How to avoid shadows on backdrop?

Lots of excellent information here, and I've been reading as much as I have time for.

A problem that I have frequently is shadows on backdrops, and even too much light on black backdrops, with both umbrellas and soft boxes. Near as I can tell the best ways to avoid it are A) Don't position the subject too close to the backdrop. B) Position the strobe, or main strobe, above the subject. C) Use an additional strobe to fill the shadow.

A and B seem hard to accomplish in a small environment. I've been reading on here about small rooms with low ceilings, and it seems obvious why a large studio would be advantageous.

And tips would be appreciated. I'll keep reading the excellent info here.

A.

D. Grid your lights and don't aim them at the backdrop or the model, feather them across instead and light your backdrop as you like seperately

Depending.... the type of modifier you use. Larger and/or more difused modifier can help minimize shadows. Flag the light.

Light the background with other lights.

Change the color of the background.

Edit in post

Angmo wrote in post #18220201
Depending.... the type of modifier you use. Larger and/or more difused modifier can help minimize shadows. Flag the light.

Light the background with other lights.

Change the color of the background.

Edit in post

Have a look at THIS. This session was shot in her living room, about 10 feet from dining room table to sliding glass door. I was under the table for most of the shoot.
Large PLM camera left, mid-sized PLM for fill over camera position, or just right. Two mid-sized PLMs for kickers and background. All had Einstein 640s in them. White muslin hanging from a background stand setup against the sliding glass door.

D. Use a blacker backdrop.

dmward wrote in post #18221243
Have a look at THIS. This session was shot in her living room, about 10 feet from dining room table to sliding glass door. I was under the table for most of the shoot.
Large PLM camera left, mid-sized PLM for fill over camera position, or just right. Two mid-sized PLMs for kickers and background. All had Einstein 640s in them. White muslin hanging from a background stand setup against the sliding glass door.

I'd be under a table too.

A lot of good advice above.

To risk stating the blatantly obvious, your choices come down to not letting your lights directly or indirectly fall upon the backdrop or, if they do, having what light falls on the backdrop be overpowered by other lights or be so little it isn't relevant to the exposure.

Looked at in this way, you can see how all the advice above makes sense. If you use a grid on your source, it limits the light coming out of the modifier, making the light coming out less wide (kind of like narrowing a flashlight beam). This makes it easier not to hit the background with the beam. If you put in flags, you are basically blocking light which would hit the background. If you are feathering the light, you are aiming the light so it doesn't fall on the background. If you are using a darker background (black velvet is about as dark as it gets), you are reducing the amount of light the background can reflect (with any luck to the point where the exposure doesn't pick it up). Moving the subject further from the background either changes the relationship to the lights so the light (and hence the shadow) falls before the background or the light has faded enough before it hits the background. If you aim lights at the background behind the subject, you are overpowering the light which is casting a shadow.

I bring all these obvious things up because it is much easier, at least for me, to only need to consider a basic idea rather than run through a list of things which might work . It also helps me see how I can change the relationships between light, subject and background.

Another cool trick is that moving the light source closer to the subject reduces how much hits the background, relatively speaking. We often think the further back we pull the light, the less gets on the background. But it's all about how close it is to the subject and how many times that distance it is to the background. It's the relationship between the two distances which counts.

The reason is that there is a larger percentage hitting the subject, who is closer, which is what you expose for. Light falls off more quickly than the distance.

If you can get the light one foot from the subject and they are seven feet in front of the background, there will be six stops of difference (plenty for it not to matter if you are exposing for the light which is one foot away). Even if you only have 4.6 feet, it is five stops. If you have three feet to the background from your subject and the light is one foot away, you still have four stops of light difference (which is 1/16th the light)--quite a difference.

The technical name for this, if you want to look it up or do calculations, is "the inverse square law."

I have started liking shadows on the back drop. Regarding don't position close to back drop, I can say you can place right next to back drop and not have a shadow. Personally I would like to see your problem shots.

