Rox said:
I can not put the fresnels closer to the bulb because then it will not properly light up the lcd.
I originally had 220/310 fresnels but in order to light up the whole lcd I had to put the 310mm fresnel towards the fresnel. The 220 fresnel then focused the light to a point too close to the lcd where I could not put my projection lens. I had to move it away and then loosing light that went outside the projecton lens.
I can asure you its not voltage, its current. If it was voltage it simply wouldnt start. Thats why when using the apropite ballast you have current and thermal protection, to protect the bulb and yourself.
Trev🙂
Trev🙂
pacing the bulb closer to the rear fresnell would move the other side focusing point to a farther point. (we are speaking about 2cm closer, that would move the other side focusing point more than 4cm) have a try.
As Ace said, the light throw the lcd will not be paralell doing this, but i belive 6 degrees maximung angle at corners is insignificant.
As Ace said, the light throw the lcd will not be paralell doing this, but i belive 6 degrees maximung angle at corners is insignificant.
Rox, his top frensel is 300mm, his projection lens is 290mm, having the throw smaller brings the lens closer to the top frensels focal, as the lens is moved out closer to the 300mm.
Trev🙂
Trev🙂
smaller trhow, doesn´t bring the lens closer to the lcd.
please, you mean trhow to the projecting distance do you?
please, you mean trhow to the projecting distance do you?
I know it doesnt, it brings it closer to the top frensels focal though dont it?
Having the projection lens closer or further from the lcd doesnt make a difference in brightness, only in the FOV it will and that comes under image quality.
Trev🙂
sorry i don´t understand you ("doesn't bring closer to the lcd but does to the focal of the field lens...")
lets say we have a perctly optimiced setup, then if you change the trhow (lets say a significant change from 7' to 12' then the light cone will not enter to the triplet as did with the optimiced setup, then you need to adjust the light cone. maybe you have every focal fresnell on you desk but it is not the comon case 😀. I prefer to move the lamp position a bit so the light cones are adjusted very easyly.
think that my friend diyeitor does have 330 field fresnell forced to somewhere 550 just by this method, and his results are terrific.
have you ever seen a OHP with the lamp position weel?
lets say we have a perctly optimiced setup, then if you change the trhow (lets say a significant change from 7' to 12' then the light cone will not enter to the triplet as did with the optimiced setup, then you need to adjust the light cone. maybe you have every focal fresnell on you desk but it is not the comon case 😀. I prefer to move the lamp position a bit so the light cones are adjusted very easyly.
think that my friend diyeitor does have 330 field fresnell forced to somewhere 550 just by this method, and his results are terrific.
have you ever seen a OHP with the lamp position weel?
Ya i have and thats the cheep, wrong way of going about things, ohp's certainly are not proffesional machines 😀
As for your throw, a 2m throw compared to a 4m throw will only move the projection lens from the 4m out by about 1cm at the most, its not enough to worry about on the gear most have, so i dont see an issue here.
Moving the lamp closer to the rear frensel will yeald hotspots and rings, so the image quality becomes worse. You cant cheat physics rox, its that simple, ive been down that road..........
Trev🙂
a throw change from 2m to 4m will mean a adjustement of 3,3cm on the triplet position for the 32cm fix focal triplet case.
on the 135 triplet case it would mean 8cm adjustement. If we are meticulous and design the light cones preciselly, this 8cm would mean more than one headacke if we don´t adjust the lamp osition.
i think it is enought to notice light issues.
the ohp case, i have tested some of them and found very interesting tool that weel.
on the 135 triplet case it would mean 8cm adjustement. If we are meticulous and design the light cones preciselly, this 8cm would mean more than one headacke if we don´t adjust the lamp osition.
i think it is enought to notice light issues.
the ohp case, i have tested some of them and found very interesting tool that weel.
"What for? the FOV?"
no, we want full light entering the triplet, 8 cm repositioning of the triplet (8cm closer to the lcd) could make the outer light rays never get into the triplet. (dimer corners).
its as easy as moving the lamp farther to prevent this.
the fact is that OHP have this posibility for something.
no, we want full light entering the triplet, 8 cm repositioning of the triplet (8cm closer to the lcd) could make the outer light rays never get into the triplet. (dimer corners).
its as easy as moving the lamp farther to prevent this.
the fact is that OHP have this posibility for something.
