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Blue Edge and Brown Edge

Discussion in 'Lighting and Electrics' started by Serendipity, Aug 18, 2008.

  1. Serendipity

    Serendipity Active Member Premium Member

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    Example: You're focusing a Source Four ERS. The designer asks you to run the barrel (you're hard focused currently) and depending on if you run it in or out, the color of the edge of the light becomes more diffused and turns either blue-ish or brown-ish.

    Question: Why does moving the barrel in either direction change the hue of the edge of the beam?

    Thanks!
     
  2. JD

    JD Well-Known Member

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    Chromatic Aberration. Lens acts a bit like a prism. (google it) This is why optical lenses such as camera lenses use compound lenses. Hard to get around it on a one element lens assembly.
     
  3. ship

    ship Senior Team Emeritus Premium Member

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    This especially if running the barrel it was blue hard edge all around but in other focuses cannot get back to there leads to say a lens train problem - perhaps a lens not properly seated or something but below the steps in troubleshooting I would take.

    I don’t have a tremendous amount of experience with S-4 fixtures, can almost count on one hand how many times I have bench focused a group of them at any sitting. Had a few examples of them which no matter what I did, I simply was not able to give the fixture a proper bench focus that I would hope in problem was later solved by those that more normally do so.

    Think it’s in part a question of as opposed to say a 360Q Leko that bench focuses in three dimensions, the S-4 only does so in two dimensions. Make sure your lamp is properly seated and hope for the best as a limitation in easier focus but in some ways three dimensional three screw focusing while a pain in the rear has its advantages.

    On the other hand at one point I got to service a Lycian 1290 follow spot that someone forgot to strap into the man-lift lifting it up to a lighting position. It fell and in getting back to the shop I gave it my best effort in optically re-aligning it. Got it back to a hard edge and even reduced the double image but end result was that I could not get rid of the half brown/half blue hard edge with a slight halo I expect you in part also see. For me it was the slightly bent frame and reflector warp caused by the fall that required a few $K in shipping and service at the factory to correct.

    Overall, since a S-4 reflector is less able to go out of round and works or won’t I would suspect it’s more about the optical train being straight. This either fully seated lamp - and or properly seated lamp and a frame for that lamp that’s not warped given a cast element or lamp cap fully installed, or perhaps a lens train that’s optically parallel in the lens train.

    A few things to be difficult here. First and easiest in troubleshooting is knobs tightened. Second in changing lens trains, third seated lamp. After that and with all bench focus of the lamp in all conditions being adjusted.

    Knobs tightened or stripped could make it seem like there but not in a bit of wiggle room. This as with missing lens train glides could allow for a slight out of focus cant. Lenses in the lens train by lot number or ones not fully or properly seated could be at a slight angle, bumpers for them missing etc. Seated lamp being a lamp and fixture question. Hard to get a lamp fully seated and in doing so enough slop in being able to do so that it does so properly. Could be wear, could be bad casting on the lamp or fixture, could be any number of reasons a lamp don't seat properly in a pre-focus socket type this fixture has. Most commonly it's a lamp not fully or properly seated however, or perhaps a bent casting in seating it as less common.

    After that, I would suspect the optics of the lamp socket alignment and change a lamp cap with one that is known to work properly in bench focus. Following this troubleshooting concept of it being the lamp base I would if still bad suspect that if I changed cap and barrel, a slight warp to the fixture. I would refine that search in changing out parts until it was corrected.

    Should be able to correct this problem, just take a bit of time. And somewhere between all also play with a different lamp in the fixture.
     
    Last edited: Aug 18, 2008
  4. ship

    ship Senior Team Emeritus Premium Member

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    My near future wife that heads up the Leko department says reflector issue - bad reflector. And while I love to see the microscopic silver confetti coming out of a Leko that’s being blown out by way of a bad reflector, I just cannot see that of a thick glass reflector changing its shape. This granted of course I only get called in on such issues to either remove without cracking a reflector, break the silly thing in being much easier than attempting to remove, or to seat the thing in getting a new one in. Seating is patience and hit or miss and a royal pain in the rear to which only the fist and luck plays a role. Had a jig set up for doing this once but it didn’t work out so well.

    Anyway, general concept in being supportive in concept is that perhaps the lens is not properly seated and slightly off. Could be as another thing to check.
     
  5. quarterfront

    quarterfront Member

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    This is perfectly normal. Generally I pick which way to go depending on how I'm going to use the special or just depending on my mood.

    You'll also notice that a gobo focused just in from sharp gives darker voids, while just out from sharp gives softer voids.
     
  6. Serendipity

    Serendipity Active Member Premium Member

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    That did happen to one of our S4 reflectors a tech was cleaning. The silver confetti is not happy confetti. It hurts and gets stuck inside your jacket...

    Thank you for your responses! I'm not terribly worried about it (it's not very noticeable) but I was curious why it occurred. And if I have extra time in a couple weeks when maintenance starts, I'll try out what Ship was saying.

    Every one of our S4s (that I can remember) does this, so I assumed it was normal, but Ship's comments seem to make it a problem rather than a feature.
     
  7. Les

    Les Well-Known Member

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    When half of your beam is blue or brown, it is a problem. However, a little blue or brown "halation" around the edge of the beam or gobo/shutter cuts is pretty normal. Donuts can help alleviate this if it is too noticeable.
     
