The Howland Digiscoping Conclusions Page
The Howland Digiscoping Conclusions PagePage by Royce
Last update: $Date: 2003/06/22 05:54:48 $ (UTC)
Note: This page is still under construction, as our equipment for and experience with digiscoping evolves.
This page documents whatever conclusions we have been able to reach as we work through testing and general experience at digiscoping. These conclusions mainly relate to our own digiscoping configuration, but some of the information is bound to translate to other configurations as well, especially ones with similar characteristics (e.g. other reflector scopes or other digital cameras with high native optical zoom, large objective lenses and movable lens elements).
We will post updates based on new experience, personal testing and information from other people and sources, but in the meantime this is our best take on what's going on. Likely there is a lot of professional and/or scientific basis for what we're trying to explain on these pages so feedback is welcomed from anybody with a more solid understanding of what we're blathering about.
The ScopeTronix 90mm Maksutov-Cassegrain scope is a great scope for use by eye. It is relatively light and compact as reflectors go, and gives bright, clear viewing. However, as with most reflectors, it is more complex, fragile and susceptible to moisture than typical refractor scopes. So if you are considering a reflector, think about whether you're willing to put up with giving more attention to your scope, or if you would prefer something more "fire and forget".
A big advantage of reflectors like the ScopeTronix, if you're on a budget, is that they are far cheaper than refractors of equivalent aperture and focal length.
Personally, we also really like the chromatic quality of the ScopeTronix, something that reflectors often have over refractors according to our research. We were really surprised at how much better the image quality was in general compared to our first Bushnell 20 - 60X refractor scope, a cheap entry level model.
We also like the standard astronomical-style 1.25" eyepiece mounting used by the ScopeTronix Mak scope. While some refractors use the same type of eyepiece, most instead use a proprietary threaded or bayonet-style mounting. If you get a scope that uses 1.25" eyepieces, you will have access to a virtually unlimited selection of eyepieces, filters and other optical widgets for every occasion. Plus, you can quickly and easily swap eyepieces without sacrificing much by way of stable, secure mounting.
Unlike most reflectors, the ScopeTronix Mak is "fast". You will see F numbers quoted for most higher end scopes. The F number is the ratio of the scope's focal length to its objective lens diameter. The ScopeTronix Mak focal length is 500mm and the objective lens is 90mm, thus this is an F5.6 scope. Most reflectors seem to be above F10.
F5.6 is called "fast" because a smaller F number means you get a faster shutter speed at a given level of magnification in a given amount of light, compared to a larger F number. (Why? The short answer is "physics.") This may be a good or bad thing depending on what you're trying to photograph. Faster shutter speeds can reduce blur in more active subjects, which is good at very high magnification. But they can also introduce "noise" into the image, which is not a good thing at very high magnification.
People doing astrophotography generally want higher F numbers because they need slow shutter speeds when photographing dim objects in the night sky. My personal, semi-educated opinion is that a lower F number should be better for nature photography as long as the photographer is aware of the trade-offs and manages the camera settings appropriately. But I won't go to the wall on this opinion.
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One key point related to the equipment upon which you mount your scope and camera -- stability! Human motion is one of the biggest enemies of good, clear photographs at high magnification, so you want to have a solid tripod and a head that securely takes the weight of your gear. There are a lot of heads out there. I originally started out with a Manfrotto 222 grip ball head. This head has a squeeze grip that, with a single control, allows rapidly altering the viewing angle through a huge volume of space. Releasing the grip instantly locks down all axes of motion. Sounds great, right? Yes it is, in general, and for lighter loads. But my scope + camera combination was simply too heavy and unstable.
So I acquired another head, a Manfrotto 700RC2 fluid head. This is a more traditional "pan and tilt" head with two separate controls, one for panning left-right and one for tilting up-down. The arrangement is less convenient than the grip ball head, and covers a smaller volume of space, but it's a lot more steady and stable under the load of my scope and camera.
You may also want to make or purchase a sliding balance plate to mount between your head and scope. If you normally use the scope for viewing by eye as well as for attaching your camera (assuming you're not one of those steady souls who digiscopes by hand-holding the camera to the scope), you will find that the camera weight can change the center of balance on the head substantially. This may make it tougher to keep the whole scope and camera assembly from shifting depending on how tight you can or prefer to dog down the head. It can also make things a little more challenging when tracking a subject with an unbalanced mass atop the head.
A sliding balance plate allows you to quickly slide the equipment mounted to it back and forth, altering the center of gravity along the long axis of the plate. This can be a handy thing.
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For many people, the reaction to magnification might be that more is better, and in fact much more is much better. Especially if you are like me, frustrated by tiny, distant subjects that you simply can't ever capture adequately with your camera's native optics. However once you start getting the magnification up there, you find that massive magnification is actually not that useful.
First off, as magnification increases, the brightness of the subject decreases. When digiscoping, this also then means that shutter speed decreases. So you may have a subject largely filling your field of view, but a photo taken at that point may be dim and subject to blurring from even the tiniest motion in the subject or tripod / scope / camera.
Second, more magnification reduces the field of view available. Depending on how high a power you reach, it can become quite difficult to actually locate your subject with the scope. In addition, if you don't have your focus close enough, the very shallow depth of field that pertains at high magnification may mean that you pan right by the subject even if you hit the right spot. So if possible you want to try to locate your subject and get an approximate focus before hammering in the highest level of magnification possible.
Thirdly, more magnification is not necessarily a good thing if it exceeds the optical resolving capability of the scope and camera. The physics of the optical system place an upper limit on how much magnification you can get before resulting photographs start going fuzzy, even if you have the scope focused exactly right. My casual research and reading seems to indicate that most good digiscopers shoot their best photos at a total magnification of 20 - 30X. So keep that in mind before you try to dial it up to 11. This is a lesson I learned the hard way. (Fortunately, the hard way is not that hard when shooting digital, as long as equipment sunk costs were not put into fundamentally wrong or mismatched gear.)
A downside that comes with the reflector type of scope is the "doughnut hole". Certain combinations of factors can produce darkened blots at the center of the viewing area, as well as spherical distortions surrounding the center of the field of view. This typically is not a problem with viewing by eye, but is a real factor when digiscoping. These effects are triggered by the central obstruction of the scope's objective lens, and the physics of the optical reflecting system.
One of the biggest challenges in digiscoping is getting the proper focus on the subject. Typically your depth of field is going to be very short, so getting the focus right is critical. If you're even slightly off, you can kiss the shot good-bye. Ideally you want to be able to focus quickly, but also have very fine-grained control over the focus as well. Unlike focusing your camera with a telephoto lens, with digiscoping you will have to focus using the scope itself. Camera focus should be set on "infinity".
The Leica scope system with both coarse-grained and fine-grained focus controls is great. I think some other vendors are starting to offer the same thing. While the ScopeTronix Mak has good fine-grained focus control, radical changes in distance to a target will be slow to accommodate. This makes it tough to track an active subject.
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