Part Two: What's Wrong with each of my Scopes
Submitted: Wednesday, 7th December 2005 by Brian Nolan
If you found yourself here by accident, don't forget to read Part One: "General Principles for Choosing your first Telescope".
I’m now going to criticize each one of my telescopes. This will be easy because happily every astronomy club has at least one member who will kindly and patiently explain to you why everything you own is junk, why in fact everything they don’t own is rubbish, and why, indeed, anything you buy as a beginner should be sent straight to landfill. You’ll go along to your astronomy club and this member will look pityingly on you as you go through the process of setting up your poor excuse for a telescope right next to their massively-apertured, apofantastic, light-sucking, LX5000, a scope so powerful that just standing next to it makes the skies darken.
The trouble with these guys is that they think they’ve scaled K2, and now they’ll just never accept that you can get some really splendid views from the top of Mt Ossa, or Frenchman’s Cap, or even Mt Wellington. I might not have the best equipment, but I know fun when I’m having it. And these guys are NOT having more fun. They’re just airing bigger egos, perhaps living smaller lives, and squandering way too much money. (At least, that’s what I tell myself whenever I’m smiling politely as they patronizingly show off their scopes. I make a point of enjoying their great views, then drift back to my thimble-sized refractor just before they start the two hour chore of packing away their behemoths.)
Just to be clear, I’m not going to spend much time criticizing the design of each telescope (refractor, reflector, catadioptric). Other sites explain much better than I can the pros and cons of the various configurations.
And the first telescope that I should be criticizing isn’t even on the list. That’s my 60 mm F12 camera store refractor from years ago. We all make mistakes. It promised me 600x magnification (a sure sign that someone is selling you rubbish), and delivered racing blurs in the eyepiece. Dampening times could be measured in minutes — a house of cards would have made a better tripod. I should have saved the OTA for a finderscope, but as it happened, all I managed to salvage was a decent 0.96 inch orthoscopic eyepiece. Amazingly, it didn’t completely kill my interest in astronomy; it just put me in a coma for 10 years.
Oh, and in case you were wondering, I’m not going to criticize my binoculars…
In part one I suggested that you should already own (and use) a pair of 7x50 or 10x50 binoculars. Please get yourself a pair of these long before you commit to buying a telescope. (And stick ’em on a tripod!) You can use them in daytime, objects are right way up, and you’ll have more success selling them later on ebay. Only you won’t sell them because you’ll find that you use them all the time. Also, if you have a lot of floaters, binocular viewing is a godsend.
And binoculars are relatively cheap. My 15x70 binoculars cost less than one quarter the price of my 80 mm refractor. (When used with a 30 mm ultra-wide-field eyepiece, the magnification and FOV of the refractor closely matches the binos.) Moreover, these binoculars gather 7697 mm2 of light and share it comfortably between both pupils, whereas my refractor gathers only 5023 mm2 of light and tries to jam it all into one eye, which isn’t natural. (Assuming a dark-adapted diameter of 7 mm, your combined unaided pupils gather 77 mm2 of light.) Dollar for dollar, photon for photon, there is simply no better value for money than a pair of binoculars. Anyone who criticizes binoculars is just a churl.
But of course, the magnification is fixed. And the tubes mightn’t be blackened or baffled, so flaring and chromatic aberration can be quite disturbing. And you’ll almost certainly want to figure out what to do about the fact that you have to ratchet back your neck just to use them. (A banana lounge and a parallelogram mount might solve this problem. And there’s a thing called a sky window, which allows you to look down instead of up. And then there are right-angled binoculars that also allow you to use interchangeable eyepieces. But now we’ve drifted far from the topic of bargain astronomy…)
Nonetheless, if you’re deciding that it’s time to buy a telescope, seriously consider just buying a bigger pair of binoculars instead. I know I wouldn’t part with mine.
200 mm (8 inch) F6 (1200 mm FL) Newtonian on a Dobsonian Mount
The biggest revolutionary innovation in amateur astronomy in the last hundred years wasn’t wide-field eyepieces, computerized goto telescopes, or mass-produced diffraction-limited optics. It was John Dobson’s marriage of a home-made newtonian with a gun-turret. (The second, arguably, was Steve Kufeld’s air-force inspired “head’s-up-display-style” Telrad finder. It’s not just NASA who owe a debt of gratitude to the military…)
“Put it on a lazy-susan.” Who would have thunk it?
