# Conventional Fixtures Changing the degree of Source Four Barrel

Discussion in 'Lighting and Electrics' started by Shawncfer, May 24, 2009.

1. ### ShawncferActive Member

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So I was wondering,

If I take a 19 degree barrel, open it up, and move then lens up, could that turn it in to a turn a 36 degree?

2. ### midgetgreen11Active Member

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Rhode Island
No, 36 degree barrels contain two lenses in them, on each end of the barrel.

3. ### derekleffewResident CurmudgeonSenior TeamPremium Member

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To further clarify, each of the lenses is unique. The same barrel is used with five locations for 19°, 26°, 50° and two lenses making 36°.

The Colortran 5/50 (and from the 1980s MiniEllipse) line of ERSs exploited the formula
EFL = (f1 * f2) / (f1 + f2 - d) [where EFL=Effective Focal Length, f1=Focal Length of Lens1, f2=Focal Length of Lens2, d=Distance between Lenses.]
to allow different effective focal lengths from the same two lenses; a principle also used by Zoom Ellipsoidals.

4. ### ShawncferActive Member

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so just to make sure I got this right, Each lense is different, so (excluding the 36 degree) if I moke the lense it wont make a difference?

5. ### jmabrayActive Member

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Dallas, Texas
It will make a difference - it will ruin your fixture. You won't get another degree measurement, you won't be able to focus your fixture - it just won't work correctly anymore.

6. ### cdub260CBModCB Mods

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To expand a little on the last point, the lenses are all different sizes and will only fit in one of the five slots, making it impossible to move them from one point in the barrel to another.

7. ### CliffordActive Member

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San Diego, California
For those who are visual learners:

This is the cross-section of a Source4 19° lens tube.

And

This is the cross-section of a Source4 36° lens tube.

Images from B&H Photo Video

Shawncfer and (deleted member) like this.