# Upgrading telescope from 5“ to 8” or 10"?

I currently have Celestron Nexstar 130STL. I am trying to upgrade my telescope to next one. I examined Meade 8"ACF Goto telescope, but I was not too thrilled about it. It gave me better view, but the details were not too different from my 130mm. Maybe my expectation was too big. I have an option of getting Orion 10" dob motorized alternatively. I am slightly concerned about the size and the portability.

I would appreciate any recommendation, thanks!

• How is the local seeing? Round here we have continuous high level Cirrus that makes anything over 120mm useless for all but 5-10 days a year. – Wayfaring Stranger Sep 12 '18 at 15:03
• The best telescope for you is the one that actually gets used- so portability and ease-of-use might outweigh getting a larger aperture. – antlersoft Sep 12 '18 at 15:10
• I really agree with antlersoft! thanks for the inputs!! – Kay Sep 12 '18 at 19:00
• I live in metro area. I typically drive out one or two hours if I want to see faint objects. If I need a quick fix, I go to local golf course , a 20 minute drive. – Kay Sep 12 '18 at 19:17

I am trying to upgrade my telescope to next one.

To compare the light-gathering power of two telescopes, all other properties being equal, you can calculate the ratio of the squares of their radii. In this sense, a telescope with a larger aperture will provide a "better" view than one with a smaller one. Keep in mind, though, that there are other factors to consider: the impact of different optical systems on light gathering power, the use of filters and eyepieces, the unpredictable effects of atmospheric interference, and skill in using whatever telescope you buy. You'll also have to consider specifically what you want to do with the scope (visual observation, astrophotography, citizen science, etc).

I would appreciate any recommendation, thanks!

This forum tends to be for scientific questions in astronomy, not for equipment recommendations. There's a forum primarily for equipment discussion on a separate site called Cloudy Nights that you might want to visit. You can certainly post here, but you may not find people who are able to advise you on specific equipment issues.

• I dislike the phrase "Increases exponentially with aperture". The light gathering capability should increase with the square of the aperture. It's not exponential, but it is a decent growth rate. – Ingolifs Sep 12 '18 at 3:05
• I was actually hesitating about posting this question since it was asking for personal opinion. However, I am glad I asked. I learned a lot from you thanks! BTW, I used to teach in planetarium, but I am trying to teach kids under the real sky. – Kay Sep 12 '18 at 19:13
• @Kay Sure thing. – Alphecca Sep 13 '18 at 0:01

The first thing I would recommend is to join an astronomy club or society. There's most likely one near you, and membership is generally very affordable (in the US, prices usually are $50 or less per year). Most clubs conduct freqeunt star parties, which would give you a chance to see a wide variety of telescopes in action and talk to their owners to find out more. As Alphecca replied, the light gathering power of a telescope is proportional to the square of the radius of the aperture. For example, your NexStar 130SLT has an aperture of 130 mm (just over 5"). If you use the formula for area (pi * r^2), this gives you an aperture area of about 13,273 mm^2 (square millimeters). If you were to upgrade to an 8" telescope (203 mm aperture), you'd get an aperture area of about 32,365 mm^2, which is about 240% the light gathering area of your 5" scope. If you go to a 10" (254 mm), you end up with about 50,671 mm^2, or about 380% as much as the 5" or 157% as much as the 8" What does this actually mean? That's a little more complex. First, there is more light gathering. Contrary to the common opinion of those not experienced in using telescopes, magnification is not the key concern with a telescope, light gathering is. But there's more to it than just that, and I'll circle back around shortly. In the case of light gathering, larger apertures are better. The telescope, in a sense, acts as a funnel for light, collecting from a larger area and concentrating on a smaller area. In this sense, a larger telescope can, quite simply, gather more light. But there's a catch: it's gathering ALL of the light that hits it, not just the light from the target object. It will gather the light of your target object and any stray light, such as light pollution. To deal with this, we need to increase contrast to make the dim deep sky object stand out from the sky. This is heavily influenced, then, by things such as focal ratio and your eyepiece selection. I spend a fair amount of time on Reddit r/telescopes, and we've had some discussions about this. One of the other regulars there wrote a pretty good article on medium.com about this. So, to put it mildly, there's more invovled than just getting a bigger aperture. Though, in fairness, having the biggest aperture you can afford and handle as far as weight and size goes is always the best way to go - you will never have too LITTLE aperture. The real questions then become what you want to do with it. If you want to do astrophotography, you're going in entirely the wrong direction. For visual observation, however, an 8 or 10 inch telescope is a good option. I personally recommend an 8 inch for any beginner that can afford one. But, based on what you said about being disappointed with the Meade 8", I think there is a question of expectation. If you expect to see what you see in photographs, then you're just plain out of luck. Even a very large scope (say a 24" Dob) won't do that for you. Our eyes are simply not capable of long exposure imaging as are cameras. But a good observer who has learned to train their eye properly can still see some pretty amazing sights. And this is another good reason to join a club: to spend time observing with other, more experienced observers and learning how to truly see through the eyepiece. Visual observation is not just a matter of pointing the telescope in the right spot and taking a look. Observing requires spending time letting your eye and brain work together to really see what's out there. I jsut said our eyes aren't capable of long exposures. This is true, but it's also true that extended observing does do something that's not entirely unlike long exposure imaging. As you spend time at the eyepiece, your eyes collect more and more light and your brain does start to synthesize a more complete image. It starts to fill in gaps and show you more and more. This is especially the case when observing from darker skies where there is less light pollution to muddle the view. A great example in my experience is M51. From my club's dark site, when it's up in the sky, I can almost alawys make out the two galactic cores, but frequently the spiral structure is hard to see. But if I have a comfortable seated viewing position and spend a few minutes, my eyes pick up hints of the spiral arms, which my brain starts to fill in. A good technique for developing this is sketching. If you sketch the object, your brain process it differently and you start to catch hints and glimpses of more detail which end up in your sketch. Your current telescope is a GoTo, as is the Meade you mentioned, and you talked about an 10" motorized Dob. While GoTo technology and tracking can be very helpful, they are also often more of a hindrance than expected. Most particuarly, the cost of the GoTo mounting inflates the overall cost of the instrument. An 8" standard Dob can be bought or under \$500 (occasionally under \$400). An 8" GoTo telescope is likely to run over \$1,000. The GoTo equipment typically will at least double the price. For the price of an 8" GoTo dob you could get a 12" manual Trus dob with almost 550% the light gathering area of your 5". (Not to mention a larger aperture offers greater detail resolution capability for planetary observation).

In the end, my recommendation is to start by joining a club and spending some time learning more. Then you can make a more informed decision on a purchase (additionally, many clubs have a thriving buy/sell/trade culture with members constantly selling off something to fund their next purchse - I've bought most of my equipment at very good prices this way).

Good luck and clear skies!

• Wow, what a good lesson provided. Thank you so much for taking time to teach me. This is superb introductory article about selecting telescope for beginners. Thank you again!!! – Kay Sep 13 '18 at 23:52
• Happy to help. We have a really good sticky-post on Reddit r/telescopes (reddit.com/r/telescopes) answering "what telescope should I get." As Alphecca mentioned, this forum is less about buying a telescope and more about the science, but the r/telescopes is very much about buying, using, and working with amateur telescopes. – J.M. Haynes Sep 14 '18 at 3:02