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DIY Fresnel LED lights
  • kronstadtkronstadt

    LED lights are awesome, save you a LOT of hassle on location, and are dropping in prices. At the same time the good old ARRI fresnel tungsten lighting gives you that beautiful cinematic lighting - so beautiful and easy to control that you might want to put up with all the hassle and cost that they involve.

    So I thought: would it be possible to combine best of both worlds? Would it be possible to have LED lights which also work as a Fresnel lights? Then I found out that this is the newest cutting edge thing that ARRI offers in it’s L-series, and LightPanels is releasing its own early models too, and they cost tens of thousands of dollars!

    I wonder if I can make it DIY?

    After all it shouldn’t be that difficult. I thought of getting a 312ASZ led panel (which, correct me if I'm wrong should give me a 250W equivalent) and sticking one of those plastic Fresnel lenses that old people use to read newspapers. Like this http://www.ebay.co.uk/itm/Magnifier-Full-Page-Magnifying-Fresnel-Lens-Sheet-XL-/320649270129?pt=LH_DefaultDomain_3&hash=item4aa82f9371#ht_3008wt_932 or fresnel lenses for Solar cookers like this http://www.ebay.co.uk/itm/Fresnel-Lens-Over-Head-Projector-Solar-Cooker-Oven-Project-OHP-310mm-x310mm-x4mm-/150826264411?pt=UK_Gadgets&hash=item231df2275b#ht_500wt_1164

    But then the question becomes, are these good enough Fresnel lenses for purposes of cinematic lighting? And how to make it so that the lens moves back and forth, so as to focus the light?

    What do you think? Any advices? Any suggestions? Any links to such DIY tutorials?

  • 6 Replies sorted by
  • bugmebugme

    Dear Muntus: Sorry to rain on your parade, but what you are proposing is not feasible. At least, not with the components you mentioned. Even if you solved the heat dissipation issue, and come to terms with the awful Color Rendering Index (http://en.wikipedia.org/wiki/Color_rendering_index) which seriously limits it use, you still need a non-convergent fresnel lens.

    What Agustin-Jean Fresnel invented, the "fresnel" type of lenses, was a way to make lenses more compact (and thus, less opaque), by "flattening" them. This expression, however, does not provide any indication regarding the Dioptric Power of said lens. (http://en.wikipedia.org/wiki/Focal_power) The one you show, the "Fresnel Loupe" is a "positive", "augment" or "convergent" lens, which means that the light beams emanating from your LED source will form a converging cone, with a single-point apex at a determined distance (Focal point). Further than that, the beams will separate in the shape of a inverted cone, symmetric to the first one. Think of it as killing ants with a magnifying glass. You project a single point, which you need to focus. .

    For the "Fresnel" lighting device used on film, however , you need a "lighthouse" lens, where each "ridge" of the lens has a different Dioptric Power, in order to make all beams as parallel as possible. This is why it can project a sharp, homogeneous circle of light at any distance.

    As far as I know, this kind of Fresnel lenses are exclusive to film lighting gear, so you should look for an old decommissioned unit to act as the shell for your device.

    Also, remember that, to replicate the effect, you need a carriage unit that can move your light source closer or further from the lens, while remaining perfectly parallel. If it´s not, the beams will arrive to the lens crooked and distort the projection.

  • Vitaliy_KiselevVitaliy_Kiselev

    I knew it would be to easy:). where to look for "fitting" like in above video?

    If you like such things, just get ready "fresnels" from ebay and fit them with real fresnel lens.

    But mostly they have little use.

  • konjowkonjow

    I knew it would be to easy:). where to look for "fitting" like in above video?

  • Vitaliy_KiselevVitaliy_Kiselev

    @konjow

    First, LED chip will fry without proper heat dissipation.

    Second, CRI and quality of such things are just horrible.

  • konjowkonjow

    Year ago and Nobody DIY this yet? What do you guys think about fit this http://www.aliexpress.com/item/Free-Shipping-100W-LED-Floodlight-Equivalent-To-1000W-Old-Floodlight-Bridgelux-Chip-50000H-Lifespan-Flood-LED/1200753612.html into As Arri fresnel. There are diferant temperatures to choose or is there better led solution to fit in?

  • muntusmuntus

    I've wondered the same thing about those fresnel sheets.

    Another approach would be exactly what you described as getting the best of both worlds. It looks like these guys took an As Arri fresnel light and put 100w led into it with a dimming power supply. More expensive and involved, but probably well worth it.

    I believe the video is in Hungarian. It's hard to tell, but I did not see any banding that is sometimes present in led dimmers. Might be a great approach to low budget lighting.

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