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Frames or Barndoors?


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#1 Brian Baker

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Posted 23 December 2006 - 02:37 PM

This may be too broad of a querstion:

What are some of the differences (effects on lighting) that adding gel/diffusion directly to a barndoor Vs adding the diff/gel to an open frame afront of the unit? And vice versa?

Are there certain effects that one can acheive better/only with either method?

Are there any immediate aesthetic differences to using either?

Any comment / direction is greatly appreciated.

Thanks in advance,
BtB
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#2 Frank Barrera

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Posted 23 December 2006 - 04:41 PM

adding colored gel to the barndoors is cheaper because you need less gel to do it. On the other hand, if it's a deep color such as a theatrical color it can burn if too close to the source; ie: on the doors. But the color will not be effected whether it's on the doors or on an empty (not open) frame a couple of feet away.

However, when using diffusion it's a very different story. First of all i have never seen diffusion burn on a barn door. But more importantly the further you take the diffusion away from the source the softer the effect will be. The rule of thumbs is the bigger the diffusion the more wrap it will have therefore the softer it will appear. For example if you take some 216 and put it on the barn doors of a 2K Fresnel to light a subject 10 feet away it will not appear as soft as the same 2K going through a 4' X 4' frame of 216 placed 4 feet away from the source. Furthermore the larger source (the 4X4) will be much more difficult to cut with solid flags than the former set up with 216 on the doors. Another rule of thumb is that when ever using a frame it is best to have the source fill the frame. In other words, it is not optimum to see the spot of the beam in your frame. You can also place the diffusion "on the inside of the doors". Which is right right next to where the scrims would go. now here you can control the beam with the doors but also may see some burning if the diff makes contact with a hot scrim.

This is a fundamental exercise that should be practiced by all students on day one.

F
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#3 Brian Baker

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Posted 23 December 2006 - 05:23 PM

Thank you very much for your insight.
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#4 David Mullen ASC

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Posted 23 December 2006 - 05:57 PM

Frank pretty much summed it up... how far you put the color gel is mainly about the heat issue and how it can cause fading. Unless you are using the gel on a very powerful spotted-in light or PAR light with a narrow lens, usually you will put it on the barndoors. Now a really big unit like an 18K HMI Frensel will probably not have barndoors and you'll need the gel on a 4'x4' frame just to cover the spread of the unit.

But with diffusion, the distance you put the diffusion is mainly about how soft you want the effect to be versus how easily you want to be able to flag it (larger sources require larger flags, etc.) A larger frame of diffusion farther away is a softer source than a smaller piece of diffusion on the barndoors.
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#5 Jon Rosenbloom

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Posted 24 December 2006 - 10:14 AM

Also, the further away the diff from the lamp, the more flags you will need to contain the "raw spill." Any flags you use in front of the diff will need to be bigger. It always helps to consider where the frame line is when deciding where to put the diff, so that toppers and siders don't start creeping into the shot. If the light is all the way up on the stand, it's easier/faster to change the gel if it's on a frame in a grip stand rather than on the barn doors.
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#6 Brian Baker

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Posted 24 December 2006 - 11:08 PM

Jim + Jon

Thanks very much for your contributions. I really appreciate it.

I'll be doing a few tests with distance of diffusion in the near future... I'm also curious to see the correlation between fall-off and distance -- assuming that there will be less, the further the diff moves from the light.

But again, thanks a lot.
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#7 David Mullen ASC

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Posted 25 December 2006 - 12:23 AM

When putting a frame of diffusion in front of a light, the frame itself becomes the source of light on the subject. The inverse square law that governs fall-off only really applies to a point source, but the general idea can be applied to soft light, in that the light falls-off proportionally. If you are very close to the source (in this case, the diffusion frame) then moving closer or farther from the source produces a visible change in brightness, whereas if the source is far away, then moving a few feet closer or farther doesn't cause much of a change in intensity.

If you are talking about the loss of light output due to the diffusion, that partially depends on the heaviness of the diffusion material and how well the light spreads to fill the frame. Since the frame of the diffusion becomes the source, one of the backwards things to note is that when you flood the lamp behind the frame, the source (the frame) becomes brighter because it is filled more completely, compared to when you spot the light into the frame and only use a small area of the frame.
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#8 Brian Baker

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Posted 02 January 2007 - 12:43 AM

David,

I was speaking in reference to lose of intensity.

And as always, your post is very educational + helpful.

Thank you,
BtB
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#9 brian hendry

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Posted 07 January 2007 - 10:29 AM

looks like everyone already covered it....only thing i can possibly say is try and use cutters more so than the doors on the head, let your grips do the work....and im sure you already know this, but when using bigger heads try and match the color with the angle of the head, always use color then dif, and match the angle of the head as well. and fill it out like everyone already said.
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