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Digiscoping with a DSLR is still a good choice in 2022! (1 Viewer)


I've been working on my digiscoping system for a while. Earlier this month I finally took it out for a birding trip along with a friend.

My birding pal uses a Canon R6 and Sigma 150-600mm (sports) lens at the 600mm end. My digiscope consists of a Nikon D7200 SLR body, and a Nikon ED78 field scope. It looks like this:


(Yeah I know my system is weirder than usual digiscopes... I'll explain it next time.)

I compared the image of my digiscope with my friend's -- it turns out that though my equipment is much cheaper (~30% the price?), it produces better resolution!

We took photos of an eastern marsh harrier simultaneously. This bird of prey was hovering above the fields, about 500 meters (1/3 miles) away. This is what I got (or see it in the gallery Eastern marsh harrier):


My eyepiece is 50x WDS. The field of view is very small, less than half a degree. Birding with it is not an easy task, but worth the effort!

(Based on the image, I've calculated the equivalent focal length of my digiscope to be around 2000mm.)


Let's zoom in and have a look at details:


As is marked in the image, the bokeh of the left image is luscious and creamy, and the foreground subject is explicit. The depth of field of the 600mm lens is not satisfying, I think that's due to the distance, though a review says it produces well-rounded even at F8.

Also, the patterns on the neck are clear. Even the shape of the eye can be marginally identified! There are only some shadows on the other image. -- Note that this camera lens was reviewed as "very sharp" in 2021.

Actually, as the FOV of the lens is much larger, the patterns are smaller than the pixel size. The digiscope produces enough magnification that the image can reach the maximum resolution of the optics.

Digiscope vs. Camera lens -- 1:0!!!

(To be clear, I'm not a professional photographer. For me, taking pictures while birding is only for two reasons: fun, or to identify birds. Resolution is critical to the later purpose. Sometimes it is essential to tell the pattern on a goose's beak or the shape of a crow's forehead, that's when my digiscope is superior to some long-focal-length camera lenses.)

I still have to point out some defects of digiscoping though:

1. The aperture size is fixed by the diameter of the field scope. Usually, a field scope's size is smaller than 100mm, which means you'll have a dimmer view compared with using large camera lenses.

2. Due to the aperture size, you have to set a very high ISO value (causing noise) when it requires a high shutter speed. Otherwise, your images will be dark. According to my experience, only during a bright day can you derive acceptable images, if you want to capture a moving object.

3. My system can only focus manually. It is definitely not easy to evaluate the sharpness of a flying bird.

4. The system is heavier than a normal camera with a lens, especially with the tripod.

5. The magnification of my digiscope is too large, sometimes it's hard to find the bird in the field, and the slightest shake can cause blur.

(Problem 3-5 have been solved.)

I'm going to use my digiscope to photograph some passing-by migrating raptors on a mountain peak next week, looking forward to seeing its performance. Please let me know if you have any questions or suggestions!
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The magnification factor is difficult to convert into equivalent focal length. With binoculars the magnification refers to nominal 50mm camera lens on full format i.e. 8x is roughly 8 times 50 = 400mm. That 8x means eight times closer not eight times bigger, we need the field of view angle and to do some trigonometry. But when we stick a camera on the back of a scope it is confused by a crop factor as we like the image circle to cover at least the sensor diagonal. We may crop in a bit more than that as a scope is inevitably sharpest in the centre and we do not want the fuzzy edges.
When we stick a camera or phone on the scope with a lens, the magnification factor is altered by that glass, assuming it can focus and fill the frame. The phone can do the digital zoom but lacks the range of controls offered by a camera.
When we attach the camera (without camera lens) typically with a T-adapter we now have to arrange the "flange to sensor" distance correctly to within a fraction of a millimetre to obtain the sharpest image possible. There is probably some gap in the scope adapter between the ocular and the T-thread to be added to the camera T adapter distance, and a standard T2-camera may be the wrong thickness.
To find this distance, remove the adapters and move the camera sans lens in and out by hand to find where the image becomes sharpest (with the scope focused without spectacle correction), you may need another tripod. Note the distance and arrange to place the camera there on its adapters. It may need a non-standard thickness camera flange adapter, they are out there, they're used a lot for astrophotography. The back focus distance is a function of the lens optics (the scope ocular) not the camera body.
My wildlife camera is the Panasonic G9 with Leica 100-400, which is huge (x2 crop), and hand-held thanks to the insane Dual stabilisation. It can be panned around like a flyswat whist tracking and bird detection AF. I do have other MFT cameras and lenses, the little Olympus E-PL7 seems to suit the digiscope very well. Scope is merely a Praktica Hydan 20-60x77 but they do provide a very reasonably priced substantial screw-on camera mount over the ocular with a spring-loaded plate on the rubber eyecup to exclude unwanted light intrusion. And that required the thinnest T2-MFT adapter, effectively zero flange (fortunately I have a selection for astrophotography).
Bird photography always requires a fast shutter to quell movement blur. Then we have light gathering. A camera lens will be "soft" wide-open The PL100-400 (and the old Bigma) want to be stopped down to f/8 or more but with enough light can still run 1/640 to 1/2500 at low ISO. The Hydan, if 20x is "1000mm" then 1000/77= f/13 and hence 20x f/26, but without the typical diffraction of aperture leaves, just the edge of the glass which we have cropped off. With the camera/lens, having to use f/13 - f/16 is common to reduce light, so f/13 is usable on the scope, but f/26, half the light, is not much fun. The Hydan does remain sharp to 50x and 60x is usable for visual but above 25x (f/16?) struggles for photography light. The scope is never going to match the quality of the camera lens but it is very much longer, the 4/3 sensor "crop" probably doubles the magnification. Hence the digiscope does not need the extreme crop-in with attendant pixelation.
Addenda ;)
As a retired scientist it is inevitable that I experiment between digiscope and camera/lens.
1) aperture, the f-number is defined as focal length divided by iris diameter, the objective size. The aperture is a ratio, a number proportional to the light transmission, irrespective of lens size and camera format.
2) ISO noise. Do see Mike Lane FRPS on YouTube assessing his OM-1 for acceptable noise. I repeated his test with my cameras. It is simple, I like simple. For my sins, amongst other things, I used to assess and characterise radiological instruments, devise the tests, simple is good, the laboratory technicians all get the same results no matter who does them. What I found is all the more modern cameras start to show noise at ISO 6400. The 2012 Nikon D600 falls into this category too, from about 2013 sensors got better, but despite many claims, have not improved much since. What has improved is the noise handling, instead of looking speckled, they now just look a bit grainy (like fast film did). This ties in with the aperture (1) above.
3) MF can be a pain. Old school with film-SLR we'd anticipate where birdie would be and trigger the shutter there. I do have MF-only lenses, like 800mm f/8 reflex, they're certainly not for quick reaction.
4) The scope is about as heavy as a big lens and lighter than some. And then we have carbon tripods, they really are light and worth getting if you have to carry. Some tripod heads are more wobbly than others.
5) I have a red dot pistol sight I can mount in the hot shoe (or elsewhere), it certainly helps. Body-IS (IBIS) takes a lot of the camera shake out whilst trying to frame the shot, even on tripod with a telescope and MF bouncing it about. With the G9 using "Dual2" there is no camera shake, I can use it like a ping-pong bat with the longest native lenses.
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