Scope DOCTOR Steve Richards
Our resident equipment specialist cures your optical ailments and technical maladies
I’m looking to upgrade from binoculars to a good scope with a sturdy tripod, mount and Go-To facility. The Celestron NexStar Evolution has been suggested, but do you have any other ideas for a budget of £1,250–£1,500?
DAVID SHADRACH
With £1,250-£1,500 you have a very healthy budget for buying your first telescope and as such there are plenty of choices available to you.
Your first decision must be the type of mount that you need and the choice here is between an altazimuth and an equatorial mount. Celestron’s NexStar Evolution 6 falls into the first category. If all you’re going to be doing is observing the night sky, then an altazimuth mount is ideal, but if you have any aspirations towards photographing it in the future then an equatorial mount is an absolute must.
Your second major decision will be the focal length of the telescope. Those with a long focal length are better for fine detail and are ideal for galaxy, planetary nebula, globular cluster, lunar and planetary observing. Telescopes with shorter focal lengths can be pressed into service for a wide range of observations and are a better bet if you’re considering astrophotography.
The NexStar Evolution 6, a SchmidtCassegrain telescope with a 1,500mm focal length and altazimuth mount, would be a very good choice for observing, and costs around £1,100.
For a similar price, the Sky-Watcher Explorer 200P-DS HEQ5 Pro, with its Newtonian reflector telescope and shorter focal length of 1,000mm, would provide you with a larger aperture for observing and a good, heavy-duty equatorial mount that would open up the possibilities for capturing images.
Either choice would leave you with spare funds to purchase additional eyepieces and accessories to complete your observing line-up. As we age, our eyes’ dilated pupil size diminishes. A 20-year-old might have a dilation of almost 5mm during the day and 8mm at night, whereas by the time they reach 50 it might have reduced to 3.5mm and 5mm respectively.
The light emerging from an eyepiece produces a circular image with a small diameter known as the exit pupil. The exit pupil is calculated by dividing the eyepiece’s focal length by the focal ratio of the telescope. To enjoy the best views the exit pupil should be less than or equal to your dilated pupil size to ensure that your eye detects all the available light. For example, if your dilated pupil is 5mm and you have an f/6 telescope, you should aim to use eyepieces with a focal length of less than 30mm (5mmx6). Bear in mind, however, that an exit pupil smaller than your dilated pupil makes observing more relaxed as you don’t have to hold your head rigidly to the eyepiece to ensure perfect alignment.
Our pupils are able to dilate less as we get older – meaning that we see less light in the night sky