I love my dob. It was the first telescope that brought me the deep sky. It’s going to be hard to criticize this critter.
If you ask me, there is a big difference between an 8 inch dob and a 10 inch dob. I know a lot of beginners go for the bigger sizes straight off nowadays, but whereas most people can carry an 8 inch dob, no one I know can carry a 10 incher. Sure, you can improvise a trolley, but straight away you’re abandoning the KISS! philosophy that informed the original revolution. (But then, why should you care? Still, it’s about now that I usually begin spouting the stuff about “the sigh factor” that I wrote in the first essay.)
Anyway, F6 is about right; I hardly ever have to collimate this scope, and the edge-of-field performance of most of my eyepieces remains pretty good. (The F5 and F4.5 owners will tell you that they’re OK too, but I suspect they upgrade their eyepieces faster than those of us with slightly slower scopes.) This scope is better on globulars than it is on planets, but it’s good on pretty much everything.
Negatives include size. This scope sat in the corner of my bedroom for about a year, and it wasn’t popular. It takes about 30-45 minutes for proper cool down (no fan – try that on 10 inches!). Also, this scope’s primary mirror cell came with collimation screws — you need to lose these quickly and get yourself a set of Bob’s knobs.
People frequently modify their dobs, which implies that they aren’t perfect out of the shop. Well, they’re not, but that’s part of what being a beginner is all about. You get to learn what sorts of things are important to you. Better eyepieces or a Crayford focuser? A Telrad or a right-angled finder? Another star atlas or digital setting circles?
And then aperture fever sets in…
(But it needs to be emphasized: chances are you will get very good views right out of the box. I think it’s still true that a dob comes closest to living up to a newcomer’s expectations.)
105 mm (4 inch) F14 (1470 mm FL) fork-mounted, goto Maksutov-Cassegrain
There’s a fairly obvious catch-22 with a beginner’s goto. Any affordable GOTO telescope is going to have to compromise optical performance for computer smarts. In effect, I’ve put money into the mount and subtracted it from the aperture. Even though the objective in my ETX is actually very good, its diameter is still only 4 inches. That’s not a big telescope. The autostar controller has cost me an inch or more of light-gathering capacity. The end result is that I’m left with a telescope that can automatically pinpoint countless objects that are far too dim for it to see.
In reality, the long focal length and narrow FOV of this telescope make it an ideal compact lunar and planetary telescope. But then, who needs a goto to find those things? Any object within the grasp of a 4 inch mak is either visible to the naked eye or fairly findable with a decent star atlas. (The ETX’s main advantage, really, is the convenience it offers in automatically tracking these things once you’ve locked onto them. And having said that, if you’re a double-star nut, and if you’ve got a list of their SAO numbers, you just might find that you adore this telescope.)
Other problems. Well, if you’re at low latitudes and you’ve polar aligned your scope, you’ll find that you have cut off from view a goodly portion of the northern sky (assuming you’re in the southern hemisphere). Also, half the time you’re eyepiece will be underneath the scope, hanging upside down in the focuser. Even mounted in the (more conventional) alt/azimuth configuration, objects within 30 degrees of zenith are either awkward or impossible to look at because your eyepiece holder will be situated deep between the fork arms (personally, I find this the biggest bugbear; much worse than “Dobson’s hole”).
