Putaendo Patrick

You now know the formula for calculating the magnification of a given EP for a particular focal length (600mm). You now know the theoretical limits of your scope, x240 approx; and you know the limit imposed by seeing conditions, x200 approx. What remains is to determine the magnification that you want when viewing the Moon. x120 will give you good detail, both for the Moon and the planets in general; x180 will give considerably more detail. It's up to you! Then you have to decide how to achieve this magnification, either with a single EP or an EP combined with your Barlow. A 5mm EP will give you x120, but you could also get the same by using, in theory, a 12.5mm with the x2.5 Barlow. The nearest you will probably find is a 12mm EP. Other options and combinations with the Barlow could be an 8mm EP. On its own it would give a userful x75, and with your Barlow making it effectively a 3.2mm, you will get x187. My personal experience is that EPs under 8mm tend to be more demanding, especially in a scope such as yours with a fast focal ratio (f5), and many have quite limited eye relief. So I would probably go for something in the 8mm to 12mm range and use it with the Barlow. This said, my favorite EPs for lunar observation are an older 5.5mm Meade 5000 which when used with a 1000mm refractor gives me x180, and an older 7.5mm Celestron Ultima, giving x133 or, occasionally x266 with a Barlow. It really is a case of individual preference. There is a good selection of EPs in the 40 to 80 pound range which will suit your purposes very well. What is your budget? Update: Sorry if this is now a bit out of date - wrote it and tried to post in the morning - but just when I hit the "post" button, the server crashed! Anyway, parts at least may be useful!

I'm pretty certain that the AZ mounted version of the Startravel 120 comes with a 45 degree diagonal, whereas the EQ mounted version comes with the 90 degree diagonal. Between a refractor and a reflector, I definitely agree the frac is a thousand times better for terrestrial viewing. As a previous poster said, before editing it out, a reflector is about as useful as a chocolate teapot. I loved that! The size-price relation is one of the main advantages of a short-tube refractor, and perhaps to be honest the only one. If you really want to get close and personal with the Moon you need higher magnifications than a 600mm focal length is capable of giving. I have a frac with the same aperture, 120mm, but a focal length of 1000mm, with this I have no problem achieving good magnifications of x250 or well above (always depending on seeing conditions). As the Moon is so bright, I don't need the light gathering properties of a larger aperture, and in my opinion a frac gives better contrast. Chromatic aberration is a problem with Achro fracs. The problem increases with shorter focal ratios. CA on my telescope (f8.3) is present but I can live with it, and the good news is the older you get the less you notice it! There are filters which can reduce this effect such as "fringe killers". Otherwise you have to spend a whole lot more money for an Apo which generally use a triplet lens made from expensive glasses. However if you want to look at very faint objects such as the dimmer DSOs, you do need aperture. Without this ability to gather light, your range of object magnitude is much more restricted. An 8 or 10 inch reflector will, sadly, give my frac a sound thrashing! For visual observing (as opposed to astrophotography, which is another kettle of fish) short-tube refractors have the worst combination: lack of aperture and lack of magnification. A short focal length is also much more demanding on eyepieces, often you just can't get away with the cheaper options, and this can translate into serious money. Others may disagree but that's my personal take. If you really want a good 6mm EP with excellent eye relief, you might consider a Pentax. But then again, as this will cost as much as your whole telescope, you might pass!

As Mars1960 says, have a bit of patience and see what comes in the box. However, along the line you might want to consider a 90 degree diagonal. You should receive a 45 degree erect image diagonal with your scope. This is great for terrestrial use, and you see everything the right way up and left/right correctly. However for viewing the night sky, the 90 degree diagonal will be much more comfortable. Image will be right-way-up but left and right will be reversed - but with the stars this is unimportant. The relatively short focal length of your telescope (600mm) is not ideal for high magnifications and essentially means your eyepiece needs to do more work! Your scope comes with 25mm and 10mm eyepieces. The latter (the more powerful) will give x60 magnification. For much lunar and planetary observation, a magnification in the x120 range would be preferable. A 5mm eyepiece would achieve this - but many come with limited eye relief, which means your eyeball has to be very close to the glass. The alternative is to use a Barlow, this effectively doubles (or triples) the magnification of an EP while maintaining the original eye relief. A half decent x2 Barlow (maybe 20-25 pounds) would extend your range of magnifications in the short term while you are deciding where you want to go. The supplied 25mm eyepiece will give you quite adequate low power views for the moment - so I would recommend waiting for a while before buying a 32 or 38 EP, you may decide it's not needed. In any case I would not go beyond a 32. Eyepieces range in price from about 20 pounds to over 400 pounds, and generally the more you pay, the better they are! But money aside, brands of EPs are also a very personal choice - if you have the chance, join up with a local astronomy club. You will be able to look through other members EPs and make the right decision for you! Remember people in shops want your money, take their advice with a pinch of salt. Good luck and clear skies.