Why is optical zoom of 3x or 4x recommended? (1 Viewer)

"If the camera's optical zoom is 4x or below, it can be paired with this adapter and used with various DCA adapters on the market."

This is from a retailers site and relates to using the Vortex Razor point and shoot attachment - PS-100. I've also read in many other places that P&S cameras with a optical zoom of 3x or 4x should be used for digiscoping.

Does this mean that P&S cameras with larger optical zooms can't be used?

Even if a camera has a larger optical zoom, why can't you just zoom out part way?

Generally, vignetting is a problem when the camera lens' physical length exceeds the eye relief (ER) of the scope eyepiece. Specifically, the lens' iris needs to stay within ER distance for it produce the image at the focal plane. Few scope eyepieces have ER>20mm. Camera lenses with a zoom range 3x-5x typically extend less than 20mm from the focal plane.

AFAIK, only Kowa and Nikon EDG offer a 25x fixed mag Long Eye Relief (LER) eyepiece with ~32mm ER. These might allow you to use 5x-10x zoom camera. But then when the camera lens exceeds 140mm effective other optical issues start to impact.

The ideal setup is an ED 80mm class scope w/30x Widefield eyepiece and a digicam with an effective lens focal length range of 35mm-105mm and aperture F2-5.6.

Well stated...

Thanks RJM - exactly what I wanted to know.