The Howland Picture Pages: Digiscoping Experiments
Round 3 The Howland Picture Pages: Digiscoping Experiments
Round 3Page by Royce
Last update: $Date: 2004/02/24 04:30:14 $ (UTC)
After several months digiscoping with various combinations of equipment (summarized in the chart on the main digiscoping page), I have stabilized on a configuration that produces good results:
I still have the equipment used in earlier, essentially unsuccessful attempts at digiscoping. These include the Nikon CoolPix 5700 camera, which I use for hand-held shooting, often with a 1.5X teleconverter. The camera is good for this purpose, even though it proved unsatisfactory for digiscoping. However the lack of a really usable manual focus capability and annoying autofocus behavior recently prompted me to move to a Canon EOS 10D digital SLR camera for hand-held shooting. More on that topic in a future update.
I also still have the ScopeTronix 90mm Maksutov-Cassegrain scope and MaxView 40 eyepiece, for example. A few recent posts with questions from people on the Yahoo group "digiscopingbirds" convinced me it was time to try a few combinations of equipment that I had not previously experimented with. Mainly I planned to try a couple of different configurations:
This page shows a collection of images comparing image quality of my current baseline configuration with the alternatives above. All photos are unretouched; the only processing that has been done is to shrink the thumbnail images directly shown on this page to 320 x 240 pixels. Quick links to the image series:
The results? While my tests were not completely systematic or exhaustive, there are two main points I could conclude from this round:
See the Digiscoping Experiments Round 1 page for my first batch of tests with my original setup, a Nikon CoolPix 5700 + ScopeTronix MaxView 40 and 90mm Mak scope. See also the Digiscoping Conclusions page for my evolving conclusions distilled from on-going rounds of testing and developing experience.
Bandwidth Warning: There are large images linked from this page! Use caution if you have a slow connection.
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Baseline: Images with CP 4500 + DCL-28 eyepiece + PF-80EDA scope |
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I did this entire sequence of test shots at the Randall Davey Audubon Center in Santa Fe, New Mexico on Sunday, February 15, 2004 . I set up my kit about 12 meters from a bird feeder that was attracting a few of the winter species visiting the Canyon Preserve. Birds not visiting the feeder would sit in a couple of trees about 3 meters further away. This situation made for good photo opportunities while switching through various configurations of equipment. Here are some baseline photos taken with my "standard" configuration, consisting of a Nikon CoolPix 4500, William Optics DCL-28 eyepiece, and Pentax PF-80EDA scope. Each picture was taken at f/6.0 which is just outside the "yellow flower macro" zoom level on the camera, and translates into about 18.9mm of camera focal length (~91mm in 35mm equivalent terms). Combined with the eyepiece and scope magnification of 21.5X, this translates into roughly 1970mm in 35mm terms. I commonly shoot at this amount of zoom to guarantee best results in sharpness. |
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Baseline photo #1:
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Here is a Dark-eye Junco at a distance of around 15m.
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Baseline photo #2:
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Here is a Dark-eye Junco at a distance of around 15m.
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Baseline photo #3:
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Here is a House Finch also at a distance of around 15m.
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Alternative A: Images with CP 4500 + MV40 eyepiece + PF-80EDA scope |
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This next series of photos was taken with an alternative configuration, switching out the William Optics DCL-28 eyepiece for the ScopeTronix MaxView 40 (40mm) eyepiece but leaving everything else the same. A variety of camera focal lengths were used to test for vignetting on the short end, and image softness on the long end. Summary result: The ScopeTronix MaxView 40 eyepiece works pretty well with the Nikon CoolPix 4500 camera and Pentax PF-80EDA scope. Given the trade-off of lower scope magnification but greater usable camera zoom range, I'd rank the MV40 as my second choice in eyepieces for common use. The reason I would still give a slight edge to the William Optics DCL-28 is that the DCL-28 is a more compact eyepiece that doesn't require a telenegative adapter lens to work with the Pentax scope, and it offers slightly more reach than the MV40 before images start becoming unusably fuzzy from over-magnification. |
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Alternative A photo #1:
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Here is a Canyon Towhee at a distance of about 12m. Notice the darkened upper left and upper right corners. This doesn't appear to be vignetting, but does seem to indicate that something in the line of sight is off-center. Camera focal length is 18.6mm, about the same as used for the baseline images. Image sharpness is good.
