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Message: <blockquote data-quote="ailevin" data-source="post: 3612490" data-attributes="member: 140149">I started out my binocular obsession primarily as an amateur astronomer.  When choosing eyepieces for a telescope for night time viewing I think more in terms of exit pupils than magnification.  I generally prefer an exit pupil of around 5mm for low power night viewing, though the choice of optimal magnification for extended low contrast objects depends both on their size and their surface brightness.  The exit pupil size (assuming there is no vignetting in the optics) is simply the diameter of the aperture divided by the magnification. Since the area of an extended object increases like the square of the magnification, and the amount of light gathered increases like the square of the aperture diameter, the magnified object has the more light spread over more area resulting in the same brightness (less the imperfections of the optics). Both the increased amount of light and the increased scale help you detect differences in contrast and see details.In bright light the exit pupil of many if not most binoculars is larger than the entrance pupil of the eye and this has several consequences.  If it is bright enough that your eye is only dilated to 3mm, your 9x45 binocular is "stopped down" to a 9x27. An 8x42 would perform like an 8x24 in the same situation. As some compensation, eye placement is less critical when the exit pupil is larger than the entrance pupil of the eye. Of course as less light is available, you eye dilates more and you can use more of the available aperture. Maximal brightness, with no light wasted and no aperture wasted occurs when the exit pupil matches the dilation of the eye.  OTH, maximum visual acuity for the eye occurs with an entrance or exit pupil of around 2-3mm.  Larger pupils tend to show more imperfections of both the eye itself and the optical instrument.This is a very long winded way of saying that the 5mm exit pupil of the Maven 9x45 is only fully utilized under low light conditions, but it generally makes it more comfortable to use even under bright conditions.  What is more important, IMO it is an excellent optical instrument for both night and day use.  There is a penalty in size and weight for a 9x45 binocular of this design, and while people spend much more, I consider $1,000 to be a significant investment in a binocular.  Yet I find that it handles very well, and the views are truly outstanding.  I hope you enjoy using it as much as I do.Alan</blockquote>

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