CN FORUMS ARCHIVE Telescope Reviews: Brightness in Exit Pupil

I would guess that the transmission percentages supplied by manufacturers are obtained by measuring the central region of the exit pupil. In this way the losses due to the unavoidable vignetting are largely avoided. In other words, only those rays on-axis or nearly so are sampled. In one way I think this is valid, as it allows to assess the efficiency of coatings and glass types used. On the other hand, it can give *potentially* inflated indications of total transmission through the entire pupil. But then, in high-end specimens vignetting is probably not so terribly different among various manufacturers' wares as to render the *comparative* transmissions an unreliable indication of performance.

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Home-made and modified binoculars
Mallincam VSS+

My Gallery (mostly DIY stuff) **UPDATED Feb 7 2013**

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