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Alternative A photo #2:
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Here is the Canyon Towhee again at a distance of about 12m. Camera focal length was reduced to the short end of the "yellow flower" macro range, and sharpness remains good. But now there is a good dose of vignetting in addition to the off-center darkening. Since the camera lens should have an AFOV of around 36 degrees at this focal length, which remains less than the MV40's 44 degrees, the vignetting can't be a result of mismatched AFOV. It may be triggered instead by the gap between the camera lens and MV40 lens, introduced by the 28mm-to-T step ring.
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Alternative A photo #3:
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Here is a Dark-eyed Junco at a distance of about 15m. Notice the darkened upper left and upper right corners are still happening, but sharpness is reasonable.
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Alternative A photo #4:
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Here is another Dark-eyed Junco at a distance of about 15m. The darkened upper corners are less noticeable in this shot because of the composition. Sharpness is still reasonable, considering that Juncos are low-contrast subjects and I took all of these images using the camera's autofocus. Nikon CoolPixes used to be notorious for having autofocus problems in low contrast situations. They are better now but still not without room for improvement.
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Alternative A photo #5:
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Here is yet another Dark-eyed Junco at a distance of about 15m. Camera zoom has been increased to 23.1mm at f/6.7. I could have dropped the aperture back closer to f/6 again but neglected to do so, which impacted the shutter speed. At this point with the DCL-28 eyepiece, image fuzziness would begin to appear but with the MV40, sharpness is still reasonably good. The darkened upper corners are still there.
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Alternative A photo #6:
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Here is a Dark-eyed Junco at a distance of about 12m. Camera zoom has been increased again to 27.7mm at f/6.7. Shutter speed is quite reduced by now. Shooting with the DCL-28 eyepiece, there really is no hope of a sharp image at this point. But with the MV40, sharpness is still reasonably good for a portion of the subject, at the chestnut back feathers and above. The blurry portion at the wing feathers and below probably results from motion by the bird. The darkened upper corners are much less noticeable here, or even gone. I presume that the increased camera zoom has narrowed the camera lens AFOV to the point where the off-center optical imperfection is not really observable at this point.
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Alternative A photo #7:
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Here is the same Dark-eyed Junco shown in the previous photo, at a distance of about 12m. Camera zoom has been reduced again to 18.9mm, just at the top end of the "yellow flower" macro range. Sharpness is good, and oddly enough the darkened upper corners are no more noticeable in this shot than they were in the previous one. So it seems that camera focal lens is not the only factor causing the light loss; could scope focal point be affecting it as well? Or perhaps I simply joggled the equipment a little bit and the camera and eyepiece are now lining up better on the scope's focal axis.
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Alternative A photo #8:
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Here is a much larger subject, a Western Scrub-Jay at a distance of around 15m. I do not have a direct comparison shot of the Jay taken with any of the other configurations, but I would say the quality of this shot is equal to what I'd expect with the DCL-28 eyepiece. Once again, the darkened upper corners are back. In terms of timing, this shot was taken first of this series. So if an equipment adjustment was responsible for removing the darkened corners in photos #6 and #7, that would make sense.
