White Background Lighting Issue

[Ilan]

Hi,

I'm trying to photograph food with a white background. I have two continuous, fluorescent lights in the front. When I do that, I get the no_flash.jpg. If I add a flash to the background (see setup.jpg) I get with_flash.jpg, which is overexposed in the foreground. I've already put the flash on 1/16, down from 1/1, and it doesn't go lower (it's an old flash--SB 24--set on manual). I have the same flash settings keyed in as I am using on my camera (I am using a D7100 with a 105mm f/2DC).

If I make the shutter speed faster, I get short_shutter.jpg. This may be because the wireless connector is only supposed to go to 1/200s. I'm not sure.

Any ideas how I can do this?

Thanks!

 

[Dave442]

Seems like the with_flash is just getting too much light bounced back from the backdrop. Move the backdrop further back, which I don't think you can do here, or try a diffuser on the flash. The short_shutter looks like you went over the max sync speed and the shutter was caught traveling across the frame.

The no-flash shot looks underexposed, you could try a spot meter off the white background and then drop the shutter speed by two stops and try that before adding any flash. There is probably a better way, but that is where I would start.

 

[Derrel]

No flash looks good, except that the exposure time needs to be longer. The lighting is flat, and shadowless, but at least "decent"...so I would slow the shutter speed down, and use a small aperture like f/16, to get as much in focus as is possible with a 105mm lens. Depth of field will be critical on food, unlkes the food is very small, flat-plane stuff and the camera is plano-parallel with the food's surface...

With_flash (the third sample illustration) has really bad "blowback", with the light from the white background paper coming back very harshly, and flooding the front of the 105mm lens with a LOT of light.

In my opinion, the setup.jpg placement of the flash is not ideal...looks like the background is not lighted uniformly, because the flash is so close to the background paper.

 

[Ilan]

Thanks, both.

I shall try a diffuser on the flash as well as move it further away from the background and report back tomorrow (perhaps it will help light the background more uniformly).

Derrel, how would you suggest I made the lighting less flat and more than "decent"? Without using flash I was able to get some OK photos (see attached--I removed the background in photoshop).

Thanks,

Ilan

 

[Ilan]

Alright, I tried again. I used f/10 with a shutter speed of 1/4 and ISO 100. I also brought the flash farther away from the background (in-line with the lens I was photographing for a test shot).

I have here two photos: one with the flash and one without. It's not pure white as the background. Is this a technical error or is it never exactly white? Other thoughts on lighting?

Thanks!!

 

[NCspotter]

Pretty difficult to tell the difference between the last two pics you posted, but it could be edited fairly easily to make the colors more natural. You might consider this cheating, but a simple Auto Fix from an editing program such as Pixlr Express should darken the lens, which would probably make the white look better. I haven't ever tried shooting something with a white background like yours, but it might be worth a try shooting at ISO 200 with a slower shutter speed if you're trying to lighten the background, or making the aperture smaller (such as around f/15) if you want to darken it.

 

[Dave442]

If you only have the one flash you are lighting the object and then the light falls off per the inverse square law and less light is hitting the background, so it is hard to blow out the background to white without overexposing the subject. Extra lights on the background can help and is often what is used to achieve a white background. Careful to not have the white background put too much light back onto the subject.
Not giving this as the solution, but more as to where to look for more info on what you are looking to do.

 

[KmH]

Your background material likely isn't "exactly white" (Red = 255, Green = 255, Blue = 255).
Most man made textiles and papers have a slight blue tint.

As Dave442 mentions, light fall off (inverse square law) will cause a gradient in the brightness across the background with the portion of the background furthest from the flash getting the least light.
To evenly light the background you'll need more than 1 light.