With the 18.5 mm f/1.8 lens now firmly attached to the Nikon V1 I headed off to Lowes to see if I could make a new digiscoping adaptor to attach the camera to the 20-60X Zoom eyepiece of the Zeiss 85T*Fl Diascope.
After perusing the plumbing aisles for a good 20 minutes I was able to come up w/ a 2" No Hub Coupler consisting of a rubber sleeve surrounded by a steel band and hose clamp assembly.
One end of the rubber sleeve slides perfectly over the 2" diameter lens, while the other end slips snugly over the 20-60X Zoom Eyepiece. An internal ring separates lens from eyepiece w/ perfect spacing (at 20X magnification I can see just an edge of a vignette circle). At first I tried tightening the steel band around the lens, but it affects the focusing motor inside the lens, and its easy to get a lens error "Check to see if lens is properly attached". So I discarded the band and just used the rubber sleeve. A strip of electrical tape was wound around the end attached to the lens just to stiffen it enough to hold the lens more securely. Good news is that the rubber sleeve can stay on the lens at all times and act as a lens hood!
When I need to use it I just push the sleeve over the eyepiece and the ribbed end slips over the eyepiece cover and snaps securely into place. This provides hands-free videocapture or self-timer captures if needed. It also still allows me to zoom the eyepiece w/o having to remove the adaptor. To remove the adaptor just apply sideways pressure to the sleeve and it pops right off the lens.
I took the rig outside to test it. At 20X magnification there is just the slightest edge of a vignette circle in the upper left corner of the viewfinder. A slight zoom removes any vignetting, but at 40X there is slight shadowing along the edges. This shadowing disappears when you zoom to 60X. The image at left (and immediately below) were captured w/ the eyepiece at 20X magnification. You can see just the edge of the vignette circle in the top left corners. The next image was taken w/ the eyepiece at 40X.
Unfortunately, with a snow storm moving through the area the skies were heavily overcast this morning, and a stiff wind was blowing. The 20X images were capture at ISO 250 at 1/60 sec. with the lens aperture set at f/1.8. The 40X image was taken at 1/25 sec (-0.7 exp. comp.). I could not get any 60X images due to the slow shutter speeds, but w/ a 2-stop advantage over the 10-30mm f/3.5-5.6 lens I would've been barely able to get a 20X capture... I did take a video of an American Goldfinch to demonstrate the amount of vignetting/shadowing present w/ the setup. Apologies for some of the soft segments as I was fiddling w/ focus.
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| American Goldfinch - 40X |
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| House Finch - 20X |
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| House Sparrow - 40X |
As soon as lighting permits I hope to perform a resolution test to compare the 18.5 mm f/1.8 on the 20-60X Zoom eyepiece with the 10-30mm f/3.5-5.6 lens on the 40X W eyepiece.
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