With a dSLR with a sensor size smaller than full frame for any given focal length lens, the effective field of view is decreased because the field size of the capture is smaller. But the lens factor of 1.5X does NOT indicate a real optical difference, it just reflects the fact the smaller sensor size make the lens seem to behave as if longer than it is if used on a full-frame or 35mm camera. So if you are using any particular lens, say 85mm, the lens determines depth of field relative to the aperture used - the smaller capture area of an APS sensor (field coverage area) has no affect on depth of field.

Thanks. Not what I was expecting. I was assuming that since fov changes so does depth of field. I never have really grasped the science between distance/aperature/focal length -- I just always take it for granted.

You are correct assuming that distance/focal length/aperture determine depth of field, which formula remains the same regardless of angle of view or image area covered. A 50mm lens set on f/8 and focused at 10 feet from the subject will provide the same depth of field whether the sensor is an APS size or full-frame 24x36mm.

Well, It's not quite as simple as that. While it is true that a 50mm lens focused at 10 feet has the same circle of confusion regardless of sensor size, the image from the APS sensor is enlarged more when a print is made. To get the same resulting circle of confusion on your final print, you need to start out with a smaller circle on the APS sensor. As a result, the DOF for an APS sized sensor should be a little less.

Quote:
I have made a few attempts on the internet to find out this info for sure, and it seems like such a basic question, but -- when using digital slrs (Nikon) that do not have a full size 35 sensor, will the focal change also change depth of field, field of view etc, just as if you were actually using a longer lens? Intuitively I would say yes, since you are taking an 85mm for instance, multiplying by 1.5 (for Nikon) and getting aprox 130mm. But I just wanted to make sure that the 1.5 affects everything. Thanks for any info on this.

Focal length does not change of course. You are simply cropping out the image, just like taking a scissors to a piece of film. Obviously nothing changed with the lens or camera; the only difference was a smaller field of view, as if a longer focal length lens were used. But the physical properties of the lens/camera did not change.

When you shoot at 50mm lens on a full sensor vs a 1.5X sensor, you have to physically *back up* to get the same field of view. Greater distance yields greater depth of field (and an altered perspective which is governed only by camera-to-subject distance). See D2x vs EOS: Depth of Field.