Yet there's not even a hint of ghosting in this image taken with a Nikkor 500mm f/8 Reflex.
Normally we would expect to see some ghosting in the area, indicated by the yellow oval, directly across the center point in the photo from the brightest light source in the scene. In shooting situations that would induce ghosting with many conventional lenses, a mirror lens does not show the same tendency: Thus any flare demonstrated by a catadioptric lens would be similar in nature to flare demonstrated by a refractive lens.Ĭatadioptric lenses with fewer refractive surfaces are more resistant to flare. But what flare they demonstrate is caused by the same properties of refractive lenses as the flare produced by a non-mirror lens. Because most catadioptric lenses used for photography have fewer refractive elements than typical refractive lenses created for creative photographic use, most catadioptric lenses demonstrate less flare than many refractive lenses used in creative photography.
This could include corrector plates, the glass in front of a back coated mirror, or even flat protective plates at the very front of the lens. If the barrel of such a telescope is reflective, the reflections from the inside of the barrel can fall on the mirror and cause flare.Īny flare created by a catadioptric lens is caused by its refractive elements. Dust and condensation on the surface of a mirror lens have optical properties than can, in the presence of off-axis light, reduce the contrast of the image projected by the mirror in a way that resembles veiling flare, but that is due to the nature of the substances on the mirror, not to the nature of the mirror itself. The reason many simple reflector telescopes have barrels is to protect the mirror from condensation, dust, and damage. Light from within the FoV is only reflected to a single point (or a blur circle for out of focus light sources) at the lens' focal length. Off axis light is, by definition, reflected outside the lens' field of view. Simple front coated mirror lenses, such as those used in reflector telescopes, that are clean do not demonstrate flare.
I've never seen a commercially available photographic lens with only simple mirrors, though. A simple mirror lens with no refractive elements is not a catadioptric lens. Catadioptric lenses are lenses that combine both refractive and mirror elements.
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