I have a film camera that has 38-70 mm zoom.
Im thinking of getting a digital camera,
everything is explained in 6 optical 4 digital.
So I was wondering what "zoom" 38-70mm is in "optical" terms.

Thanks

Assuming you get a digital camera that can accept your 38-70 mm lens then it will convert to approximately 50–98 mm, plus or minus a bit depending on the make of the system.

The 6x or 4x zoom ratings are a hold-over from the old video days. (Digital camera CCDs have their origins in video cameras.)

A 38-70mm would be around a 2x zoom.

My question is why would you even consider moving to digital when you already have a film SLR?

Most people associate the focal length of a lens with the 35mm film format. Thus we have a standard zoom lens that is 38-70mm.

A standard prime lens for a 35mm camera is usually 50mm. This is also called the normal lens because it emulates the angle of view by the human eye... approximately 45 degrees.

Now when the film format changes... if the sixe of the film or the imaging element (CMOS or CCD sensor devices found in digital cameras) changes in terms of its size, the focal length of the normal lens also changes.

A few examples...

The normal lens for 35mm film camera is 50mm.
The normal lens of a 6x6 cm (120 format) film camera is 80mm
The normal lens of a 6x7 cm film camera is 90mm
The normal lens for a 4x5 inch sheet film camera is between 120 - 210mm.

150mm would mean a telephoto lens for a 35mm camera while its 'normal' for a 4x5 inch sheet film field or view camera.

Similarly, digital cameras, that have much small CCD dimensions than 35mm film will require lenses of a shorter focal length to be the 'normal' lens. Thus we have a multiplication factor when we relate lenses for most digital cameras with a 35mm film camera. Normally, for most D-SLRs and digital compact cameras, this is a multiplication factor of 1.5x to 1.7x, depending on the dimensions of the CCD.

Most manufacturers of digital cameras refer to lens focal length in 35mm film camera terms because it is easier for the customer to understand. Usually, they also put down the actual focal length of the lens.

Just some useful information there, in case it helps.

Zoom lenses normally are denoted by the factor of magnification into the image. This is proportional to the extent of zoom. for instance a 35-70mm zoom lens has a mgnification factor of 2x. Simply put, the lens sees approximately double the total area or the scene at 35mm as compared to what it sees at 70mm.