Binocular Magnification Question (1 Viewer)

Red_Shoulder · Mar 2, 2015

When you look through 10x50 ruby coated, then 8.5x42 Swarovski, the image is bigger in the 8.5x. I've noticed the same thing in 7x20 Nikon vs. early to mid 80's 7x50 Swift Aerolites. Even though magnification is supposed to be the same, one looks bigger.

Why do some binoculars show a bigger image than others? Even with same/less magnification ?

Does the focal length of the objective/focal length of eyepiece give the same magnification, even though perhaps a wider field or something gives a bigger view?

Binastro · Mar 2, 2015

. It may be that the 10×50 Ruby coated binocular magnifies less than 10 times.
The marked binocular specifications are often incorrect, especially with binoculars from other than the top makers.

Also you are unlikely to find a ruby coated binocular from the top makers as the image is usually blue.
Additionally, if the objectives look red coloured, I think that any bird you are looking at would fly away.

BruceH · Mar 2, 2015

Is the ruby coated wonder a porro design? If so, then the difference is likely due to the difference in image scale between a porro design and a roof design. This is true even if the porro is a quality binocular. There are some threads on this.

Red_Shoulder · Mar 2, 2015

Yes the ruby coated is a porro. The ruby coated aren't that bad, I leave them in the car.

Could you post some links to these threads on roof vs. Porro ?

I've noticed field of view doesn't seem terribly accurate on binoculars.

Also I think the reverse porro Nikon are a bit bigger image than 7x50. Both from good manufacturers, both porros.

henry link · Mar 2, 2015

It's not so much Porro vs roof but rather widely spaced objectives vs narrowly spaced objectives. The narrower the spacing the higher the magnification appears to be. That's why reverse Porros seem to have the highest magnification. The effect is caused by the eye/brain's use of parallax between the right and left views to judge the absolute size of objects. Wider spaced objectives create a large parallax difference that suggests objects of a given size must be closer and therefore smaller. The effect disappears if you use only one eye and eventually disappears at long distance with two eyes as the difference in parallax diminishes. Of course, your ruby coated binoculars could also be off, as Binastro suggested.

SUPPRESSOR · Mar 3, 2015

henry link said:
It's not so much Porro vs roof but rather widely spaced objectives vs narrowly spaced objectives. The narrower the spacing the higher the magnification appears to be. That's why reverse Porros seem to have the highest magnification. The effect is caused by the eye/brain's use of parallax between the right and left views to judge the absolute size of objects. Wider spaced objectives create a large parallax difference that suggests objects of a given size must be closer and therefore smaller. The effect disappears if you use only one eye and eventually disappears at long distance with two eyes as the difference in parallax diminishes. Of course, your ruby coated binoculars could also be off, as Binastro suggested.

Henry,
As always an informative post.
We are lucky to have you and kimmo to spell it out when discussing optics as most of the posts are so much guff!!!
Suppressor.

henry link · Mar 3, 2015

Thanks Suppressor. In this case I was too lazy to track down one of the old threads about this. Some of those have better and more complete information about the subject.

Henry

Binocular Magnification Question (1 Viewer)

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