A Few Notes about Equipment

 

 

 

What My Kit Includes:

A lot of Sky & Telescope readers write me to ask what sort of equipment my wife Karen and I use to observe the night sky. In many ways, I dislike this question, because the most useful tools I own, and by far the most used, are my eyes. And when it comes to telescopes, it is by now abundantly clear that the equipment is secondary to the skill and enthusiasm of its operator when it comes to deriving enjoyment from astronomy. Nevertheless, it is natural that the tools of the trade are of interest to people, so here are some words about our telescopes and accessories, and about equipment in general.

We own several telescopes. My wife’s telescope is an Astro-Physics AP-130 EDF made in April, 2000; that’s a 5" f/6 APO refractor for those who don’t follow the refractor scene. She has mounted this on a Losmandy GM8 mounting. Her primary interest is in solar observing, so she has equipped the telescope with a Baader Astro-Solar white light filter and a Coronado Instruments Group hydrogen-alpha filter. This is definitely the sports coupe of our telescope collection – lots of fun and frequently used.

One of my favorite telescopes is our 8" f/6.7 Cave Astrola, which dates from 1956. Cave Optical is noted, at various times in its history, for producing fine primary mirrors, and this example does not disappoint. A very good showing on the Foucault test stand motivated me to have the mirror interferometrically tested, and we find that it is 1/59 wave RMS (e-line). This corresponds to 1/28 wave or so peak-to-valley on the wavefront for this particular optic, but as anyone who knows anything about optics will tell you, p-v wavefront numbers are next to useless – use a useful measure such as Strehl ratio or RMS wavefront instead. So, basically, the mirror is a good one - doesn't give anything up in image quality, though the air often does. The Cave is the luxury sedan of our telescope collection – a bigger car offering a fine ride.

We have a 10" f/4.5 reflector, rebuilt from the carcass of a Meade Starfinder EQ. This mirror is not nearly so good as the Cave mirror, but most people who look through it rate it a superb Newtonian – adequate commentary, I think, about the typical person’s ability to distinguish good optics from poor (including my own). The telescope has really been orphaned by the 8" Cave, which shows a fair bit more on the planets and moon (my primary observing venues) due to its close size and much better correction. Therefore we have loaned this telescope out to a friend of ours from El Paso, Texas for a year or two. This telescope would be the pick-up truck of the collection, which everyone borrows when they need to haul something.

We also have a Meade 12" LX-200, fitted out with an SBIG ST-8E CCD camera, which operates wholly robotically and does nothing but take images for asteroid research all night, every night. We never look through it. It is kind of like a U-Haul – its always being used, but we’re rarely at the wheel.

In addition to this bevy of completed telescopes, we have several that are in the midst of being built or being rebuilt. There is an antique 4.5" f/7 primary mirror which will go into a new tube assembly sometime next year; this plate glass mirror is actually the mirror from my very first telescope. There is a 5" f/11 primary mirror which was intended to be the prototype for a Springfield mounted telescope. There is also the 8" f/9 that I am grinding and hand-figuring, intended to be a planetary Newtonian. It is currently about ¼ wave and I’ve taken a break from figuring, since I’ve recently moved house etc. I hope to pick it up again soon and improve it well beyond its current figure. When these telescopes are done is anybody’s guess – this is a hobby for me, and I’m having fun, that’s what counts.

In addition to these, friends have a 10" Newtonian, a C-14, a 16" Meade LX-200, an 18.5" dob with Pegasus optics, a 20" dob with Galaxy optics, and a 36" dob; all of these telescopes I more or less frequently use.

 

Acquisition, Development, and Justification:

The basic eyepiece collection for many years here consisted of several short focal length University Optics Abbe orthoscopics, and two Edmund RKE eyepieces in the longer focal lengths. The reason for this is that I got my start when I was a young teenager, or younger, and I bought only what I could afford as a junior member of a far from wealthy family. At the time this was a 28mm and a 15mm RKE, and a handful of orthoscopics. In recent years I replaced several of the orthoscopics and ended up with a kit that included the old RKE’s plus new UO orthos in 9mm, 6mm, 5mm and 4mm focal lengths. A 2.8x Klee barlow, a set of color filters, and a few nebular filters round out the basic kit. Recently, I completed my set of University orthoscopics, so that I now have one of every focal length they have ever made. (For some notes about how to use high-power, short eye relief eyepieces, see the How-To Pages.)

