• State Suggested Answer
  • Date
    Rick36616
  • Date
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 41 subscribers
  • Views 9967 views
  • Users 0 members are here

How to choose a lens for D40 or D60

I am looking to create a high side wash using D40s and D60s.  How do the lenses work for these units?  In my case, the units are Lustr+.  From the comparison sheet, it appears these are 17 degrees with no lens.  As best I can determine, the various Narrow, Medium, Wide, spread the beam in one direction only; the other remains at 17 degrees.  To get a wider beam, you would use two lenses, one to spread horizontal and the other vertical.  Is this correct?  Thus if I wanted a 27 x 42 degree I would use a Narrow combined with a Medium.  Alternatively, I could use a single lens and get 20x40 degrees or 30x70 degrees if I used the oval lenses.  I see round lenses in the data sheet but not on the comparison page.  Do the round lenses spread in both horizontal and vertical equally?  For example, a Narrow round would produce a 27degree spread in both horizontal and vertical?  How are these lenses normally used?  How much light is lost by using two lenses instead of one? 

  • 0

    Round lenses spread the light in all directions evenly. Oval lenses bias along one axis and can be rotated in the frame.

    Lenses can be stacked with no appreciable loss in output (there's actually a measuring quirk whereby adding a lens can improve the measured output). They don't behave the same as diffusion material.

    The math of stacking lenses is a bit complicated. It involves some trigonometry. Adding a 35 degree lens to a 17 degree fixture doesn't produce a 35 degree lens, nor a 52 degree lens. I think the result is a little less than 30 degrees but I can't remember the formula off the top of my head.

    ETC's article comparing Desire lenses to Source Four PAR EA provides some good reference information which can help you get in the right ballpark.

  • 0 in reply to sk8rs_dad

    Thanks for the feedback.  The comparison you reference is included in the data sheet along with some other information.  I found spreadsheets with detail as well. I spoke with ETC support who tells me the lens was spec'ed to the actual size of the resultant beam, so you don't need trig to figure out the resultant value.  The problem I've been having is I expected a VN, N, M, W lens to match S4PAR or PAR definition for these, but they do not.  For Selador, the VN, N, M, W, etc. are surrogates for 22deg, 27deg, 42deg, 69deg etc., but in one direction only.  The other direction has zero spread, meaning 18deg.  The comparison sheet you reference lets you pick a combination that is closest to your needs, but it's not possible to match the S4 PAR exactly.

  • 0 in reply to Rick36616
    There are three, different kinds of lenses available for Desire fixtures: linear, oval, and round. For each kind there is a small range of available beam sizes.

    Linear lenses are useful for things like wall grazing, where you might want to spread the light horizontally across the width of the wall but keep the vertical spread very tight for good control and focus. Linear lenses can be double-stacked, and depending on how you rotate them, you can create different custom shapes. For example, with the lenses rotated 90 degrees from each other, you can make a square or rectangular beam. In general, beam edges stay fairly tight with linear lenses (not unlike a soft, barn-door-type cut).

    Oval lenses are similar to the linear ones, but whereas linear lenses spread the beam in literally only one plane, the oval lenses both lengthen and widen the beam, albeit more in one direction than the other. Oval lenses produce a much softer beam edge, which is useful when blending light from multiple fixtures.

    Round lenses produce a round beam. The widening is uniform in all directions, which is why these lenses are cut in a square shape (since rotating them in a gel frame would have zero effect). Like oval lenses, these produce a softly tapered beam edge.

    Each one of these lenses is far more optically efficient than standard diffusion media. We have measured approximately 8-10% light loss on each lens. This is all related to standard Fresnel light loss, and for that reason, they are more efficient with the rough or patterned side facing inward toward the light.

    Any combination of multiple lenses may be used. Expect a roughly 10% reduction in output with each one. When stacking linear lenses, if their rotation is significantly less than 90 degrees apart from each other, you may sometimes see a kind of moire effect of light and dark stripes. This never happens with oval and round lenses, thanks to the random microstructures that make them work.

    You can find an Excel spreadsheet here that shows very detailed beam distribution and efficiency information for each lens individually:

    https://www.etcconnect.com/WorkArea/DownloadAsset.aspx?id=10737480447

    The worksheet tabs are labeled "__R" for round lenses, "__L" for linear, and "__O" for oval.

    We initially labeled these lenses with a specific beam-angle designation (e.g., 30deg round), but we found that this was creating confusion because our different LED fixtures sometimes have slightly different native beam angles, which changes the effect of these secondary lenses. The softly tapered edge of the oval and round lenses also made it difficult for users to consistently agree at what angle the beam edge lies. Generic beam designations are simply more appropriate for these accessory products.
Related

www.etcconnect.com