I don't know about the optics--someone will surely share their expertise on that. But my immediate reaction when I saw your post was that I'd let her take both for a while, to see which worked best and was most comfortable for her. Then she could return the other pair to you. Any reason that wouldn't work?

I can tell you from a technical perspective that the Zen-Ray has higher magnification (10X vs. 7X) and has a larger front lens. However, binocular optics is complicated by other factors, like the ratio between the size of the front lens and the magnification. If you want to read about all these factors, look at the link below. However, be aware that sometimes you can have a set of binoculars with great specs, but poorly-ground lenses, so actually looking through them to determine which is best for the purpose is the final word. So I think azzalea's suggestion is the best way to go on this.

Here is a link that might be useful: Binocular Basics

I don't want to fool around with having her try both pairs; she lives in another state and I'll be mailing them. I'll take them both outside and watch for an airplane, look down the street, etc., make my own decision. Thank you both.

s

7 x 35 Guide no= 35/7=5

10 x 42 guide no= 42/10=4.2

The 7 x 35 is a litle brigher.
The 7 x 35 has a field of view of 487 ft @ 1000 yards
The 10 powwer has a field of view of 293 ft 2 1000 yards.

For general puropse use, the 7x35 is the better choice. Its also better for spotting planes due to its wider field.
The 7x35 is useful handheld; The 10x42 will be shakey and will need a support. It will be difficult to 'find' a plane quickly due to its narrow view.

I own a 7x35 and a 10x50, both used for birding. I do enjoy the greater power of the 10x and use it for special occasions, but the 7x35 has proven far more practical on hikes, etc. The 10x50 is better for viewing the moon.

Send the 7x35.

Par for the course: if you need help ...

... just come here to ask!

ole joyfuelled