projector.The hole project did not get out well and costed me money🙁 .
The proplem was that i was now projecting a virtual image of the subject consulting in low brightness and heavy goasting!!!
The OHP design we use has limitasions and only very expensive gear will do,something that is not worth it.
Anyway i agree that the results we get to the money we pay are awesome but if you want to go deaper many surprises are waitting 🙂.
One thing is for sure,smaller lcds is the key if you want top image.
Oh and something else,big optics waste a lot more light.
The only reason i would bother in building another projector now is if i find a true 1920X1080 15" panel!!!If this happens then interest will go way high!!
At the moment i built two identical 10" toshiba projectors with different polarization (after replacing the one lcd polarizers) for 3d viewing but again i have stuck because i must invert the polarity to the one controler and have not done it yet.After replacing with S polarizers the image is like the negative films!!!
Anyway it will be a linear polarized 3d system driven with my dual head nvidia that you will not be able to move your head a lot 🙁 .
Sorry for the long post guys but remember there are many more things we can do with our projectors.
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WMT,
yeah, I got it and a good explanation again dude.
If I could get a reasonable 2.5 - 3" lcd with a vga or ( just dreaming svga or xga) reso I'd do it without fresnel and send a parallel light beam through. similar to a slide pj.
some ppl do, but they are using these crappy 1.8" lcd w a horrible low reso. Then its possible to use the multi- element-coated objectives of the slide pj's.
So I keep on dreamin, the only thing I found was a 2,5" with 320x240 native for 139 Euro.
BTW interesting experiment w your stereo-beamer and polarizing shields. but on this issue it seems to me that you're the geek. ;-)
Well, back to topic. We found out:
An objective lens' FL has to be abit bigger than the lcd's diagonal.
Best would be it has the same diameter as the LCD due to less distortions, aberrations a.s.o. and should be a multi-coated triplet at least.
IEF
yeah, I got it and a good explanation again dude.
If I could get a reasonable 2.5 - 3" lcd with a vga or ( just dreaming svga or xga) reso I'd do it without fresnel and send a parallel light beam through. similar to a slide pj.
some ppl do, but they are using these crappy 1.8" lcd w a horrible low reso. Then its possible to use the multi- element-coated objectives of the slide pj's.
So I keep on dreamin, the only thing I found was a 2,5" with 320x240 native for 139 Euro.
BTW interesting experiment w your stereo-beamer and polarizing shields. but on this issue it seems to me that you're the geek. ;-)
Well, back to topic. We found out:
An objective lens' FL has to be abit bigger than the lcd's diagonal.
Best would be it has the same diameter as the LCD due to less distortions, aberrations a.s.o. and should be a multi-coated triplet at least.
IEF
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