[airgee]

Hello,

I've learned the hard way that a wide apparent field of view is an integral part of my pleasure to use a pair of binoculars. I also learned that in dark, foggy and otherwise hard viewing conditions, alpha-class binoculars clearly show their strengths against more reasonably-priced ones. For example, a mid-priced (~500 €) 8.5x50 from a well known American manufacturer did not appeared to me to produce an image any brighter than my Zeiss 8x42 FL, despite a significantly larger exit pupil (at least on paper) and despite having spent about 1 hour in the middle of the night with both binocs, with a half moon as the only light.

I'm seriously looking for a good, bright, alpha-class or near, 8x50 binocular for late dusk and night use. Unfortunately, it seems to me there's very few 8x50 models and none has a really wide FOV (let's say wide = 7.5° or more for a 8x, 7.1° or more for a 8.5x).

A few examples :
- Swarovski 8x50 SLC Neu => 7.04°
- Leica Ultravid HD 8x50 => 6.72°
- Zeiss Conquest 8x50 => 6.30° (no 50mm Victory FL unfortunately...)

The Swarovski is the widest, unfortunately it doesn't seems wide enough and it's quite heavy.

It seems that my only current solution is the Zeiss 8x56 FL (7.44°) but it's heavy (about 250g heavier than 50mm models) and being 39 years old, I won't be able to truly benefit from 7.0mm exit pupil.

I may have missed something, is there a fundamental barrier with 50mm+ objectives to truly wide field a view ?

[brocknroller]

The Carl Zeiss Jena (aus Jena) 8x50 Octarem has a 7.5* FOV. It weighs 45 oz, but the weight is very well balanced and very well distributed with its large body so it feels lighter.

They also made a Nobilem version of these bins with rubber armoring.

Looking out my backyard in the evening and at night, it was like shinning a light on the trees and bushes. I used the Octarem primarily for watching owls, nocturnal flying squirrels, and other nocturnal critters.

They are discontinued but they show up from time to time on ebay and elsewhere. They cost btwn $500-$600 in VG shape. I highly recommend them.

However, I find the ZR 7x36 ED2 provides sufficient brightness at dusk and even into the evening, and it only weighs 23 oz.

The view isn't quite as 3-D like as the Octrarem, which is exceptional in that regard, but it's better any other midsized roof I've tried.

Unless you do a lot of "glassing" in the evening and at night, I don't think the weight, FOV, and price of an 8x50 alpha is worth the trade-offs, given that you already have an 8x42 FL.

An 8x50 is a specialty bin. You have to weigh the cost and trade-offs against how much you intend to use it.

If you really do need that extra bit of brightness, you might be better off trading the 8x42 FL for a 7x42 FL.

[NWBirder]

If you just want to 8x50 with wide field of view, there aren't many options. For night use, those star watchers like 7x50 size. If wide angle is the most important thing for you, I will go with 7x, anywhere from 7x36 to 7x50. But if you really need 8x, with 50mm size, with wide angle, and being alpha, it seems Swarovski one is what you really want.

[ronh]

"I may have missed something, is there a fundamental barrier with 50mm+ objectives to truly wide field a view ?"
Yes, but only a practical, not a theoretical one.

The bigger the objective lens, the bigger the beam spot on the prism. If you want the prism to transmit all the light cleanly, even though that incident beam swings all around in a big true field, the prism must be quite large. Both the Octarem and the 7x50 Fujinon have 7.5 degree true fields, and both are quite bulky due to their large prisms. So, other things being held constant, prism size limits the true field, or the size of the eyepiece field stop which can be well illuminated.

Again holding everything else constant, as magnification increases the focal length of the eyepiece becomes shorter, so the view of that maximum sized eyepiece field stop occupies an increasing apparent field.

So, given a manufacturer's willingness to use large prisms, small objectives will generally have larger true fields, and high magnifications will have larger apparent fields.

This (nor anything else much) is not strictly true in the real world, where sometimes the optical design is altered within a series. Also, short focal length widefield eyepieces with decent eye relief are expensive, heavy, and large, so practical constraints on the eyepiece can impose the field limitation in such a case. But it's a pretty good rule of thumb.
Ron

[airgee]

I will certainly take a look at the old Zeiss 8x50 porro, thanks for the tip Brock !
And thanks Ron for this detailed and very interesting explanation.