Using camera lenses and some other prime objectives like finder scopes with NV is great because they provide such wide FoVs to see enormous areas of nebulosity or to see how different structures that we think of as individual deep space objects, actually fit together. But hand holding the NVD with these objectives does become bothersome because as we fatigue, which doesn't take long, jitters set in, or we set it down for a rest. I thought it would be great to have a diagonal attached to my NVD for more convenient use with my camera lenses. After Jeff Morgan recently posted about his excellent "sky window," I decided to see if I could attach a diagonal to the ocular of my Mod 3C.
I designed an adapter that would work and I thought I was going to need Precise Parts to make it; but it turns out I already have an adapter that works sufficiently for my needs. The RAF Envis to T2 adapter is all that's needed to attach a T2 diagonal to the ocular of all the popular NVD's used for NV astronomy. The threads at the back of the ocular (under the metal eye guard ring) are the same as the front of the Envis lens!
To make it work, the aluminum ring that holds the rubber eye guard, at the very back of the NV ocular must be unscrewed. Some of these rings are screwed in VERY tight, so use care not to damage the ring. Once it is removed, screw in the RAF Camera, Envis to T2 adapter, found here:
then screw in the male threads on the T2 diagonal and you are set. I use a T2 15mm extension tube on the other side of the diagonal to keep my eyelashes away from the prism in my diagonal, but it is not essential.
I said that it is "sufficient for my needs" which means that it is not "perfect" but it is really close... there is slight vignetting at the very edge of the image because the inside diameter of the Envis side of the adapter intrudes ever so slightly on the image from the NV ocular. I took an image to show the effect, but it is pretty minor and probably not even visible at night.
I would like to hear from anyone else who tries this. I know many already have the RAF adapter because it allows the use of 2" filters in front of an Envis lens (with a step up adapter ring), I also use it for a hard connection between certain eyepieces and the Envis lens for AFOCAL. But I don't know how many have a T2 diagonal AND a camera lens or finder that already attaches to their NVD. I'd like to hear a confirmation before others invest in this effort. The hardest part of this might be removing the eye guard ring from the ocular to expose the Envis (M30.3 x .8mm) threads.
Here are some photos to help. This one shows the metal eye guard ring removed and the RAF adapter between the NVD and the T2 diagonal.
This shows the T2 diagonal actually attached to the NVD
Here, it is shown with the NVD attached to my Nikon 300mm lens on my larger alt/az mount
And this shows the Envis lens removed and the T2 diagonal attached to the NVD with a Nikon 105 lens for a 10° FoV