Question about Black Backdrop

[VegasGeorge]

I ran my first mass production photo shoot/print tonight at a sock hop held at our community center. I hung a black bed sheet on the wall to use as a backdrop. To my surprise, it seemed to literally suck up about half the light from my two flash units. I tried different positions and shooting distances. Nothing worked right. I wound up removing the sheet and shooting against the wall which had an ugly rose beige color. As soon as I removed the sheet, the exposures looked OK. Have any of you had experience shooting against a flat black backdrop, and if so, how do you overcome the loss of light?

[robertwgross]

I have one photo-black backdrop, one black velveteen backdrop, and one medium gray blackdrop.

The black velveteen will soak up just about every photon of light that you throw at it. If I put it just a few feet behind a subject, then I let the flash do its thing with the subject lighting and the backdrop will be gone completely.

---Bob Gross---

[mjordan]

How were you judging your exposure? After you took a test shot did you use your histogram or the LCD to judge exposer?

Probably what is happening is that the black background doesn't reflect light (it does, but very little) so your image looks darker than it is. The lighter color wall reflects lots of light, so your image looks brighter... but it still might not be properly exposed.

The best way to check your exposure is to use a flash meter. Another way is to use a black/gray/white card in the spot the people will be standing (have someone hold it at chin level). Then take pictures and look at the histogram and adjust your exposure until you have a spike on the left, in the middle and on the right. This will be your black/gray/white card shown. An alternative is to have a black/white card (a little easier to find) and look for a spike on the left and right. If nothing else, a black, gray or white card can be used and look for the spike in the appropriate spot. One of these methods is going to be a lot more accurate than judging from the LCD screen.

Mike

[wcstory]

Could you post a black background vs wall background shot of the same subject? I can't help with suggestions, but I'd like to see for future reference. Doing something for my daughters school.

Bill

[VegasGeorge]

We were judging exposure by immediately downloading and displaying on a 19" PC flat screen monitor. Our object was to get an acceptable exposure so that we could download and print directly, without any image editing.

I think robertwgross might be onto something. I was putting my subjects right up against the black backdrop. Maybe if I had moved them forward toward the camera, and away from the backdrop, the scattered light would have been more normal.

This was a club project, so I'll have to see if I can get a couple of examples to show you. I don't have the image files right now, and I don't know if any of the bad ones were saved.

Thanks, mjordan, for the exposure setting suggestions. I will definitely use them next time.

[PhotosGuy]

As soon as I removed the sheet, the exposures looked OK. When you have a static set up, there's NO reason to not shoot on "M", and a LOT of reasons to get off "Auto", Tv, Av, etc!
You've just learned that lesson. Put a piece of white, matte, paper where the subject will be lit by the main light (not both if you use a fill light) & take a shot. Chimp the exposure near to the right edge, then use those settings on "M" and you've solved your problem. Tweak, if necessary, in post since you've already made the excellent decision to shoot RAW.

[DocFrankenstein]

Don't they make flash meters for this?

[PhotosGuy]

Don't they make flash meters for this? They do, but when you have a $1,500 20D "histogram flash meter", why buy one of those, too?

[RichardtheSane]

They do, but when you have a $1,500 20D "histogram flash meter", why buy one of those, too?
Simplicity
I have just been thought the same dilemma. Ordered my lighting and couldn't decide wether to get a flashmeter. In the end i bought a cheap one, just because I wanted to be able to get the lights set up about right then tweak it with the histogram while shooting.

Right tools for the job etc...

[DocFrankenstein]

They do, but when you have a $1,500 20D "histogram flash meter", why buy one of those, too?
I can't judge lighting ratios on the LDC very effectively. To be sure, I need to see it on a monitor.

But then I've never used a lightmeter yet

[PhotosGuy]

Take a look at this, Doc:
Fill light at sunset
http://photography-on-the.net/forum/showthread.php?t=66353
"Here's something that will help you figure light fall-off in your head:"

[tuggnet]

...
Another way is to use a black/gray/white card in the spot the people will be standing (have someone hold it at chin level). Then take pictures and look at the histogram and adjust your exposure until you have a spike on the left, in the middle and on the right. This will be your black/gray/white card shown.
...
Mike
Okay, excuse my ignorance, I'm new to this also. When using a black/gray/white card, do you fill the frame with the card or just take a shot from where you will be shooting the pictures and look for the spikes?

I'm guessing I would just take a shot from my selected position and look for the spikes. But if you're using a black background, wouldn't you have a huge spike to the left?

[PhotosGuy]

I'm guessing I would just take a shot from my selected position and look for the spikes. But if you're using a black background, wouldn't you have a huge spike to the left?

"huge spike to the left" :
black/gray/white card would be used for exposure or post processing info. For just exposure, ignore the black. You want to get the white near the right side. It doesn't matter if it fills the frame AS LONG AS there isn't a highly reflective object in the frame with it.

For WB, you should fill the frame. Some say only the center, but I think that's BS. It doesn't matter if it's in focus or not for either WB or exposure, either.

[Longwatcher]

I have learned that between my white, my grey (which is really, really close to 18% grey) and my black backdrops, that I have to read my histogram differently. This also applies depending on the skin color of my model (there are times when I think Canon has designed their camera to be racist).

I have learned that once I get my lights set correctly for a particular model, I just leave everything in manual on the same setting and basically ignore the histogram from that point on. But the model's skin color (and outfits) seems to make a huge difference in how much light comes back to the camera, so I have to adjust for that. It took me about a year to catch on the that little issue.

If using my white backdrop, I aim for the spike being way over to the right, if using my black backdrop, then the primary spike needs to be on the left third of the histogram, with a tiny spike near the right side ( for the model)

As to W/G/B cards, in theory you should fill the view with the card for using custom white balance, but for post correction you only need it somewhere in the frame. I recommend using what ever lens will allow you to get the whole card in the frame and then swap to the lens you will be using to take the rest of the pictures.

Just my experience and opinion,
Nothing is ever as simple as it should be.

[Jon]

For WB, you should fill the frame. Some say only the center, but I think that's BS. It doesn't matter if it's in focus or not for either WB or exposure, either.

Well, Canon says it only needs to fill the central partial metering circle. I'd hope they know how they figure the CWB.