Scope DOCTOR Steve Richards
Our resident equipment specialist cures your optical ailments and technical maladies WARREN BROWN
With a budget of £1,500, I’m trying to decide on a scope for my roll-top roof observatory. I’m torn between a Celestron 9.25 Schmidt-Cassegrain or a Sky-Watcher 250-300 Newtonian. Can you advise?
There are several pros and cons for both Schmidt-Cassegrains and Newtonian telescopes, but in a observatory there is one key issue: the position of the eyepiece holder on a Newtonian reflector when it is installed on a pier.
This is an important consideration because the height of the observatory walls will dictate how high you need the pier to make sure you are able to observe close to the horizon with your chosen telescope. The higher the pier, the greater the risk of having to use a stepladder, a high seat or even stand on tip-toes when observing objects near the zenith with a Newtonian like the Sky-Watcher ones you mention. From direct experience with a Sky-Watcher 250, a Newtonian can be a disadvantage in an observatory environment, and a Schmidt-Cassegrain like the Celestron 9.25 would avoid this problem.
It would be possible to mitigate some of the issues using a Newtonian by adding weight to the front of the telescope, thus allowing the telescope tube to be moved down the tube rings a little. However, a telescope of this size already requires a heavy duty mount, even without this additional weight, and this would put your budget under pressure for a less
than satisfactory solution. Bridge cameras aren’t particularly suitable for astrophotography as their large physical diameter lenses are not interchangeable, but they can be pressed into service for afocal imaging. This is where you hold the camera up against the telescope’s eyepiece, rather than the usual method of attaching a camera body (without lens) directly to the telescope’s focuser, which is called prime focus imaging. The problem with afocal imaging with this type of camera is that the large lens diameter produces a ‘port hole’ view of the night sky!
There are several adaptors that support ordinary compact digital cameras but these are mainly unsuitable for bridge cameras. However, the 365Astronomy Digital Camera Microstage Adaptor for Telescopes or the Baader MicroStage II Clickstop Digital Camera Adaptor both have a wealth of adjustment to help align the camera’s lens with the eyepiece and should be able to accommodate the Sony H300.