Hmmm....

Here is a formula that explains the relationship between the focal length of a lens, the distance between the lens(object distance) and the length of bellows (image distance).

(1/focal length) = (1/object distance) + (1/image distance)

Amoung other things, the equation shows that for any given lens focused at infinity, the distance between a point in about the middle of the lens and the film plane is exactly equal to the focal length of the lens. Thus, if your bellows can extend a maximum of 12 inches, then you would not be able to focus a 13 inch lens at infinity -- let alone anything closer than that. To focus closer, you always have to extend the bellows.

If this is just so much mathematical gibberish, may I suggest that you try a few "hands on" experiments with the kit you have....I'll assume that you have a 190mm lens

Set your camera up and focus on something far away -- at least a few hundred feet -- then, your bellows draw would be about 190mm or, about 7.5 inches (about the same as the focal length of your lens). Now, with a twelve inch bellows (12inches = 304.8 mm) and a 190mm lens, the closest you can focus is about, 504.5mm or, about 20 inches away. The equation above can be used to predict this....

1/190 = 1/x + 1/304.8

solve for x....

(1/190) - (1/304.8) = 1/x

so,

x = 1/{(1/190) - (1/304.8)}

x = 504.5 mm

so, focus on an object about twenty inches in front of the camera and see if it doesn't take just about 12 inches of bellows.