Rox, thats kinda a silly post, i think moving a projection lens 8cm is kinda stupid in the first place, where you got that from ill never know, it speaks for itself.
The most ive ever had to move a lens is 3cm and thats with a throw of 6ft - 20ft!!!
Trev🙂
The most ive ever had to move a lens is 3cm and thats with a throw of 6ft - 20ft!!!
Trev🙂
Yeah and thats the wrong way to go about it, use the right optics in the first place for the aplication and you wont have this issue, infact, if we had a zoom lens, we would have any issue regarding this.
Trev🙂
ace3000_1 said:
it is based on your data;
lets say we have 450mm triplet. And throw from 2M to 4M.
1/45=1/200+1/X 2m throw means X=58cm lcd-triplet dist
1/45=1/400+1/X 4m throw means X=50,7cm lcd-triplet dist
well it is not 8cm difference but is 7,3cm. Do you agree?
My data isnt a 450mm triplet, try 240mm, using a 450mm triplet is nuts on a small sceen for starters.
And Rox, im not going to hijack this thread, so if you want to continue with this maybe take it over to the optics forum.
Trev🙂
And Rox, im not going to hijack this thread, so if you want to continue with this maybe take it over to the optics forum.
Trev🙂
it all started because (i don´t remenber the thread starter's name) X said he losses lots of light when shortening the throw.
he says that the focusing point is too close from the lcd soo the light diverges again and goes outside of the triplet. Well, the repositioning of the triplet depends on how much does the throw change and also depends on the triplet focal, but even if the repositioning is little, i would move the bulb so everithing is optimiced again. just have a try, if it is better image, then keep it that way, if not, go back again 😀.
teorically, every throw distance should have it's correspondent bulb placent. but i agree with ace that if we design it properly, (midleway trhow) there shouldn´t be any adjustement. the problem comes when there is a significative throw change. I like designing things to the limit. I like thinking every little detail so the design is optimal. (just my opinion).
by the way let me tell you that a zoom lens is something to take care about the bulb placemnt more than any other setup, since there are max/minimal trhows that could have very large separation between.
Ace, i think we have keep on the thread speaking about what he asked, but if you (or him) think it is out of thread, delete/move it.
he says that the focusing point is too close from the lcd soo the light diverges again and goes outside of the triplet. Well, the repositioning of the triplet depends on how much does the throw change and also depends on the triplet focal, but even if the repositioning is little, i would move the bulb so everithing is optimiced again. just have a try, if it is better image, then keep it that way, if not, go back again 😀.
teorically, every throw distance should have it's correspondent bulb placent. but i agree with ace that if we design it properly, (midleway trhow) there shouldn´t be any adjustement. the problem comes when there is a significative throw change. I like designing things to the limit. I like thinking every little detail so the design is optimal. (just my opinion).
by the way let me tell you that a zoom lens is something to take care about the bulb placemnt more than any other setup, since there are max/minimal trhows that could have very large separation between.
Ace, i think we have keep on the thread speaking about what he asked, but if you (or him) think it is out of thread, delete/move it.
Rox, i have tried it, how you think i know 😉.
Zoom lenses work differently and it is another area of discusion with technicality, but you will find in a zoom lens the rear of the projection lens doesnt move closer or further from the lcd, or at all, the optical elements inside of it do, thats a big diff.
Trev🙂
you mean a varifocal lens or a zoom lens?
because they are very different things.
If we would like to do a zoom lens, (with the pro lens ,that is a varifocal; the one from lumenlab for instance) then we need to do some kind of moving sistem for the projection lens. That way, combining the varifocal and the triplet position in a propper way, we can do a zoom to the image (biger/smaller always focused and without the need of changing trhow). But i would like to check any example of it and see what triplet position would need so it could happen that the light cone from the lcd needs to be readjusted.
because they are very different things.
If we would like to do a zoom lens, (with the pro lens ,that is a varifocal; the one from lumenlab for instance) then we need to do some kind of moving sistem for the projection lens. That way, combining the varifocal and the triplet position in a propper way, we can do a zoom to the image (biger/smaller always focused and without the need of changing trhow). But i would like to check any example of it and see what triplet position would need so it could happen that the light cone from the lcd needs to be readjusted.
Zoom, i know all about the varifocals and they are totally diff, though they do share one element, and thats focus.
Trev🙂
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