# 6x9 or degree

Discussion in 'Lighting and Electrics' started by mixmaster, Aug 12, 2008.

1. ### mixmasterActive Member

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I'm a sound guy by trade most of the time, although I do enjoy lighting work too. I'm standing in for my boss who's on an extended vacation and had a question come up that I need help answering. A show coming in is looking at our FOH lighting inventory, all of which is indicated in degrees of beam width (19 and 24 degree Source 4), it's silk screened right on the end of the barrel. That's fine I understand that. The LD for the show is looking for more ellipsoidals, but is referring to them dimensionally, as 6x9s or 6x12s. I understand those terms also but am having trouble making the conversion between dimensionals and degrees. I've worked in venues that use one term or the other but never had to mix them. Is there a conversion chart that someone could post, something like a 6x9 is an xx degree instrument?
Matt

2. ### waynehoskinsActive Member

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4.5x6 = 50
6x9 = 36 or 40
6x12 = 26 or 30
6x16 = 19 or 20
6x22 = 10

Altman and CT like to use even-ten-degrees notation, ETC and Strand like to use the other numbers, which are in my experience more commonly quoted.

You can tell what era somebody learned lighting in by what they call fixtures.

3. ### CharcWell-Known Member

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I'm curious, so someone correct me if I'm wrong, but here is my hypothesis:

19, 26, and 36 are what the x9-x16 actually breakdown into as real angles. I hypothesized that ETC went with these angles, so that the beam spreads would be familiar to LDs, and thus facilitate the transition to the S4. Whereas, it looks like other manufacturers who went with 20, 30, 40, were trying to have "nicer" numbers, akin to the metric system in its logic.

Was I close?

4. ### waynehoskinsActive Member

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That's been my thought on it. Alt's and CT's (and maybe others; I forget) numbers were picked because they're nicer (and that seems to have been the trend in the '80s: see 1KL). After all, why use such an archaic description as the descriptions of the lens geometry to express the size of a unit when you could just use a beamwidth in degrees? Especially when your fixture may not even have a pair of 6" optics (see S4).

I learned the lens geometry notation first, and then the ETC/Strand-style notation. When I have to use Alt or CT fixtures, I end up converting that to geometry in my mind: "okay, a 30 is a kluge of a 6x12..."

By the way, I left something off earlier:
6x22 = 10 = stupid front-heavy
5 degree = why?

5. ### cdub260CBModCB Mods

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As I understand it in the 6xwhatever notation, a 6x9 was an elipsoidal reflector spotlight with 6 inch lenses that had the focal point of the beam 9 inches out from the front of the light. A 6x12 would have it's focal point 12 inches from the end of the light, etc.

As an experiment, you might try putting on a thick pair of gloves and holding your hand 16 inches from the front of a 6x16 or 19 degree. I did this, probably 15 or so years ago, and smoked a ratty old pair of gloves. Just don't try putting your bare hand in the beam.

6. ### CharcWell-Known Member

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I don't think it's from the front of the light, but rather the center of the lamp. Think of the two focal points of an ellipse.

7. ### CharcWell-Known Member

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I think isn't the 6x22 something like 11º or 12º? The fact that it's a "torpedo" is a PITA, and it's obnoxious and front heavy, but still it's alright.

5º, clearly there was a need for this unit. I can think of some applications, and most have to do with really long throws, or really tight shows, or possibly the homebrew followspot?

8. ### cdub260CBModCB Mods

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Why use a 5 degree?

My venue is a 2600 seat ampetheatre. From my rear of house trusses, the only lights that are affective are 5 degrees, 10 degrees, and 19 degrees.

As for the issue of front heavy lights, while is true of my old Colortran 5 degrees and 10 degrees, which I haven't used in the last 5 years, are all around heavy lights, my ETC Source 4, 5 degrees and 10 degrees have 1/4 inch thick plastic fresnel type lenses, making them only slightly heavier than a standard Source 4. Focusing them can be a challenge, due to the long barrel, but once you learn to compensate for that issue, they're actually fairly easy to use.

9. ### CharcWell-Known Member

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I take it you don't have any 14º units?

10. ### LightStudActive Member

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Hogwash. You DO know that 6x9 and 6x12 have TWO lenses, don't you? So much for your understanding. Do an search for "effective focal length" of a lens system for the formulas.

