Digiscoping DSLR vs Point & Shoot
This set up offers fantastic imaging opportunities although it does not offer rapid exchange between imaging and viewing as a true digiscoping setup does. However, it is safe to suggest that this is one of the most fool-proof methods for imaging with a DSLR/SLR through a spotting scope, as you completely eliminate the coupling issues often associated with digiscoping (shadowing, vignetting, improper distance between lenses, etc.)
Leica APO Televid 77 spotting scope with Leica D-Lux 3 point and shoot camera
"Digiscoping", by definition, is the coupling of a camera with a lens to a scope with an eyepiece. This style of mounting (or holding) a camera with a lens behind a scope eyepiece to capture in image is referred to as an "afocal coupling" of two lenses. Unlike the previous example, afocal coupling is prone to a whole host of alignment issues which may result in vignetting, shadowing, flare, etc. However, the two great advantages of this type of imaging is it allows the user to rapidly move from viewing to imaging and back, and it offers far greater magnification than the SLR adapter above.
In the early days of digiscoping, cameras used were always smaller, lightweight digital point & shoot models, however, of late, some digiscopers are experimenting with mounting 35 mm DSLR's with 50 mm (or smaller) lenses attached. As with any digiscoping technique, opinions and quality of available information vary tremendously and some may even be a bit suspect. Below, I will try to fairly address advantages and disadvantages of digiscoping (afocal coupling) of both digital point & shoots, and DSLR bodies with 50 mm (or similar) lens.
Leica M8 rangefinder with 35 mm f/1.4 aspehrical lens (not a true DSLR)
The first thing one notices about a DSLR and lens vs. a digital point & shoot is a dramatic size and weight difference. DSLR's are getting less expensive and lighter weight all the time but still one of lightest DSLR's (with a plastic body) on the market today, tips the scale at 22.4 oz, the least expensive, lightest 50 mm (f/2.0) lens for this body weighs 5.1 oz, and a typical tubular adapter weighs an additional 7 oz. So all in all, a DSLR afocally coupled to a spotting scope will weigh (at minimum) 38.5 ounces or a bit over 2.4 pounds. Higher quality bodies and lenses will naturally weigh much more.
By comparison, a point and shoot camera with adapter such as the Leica D-Lux 3 and the Leica digital adapter 2 (shown mounted on scope above) are 7.8 oz & 9 oz respectively for a comb ined weight of 16.8 oz or barely over one pound. Many point and shoot cameras and adapters are even lighter as well. So this may represent near the maximum weight. The sleek Leica C-Lux 2 camera (pictured below), for example, is a mere 5.4 ounces. At any rate, for portability and weight the advantage clearly goes to the digital point and shoot. As a result, there is concern in some camps that the heavy DSLR's, could have lasting effects on both the scope eyepiece mount as well as the thin metal filter thread rings on the lens (which most DSLR adapters mount to). The filter thread rings are not built to support the weight of the lens and camera body, and there is concern that the DSLR would act like a lever on your eyepiece and (over time) could potentially compromise the waterproofing of your scope. As a result, it is wise to support the camera as much as possible when attached to the scope and remove this ASAP after imaging.
However, a 35 mm DSLR does offer some very real advantages in some digiscoping applications as well. Most DSLR's offer a wider range of manual control over most point & shoot (P&S) cameras, and a sophisticated photographer who understands these controls, can do more to increase the percentage of quality images they take. DSLR's are also capable of shooting bursts of images very quickly (as many as 7 shots per second in some cases), which is far faster than typical digital P&S cameras. Also, most DSLR cameras have a larger sensor screen than most digital point and shoot came ras (not surprising considering the average size differences). As a result, the larger sensor on the DSLR averages less "noisy" than the smaller sensor on a digital P&S. Digital "noise" is the equivalent of graininess in film cameras. Because of this, a DSLR can generally be set to a higher ISO setting, which results in higher average shutter speeds as compared to P&S cameras.
Unfortunately, some of this benefit is negated because a DSLR has a mirror that flops out of the way of the sensor. This mechanical "mirror slap" causes vibration in the camera. As a result, with all else being equal, a slow exposure on a DSLR will often show motion blur where a digital P&S camera may not.
DSLR's lose the ability to autofocus when mounted afocally behind a scope, while P&S cameras still offer this functionality. As such DSLR lenses need to be set at infinity with the autofocus switched to off. Focusing is accomplished by looking through the camera viewfinder and manipulating the scope focus until the image appears well focused. Some newer DSLR's do allow "live view" modes where you can use the LCD screen for focus, but on average modern DSLR screens are smaller and not as bright as newer P&S LCD screens (important note: screens on new models of P&S have incorporated backlighting and/or reflective features which make them far brighter and easier to see than cameras that are even 2 years old).
A few DSLR models offer image stabilization in the camera body but most don't. Some digital P&S cameras are also offering stabilization, but there is probably no clear cut advantage between DSLR & P&S across the board only between individual models in both categories.