KatManDEW wrote in post #18220171
A problem that I have frequently is shadows on backdrops, and even too much light on black backdrops, with both umbrellas and soft boxes. Near as I can tell the best ways to avoid it are A) Don't position the subject too close to the backdrop. B) Position the strobe, or main strobe, above the subject. C) Use an additional strobe to fill the shadow.

First of all, Fill NEVER 'fills shadows', it merely reduces the contrast difference of the shadow...once the shadow is cast it never goes away!

Of the three points you listed, the first two are to make it so your shadows cast on the background merely have fallen out of the line of sight of the lens (down, and/or to the side) , or are hidden by the body of the subject...and this is true regardless of the light comes from the Main or from the Fill source.

More distance to the background, COMBINED with less distance to the subject, takes advantage of the Inverse Square law to reduce the relative intensity of the light on the background vs. the subject. For example...

• Subject-to-light distance 2.8', background-to-light distance 5.6' (background 2.8' behind subject), light on backdrop is -2EV relative to subject
  
• Subject-to-light distance 4', background-to-light distance 6.8' (background 2.8' behind subject), light on backdrop is -1.5EV relative to subject
  
• Subject-to-light distance 5.6', background-to-light distance 8.4' (background 2.8' behind subject), light on backdrop is -1.1EV relative to subject
  
  
• Subject-to-light distance 2.8', background-to-light distance 6.8' (background 4' behind subject), light on backdrop is -2.6EV relative to subject
  
• Subject-to-light distance 4', background-to-light distance 8' (background 4' behind subject), light on backdrop is -2EV relative to subject
  
• Subject-to-light distance 5.6', background-to-light distance 9.6' (background 4' behind subject), light on backdrop is -1.5EV relative to subject
  
  
• Subject-to-light distance 2.8', background-to-light distance 8.4' (background 5.6' behind subject), light on backdrop is -3.1EV relative to subject
  
• Subject-to-light distance 4', background-to-light distance 9.6' (background 5.6' behind subject), light on backdrop is -2.6EV relative to subject
  
• Subject-to-light distance 5.6', background-to-light distance 11' (background 5.6' behind subject), light on backdrop is -2EV relative to subject
  

...so you see the benefit of both positioning the light closer to the subject AND the subject farther from the background, in terms of the relative amount of light falling on the background.
Distance to the background increase also helps for flagging off light from getting to the background, and it allows more space for YOU to delivberately PUT light behind the subject to fall specifically on portions of the background, if YOU wish.

bobbyz wrote in post #18221545
I have started liking shadows on the back drop.

I also prefer a shadow on the b/g, the better to show off hard lighting. The current custom in catalog is shadow for high end (Nordstrom), and shadowless for low end (Macy's). As for velvet, it really is a light sponge, but even the cheap stuff (100% Rayon) is expensive. Example below uses velvet (80% silk) with subject at point-blank range. Shadow on right indicates a hard light, moderate fill. Shoes themselves cast no discernible shadow whatsoever.

F2Bthere wrote in post #18221306
A lot of good advice above.

To risk stating the blatantly obvious, your choices come down to not letting your lights directly or indirectly fall upon the backdrop or, if they do, having what light falls on the backdrop be overpowered by other lights or be so little it isn't relevant to the exposure.

The other option is to light the subject so that the shadow falls outside of the frame or fov

Blackey Cole wrote in post #18221770
The other option is to light the subject so that the shadow falls outside of the frame or fov

Sample shot?

Someone kinda hit on the best solution with stating move the light source closer.

I do a LOT of green screen. Shadows on the backdrop totally hose the chromakey process. There are two solutions. The easiest is a larger light source. Aka get the biggest softbox or umbrellas you can find. Option b is light the backdrop. I do this sometimes with my 12 foot backdrop using 4' strip boxes.

The closer your light source is to the subject the larger it is to that subject.

Here is basic lighting setup I start with, I never get a shadow on the background.
Listed is the main camera and lens I use.

Photo from m.good's gallery.
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