Bino's with compass built in. Why not?

[HawkenBob]

While waiting for the ZRS to be available, I have been using the Nikon Pro mariners I have for my boat. There 10 x 50’s with a built in compass.
This weekend while glassing for Blackies, I handed them to a bud and said “check that out at 160 on the tree line”. He immediately was able to see what I saw. No fuss, no muss.
Then it dawned on us that this is soooo handy! Especially if both have glasses with built in compasses.
Sure it might add weight but who cares? The convienence was totally worth it and now Im thinking there all I need. For big Bino’s they sure dissapear with the Nimrod straps anyway. Its also a great survival tool should you get lost. Or just to keep reference without having a compass in hand.
So why don’t they? With heavy, bad ass glass, weight of a compass can’t be much.

[ZRS-8x42]

We have a line of 7x50 Marine binoculars that have built-in compass.  They are quite heavy from because it is 50mm glass and extra weight from compass housing.  We don't put compass on hunting binoculars (like all other manufacturers) because there is virtually no space available inside the compact frame of roofprism binocular body to house the compass, reticle and battery unit.  For example, the ZRS(summit) has 10 pieces of glasses in each side of barrel plus the prisms unit.  There is no room to add compass unless we make the binoculars significantly bulkier.  Design of optics is often about finding the best compromise.  When other factors (such as image quality, weight, etc) prevail, we had to let go off some other important or nice-to-have features.  This is also why there are varieties of binoculars with different features.

[HawkenBob]

I did check and mine arnt the pro mariner. They are below. They have the compass option and add 40 grams. Less than 2 ounces.

http://www.nikon.com/products/sportoptics/lineup/binoculars/marine/ifwp_x50/index.htm

The body of each is the exact same but the compass is an added protrusion. Not much though and well worth the extra bulk if you wanna call it that. No batteries. Light comes thru the top of the compass were the white round dot is. Compass is viewed thru the left eye piece.

Im sure Im missing something but what? Is it because the hunt styles are a straight shot thru and these arnt? It seems mirrors or something must be used in these since the eye pieces dont have the same spread the big end has? Im a 15 year senior mech engineer. But I dont know much about optic design.

Its really cool to discuss with an actuall manufacturer though.

[ZRS-8x42]

To project the image from compass reticle, extra mirror is needed to erect the image through the prism so the compass and rangefinder values can overlap with the actual image.  For a 7x50 Porro binoculars, there is plenty of space to allow it to happen.  That's why both Nikon and Zen-Ray choose 7x50 to offer this design.  One downside, they are 2.5 to 3 lb in weight, almost doubles the weight of VISTA 10x42 binoculars (23oz).  In additon, both Nikon 7x50 IF and Zen-Ray Mariner use individual focus, which means you need to ajust both eyepiece to focus. It is more cumbersome than center-focus/diopter adjust mechanism that most hunting binoculars use.  Again, some people like IF because from 75 ft and out, there is little need for fine focusing. But the sharpness can never compare with fine tuning with center focus binoculars. 

[HawkenBob]

It makes sence now. Thanks allot. Im still ordering Summit's just after Christmas.