This kit fit my preferred style of observing very well. I’ve been a lunar and planetary guy for years. This is not to say that I don’t look at deep sky objects; in fact, I did the Herschel 400 with my 4.5" Newtonian after I moved to Arizona and I’m still actively looking at deep sky denizens. The 28mm RKE provides well over a degree of field in the 4.5" telescope, and isn’t badly corrected either since the 4.5" is a fairly long focal ratio. When the 10" came on the scene, the eyepiece didn’t look so good, but I also wasn’t using the 10" for wide field DSO views – I was using Dave Healy’s 14" telescope, Glen Sanner’s 18.5" telescope, and later Doug Snyder’s excellent 20" telescope for that (mooching is always cheaper, and these guys are fun to be with). I couldn’t see upgrading my eyepieces, except perhaps to include some Zeiss orthos, since what I had matched my interests reasonably well.

But one evening over dinner, Karen dropped the bombshell that she wanted to look at the sun with hydrogen-alpha, and would like to get a little refractor to do it. After a few weeks search, we found an AP-130 and borrowed it from the seller for a little test drive. It worked out and seemed to be a good match for her, so we bought it. (Reflect, my friends, on the silver-spoon privilege of a person whose first telescope is an Astro-Physics on a good Losmandy equatorial mounting. I hope you are at least half as envious as I am!)

It was only at this point that the prospect of some wide-field eyepieces first became important to me. With this telescope and a 40mm Pentax XL or a 31mm Nagler, we can fit the whole Veil nebula into the field, or the North America and Pelican together. There are dozens if not hundreds of diffuse or dark nebulous targets in the milky way that had previously been unavailable to us. Its an ideal instrument for wide field milky-way observing, or for looking at the very large and low surface brightness dwarf galaxies in the local group, such as Leo I and Leo II. To have over three degrees at five inches aperture is a wonderful thing.

 

The Limitations

Everything in our kit has its drawbacks. Our AP-130 is perhaps the best made 5" telescope I’ve ever used, both optically and mechanically, and it is by far the most versatile telescope I’ve ever seen. But five inches is a pretty small telescope. Contrary to popular web reviews and scattered reports, I’ve never had a night in which our 8" telescope doesn’t clean its clock – whether it is showing detail on the planets or looking at the deep sky (though there have been plenty of nights where the 5" AP proved itself to be the best telescope of that general size on the field – and sometimes by far the best). Doug Snyder’s 20" is in an entirely different class when it comes to showing detail on Mars – the bigger instrument is far superior. Its fairly obvious that anyone who reports otherwise as a matter of routine is comparing it to poorly made telescopes, or grinding axes. (I’ve also heard online that the AP-130 has perfectly matched diffraction patterns on either side of focus – it doesn’t, it isn’t supposed to, and you need only look briefly to see this; besides, telescopes are best used when focused!)

That said, you should ponder for a moment the merits of a five inch telescope that inspires no other comments about its limitations than that it is five inches. Yes, folks, it is a damn fine telescope. (I’m just not convinced it is magical.)

My Edmund RKE’s don’t have a lot of glass in them, and there is a legend which suggests that these will be great high-transmission eyepieces with good contrast because of that. Wouldn’t bet on it. For one things, the coatings aren’t what they could be. For another, the eyepiece really isn’t that well corrected. The off-axis astigmatism is quite noticeable, and the field distortion – while not nearly as bad as on some of the wide field designs – is evident. Also, I bought these twenty years ago – they are getting a bit old and well used! I’m not sure what I would order for a couple cheap low-power oculars today, but it wouldn’t necessarily be these.

I’m a well known admirer of the University Optics Abbe orthoscopics. I stand by my high opinion, but their coatings aren’t the best either. It just isn’t as good as the coating found on a Pentax or Zeiss ortho. The question is whether or not the difference is worth the price – the University orthos are a factor of several times cheaper than either of the higher-end brands and you can get a whole set for a bit more than the cost of a single Zeiss ortho – I rate that a fine deal indeed. I certainly didn’t need anything better when I was using my older, lesser telescopes, though I’m tempted to increase the pace of my upgrades now that we have two fine telescopes in our collection. Through long experience and even some bench testing, I have learned that the differences will be incremental only – the UO orthos are an under-priced bargain and probably the best kept secret in eyepieces today.

