Wildlife photographers often wish they owned a longer lens of 500mm or so to taking close ups of birds and other smaller creatures. And often they may  already have such a lens in the form of a spotting scope. By attaching the camera to the rear end of the spotting scope you create a lens with a similar  magnification to that of around 800mm
This technique is referred to as digiscoping.

You need to buy an adaptor to attach the camera to your spotting scope. These are often specific to the spotting scope and with the exception of a few

camera brand adaptors, they usually all have a T2 mount thread at the camera end. So you buy the adaptor, attach it to the scope and then screw in a T2  adaptor that’s specific to your camera mount. We have the T2 camera mounts here at PhotographyAttic

Camera specific scopes such as the Pentax PF80D need the PF-CA35 which has a direct camera mount.
The Nikon Fieldscope range including the EDIII A need the FSA-L1. Nikon also produce the FSA-L2 for exclusive use on EDG Fieldscopes

Opticron have a wide range of scopes and several adaptor combinations all requiring a T2 mount at the camera end.  See the Opticron Telephotography and Digi-scoping page for more details

Swarovski also have a range of scopes and a really informative page on digiscoping: Equipment – spotting scopes, cameras, etc.  You need a T2 mount with their systems

Barr & Stroud supply a spotting scope adaptor for their Sahara and Bresser Safari spotting scopes. T2 mount required. This adaptor also fits some Helios, Bresser,  Meade and Praktica spotting scopes.

Leica’s DSLR Photo-adaptor allows T2 mounted SLRs to be attached to the Leica Spotting scopes

T2 adaptors do not have any form of electrical contacts so you have to use your camera’s manual or aperture-priority mode.  As the spotting scope doesn’t  have apertures you just point and shoot and the camera will set the correct shutter speed. You could use the ISO setting to adjust shutter speed and increase the ISO for a faster shutter speed.

Focusing is manual. Focus the scope like you normally would but take more care on accurate point as the lack of depth of field will mean you have to be spot on to get a sharp photo. Also the increased magnification will make it difficult to hand hold so it’s better to use a tripod.

Further reading
Peta Pixel have an interesting article comparing the use of a Spotting scope against a Canon Super telephoto

To be successful with bird photography you either need a very long lens or a shorter lens with a remote control (or hide) so you can position yourself far enough away to avoid frightening the creature.

The long lens approach needs to be around 500mm allowing you to magnify the bird so it appears substantially more than a spec on the photo.

The shorter lens approach (300mm or less) and you probably need to hide (in a hide), or use a remote control.  This is the approach I took for this shot of a blue tit preparing to nest in a box in the garden. I’d watched the bird’s activity for a few hours and noticed it landed on a particular branch of the nearby tree. So I mounted the camera (an Olympus OM-D EM1) on a tripod and focused on that particular branch. It  was about a meter away from the branch and using the 40-150mm gave me a reasonable crop.

The focusing was set to manual so nothing could cause it to shift out of focus and the exposure was also set to manual adjusting to ensure that highlights on the bird wouldn’t be blown out.

I used a Hahnel Gigi T Pro II remote control and attached the receiver part on the camera flash shoe and plugged the cable into the camera.

I could then take the transmitter and sit out of sight, triggering the camera when the bird landed on the branch. To make things easier I used a  pair of 8×21 binoculars. With these I could look at the bird and fire when it was in the right position, and then look at the camera LCD as it flicked up the preview of the shot just taken.
To get a cleaner background you should ensure that any background bush is further away from the landing position, also use a large aperture to reduce depth-of-field.

If you don’t have a modern camera with an electronic socket for a remote release you can buy an air release with a bulb to trigger the camera via the cable release socket.

Here are some cable releases and remote controls