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26 degree issue

Discussion in 'Lighting and Electrics' started by bdkdesigns, May 13, 2008.

  1. bdkdesigns

    bdkdesigns Active Member Fight Leukemia

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    I couldn't find anything on this using the search. We have about 15-20 26 degree barrels that act like zooms. Basically, with the barrel all the way in, they have a sharp edge with the correct beam spread. Start running the barrel out and it slowly starts zooming in with a slight fuzz to it. All the way out produces a soft focus w/ a 19 degree beam spread.

    They are the Rev-J barrels. I pulled them apart and the dot is facing the right direction and the lens is in the correct spot. Bench focus is not the issue because swapping barrels with one that behaves properly only moves the issue to a new location. Our only solution has been to drop diffusion into it to achieve the desired softness.

    Anyone ever hear of or have this problem before? I can't think of anything else at this point other than several defective lenses.
     
  2. Footer

    Footer Senior Team Senior Team Premium Member

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    Thats what they are supposed to do. When you "run the barrel" the light will get a bit smaller but will push pool in a bit. If you are still getting a sharp clean edge with the barrel in, then the fixture sounds like it is working properly. I would suggest buying some more R119 or R132 frost if you so desire. Is this your entire 26 deg stock or just a few instruments?
     
  3. bdkdesigns

    bdkdesigns Active Member Fight Leukemia

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    Just a few. All the way in and all the way out should both be soft focuses. However with these select few, all the way in is sharp, and all the way out is soft however excessively smaller than any of the others in the system. I know R119 and R132 would solve it, however I am trying to figure out if I can actually fix them rather than an annoying temporary fix since it slows down focus to get the correct gel in it to match the rest of the system.

    We actually always keep in stock anywhere from 10-30 sheets of every Rosco color uncut since it takes forever to receive shipment in Montana. So the frost isn't an issue since we have more than enough of it. I'd just like to actually fix them if possible.
     
  4. Footer

    Footer Senior Team Senior Team Premium Member

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    Give ETC a call, they might have a solution. Could have been a bad batch, doubt it, but could have been.
     
  5. BrentSmith

    BrentSmith Member

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    Have you tired dissecting a 'good" barrel and 'bad' side by side? If the problem is indeed in the barrel, there should be some visible difference between them.
     
  6. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    The one thing you didn't state was that the dot on the lens was black. I've never heard of anything to explain the problems you're having. Very curious as to what's wrong. In my experience, a hard edge on every SourceFour™ is achieved with the lens almost all the way "out" (away from the lamp), as the attachment indicates, vaguely.
     

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  7. Grog12

    Grog12 CBMod CB Mods Premium Member

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    It doesn't say that at all...in fact it shows two soft focuses and a hard focus.

    Here's something to remember when talking about focus is that also matters how far the throw is where the barrell is roughly for sharp at 10' is different than at 30'.

    I've had the same issues as the OP...generally I have it with instruments out of bench. At my current place of occupation I've had the issue more often than just with instruments out of bench and with those instruments I usually hard focus it and throw in 119.
     
  8. Clark

    Clark Member

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    Exactly, the "focus knob" on all ERS instruments is really just changing to focal length of the optical system. What focal length achieves a hard edge will change drastically as one changes the throw distance, though it will tend to be in the middle for most throws.

    This is why you should direct your light before adjusting focus when focusing conventional fixtures.

    Clark
     
  9. Charc

    Charc Well-Known Member

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    Weird? Tonight I focused a S4... sharp was all the way in.
     
  10. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    I was referring to the not applicable under Soft Focus Forward (Lamp "Cosine"). I know of very few people who purposefully bench their SourceFour™s to "other than cosine".

    I'll agree that sharpness varies, somewhat, with throw distance. I generally use the closest fixture that produces an 8-12' pool at any given distance. And the barrel is more often than not closer to out than in for a sharp focus.

    However, the EFL of a lens system is independent of the len(ses)'s distance from the lamp. The only way to change a fixture's focal length is to change the distance between the lenses, as described in this formula:
    For a two-lens system: EFL= (f1*f2)/(f1+f2-d), where EFL=Effective Focal Length, f1=Focal Length of Lens1, f2=Focal Length of Lens2, d=Distance between focal points of the two lenses.
    This is the principal of optics that allows zoom lenses to function, and is among the reasons why 4.5x6.5s, 6x9s, 6x12s, and 6x16s have two lenses.

    [user]bdkdesigns[/user], were all these 26° tubes purchased at the same time? I'm suspecting either the wrong lens or a bad batch of lenses. You say you have ruled out bench focus. I wish I had some fixtures and lenses in my garage to attempt to duplicate your symptoms.

    Try this, just as an experiment: Put a gobo, any gobo, in one of your bad 26° fixtures. Does the gobo remain sharp but get smaller as you move the tube out?

    What degree and what was the exact throw distance? And what time was it? What did you have in your pockets at the time? Are the walls in your room still "live" with EMR?:twisted:
     
    Last edited: May 14, 2008
  11. Grog12

    Grog12 CBMod CB Mods Premium Member

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    A man after my own heart.....except that more often than not mine are sharp in the middle.

    Except that you were trying to tell us where a hard edge is achieved. According to your chart there is a soft focus forward (lens away from the lamp), a soft focus backward (lens towards close to the lamp) and a sharp focus, which leads one to believe that it would be in the middle. As opposed to "almost all the way out".
     
    Last edited: May 14, 2008

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