Kevin Purcell
Well-known member
This may be an dumb question, but why do none the porros I'm considering have CF?
Because most 7x50 bins are designed for boats or ship use and so are easier to seal with IF.
The targets sailors are looking for are all "at infinity" (given the usual depth of field that's 100m or so and father out). So they focus them and use them as needed without worrying about focus. Same for soldiers and hunters who are all looking for big(ish) targets at infinity (not small warblers moving quickly between 3m to 40m).
You can find quite a few CF 7x50 out there though.
But unless you are in a really dark environment (outside of urban or suburban areas ... rural or wilderness) you'll probably not get an eye entrance pupil wider than 5mm (though individual results vary). You might want to measure yours (ruler, digital camera with flash and a dark room ... it's easy to photograph your own eyes) to get a feel for how much exit pupil you can use. A similar measurement in the "target environment" can be very handy too to help select the right bin.
The 7x50 was chosen for fit young sailors with big entrance pupils in oceanic dark environments. You may not need that.
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