Binoviewing with a Quark in Observing - Solar Posted November 29 · Edited November 29 by astro_al I used a binoviewer with my Quark while I had it. I had no issues with backfocus with the Takahashi FC-76DC due to the Quark’s built in 4.2x Barlow - assuming you don’t have the combo model. I did replace the eyepiece holder with a T2 fitting so I could use a bayonet fitting though as that is what my binoviewers use. Saves some backfocus as well. At the time I had a pair of Zeiss binoviewers with a clear aperture of 25mm. I believe the clear aperture of the Quark is 21mm so I stuck with 25mm Televue plossls as these have a field stop of 21.2mm. Ideally I would have used longer focal length eyepieces to drop magnification and increase image brightness to offset the drop in brightness from using the binoviewer. Working with the 25mms at 95x was OK for many sessions but the exit pupil was a bit low for me. I think that is one of the challenges of visual work with a Quark. I now use Baader Maxbright II binoviewers which I find to be good. These are coupled with an F7 100mm Lunt scope but need a 1.5x glasspath corrector to accommodate the required backfocus. I can still get down to 42x with the 25mm plossls though but tend to mainly use 20mm or 15mm eyepieces which give about a 1.4 or 1.8 mm exit pupil which I like - compared to 0.8mm with the Quark.