Sunday, February 8, 2009
Limitations! - 08 Feb 2009
I decided to put this post together after playing a bit this morning with the digiscoping setup. The Common Redpolls, Pine Siskins and American Goldfinches were going to town on the thistle feeders outside the kitchen window, so I decided to open the window and digiscope from inside the house. I set the tripod in the kitchen sink (I moved the dirty dishes!....) and aimed the Zeiss 85T*Fl w/ 20-60X Zoom eyepiece to the feeders approximately 20 feet away. The Nikon Coolpix P5100 was set to Aperture-priority and I took my normal hand-held shots using my homemade adaptor (see previous posts). I've found recently that my most reliable photos come from setting the zoom eyepiece to 20X and the camera at its lowest setting (7.5mm). This gives me some vignetting, but also allows me to verify that I have correct camera / eyepiece distance when the vignetting is sharp. The magnification I get w/ the P5100 at 7.5mm is approximately equal to the view I get w/ the Nikon D300 and Sigma 400mm f/5.6 (actually its slightly larger: 1.3X). With the 1.5X crop factor of the D300 the 35mm equivalent for the DSLR setup is 600mm, so the digiscoping setup at 20X / 7.5 mm is ~ 780mm. Zooming the P5100 to 15 mm (or 2X) removes the vignetting and still gives a sharp image. Compare the image w/ the image taken at 7.5 mm and cropped to give roughly the same image magnification as the 15 mm image. Processing both images using the same workflow (Noiseware / sharpening in Photoshop) results in the cropped image appearing more sharpened with slightly more jpg-artifacts. Still, the image is acceptable even if the uncropped, 15 mm image looks nicer. Take home message here is that cropping to remove vignetting will give a very nice image for web viewing. I've found that image quality degrades drastically if I try to zoom the P5100 to the 3.5X setting (or 26 mm). Because the camera is not an internal zoom (its vari-focal) I believe that my adaptor prevents proper lens/eyepiece distance from being achieved (coupled w/ vibration magnification) that results in a soft image. So I've decided to not push the camera past about 2X if I want to maintain a sharp focus. The beauty of the 15mm setting is that images can be cropped to give a magnification equivalent of 26 mm without the aforementioned vibration issues. I can be happy with these images. As a side note: with a steady tripod, however, I will use the camera at 3.5X zoom setting in the Video Mode and get sharp videos. Note, however, that scope-to-subject distance drastically affects image quality. For example, this Cooper's Hawk was roosting in a pine tree behind the house approximately 80 feet away. Even though image quality was good at the 7.5 mm and 15 mm settings, there is significantly more of a grainy quality to the images and an overall softer focus, especially after cropping the 15mm image.