Can you use multiple fresnels to reduce the overall focal length and still keep the collimating effect of the fresnel? For other lenses, I know that 1/FL1 + 1/FL2 = 1/Total FL. Does this hold true for fresnels? And would I still get parallel light out (smooth side of each fresnel facing the light)? Hopefully the picture will help explain it.
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That's fine, but you might want to have a little bit more distance between the fresnels so the first one would work as condencer and gather some of the light that would otherwise be wasted.
In fact as my condencer broke I am now planning to use another fresnel as condencer lens.
In fact as my condencer broke I am now planning to use another fresnel as condencer lens.
mehlin
i was thinking in using a frensel as a condenser the other week actually keep us posted if u try the idea out, heat could be the issue though
Trev
i was thinking in using a frensel as a condenser the other week actually keep us posted if u try the idea out, heat could be the issue though
Trev
Big question, if i have a diylabs fresnel with an 8.9" focal length (i think) and its measurements are 12.2 x 12.2 (i think), if i were to cut the fresnel down to 5 x 5 would that change the focal length at all, if so, how would i go about figuring out the focal length, this is probably a stupid question and i think it wouldnt change the focal length but i wanna be absolutely sure, and if nobody replies i understand, thanx
free
heya free, i cut a frensel down different from what u guys are using typically, and it changed my focal , it made it longer, the focal was originally 3 inches but now its about 7, i think when u cut it down the angles on the frensel u cut off make the difference as they are at a sharper pitch, the ones in the middile are less of a pitch so in turn i would think u would loose magnifaction or you are altering the focal pitch of the lens, thats my theries it did change mine, but that doesnt mean to say it will change yours.
Trev
heya free, i cut a frensel down different from what u guys are using typically, and it changed my focal , it made it longer, the focal was originally 3 inches but now its about 7, i think when u cut it down the angles on the frensel u cut off make the difference as they are at a sharper pitch, the ones in the middile are less of a pitch so in turn i would think u would loose magnifaction or you are altering the focal pitch of the lens, thats my theries it did change mine, but that doesnt mean to say it will change yours.
Trev
thats cool, i plan on using two of them to reduce focal length on the first post, my problem being tho, i dont know exactly what it willl change to, could i just setup my fresnels and lcd and keep moving my light back and forth untill i get a better picture or something, thanx fer all yer help
-josh
-josh
Update
Well, I tried using 2 fresnels sandwiched together. It seemed to help my focal length (shorter), but it creates other problems.
First, in light colored scenes, especially ones where it covers a large area of the screen, Moire effect can be seen. Second, ghosting is now a problem. I believe both of these problems could be eliminated if I were able to get the 2 fresnels to line up EXACTLY on top of each other, but I don't think that's possible. If they're off even a slight bit, these two problems crop up.
Just posting my results.
Well, I tried using 2 fresnels sandwiched together. It seemed to help my focal length (shorter), but it creates other problems.
First, in light colored scenes, especially ones where it covers a large area of the screen, Moire effect can be seen. Second, ghosting is now a problem. I believe both of these problems could be eliminated if I were able to get the 2 fresnels to line up EXACTLY on top of each other, but I don't think that's possible. If they're off even a slight bit, these two problems crop up.
Just posting my results.
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