Talk:Catadioptric system

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[edit] Problem with "aperture"?

Halfblue's recent change comment: "(→Photographic catadioptric lenses - "Aperture" is the problem word since it has two meanings-- the second being "diameter" of the Objective (optics). Catadioptrics do not come in one diameter.)" essentially for the phrase "but typically lack an adjustable iris and operate at a high fixed f-number equal to the focal ratio of the total optical system" to replace "but typically has a smaller ("slower") and fixed aperture"

I don't understand. Three problems here. First, what is the other meaning you're worried about? The aperture of this system is the diameter of the objective mirror; for any such device, it is typically fixed, not variable. Second, since the topic here is photography, why introduce the astronomical term "focal ratio" where you've just said "f-number"? Third, before we agonize too much over how to say it, is this even really true? Do catadioptric 500mm lenses have smaller apertures than 500mm lenses? And if so, why?

Dicklyon 03:00, 24 October 2006 (UTC)