The background is not white

[bango707]

I take the photo in manual mode, at F4. The background is not perfect white, I use a DAYLIGHT bulb (6400 K). The same problem happen with two bulb.

What color are the walls in the room? They look really dark, almost black. Like many people have mentioned the darker color will bleed onto your background. Seems like you are getting some negative fill from the dark walls which can be corrected by either adding a background light or by placing foam core or a reflector on either side.

 

[akazoly]

In manual mode, at lower shutter speed, for example : 14 and F4 aperture the background is pretty good (white), but the center image not has natural colors.

 

[RacePhoto]

Is a good idea to light the box from bottom ?

Yes that will help.

And contrary to what someone else wrote. Expose for the subject, not the background, and let the white background blow out and disappear. Do Not expose for the white background!

If that's difficult, just meter and over expose one stop. Look and see how it looks. Then try 1 1/2 stops, 2x Etc. until you get where you want it.

Yes to what everyone else said about either white sides, to fill the shadows, or wrinkled aluminum foil, to diffuse the reflected light.

You need to diffuse the top light by putting tracing paper or silk over the top of the box. Your open bulb is going to produce harder shadows.

You will get longer exposures, but use a tripod and the self timer, so the camera is steady.

Your goal is soft, even lighting over the whole inside of the box.