The flattener or field flattener is a lens that evens out the field, as this is slightly curved by the primary optics. This curvature causes stars that are imaged at the edge of the field of view to be less sharp. Astrophotographers can then enjoy images where the stars remain sharp right out to the edge of the exposure. The flattener is installed between the telescope and the camera.
The Sky-watcher M48 Field Flattener is an optically-matched M48-fitting doublet field flattener, used with Sky-Watcher's Esprit-80ED triplet refractor.
The M48 size fitting provides a large clear aperture to reduce halation, while a precision thread ensures the triplet and doublet lens groups are precisely aligned on the optical axis perpendicular to the image.
When used with the field flattener the Esprit-80's imaging circle is changes to 33mm.
Notes
When fitting a DSLR camera you need only a M48 Ring for Canon and Nikon is needed to fit the The flattener (M48 spacer is included).
The rear thread of the supplied spacer is M48.
The spacing for dedicated CCD imaging cameras is 55mm from mating surface when using supplied M48 spacer. Spacing from flattener mating surface without supplied spacer is 61mm (flattener has M62 thread).
For more information about, SkyWatcher M48 Field Flattener For Esprit-80ED Telescope website.
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