The ETX has it’s own peculiar problems, some of which have spawned an entire industry in third party add-ons. The first curse is the focuser knob, which is tiny and needs to be replaced straight away with either a peg or a long, flexible wire-cord (e.g. the “Flexi-focus”). The finder is frequently vilified for being too small, and for getting in the way of your nose if you’re using short-bodied EPs. (Meade has dispensed with the finder altogether in the new ETX Premier Edition, replacing it with a RDF that has also come in for a fair bit of criticism.) The scope’s plastic components are, well, cheap. The batteries get drained by the cold, so people use an external battery pack, but this adds considerably to the weight and transportation hassles. The OTA is held in the fork arms by friction knobs, which tend to lose their grip over time, leading to excessive strain on the RA and declination locks, and these can then crack and break. And although the initialisation procedure isn’t particularly complicated (curiously, the Autostar remembers your latitude and longitude, but it needs to be told the date and time), this and automatic slewings still take longer than simply swinging your dob or refractor around in its alt/az axes. Also, every ETX owner lives in dread of the day that their Autostar will simply refuse to respond at power-up, necessitating at the very least an expensive trip back to the supplier (or overseas?), and perhaps leaving you without a telescope for weeks or months. Oh, and for such a small scope, it takes ages to cool down (longer than my dob).
Then why the hell did I buy it? Well, the short answer to that is Mike Weasner’s Mighty ETX web site (http://www.weasner.com/etx). And this brings up another revolution in amateur astronomy: the internet. Half your telescope nowadays (how many halves are we up to?) may well be a well-subscribed internet users group. No matter where you live, you can find people who know your telescope, know all its foibles and fixes, and who are happy to email you practical advice. You get to read the real-life experiences of other users, learn some imaginative improvisations and improvements that you can apply to your own telescope, and learn what some dedicated amateurs have managed to achieve with amazingly limited equipment. (Check out the astrophotography section.) It’s what “customer support” should be, but never is.
And let’s face it, there’s another reason for owning an ETX. It’s just dog gone fun playing with the Autostar and watching the cutest telescope in the universe steering itself around the sky (even in day time, or indoors).
80 mm F6.25 (500 mm FL) short tube achromatic refractor (William Optics Megrez II SD)
Aperture rules? Not anymore. For a long time my dob was my workhorse telescope. Now short tubes are taking over the world.
Basically, at the moment, you have to make a choice. Either you can buy a short tube refractor that is mechanically sound but has medium optics, or you can get yourself an ED (i.e. Extra-low Dispersion) or apochromatic quality objective, but in a mediocre tube assembly. I would have gone for the Orion 80 mm F7.5 ED (which epitomizes the latter), but the Megrez (which typifies the former) came as part of an unbeatable package (including dielectric diagonal, finder, and padded back pack). As it happens, I’m glad I got an F6.25. Although it came with a finder, you don’t need it, and I traded mine for a William Optics 2-inch 45-degree angle diagonal so that I can use this scope in the daytime.
You cannot criticize this scope mechanically. I’m not sure what “heirloom quality” means, but this scope must come close. It looks good, feels good, and works smoothly. It has a good quality Crayford focuser (which, incidentally, you can rotate 360 degrees — a more useful feature than you might think, and essential if you’re using an EQ mount). William Yang does not know how to make a rubbishy looking telescope.
Willam Yang calls this scope a semi-apo. This is a meaningless adjective. (Even “apo” is doubtful, but at least people seem to agree more often on what that should mean.) The SD Megrez is an achro, not an apo, and at F6.25, expect to see false colour on the moon’s rim. (I haven’t looked through the ED or other versions, but naturally I expect them to be better.) This version has only mediocre foam-rubber baffling. (William Optics’ Zenithstar 80 has much better baffling, and even though it’s an F6, the vendors tell me that it is significantly better colour corrected than the Megrez. I expect William Optics will change the baffling in the Megrez at some point, or else rationalize their product line.)
I haven’t tried any photography with this scope yet, but you will find on various internet sites some amazing (unbelievable?) wide-field images supposedly taken through an SD Megrez. You certainly will love the wide fields (especially with a 2-inch eyepiece!).
Visually, I would like to say that this scope’s optics are better than a typical 80 mm achromat. But I can’t. The Megrez’s overwhelming advantage is portability and lightness (you can carry the scope, tripod and mount all with one hand; you can take the OTA, diagonal, finder, and your 2-inch eyepieces on a plane as hand luggage). If you have a bad back, then you should look closely at a short tube refractor. (It wasn’t that long ago when that wasn’t much of an option. With today’s exotic glasses, however, beginners can finally afford excellent optics. If you’re going to own only one telescope, then you really should choose superior optics over build quality. Go for the Orion 80 mm ED.)
