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Light falloff in a canopy?
Old 06-01-2007, 08:02 PM   #1 (permalink)
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In my insanity, I have bought a 18' x 30' canopy to use as a portable studio. Yes, I'm nuts. However, the canopy has a white tarp top. To shoot bikes with, I'm going to make a large difusion panel. 5' x 18' and hang it like a ceiling in the canopy at one end. I'm going to place two WL x3200's above the panel. The bike will be place about 3 ft from the end of the canopy on the inside, directly below the panel. I'm going to overpower the daylight and use a ND filter. I'm putting the bike so close to the end of the canopy to catch the ambient light coming off the bike. I'll be shooting into the canopy. Inside the canopy, I have a white backdrop cloth that spans the width of the canopy (18'). (I could get an extra 2 more feet at each end. the cloth is 22' long.)

Now, having said all this, my question follows.

How far back from the subject (the bike) should I put the backdrop? I'm not looking to have the backdrop show up has white, but somewhere between a light and medium gray. Maybe a gradient kind of effect.

The reason I ask this is because it would be easy to hang the rod for the backdrop on the canopy legs, which would put it about 6 - 7 feet away from the bike. If I don't attach it to the legs, then i need to build a couple of support legs for the backdrop rod, and then I could put the backdrop rod at any distance I needed, til I reached the other end of the canopy.

Any suggestions would be appreciated.
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Re: Light falloff in a canopy?
Old 06-01-2007, 11:48 PM   #2 (permalink)
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Why not just take a couple of s hooks, big enough to fit over the horizontal supports running between the vertical posts, a length of parachute cord, and suspend your backdrop off of the parachute cord. This way, you can move the s hooks forward or backwards, to change your background depth? ( Did i make sense on this?)
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Re: Light falloff in a canopy?
Old 06-02-2007, 12:05 AM   #3 (permalink)
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Yeah you made sense. I already have 1 x 2 alum tubing that is two pieces that I have made a joint for and can put them together to span the width. I still need to support the middle of the bar with a chain or cable from above to get it level. The legs are 1 5/8" 14ga. the rest of the pipe is 18 ga. I didn't want to put any weight on the purlins and I want to hang the bar under the purlins so I can get the most width I can from the backdrop cloth. The bar is a little over 19'. The cloth is 22'. If I had too, I could stick something in the ends of the bar to get the full 22'.
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Re: Light falloff in a canopy?
Old 06-02-2007, 07:29 AM   #4 (permalink)
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To many variables to give a very good answer. When setting up the backdrop based on light falloff from your light source you need to know how much ambient light will be coming into the canopy. This is going to change throughout the day as the sun moves around also. What type of lens will you be using? If you move the backdrop further back you will need to be shooting with a longer lens to keep from showing the ends of the canvas. How much space in front of the canopy will you have to work with?

Given a choice I would want as much room as I could get behind the bikes (minimum of 6') and shoot with a longer lens if you have room in front... but that's just me!

Great idea, good luck pulling it off!
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Re: Light falloff in a canopy?
Old 06-02-2007, 10:27 AM   #5 (permalink)
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Not to burst your bubble...but do you have any idea how hot it's going to get in the roof section of your canopy...without 2 WL3200s even!

I shoot sports events all summer and use a 10x20' canopy for my viewing and sales tent. It gets hot in the tent...very hot. I have two 16" fans going to whole time and it's still hot. Once a small child let go of her animal shaped balloon..it floated right to the top. When I pull the string, it got caught up in one of the joints...so I stepped up on a chair to unhook it. I couldn't beleive how much hotter it was. At least 4-5 degrees C...so like 10-14 degrees F. Even with airflow through the canopy, very little gets up into the roof area.

If you stick two 3200s up there....you had better makes sure you have some way of exhausting the air. Especially since you are putting a diffuser roof up. There will be no airflow in that space...and it doesn't take much to *melt* the canopy material. That's right melt...which I did once use two 500W halogen contruction lights at night on my older 10x10 canopy. Melted two small holes in the canopy top and I had to buy a replacement. The lights were almost 6 inches away from the canopy and it was only 16 degree C that night...not exactly hot.

Just want to throw that out there....
sean
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