exposure - Why can't I get a decent white background with product photography?

I'm a new photographer, and I'm trying to take photos of a product with a pure white background (#ffffff). I'm using a light box (something like this one), so my lighting should be solid.

But I can't seem to find the right settings for a good photo. I've taken lots of photos (100+), with a lot of different settings and basically my photos are either overexposed, or the background is not white. Here are some examples:

1.

The product is great on this photo. Only the background is WAY to grey.

f/8 -- 1/2000 sec -- ISO-6400

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2.

The background is pure white. But the product is overexposed.

f/8 -- 1/320 -- ISO-6400

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3.

Too grey and the product is overexposed

f/22 -- 1/200 -- ISO/128000

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Based on feedback, I have adjusted the exposure parameters and gotten somewhat better results, but that that alone doesn't solve the fundamental problem. What else do I need to do to get a pure white background without overexposing the subject?

Answer

There are many improvements that could be made here. Firstly, you need to use a much longer exposure, and a lower ISO setting. Get a tripod, even a cheap one, and use mirror lockup. Could do with stopping down a bit further for depth of field.

Post processing

You might be able to get away with your current shots, with some post processing. Here I've taken the second shot and used levels to darken the product whilst leaving the background pure white:

Lighting

The proper solution is to look at your lighting. The reason that you cant get the right balance no matter what settings you use is that both the product and background are being lit by the same source, so you can only alter the brightness of both, not each one individually.

Usually you'd have one light for your subject and one for the background. This gives you the correct amount of control for optimum results. However that is only if you have a large curved white background. Compact light tents such as the one you're using wont allow you to light your subject individually.

One solution is to black out any parts of the light tent not visible in the shot. That way the amount of light hitting your subject will be decreased, making it darker, without affecting the brightness of the background (since you wont touch any parts that are in shot). Get some thick black card, cut it to size and tape it inside the light tent.