# Instrument Selection



## Grog12 (Mar 4, 2009)

You're designing in a new venue and are deciding on an instrument for your area front light, the FOH position is 25' DS of the edge of the stage, and 30' in the air above stage deck.

Tell me:

1. The throw from position to deck.
2. What instrument you would choose for your front light.
3. What size the beam and or field diamaters are at head high (6'-0")
4. Why you chose the light you did.

Those of us that can do this in our sleep are disqualifed from answering...you know who you are.


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## rochem (Mar 4, 2009)

Sweet, one of these I might actually be able to answer. 

1. Throw would be about 35 feet.

2. Source Four 26°

3. Beam would be 9.4 feet at head height, field would be 15 feet.

4. At 575W, the S4-26° will put out about 120 footcandles, and will have a beam angle of just under 10 feet. Assuming a 40'-50' wide stage, you can use 5 areas across and cover the entire width of the stage. Going up to a 36° only gives you about 60 footcandles, while going down to a 19° will only give you a 7' beam spread.


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## sk8rsdad (Mar 4, 2009)

1 & 3. What rochem said
2. S4 15-30 Zoom lamped at 575W
4. I like the flexibility of zoom instrument for a fixed venue. If you need to free up instruments for specials you can cover the stage fairly well with 3 FOH instruments using broadway-T zoning. If extra punch is needed for saturated gels you can lamp up to 750W.


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## Grog12 (Mar 5, 2009)

rochem said:


> Sweet, one of these I might actually be able to answer.
> 
> 1. Throw would be about 35 feet.
> 
> ...




Tell me how going to a 36degree gives you 60FC


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## rochem (Mar 5, 2009)

Grog12 said:


> Tell me how going to a 36degree gives you 60FC



(all data taken from ETC's S4-36 cut sheet)

I actually skipped a few steps in that calculation without realizing it. At 750W and a 39 foot throw, you would get 59.8 FC, according to the equation: FC = candela / throw^2. However, I should have done the calculation at 575W and with a 35 foot throw to get the distance to head height. Candela with an HPL 575/115 would be 60,893 (90,885*0.67), so you would get about 50 FC.


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## Grog12 (Mar 6, 2009)

While I misread your original post you've done a good job of clarifying.


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## Grog12 (Mar 6, 2009)

sk8rsdad said:


> 1 & 3. What rochem said
> 2. S4 15-30 Zoom lamped at 575W
> 4. I like the flexibility of zoom instrument for a fixed venue. If you need to free up instruments for specials you can cover the stage fairly well with 3 FOH instruments using broadway-T zoning. If extra punch is needed for saturated gels you can lamp up to 750W.



No one ever said this was a rep plot. That being said you need to clarify your answer to #3 as its not just what rochem said. He's using a different instrument. What do you set your zoom too? What size is it set at for typical area light, FOH Specials, and 3 FOH broadway-T zoning? And what are those sizes at head high?


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## sk8rsdad (Mar 6, 2009)

Grog12 said:


> No one ever said this was a rep plot. That being said you need to clarify your answer to #3 as its not just what rochem said. He's using a different instrument. What do you set your zoom too? What size is it set at for typical area light, FOH Specials, and 3 FOH broadway-T zoning? And what are those sizes at head high?




Nobody saiid it wasn't a rep plot. The exact words were "new venue" which for me meant new performance space. I assumed about a 12m proscenium since it's the typical space I'm used to working with these days.

Throw distance is approximately 15m using pythagorean theorem (and some fudge factor for center of beam, height of an average person, and physical displacement from hang point caused by the yoke). Setting the beam angle at 15 degrees yields a field diameter of about 4m at about 1800 lux if lamped with a 750W lamp (approximating from the photometric charts rather than breaking out the calculator). So tweaking them up to 16 or 17 degrees with soft focus would provide good blending and shuttering. Using McCandless method increases the throw distance so dialing back to 15 degrees would cover about 4.5m.


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## rochem (Mar 7, 2009)

sk8rsdad said:


> If you need to free up instruments for specials you can cover the stage fairly well with 3 FOH instruments using broadway-T zoning.



I'm afraid I'm not familiar with the term "Broadway-T Zoning". Care to explain?


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## sk8rsdad (Mar 8, 2009)

rochem said:


> I'm afraid I'm not familiar with the term "Broadway-T Zoning". Care to explain?



I'm not sure where I got the term from anymore, but I think I read about it in a book. I expect there are many names for it.

Primary light comes from high sides with lower intensity facial fill light from the front. In a plan view, the frontal light is the base of the T and the high sides are on either end of the top of the T.

It uses half the FOH instruments that McCandless would use to light the same area, and shortens the shadows somewhat since the frontal light is coming from a steeper angle.


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