Lighting Test

[JohnC]

I've borrowed a test from a discussion that I had someplace else. Take a look at the attached file.

The camera and subject were not moved between these two shots. The aperture is the same in both, too. The same light was used for both images. The exposure is equivalent. Why do they look so different?

Some things to compare:

1. the appearance of the background surcface

2. the highlight on the cap

3. the size of the shadow cast by the film cannister

4. overall image contrast

Some questions:

1: Is the light softer in A or B?

2: Which image looks more contrasty?

3: Why is there such a difference in the background surface between the shots?

4: Is the shadow cast by the film can darker in A or B?

5: Why is the shadow in B longer than the shadow in A?

6: Why is the highlight on the cap more pronounced in A than B?

[JohnC]

Message deleted to foster more discussion

[Blinky]

Originally Posted by JohnC

Correct
...
John

I've deleted my answers in case you may want to delete yours as well and let some other folks give it a try.
Chip

[JohnC]

Good idea. I was hoping this would generate some discussion.

[4jallday]

A has more contrast. It looks to me the light in B looks softer and was moved further away and maybe more towards a 45degree? I am a rookie at lighting so if I'm wrong forgive me.

[JohnC]

Nothing wrong with being wrong here, you are forgiven! Let's let a few other folks join in before posting the answers again. Thanks for replying, we're all here learning.

John

[scoundrel1728]

I've sent my own reply as a PM to JohnC.

[JohnC]

One thing I should mention, don't try to equate the light with the position of the sun in the sky. This is more about sudio light control. We don't have the luxury of being able to move the sun closer to us (and we wouldn't really like it if we could!). So even though the shadow changes like mid-day to early evening, sunlight is still pretty close to a point source and will still have strong shadows and chiselling modelling. To soften sunlight you have to modify it (either naturally with clouds/overcast or put a scrim up). The light used in this test has not been modified between the shots.

John

[scoundrel1728]

In this particular instance, the lighting angle seems to have made the most difference. It is difficult to see the widths of the penumbrae in these shots, especially shot B, so is correspondingly difficult to judge tha angular extent of the lighting. A wider angular extent would be achieved with a wider, more diffuse light source or by moving it closer to the object. In this instance, the angular width seems to be about the same in both shots, possibly a bit less in shot B.

[JohnC]

For those following along, the penumbra is the edge of the shadow caused when the light source is not a point source. The change in the lighting between the shots is raising/lowering the light. The light was not moved fore/aft in regards to the subject, but the angle does change by moving it in closer. One shot is with the light 8" above the can. The other is with the light 16" above the can.

One of the things I'm trying to show here is that it isn't always just the size of the light by itself, but rather the size in relationship to the subject. Say you are taking a head shot for an actor and you have a 24" square soft box. If you set the softbox up 8 feet away from the actor the light is going to be a lot different than if you set that same 24" softbox 12 inches from the subject. At 8 feet the shadows on the face are going to be hard (narrow penumbra). At 1 foot the penumbra is going to be wide and fall off more smoothly. The light is more diffuse when closer. The light at 8 feet will produce smaller/hotter hot spots on the face (tip of the nose, forehead). Moving the light in closer will diffuse those highlights and make them larger and better looking.

[captlen]

Relitively new here but willing to take a shot at this If wrong on any I will learn if right I will pat myslef on the back.

1. & 5. The light is A is softer and the shodow is shorter because the light is closer.

2. A is more contrasty.

3. The background difference could be a longer shutter speed9 You did not say that was constant and the light is closer.

4. The shadow is not darker it is shorter. It appears darker only because the background is lighter.

6. Because the light is closer it now reflects of the cap in b B it is further back and does not.

OK how did I do and why. Thanks.

[JohnC]

Thanks for adding in Len. I've sent my response in a PM. In a few days, after a few more people add their comments here, we can bring the discussion back onto the board.

John

[dvdowns]

I would think that the light is closer in B since there is more fall-off of light behind the canister , like taking a flash shot outdoors of someone right on front of you ?

[JohnC]

Here are (really bad) photos of the setup.

The light is 16" away in A and 8" away in B.

John

[Stormdancing]

Thank you for posting this JohnC. I'm so new to lighting, I don't have a clue, but this discussion has helped clear up a few things for me. I'll keep coming back to see more discussion. Thanks!

[JohnC]

A logical extension from this would be to try this with a head and shoulders portrait. Use a small size soft box (may 24" square) and try it with the softbox about 5 feet from the subject. Then move it in so that it is around 1 foot from teh subject, just outside the frame.

Where I think a number of people get caught up is that they think the light being closer will make the background brighter. But the opposite is true. When the light is far away from the subject and the subject is close to the background you have a situation where relatively the same amount of light is hitting the subject and background. As you move the light closer the relative amount of light hitting the background falls off according to the inverse square rule.

At 60 inches light to subject and 72 inches light to background the light is pretty much the same on both. At 12 inches light to subject and 24 inches light to background there will be a drastic difference.

Going back to some of the original questions...

The can is more contrasty in A because the light is smaller and casts stronger shadows. But the overall scene is pretty flat. The can is less contrasty in B, but the overall scene is more contrasty because of the quick falloff of the light. Didn't mean for it to be a trick question. But that's the way it works.

The highlight on the cap in A is more pronounced because the light is smaller (further away). It is more concentrated. The highlight on the cap in B is more diffuse because the light is larger (closer). It gets to spread out across the cap.

John