Old Nikon manual focus lenses are a favorite of NV device users especially for wide field views of emission nebulae. Viewing at the zenith with the longer focal length lenses can be challenging, however, and at least one previous post has attempted to solve this problem (LINK). My new approach takes advantage of using an eyepiece with the lens in an afocal observing setup (LINK). I am using a Nikkor 300mm f/4.5 lens with 2" adapter in combination with the Russell Optics 85mm Super Plossl. Because of the exceptionally long eye relief of this lens I can screw on my Baader BBHS T-2 diagonal to the top of the lens and still have plenty of eye relief left to interact with the NVD Micro. I have only tested this during the day thus far but the 85mm works so well with my TV-140 flat field telescope I think it will work well in this new mode. Since the 90o turn happens after the eyepiece and before the device the 'feel' to this arrangement is very much like normal use of a refractor.
This setup provides ~6.7 degree FOV at f/1.4. Nikon made about half a dozen different 300mm f/4.5 models over the years and they are plentiful on the used market. I see no reason why even longer focal length lenses that are f/4ish could not be used as well if one is willing to put up with greater length and weight.
I will update this post when the skies cooperate and I can report on the FOV in a nighttime setting. Sometime during the coming week looks promising in that regard.
Edited by chemisted, 02 January 2021 - 12:15 PM.