What can you see with a 110 mm reflector? What about Sun filters?
On the planets you will see (with practice and patience, as with all telescopes) a good amount of detail on the planets. Actually, this size of instrument has a resolving power (ie smallest detail visible) of around 1 arc second, which is rather better than the average seeing in the UK. The main advantage of larger instruments as far as the planets are concerned is that the images are brighter and therefore easier to see, and they can make use of those occasional moments of good seeing when it improves so you can see down to maybe 0.25 arcsec. However, the size of the cells of steady air is not much bigger than 10 or 15 cm on average, which can result in significantly larger instruments giving apparently worse results because they are viewing through more than one blob of air at a time. So telescopes in the size range 10 to 15 cm usually show as much detail as there is to be seen on planets for most of the time.
I have been making some enquiries about the models you recommended and the one that keeps cropping up is a TAL-1M 110mm 4.5".
Many user reviews says it is a very good entry level telescope but before I
commit to anything, could you tell me exactly what I could expect to see (in
fairly good detail) with this? I have no idea about what is
realistic...seeing the craters on Pluto? Seeing the Horsehead Nebula under
Orion’s Belt? (At least I think it’s the Horsehead).
Oh, and another thing...it's probably a really dumb question but I was always under the impression that you NEVER, with exception, look at the Sun through a telescope...does this "Sun/Solar filter" thing change that? Or is it only to enhance the image you would project onto a piece of paper? –
Jupiter through a telescope of this size will show a mass of fine detail which you can't take in all at once but need to study in order to see it all. Mars is more of a challenge at most times because the features are rather low contrast, but later in 2003 when it is very close you should see most of the major features.
As far as deep-sky objects are concerned, in a reasonable dark sky you will be able to find maybe a couple of thousand or so objects – I've never seen a figure for this – including many galaxies, nebulae and clusters. However, I would caution that you need a telescope of around 45 or 50 cm aperture to show the majority of these really well, and then only under good conditions. In a 110 mm telescope the brighter galaxies will show up clearly, and their shape is evident, but you will be hard pressed to see spiral structure really clearly. Lord Rosse, who discovered the spiral structure of galaxies, used a 72-inch telescope in the black skies of central Ireland in the 19th century, though a much smaller telescope will do this today.
A globular cluster such as M13 will resolve into stars and actually does look like a ball of stars rather than a fuzzy blob as it does with smaller instruments. Planetary nebulae, too, start to show their shape and size rather than being unresolvable blobs.
In my view a four-inch (eg 110–115 mm) telescope is really the smallest with which you can start to see a good number of objects and not be disappointed. This is not to say, however, that a larger telescope is not better, and I would say that a 150 mm telescope is a good all-round instrument, but then you are talking about more money. I think the TAL-1 represents a good compromise of reasonable aperture with enough sturdiness that it does not vibrate as soon as you touch it, and at a price that does not force you to make critical decisions over priorities!
The Sun filters with small telescopes are condemned by anyone who knows anything about telescopes, and yet some manufacturers still seem to include them. They can and do crack, leaving the observer with eye damage. These are eyepieces that fit into the eyepiece, with no other form of dimming, so they have to absorb the full power of the Sun. However, these days you can get (moderately costly) filters that fit over the front of the telescope so they are at little risk of damage. You often have to use a dimming filter in the eyepiece, but it is not at risk as most of the work has been done by the full-aperture filter. Some even filter the light down to the hydrogen-alpha line which shows masses of detail and the prominences, and these are very expensive. Normally, you should use projection and I believe the TAL comes with a solar projection screen anyway.
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