As to others, Berkey Colortran may have bben the first to do the 30,40,50 degree with the horrible, but great for it's time and better than the Altman 3 1/2x6,8,10,12; MiniEllipse--still a good concept becuase to change degrees you just opened the lens tube and put the same lenses in different slots. Through the 80s/90s Strand and Colortran continued with 5, 10, 15, 20, 30, 40, 50 degree units, until ETC took a huge step backwards by saddling us with 19, 26, 36 units. Had they had any confidence in the success of the sourceFour, they wouldn't have had to use the "it's the same size beam as the 360Q" sales pitch. Maybe it was just that they could obtain lenses in the focal lengths to achieve those degrees, which were close enough to the Altman units. Hell, it took them until 2005 to produce a fixture with a 6 inch lens. Bigger lens=more light through it. ALL UNITS SPACE ON 18" CENTERS, so why the need for a fixture smaller than a 6"Leko? Think what the Source4 could be if the had used six inch diameter lenses? Maybe wouldn't have need a 750 version, and I'm still waiting for a 1000watt, but it will probably be a 975watt lamp. Sorry to rant.

11. ### derekleffewResident CurmudgeonSenior TeamPremium Member

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The fact that one can interchange lens tubes, as well as the fact that all ERS fixtures in a family have the exact same reflector, would indicate flawed logic.

I don't think it was explicitly stated above, in the FEL-based units, the 10° was an 8x13, and the 5° a 10x23, single plano-convex lens.

12. ### CharcWell-Known Member

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Your statement makes absolutely no sense.

That's the whole point. One point is constant, the lamp, inside the reflector. However, the second focal point will change, based on the lense.

13. ### cdub260CBModCB Mods

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As a matter of fact I do know that they have two lenses, having first worked with Altman 6xwhatevers 19 years ago.

As for Colortran Mini's, I have 40 of them in my inventory. While I agree that they are a good concept (The ability to quickly change from one beamspread to another is always a good thing.), they do have their drawbacks. Foremost among those drawbacks is that even a well maintained Colortran Mini doesn't have a lot of punch. This is in large part because it can be a little tricky locking down the lamp alignment, not impossible, mind you, just tricky. Also, on the subject of the lamp, why did Colortran pick a lamp with a mini screw base? Have you ever tried to change one of these things? Unless I wear gloves, I have a hard time not leaving fingerprints all over the lamp. Another issue, though a relatively minor one, is the non-standard gel frames and gobo holders. Of course, the same thing could have been said about the Source 4 before it became the standard.

14. ### SeanActive Member

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Umm.... except 6.25" WAS used in fixtures before the S4.....check out Altman's Mini-zoom.

--Sean

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15. ### mixmasterActive Member

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Thanks to everyone for their timely replies. I knew the answer was out there. This is what I get for taking over the whole department for a month.
Matt

16. ### Darthrob13Active Member

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Don't forget the 1KL......(shutter at the box of light)

17. ### cdub260CBModCB Mods

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Thanks for the correction. I've never worked with that fixture.

18. ### gafftapegreeniaCBModCB Mods

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Did someone say 1KL?

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19. ### derekleffewResident CurmudgeonSenior TeamPremium Member

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Could you elaborate further? I'm more than a little confused as to how the Primary Focal Point (filament) remains constant, and yet the Secondary Focal Point ("lense," says you? Is that your final answer?) will change, without some alteration of the size or shape of the reflector. Does a 490 have a different distance between its reflector's focal points than a 405? I thought a 6x22 used the exact same reflector as a 4.5x6.5? Do Variable Focal Length ERSs (Zooms) vary their reflector somehow when moving the Lens knobs?

How ABOUT a diagram, this time depicting a longitudinal section of an Ellipsoidal Reflector Spotlight, with a few representational paths of its light rays. If I'm not mistaken, there's one in A Method of Lighting the Stage. Stanley McCandless. Theatre Arts Books. First publication, 1932. (There might even be one in that shaver guy's book, on page 54.)

20. ### CharcWell-Known Member

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I'm essentially disregarding what you're writing, and attempting to explain my perceived understanding of ERSs, but am open to correction.

Looking back at the previous diagram, the Primary Focal Point is the Filament, and that point is static for the 405 through 490, simply because all of those units use the same lamp, same housing, and same reflector. That makes their relationship to each other constant. If you were to remove the barrel from both your hypothetical 405, and 490, then the output of light from both bodies should be the same, no?

No when you put in the barrel, you're also putting in the lens, or lenses, whatever the case may be for whichever barrel you're using, you introduce a new factor into the path of the light. These optics direct the light to the Secondary Focal Point, but are not themselves the Secondary Focal Point.

The Primary focal point has to be the lamp (filament), because that's what the source is. The secondary focal point is where the light, once again, (theoretically) comes back to one point, before spreading out again. The focal length would be the distance between the foci, right?

Here is another diagram: