The 24mm Vernonscope Brandon eyepiece is designed for nigh-perfect medium power deep sky observing with any telescope type, at focal ratios f/7 and above. Emission nebulas, globular clusters, the more compact open clusters – all are fair game for the tack-sharp high contrast/dark sky background performance of the 24mm Brandon. With shorter focal length scopes, down to f/4, it is still exceptionally sharp at the center of the field (although somewhat less so at the edges).
While the designed and technically correct eye relief is substantially longer at 19mm, because the eye lens is recessed 10mm below the rolled down eyecup, the measured usable eye relief of 9mm is somewhat short for unvignetted use with eyeglasses. However, most objects being observed will typically be placed at the center of the field, where vision is sharpest and vignetting of the edge of the field due to eyeglass use is less of an issue. As a personal aside, your author uses this eyepiece in both his 3.5” and 7” Questars and has never had a problem with the eye relief, even when wearing glasses.
For a brief discussion of how we define and measure usable eye relief and its importance to you, an explanatory text box will pop up when you move your cursor over the term “Eye Relief” in the "Tech Details" pull-down tab above. Removing the eyepiece’s rubber eyecup will provide several mm of additional usable eye relief, but at the expense of exposing your eyeglass lenses to the metal top of the eyepiece.
The Brandon is the sharpest design currently available for eyepiece projection photography. The body of 24mm is considerably narrower than most similar focal length Plössl eyepieces, allowing its use in an eyepiece projection adapter much more readily than a wider Plössl. Its rolldown rubber eyecup can be removed, should the eyepiece/eyecup combination still be too wide to fit easily into your eyepiece projection adapter.
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