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Alternative B: Images with CP 4500 + WA18 eyepiece + PF-80EDA scope |
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This next series of photos was again taken with an alternative configuration that involved switching out the eyepiece used in the baseline setup. In this case, a ScopeTronix WA18 (wide-angle 18mm) eyepiece was used instead of the William Optics DCL-28 eyepiece. Summary result: As I have found before, the ScopeTronix WA18 eyepiece is only marginally suitable for digiscoping. (Its sibling eyepiece, the WA14 at 14mm, is not suitable at all.) Images are simply too fuzzy across too much of the camera zoom range for my taste. The eyepiece is borderline at lower camera zoom levels, but why mess with such a suboptimal situation when either the William Optics DCL-28 or ScopeTronix MaxView 40 works much better across much more of the camera zoom range? |
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Alternative B photo #1:
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Here is a Dark-eyed Junco at a distance of about 15m. The eyepiece has no trouble with vignetting, nor with the darkened corners that were evident in a number of the MV40 images above. This shot was taken at 18.9mm zoom on the camera, which is at the top of the range I normally shoot with the DCL-28 eyepieces ("yellow flower" macro). The thumbnail at left probably looks okay in terms of sharpness. But when the full resolution file is opened, it is noticeably fuzzy in comparison to shots with the DCL-28 or MV40. At 18mm, the eyepiece is producing around 28.75X magnification on the scope. This image therefore is around 2630mm in 35mm equivalent terms. To get down to around 2000mm where I find sharpness comes through well, camera zoom theoretically would be limited to perhaps 15mm at most. But see the next image for an example of theory not working out in practice.
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Alternative B photo #2:
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Here is another Dark-eyed Junco, also at a distance of about 15m. Camera zoom was reduced to 14.2mm, near the bottom of the "yellow flower" macro zoom range where I normally shoot with the DCL-28 eyepiece. This translates roughly to 1975mm in 35mm equivalent terms. While the thumbnail looks reasonable, and indeed the full resolution image is not terrible, it still isn't up to the quality of either the DCL-28 or MV40 eyepieces at an equivalent 35mm focal length. Dropping camera zoom even more can help with the WA18 eyepiece, but at this point the camera zoom range is heavily restricted. With alternative eyepieces available that allow much more of the camera zoom range to be used, I wouldn't see any reason to prefer the WA18, even though the wide angle (66 degrees of AFOV) is very attractive. The eyepiece is simply too powerful with my combinations of equipment.
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Alternative C: Images with CP 4500 + MV40 eyepiece + 90mm Mak scope |
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With this alternative configuration, I switched out the Pentax PF-80EDA scope for the ScopeTronix 90mm / 500mm Maksutov-Cassegrain scope. Since I had the MaxView 40 eyepiece mounted at the time, I kept it in place. See the final series (Alternative D below) for images using the DCL-28 eyepiece. The 90mm Mak is a light, compact reflector that I purchased for my first digiscoping configuration. I chose it because of its low price and the excellent reputation of reflectors for brightness and true color. At the time, I was using a Nikon CP 5700 camera and MaxView 40 eyepiece, and was unable to get satisfactory results. (See the Digiscoping Experiments Round 1 page.) After a bunch of research and chatting with other experienced digiscopers, I concluded the weak link in my equipment chain was the scope, so I immediately retired the 90mm Mak and went with a Pentax PF-80EDA. This scope didn't work all that well with the CP 5700 camera either, although this time it was mostly because of the camera. So I retired the CP 5700 from digiscoping and acquired a CP 4500 with a William Optics DCL-28 eyepiece. This camera and eyepiece worked well with the Pentax scope, and has become my standard digiscoping setup. However, out of a sense of needing to close the loop on possible equipment configurations, plus curiosity to respond to a few folks with questions about the suitability of short focal length Mak scopes, I decided to try the 90mm Mak once again. This time with my latest camera and eyepieces. In this series, I used the ScopeTronix MaxView 40 eyepiece. It should be noted that most of the images in this series use a high camera zoom level, none of them down in the "yellow flower" macro zoom range that I normally shoot at. The reason for this is that I could not avoid donut or spherical image distortion in the image when the camera was zoomed less than about 27mm. This was a somewhat perplexing interaction between the scope, eyepiece and camera. Changing the eyepiece for the DCL-28 (see the next series) produced very different behavior, avoiding the optical distortions across a much greater camera zoom range. Summary result: The ScopeTronix 90mm Mak scope doesn't work at all well with the CP 4500 and MaxView 40 eyepiece. Images are washed out and fuzzy, and the usable camera zoom range is heavily restricted by donut-shaped optical distortion in the image caused by the central obstruction in the scope's objective lens. This configuration is not one I can recommend at all for digiscoping. |
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Alternative C photo #1:
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Here is a Dark-eyed Junco at a distance of about 15m. In this photo, maximum camera zoom of 32mm was used, equating to roughly 1940mm in 35mm terms. Despite this being within the theoretical range for sharp images, the full resolution image is noticeably soft. It is also somewhat washed out in comparison images from the Pentax scope.
