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Grid Cloth and Frames


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#1 Barry Cheong

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Posted 03 July 2006 - 10:52 AM

I've been putting grid cloth onto 3x3 aluminum gel frames and taping them on with double sided tape on the surface of the frame all away around and then putting cloth tape around the edges. I'm hoping to keep the grid cloth permanently mounted. After a few days though the grid cloth gets all loose and puckers, like it's being stretched, and I have to go and pull it off and re-mount it. Any suggestions on how to keep it nice and tight on the frame?
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#2 David Mullen ASC

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Posted 03 July 2006 - 11:00 AM

Sort of inevitable to have to restretch them, but you may have better luck using snot tape on the frame instead of cloth tape. You may have to restretch them less often.
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#3 Sasuke

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Posted 03 July 2006 - 01:06 PM

I've been putting grid cloth onto 3x3 aluminum gel frames and taping them on with double sided tape on the surface of the frame all away around and then putting cloth tape around the edges. I'm hoping to keep the grid cloth permanently mounted. After a few days though the grid cloth gets all loose and puckers, like it's being stretched, and I have to go and pull it off and re-mount it. Any suggestions on how to keep it nice and tight on the frame?



Get a hole punch from the school supply section at your local drug store. Punch holes in the fabric about every 5 inches along the border, at least 2 inches in from the edge. Then use Matthties to hold them to the frame. Check these out :

http://cinemasupplie...o.net/ma12.html

FILMTOOLS filmtools.com SELLS them. Hope this helps.
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#4 Phil Rhodes

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Posted 03 July 2006 - 04:12 PM

Hi,

I made up my diffusion frames using elastic loops, so it's always under tension.

Phil
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#5 Stuart Brereton

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Posted 03 July 2006 - 04:26 PM

Mine too, a couple of inches of elastic sewn at 45 degrees to the corner should do the job.
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#6 G McMahon

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Posted 06 July 2006 - 10:53 AM

How is the look of grid cloth different to that of say 216? More diffusion? More loss of stops? And referring to the hard vs. soft post, disregarding the size of the source of diffusion (the whole factor of the larger broad source the softer the light is), is the light more diffused the further away the frame is from the point light source? I believe so, but sometimes I see things which seem to defy all previous shooting and physics, and scratch my head and think I should go and work in the family business.
Thanks,
Graeme

Edited by G McMahon, 06 July 2006 - 10:55 AM.

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#7 David Mullen ASC

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Posted 06 July 2006 - 11:20 AM

What determines the softness of the light is the SIZE of the source (the source being the diffusion frame, not the light behind it) relative to the DISTANCE to the subject.

In other words, if you were the subject and looked over at a 4'x4' frame that was close to you and a 20'x20' frame that was much farther away, it would be possible that from your perspective, they were the same size in your field of vision and therefore would be the same degree of softness, cast the same soft shadows.

The difference would be fall-off, not softness: if you stepped a little closer or farther towards the far-away 20'x20' frame, you would not get much brighter or dimmer. But if you stepped closer or father to the nearby 4'x4' frame, you'd get visibly brighter and darker.

Now if you use a thin diffusion material or put the light too close to the frame, you get a hot spot in the center, so now that hot spot is more the true "size" of the source and therefore the light is less soft. If you flood-out and back-up the light so that the frame is filled evenly and/or go to a heavier diffusion material, the frame will be filled evenly with no hot center and now the size of the source is at its maximum, the size of the frame. Adding even heavier diffusion at this point will just make the light dimmer, not softer.

Not to say that you must fill a diffusion evenly with no hot spot, because sometimes you do want less softness or need more light output, hence why we carry different grades of diffusion like Opal, 250, etc.

Since no diffuser is perfect, it does impart some texture and even color cast to the softlight -- for example, full grid cloth is a very dense material and so is muslin, but grid cloth is more neutral in color cast, and muslin is a little porous, so a faint amount of hard light can leak through all of the diffused light, sort of a mix.

