Afocal coupling experiments

The “proper” way to do astrophotography is to use a camera with interchangeable lenses such as a single lens reflex (SLR) camera. The camera lens is removed and the telescope objective or mirror is used instead. This “prime focus” technique gives the best quality but the magnification is fixed unless Barlow lenses or focal reducers are used.

I’ve recently bought a digital SLR (DSLR) camera, but before then I experimented with another technique — “afocal coupling” or “digiscoping”. In essence, this is no more complicated than focusing the telescope visually, then holding the camera lens up to the eyepiece and photographing the image. The difficult part is holding the camera in the right place.

One of the reasons I bought a Nikon Coolpix 4500 camera is that it has a 28mm filter thread at the front of its lens, and that this is rigidly fixed to the body. This makes it fairly easy to securely attach the camera to an eyepiece.

Initially I used generic Plössl eyepieces with a T-threaded adapter ring made by ScopeTronix that clamps to the eyepiece in place of the rubber eyeguard. I soon invested in two eyepieces that already had threads: a 40mm “SuperView” Plössl with a T-thread from Teleskop-Service and a 14mm “MaxView” widefield with a 28mm thread from ScopeTronix. Since then I’ve bought other eyepieces with 43mm threads: 17mm & 13mm Baader Hyperions and a 10mm Pentax XW.

I’ve tried various combinations of eyepiece and telescope, and have written up the results in these pages:

You can see some astrophotos taken with some of these eyepieces on my astro photos page.