Choosing and using a telescope
substitute for a bit of practical map-reading using charts and the naked
eye. If your goal is to learn where things are in the night sky, the use of a
Go-To mount is best avoided or at least limited. Then there’s the issue of the
onboard picking database, which for a typical Go-To system is measured in
the tens of thousands of objects. Many generic Go-To systems are designed
for a large variety of telescopes so using the database with a small-aperture
instrument will invariably result in having access to many objects which
simply cannot be seen through the eyepiece.
This is not to say that Go-To is all bad. If you know you’re a casual
observer who isn’t that interested in learning your way around the
constellations but would rather just "see" the items of interest that are up on
any particular night, then Go-To is a good choice. Similarly, if you have very
light-polluted skies so that navigating around the stars with the naked eye is
tricky at best, then Go-To may help you out here too.
Go-To also works well for imagers where locating objects by eye can
be wasteful of precious imaging time. And Go-To may be the only way to
quickly locate objects which are below your scope’s visual threshold.
Go-To systems can be used with alt-az and equatorially mounted
telescopes. Computerized alt-az mounts are not really ideal for imaging
as they introduce an unwanted effect known as field rotation during long
exposures. This makes the imaging target rotate around the central axis of
the image frame.
Solar Telescopes
Generally, any one type of telescope can be used for viewing any type of
object. Even if, as described above, the scope’s focal length isn’t ideal for the
job, you can usually get some sort of view of the object you’re after.
By fitting a white-light filter to the front of the telescope so that the entire
aperture is protected, and capping or removing the finder, it’s possible to
turn a night-time telescope into an instrument capable of viewing the Sun in
white light. However, this won’t reveal much detail beyond what can be seen
on the Sun’s visible surface, the "photosphere".
For a look at the exotic features which inhabit the hot magnetically-
influenced environment just above the photosphere, you need to use a
1213[12] A long-exposure wide-field image, such as that taken with a camera on a fixed tripod,
will show the stars trailing. The trailing is caused by the rotation of the Earth on its axis,
the stars appearing to rotate around the celestial poles.
[13] A sequence of images of a large and intricate prominence taken through a night-time
telescope fitted with a solar hydrogen-alpha filter set.special filter known as a hydrogen-alpha (H-alpha) filter. These are
available as a filter set used to convert existing night-time telescopes
for H-alpha viewing or as dedicated telescope packages. H-alpha filters
do tend to be quite expensive, and a dedicated H-alpha telescope cannot
be converted for night-time use; this can only be done if using a filter
set. The cheapest dedicated H-alpha scopes can often retail for
around £500.
Unlike their night-time equivalents, dedicated H-alpha scope apertures
tend to be more restrained, the normal amateur range extending from
35mm up to 100mm. Larger amateur H-alpha scopes are available but price
tends to keep their numbers rather limited.