  8. icewolf08

    icewolf08 CBMod CB Mods

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    It is my understanding, though I could be wrong, that you should get a nice blue outline around your beam when you have a properly bench focused unit in sharp focus. This, as has been mentioned, is due to different wavelengths of light refracting at different angles through the lens. Here is an image from Wikipedia:
    [​IMG]
    You can see that the colors with shorter wavelengths (the blue and UV end of the spectrum) converge at a focal point closer to the lens, thus, ending up at the outside of the field when you focus a light sharp. Since the reds end up inside the bulk of the field we don't tend to see them. However, as you move the lens to focus and you get closer to the different focal lengths of the different wavelengths you may see some of that color show up on the edge of the field. Hence the red-brown "halo."
     
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  9. LekoBoy

    LekoBoy Active Member

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    My teacher says the biggest problem with the Source Four is that it doesn't soften as nice as other Lekos used to. This makes them better for gobos, but harder to use for acting area lights.
     
  10. Sony

    Sony Active Member

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    This is true, but in my experience Leko's should only be used as Front and Special (Gobo's and spots) lighting. Fill light (Side, Top and backlight which I assume this is what you're refering to when you say Acting Area lights) should be provided by Frenels and Par's. Front light usually requires more focused light for shuttering and defined facelight to create more shadows and depth.
     
    Last edited: Aug 19, 2008
  11. SteveB

    SteveB Well-Known Member

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    Seems a little dogmatic, IMO.

    I like to advise that the designer choose whatever tools - I.E., ellipsoidal, Par, scoop, fresnel, 100w A lamp in a socket, you need for the job and do not pay attention to popular convention or other opinions.

    Experiment until you develop a sense of your own needs and a grasp of what the tools bring to the design.

    I haven't had a fresnel in my theater in 25 years. Few have asked for one. If need be, I can make an S4 ellipsoidal do what a fresnel does, but have yet to master the trick of making a Fresnel project a gobo. I prefer ellipsoidals as side lights, as they offer shuttering off legs and scenery. But this is particular to my space and I would never presume to tell someone that a particular type of fixture should "Never" be used for something.

    My $.02

    Steve B
     
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  12. Sony

    Sony Active Member

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    That's why I stated that it was "In my experience." I personally prefer to stick mostly to the standard...that's not to say I've never tried other methods and fixtures...I just find that the standard way is that way for good reason and IMO is the best. I've used frenels for front light and leko's for top and back light before and I just personally don't like how they look. I do however agree that they are good for side light and such, unfortunately at my college we never had enough lekos to do both the sides and fronts in lekos. I do however enjoy playing with lots of different colors, thats always a lot of fun. :)
     
  13. Serendipity

    Serendipity Active Member Premium Member

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    This may be why almost every designer who uses our Black Box rep plot uses frost with our S4 front light system? (The one who hadn't was using striped gobos, which were supposed to be as hard edged as possible.) I hadn't thought about that reasoning before.
     
  14. cdub260

    cdub260 CBMod CB Mods

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    :shifty:Have you tried drawing on the back of the lens with a sharpie?:lol:
     
  15. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    R114 was sometimes used in 360Qs, but R119 and R132 were invented after the 1992 introduction of the Source4. So your reasoning skills are accurate, 'Dip. :clap:
     
  16. Serendipity

    Serendipity Active Member Premium Member

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    Thanks! :grin: (Yes, R132 is what I had in mind.)


    Hahahaa. But because the ridges of a fresnel lens are on the outside, wouldn't that just cut the light output of the fixture when the light hits the ridges? Which leads me to wonder, where, if there is one, is the second focal point of a fresnel (spotted or flooded)?

    (Nah, what you want to do is draw on the lamp since it's a focal point... :twisted: )
     
  17. Sony

    Sony Active Member

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    Fresnels usually only have a single focal point, as far as I know. The reflector in a Fresnel reflects the light beams so they are in Parallel and then the lens refracts them.
     
    Last edited: Aug 20, 2008
  18. icewolf08

    icewolf08 CBMod CB Mods

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    Only about half of that is true. A Fresnel has a a spheric reflector. With a spheric reflector, all the light is reflected back at the same angle it hit the reflector at (in a perfect point source system). So Yes, the fresnel reflector has only one focus, which is at the lamp, and the light that bounces off the reflector goes back through that same point before hitting the lens.

    Parabolic reflectors put the light into parallel rays.
     
  19. JD

    JD Well-Known Member

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    Projecting a gobo with a Fresnel? No problem, just follow these simple steps:

    1) Remove the glass from the bulb.
    2) Spot weld the gobo to a lamp support about 1/8 inch above the filament facing the front.
    3) Reinstall the glass and suck the air out of the bulb.
    4) Add some inert gas and seal well.
    5) Remove the reflector.
    6) Replace the lens with a PC lens.

    See! Nice gobo projector! (Ignore the big white springs visible on the projection.)
     
  20. quarterfront

    quarterfront Member

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    Projecting a gobo with a Fresnel? No problem.

    1) Remove lens.
    2) Blackwrap over the reflector.
    3) Make a gobo the diameter of the lens.
    4) Insert this gobo where the lens goes.

    Voila. Linnebach projector. Make the gobo out of glass, you can paint on it.

    Okay, admittedly this won't go very sharp. How sharp you get depends on how compact your lamp filament is and the distance from the lamp to the "gobo". And, admittedly, this won't be very bright, a Fres isn't very efficient to begin with and eliminating the reflector cuts, say, 3/8 of what you would normally get out of the mix. But one summer when I was a wee lad doing summerstock I did a production of I'm Not Rappaport using this method to project leaf dapple 'cause I didn't have a bank of lekos to spare and it did the trick.
     
    Last edited: Aug 20, 2008

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