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Alternative C photo #2:
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Here is another Dark-eyed Junco at a distance of about 15m. A camera focal length of 32mm was also used for this shot, and again I find the results to be soft and washed out in comparison to images from the Pentax scope.
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Alternative C photo #3:
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Here is a different subject, a House Finch at a distance of about 15m. Camera zoom was reduced slightly to 27.5mm, or about 1665mm in 35mm terms. This is now well inside the range for sharp images, but the photo is still soft and again seems drab and washed out.
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Alternative C photo #4:
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Here we have the same House Finch at a distance of about 15m. Camera zoom is back to 32mm, and as before the image is soft and washed out.
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Alternative D: Images with CP 4500 + DCL-28 eyepiece + 90mm Mak scope |
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With this final configuration tested, I kept the ScopeTronix 90mm Maksutov-Cassegrain scope in the mix, as with the preceding series, and switched the eyepiece back to the William Optics DCL-28. Given the trouble I had with optical distortions in the previous setup, I was expecting this combination to be worse since the DCL-28 is a higher powered eyepiece. However, the opposite was the case -- donut and other spherical distortions were absent across a much larger camera zoom range than was the case with the MaxView 40 eyepiece. Summary result: Despite less trouble with optical distortions, image quality is still unacceptably soft and washed out, in my opinion. I surmise that the resolving power of the scope's optics are not up the same level as the Pentax scope. Thus the ScopeTronix 90mm Mak strikes out permanently in my books as far as digiscoping goes. I still like it for visual use, however. |
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Alternative D photo #1:
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Here is a Dark-eyed Junco at a distance of about 12m. Camera focal length is 18.9mm, at the top my normal shooting range in "yellow flower" macro mode (about 1970mm in 35mm terms). The optical distortions that plagued the MaxView 40 eyepiece are not present with the DCL-28 until much, much lower zoom levels. However, the image is still washed out and image softness is far worse than it was with the MV40 at 32mm of camera zoom. Shutter speed wasn't great for this shot, so perhaps some of the blur is due to motion in the subject. Still, this kind of result is very poor compared to what one would expect.
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Alternative D photo #2:
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Here we have a House Finch at a distance of about 12m. Camera focal length is slightly increased to 19.5mm. Things are still washed out, and sharpness is improved from the preceding image. But it still is poor considering the low compound focal length, good light, close distance, etc.
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Alternative D photo #3:
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Here is another House Finch at a distance of about 15m. Camera zoom is increased. As before the image is very soft and washed out. I suppose this shot might have some artistic value in an impressionist vein.
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Alternative D photo #4:
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Here is the friendly Canyon Towhee at a distance of about 12m. Camera zoom is up at 29.7mm. While detail is evident in the image, the quality is still soft and faded rather than crisp and more vibrant as with the Towhee image taken with the MV40 eyepiece and Pentax scope.
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Alternative D photo #5:
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Here is a second shot of the Canyon Towhee at a distance of about 12m. Camera zoom is back down to 17.5mm, well within the range that should produce sharp results. But the image is still soft and faded.
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Alternative D photo #6:
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Here is a more elusive subject, a Spotted Towhee at a distance of about 12m. Camera zoom is at my standard shooting focal length of 18.9mm. A shot that should have been nice and sharp turned out very soft and washed out.
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Alternative D photo #7:
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Here the Spotted Towhee again at a distance of about 12m. Camera focal length remains at 18.9mm. This shot is a bit clearer than the preceding image, but remains very soft and washed out.
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