what is the....

extra zoom a digital camera adds to a lens?

What do you mean? The focal length multiplier factor? Have a look here: Understanding the DSLR Magnification Factor.

"Focal length multplier" is a wrong name for this effect. The effect is caused by the fact that sensors of most digital cameras are smaller than a standard 35mm film image (which is 24 x 36 mm). The sensor doesn't record the full 24 x 36mm image, but only the middle part (for example, the sensor of the Digital Rebel and 10D is 15.1 x 22.7mm). The 1.6 factor is really a crop factor, not a focal length multplier.

The so-called "digital zoom" doesn't add anything to the lens. It only makes up pixels. It's like enlarging a picture to several 100% with photoshop and smoothening the edges.
--Jens--

Boy O Boy

Did I ever get garbage for information from Ritz Camera!

Kinda like joining the service, all the good information you get at the recruiting office.

Oh well I am learing.

Yeah, I've got a digital video camera which claims "500x digital zoom" on top of it's 20x optical. The digital zoom is hillarious. You end up with a couple of really BIG pixels on your screen and that's about it

There used to be huge arguments about whether it was a focal length magnifier, or a field of view factor, or a cropping factor. It went on and on. It is much easier to simply call it the 1.6 factor and leave it at that.

---Bob Gross---

thanks guys that's what i was looking for

Used to be???

Yes, as in past tense. History.

A lot of people cannot think about it in terms of a cropping factor or a field of view factor. But if you tell that that it "sorta makes your 100mm lens act like a 160mm lens", then they understand that, even though that is a gross simplification.

---Bob Gross---

lol,.. I'm going to remember that term...

When we need to soften the complexity of an issue.. we will call the resulting explanation a "Gross Simplification" t.m.

Excellent!