One thing to note. I tried the William Optics 2-inch 2.5x barlow on this telescope. Despite what I’d been told, none of my eyepieces would come to focus on their own. Try any barlow on your short tube before you commit to buying it, or else factor in the cost of an extension tube. (The barlow didn’t work on my newts, either, and the problem then was insufficient in-focus, so an extender wouldn’t have helped.)
By rights, I should sell either the Megrez or my binoculars. (Tough choice. An easier choice would be to upgrade to an ED…)
200 mm (8 inch) F4 (800 mm FL) Newtonian on an Equatorial Mount (Southern Cross OTA on Skyview Pro EQ mount)
I’d better come clean: I’m not a GEM kind of guy. (Beware, in certain circles that’s a bit like admitting you’re a paedophile.) Until Sigma Octans goes nova, I’m not going to recommend an equatorial mount to anyone in the southern hemisphere. And especially not to beginners. Beginners need early success. Aligning an equatorial mount, although unquestionably a skill that some serious amateurs will need to master, is merely slavish for someone who doesn’t even know what they expect to see once they’ve done it. Life’s not always about the journey, sometimes it is about the destination.
And putting a Newtonian telescope on a GEM is especially cruel. The polar scope is down around your knees, so you start your observing session by lying in the dirt while peering upwards through a tiny peephole, trying to find one of the dimmest asterisms in the galaxy. Then if you do finally get the thing lined up, chances are the first object you aim the OTA at will place the eyepiece either high out of eye’s reach or pointing straight down at the ground. (No, I knew when I got this telescope that the mount was destined for my short tube refractor with its rotatable focuser. A refractor also means that the tripod legs will be more fully extended, which means the polar scope will be slightly higher off the ground. Even then, I’m thinking of astrophotography. I’m thinking of an end-product, a photograph. I’m not actually anticipating that any of this will be fun.)
This GEM, however, is good of its kind. And for once, a mount comes properly lubricated, without that black clag you so commonly read about.
But as presently packaged and sold, I find this particular configuration very frustrating. This is a great pity, because the F4 mirror is actually optically very good. And the OTA is robust. I could dispense with the heat-retaining metal plate behind the primary (why do they put those things there?), but the collimation knobs are pleasingly easy to grab and manipulate (probably out of deference to an F4’s tendency to go out of collimation easily). The included eyepieces are GSO plossls, which enjoy a good reputation. And the finderscope is decent.
Unfortunately, the OTA and counterweights are just a bit heavy for the mount (my opinion only, but you hear this is a problem with a lot of new telescopes on GEMs, especially newtonians). The tripod is extruded aluminium, whereas tubular stainless steel would be better.
I always start off thinking that I simply must figure out a way of getting the OTA onto an alt-azimuth mount. And then I get to thinking, well, if you are going to start off with a GEM, then an F4 scope sounds like a good idea: a large FOV will surely compensate for any inaccuracies in your initial polar alignment. And then I come around to thinking that I really should give this scope more time to grow on me. And I do, but it doesn’t. So then I go back to thinking… Well, you get the picture.
But I still wouldn’t recommend it for beginners.
So What Would I Recommend?
If your lifetime interest in astronomy were absolutely guaranteed, then I’d recommend that you buy an optically fine refractor, the best you can afford, with a focal ratio somewhere between F6 and F9 (depending on what you prefer to look at), and that you put it on a good quality alt-azimuth mount. No matter what you do next, you will always find uses for such an instrument. Ultimately, it might become the finderscope on your observatory mounted SCT.
However, most beginners have an enthusiasm that needs to be nurtured. And since a beginner’s telescope is always a compromise between price, performance, and usability, the usual advice given to beginners — i.e. that you should start with the largest Newtonian reflector on a dobsonian mount that you can easily carry — is fundamentally sound. Therefore, I recommend that you assume that a dob is your best choice, and then ask yourself why it might be wise to choose something different. Hopefully this essay will suggest some relevant questions.
Before you decide, join an astronomy club. Ask for advice — many people have travelled the same road before you. Look through as many scopes as you can. At the very least, have an idea of what you’re likely to see through a particular scope before you outlay your cash.
And then have fun.