Or look at silk, which causes the light behind it to produce a star-shaped smear, plus it also is a little porous. That becomes the shape of your soft light, with a faint hardness creeping through. So fabrics like silk and muslin produce a textured softlight whereas plastic diffusers tend to create a simpler softlight with less texture.

But also remember that they are all similar in some ways so don't get too worked up over it. You can mix and match all the time. I've doubled-diffused lights many times, like putting a big light through a 6'x'6' frame of Light Grid and then thrown a 4'x4' frame of 216 between the frame and the light to further soften it. Sometimes I think people overthink diffusion. It partly just a practical matter as to what is the best technique.
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#8 G McMahon

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Posted 07 July 2006 - 11:02 AM

What determines the softness of the light is the SIZE of the source (the source being the diffusion frame, not the light behind it) relative to the DISTANCE to the subject.

In other words, if you were the subject and looked over at a 4'x4' frame that was close to you and a 20'x20' frame that was much farther away, it would be possible that from your perspective, they were the same size in your field of vision and therefore would be the same degree of softness, cast the same soft shadows.

The difference would be fall-off, not softness: if you stepped a little closer or farther towards the far-away 20'x20' frame, you would not get much brighter or dimmer. But if you stepped closer or father to the nearby 4'x4' frame, you'd get visibly brighter and darker.

Now if you use a thin diffusion material or put the light too close to the frame, you get a hot spot in the center, so now that hot spot is more the true "size" of the source and therefore the light is less soft. If you flood-out and back-up the light so that the frame is filled evenly and/or go to a heavier diffusion material, the frame will be filled evenly with no hot center and now the size of the source is at its maximum, the size of the frame. Adding even heavier diffusion at this point will just make the light dimmer, not softer.

Not to say that you must fill a diffusion evenly with no hot spot, because sometimes you do want less softness or need more light output, hence why we carry different grades of diffusion like Opal, 250, etc.

Since no diffuser is perfect, it does impart some texture and even color cast to the softlight -- for example, full grid cloth is a very dense material and so is muslin, but grid cloth is more neutral in color cast, and muslin is a little porous, so a faint amount of hard light can leak through all of the diffused light, sort of a mix.

Or look at silk, which causes the light behind it to produce a star-shaped smear, plus it also is a little porous. That becomes the shape of your soft light, with a faint hardness creeping through. So fabrics like silk and muslin produce a textured softlight whereas plastic diffusers tend to create a simpler softlight with less texture.

But also remember that they are all similar in some ways so don't get too worked up over it. You can mix and match all the time. I've doubled-diffused lights many times, like putting a big light through a 6'x'6' frame of Light Grid and then thrown a 4'x4' frame of 216 between the frame and the light to further soften it. Sometimes I think people overthink diffusion. It partly just a practical matter as to what is the best technique.


To be more specific, light waves come from source "z"; Subject is at point "X". Point X and Z are constants. A diffusion frame of "Y by Y" is at point "a" and a shot is taken.
Now the frame is moved to position "b", closer to subject "X", The frame is changed so the size is proportionate to that of position ?a", (closer to subject decreasing the size of the frame to {1/p x Y} x {1/p x Y} - "P" being a number that would allow the line of sight at "X" to see the frame at equal size.
A shot is taken. Looking at the quality of light, the light waves from the source (frame), would there be any difference, or would that only show on the backgrounds that more light was splashed on the backgrounds when the frame was at point "a".
Make sense, I feel lazy that I haven't just tested this.
Thanks much,
Graeme
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#9 David Mullen ASC

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Posted 07 July 2006 - 11:26 AM

The fall-off in intensity would be more noticeable on the small frame up close to the subject. If it's really close, you can see the effect on the face where the tip of the side closest to the frame is very hot.
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#10 G McMahon

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Posted 08 July 2006 - 03:12 PM

In essence, the inverse square law would take affect from there by being the new light source?
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#11 David Mullen ASC

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Posted 08 July 2006 - 09:22 PM

In essence, the inverse square law would take affect from there by being the new light source?


Well, sort of, but the inverse square law technically applies to a point source so the exact mathematics don't apply.
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