Sunday, July 4, 2010
My Newest Digiscoping Adaptor - 04 Jul 2010
With the purchase of the new Zeiss 30X/40X Eyepiece I needed to build a new digiscoping adaptor for my Nikon Coolpix P6000. At 48 mm diameter the eyepiece is 8 mm narrower than the 20-60X Zoom Eyepiece, and thus too small for my current adaptor. So, in order to fully test the eyepiece in the field it was important to have an adaptor that is quick to set up and stable in the field. A trip to Lowes, and $5 later I had the materials for an adaptor that I think I'm gonna love. The adaptor consists of a 1 1/2" x 1 1/4" PVC connector from the plumbing department. The 1 1/4" side has a threaded ring cap with a plastic compression ring. The 1 1/2" side is smooth, and to that end I pushed on the reliable teflon tape dispensor cap. Why? Because the 1 1/2" side slides smoothly over the eyepiece and rubber eyecup, but doesn't hold the connector snug enough. The tape dispensor cap actually 'snaps' over the eyecup and holds the connector firmly. The next issue, however, is getting correct lens-to-eyepiece distance to generate a sharp vignette circle at the 6mm camera lens position. To correct this, I pulled the eyecup all the way out, snapped on the connector and camera, then pushed the eyecup in until the vignette circle becomes sharp. This position is approximately 1/8" from being pushed in fully. To maintain this distance I wrapped teflon tape around the rim of the eyepiece rim to form a 1/8" spacer. I then pushed the eyecup in, and then wrapped a strip of electrical tape around the eyecup to hold it in position. Now, when I push the connector onto the eyepiece it snaps on to form a secure adaptor that is stable and won't wobble with the camera attached. With the cap and compression ring I can use the Coolpix handheld, or with just a slight turn of the cap, I can secure the camera to the adaptor for hands-free operation. One word of caution, however, with the camera secure I am unable to zoom the lens without getting "Lens Error". I therefore have to loosen the cap before I can zoom in or out w/ the camera. But its easy enough to loosen and tighten and I can quickly make adjustments on the fly. To make the cap operate smoothly I wrapped the threads of the connector with the teflon tape. To test the setup, I taped a resolution chart to the garage door and set the scope up about 20' away. I focused the scope and 40X eyepiece on the center of the chart, noting that the black frame of chart is at the widest point when looking through the eyepiece. I then took images using the 10 sec. self-timer with the camera set to Aperture Priority, each time zooming the camera in from 6mm, 7.3mm, 11.1mm, 16.7mm, to 24 mm. Note that the slight amount of vignetting at 6mm is just about eliminated by 7.3 mm. Compare with the vignetting at 6mm using the 20-60X zoom eyepiece. Magnifications remain sharp all the way to 18 mm, with images appearing slightly soft at 24 mm. At 24mm the lens barely touches the eyepiece, causing a slight amount of center-shadowing. If I move the camera back about 2 mm I get more even illumination, but still end up getting a soft image. For this matter, It is better to capture an image at lower magnification (12-18mm) and crop - you'll find that your images are much sharper. And at this magnification you do not need to worry about pixel loss. Even under bright sun and high contrast the 40X eyepiece shows almost no chromatic aberration. If you look along the edges of the black square there is the slightest amount of bluish or magenta tinge, but this shouldn't be noticeable except in the most extreme conditions of lighting. So, how does it perform in the field? I took the adaptor out to Pt. Mouillee SGA in Monroe Co., MI yesterday morning and digiscoped these Mallard ducklings from about 80'. Here are the images (uncropped) at 6mm, 12 mm, 17 mm, and 24 mm. Pretty darn cute at all magnifications! I will say that the adaptor was not quite aligned yesterday as it is today, since the 1/8" spacing was about 1/4", resulting in a bit more vignetting at 6 mm and more shadowing at 24 mm. I think image quality will only improve now that things are a bit more centered. Here's a Dunlin in worn alternate plumage with a missing foot. Digiscoped from about 70'.