The 31mm Nagler has been reported in online reviews to be "color free to the very edge." The recreational virtues of distilled alcoholic beverages clearly do not extend to the discipline of evaluating eyepieces. ;-) Put a bright star a full ten apparent degrees from the field stop and blue and green chromatism is quite evident, no matter what telescope I try. This is not a condemnation of the eyepiece, but of the reviewer. Every optician makes design compromises in pursuit of the best balance of aberrations, tries to find the best combination of optical characteristics to produce a pleasing view. I think Al Nagler has succeeded with the 31mm Nagler, and I’d rather have mild chromatic aberration than severe; or mild chromatic aberration in place of severe off-axis astigmatism – or whatever the give and take here entails. It’s a fine balance but, like any other piece of gear, it has its limitations.

That 8" Cave of ours is a terrible telescope. There is a difference between a "telescope" and a "telescope mirror," and the excellent part of this telescope is its mirror. The telescope itself leaves much to be desired. The biggest deficiency is the lack of cooling fans – I am of the opinion that no serious Newtonian can be without a cooling fan as a matter of definition. In addition to that, the focuser drawtube is bare metal, no blackening. There is no light baffle below the focuser or behind the primary mirror – two more should-be standards. The tube interior is painted dark gray (black would be preferred, of course). The mounting is, basically, mid-1950’s technology, in which massiveness is apparently intended to make up for a lack of fine bearings, dual-axis slow controls, low-backlash worms, and other design amenities. One of the biggest motivations for completing my own 8" mirror is to build it into an OTA that corrects these deficiencies. (I’m certainly not going to do a rebuild on an historical classic like a mid-1950’s Cave!)

All of these complaints may have you of the opinion that I don’t much care for the equipment I use. That’s not correct. I would say that at this point in time, the visual astronomer is equipped, or potentially equipped, far better than has been possible at any other time in history. And in the context of absolute quality, much of the gear available to observers is literally state of the art – much of it simply could not be any better, at least not without redesigning it and starting again from the ground up. I do like the equipment I use, I’m just perfectly willing to acknowledge its weaknesses.

 

Skill

That willingness to acknowledge where some equipment doesn’t perform well is one building block in a set of observing skills that I think are far more important than the equipment itself. The goal of amateur astronomy at its most fundamental level is to have fun. Most amateur astronomers derive that fun from observing the sky (a small minority derive it primarily from buying or selling telescopes, making telescopes, photographing the sky, or what have you, and if that floats their boat, then that is fine; but I’m addressing the observers out there).

As long as fun is being had, skill under the sky is the most important thing to furthering that fun and maintaining its keenness – at least in my opinion. Smart observers use their skills to have a more fulfilling experience (what is really meant by this noble-sounding phrase is that they have more fun). Observers with poor skills get frustrated at not seeing what is there, at not finding what could otherwise be seen, and at a whole host of other factors that erode their enjoyment of the hobby.

In this case, knowing the limitations of equipment allows me to better choose the tool for the job. To hear some of the online reviews, a six-inch APO refractor is all that is needed to see all the galaxies visible in a 22" dob. To hear some other online reviews, fourteenth magnitude stars are rarely and barely visible in 8" telescopes. Both propositions are equally preposterous and a very little bit of equipment savvy will serve to keep us sensible of this. My knowing that the 31mm Nagler has a bit of chromatism around the edges relieves me of the temptation to use it in longer focal length telescopes on the moon – although it works great on starfields and DSO’s, the last thing I want is a smeared-out green cheese look for old luna. My knowing about the collimation tolerances of my Newtonians – tight tolerances, folks! – relieves me of wondering about the cause of the poor view when it looks like I am looking through a bathroom window of frosted glass. Know the gear – know it realistically and functionally – and you will enhance your experience.

Know your art, as well. Someone once told me that, given the choice between a small telescope and a large one, they would choose the large one. The reason was that, supposing both to be pointed at M51, the large telescope would always show the observer more. Does it follow that the observer using the small telescope has less fun? I don’t think this is necessarily true, though I admit the view of M51 through a big dob is an impressive thing. Yet no matter which telescope is used, most of what is to be seen lies in the tough, faint, low-contrast zone. You have to work to see it. You have to play some tricks, use a little bit of craftsmanship. The person looking through the 22" dob at M51 has to work just as hard as the poor chap stuck with a 5" telescope in order to see everything that the telescope is capable of revealing. And averted vision is only the beginning – jiggling the telescope, judicious use of filters (ever try a light blue filter on a spiral galaxy? No? Why not?), and a hundred other things can be done to squeeze out the last drop of performance from a telescope. You don’t have to go overboard with this – do as much as you need to have fun – but a lot of people have more fun when the telescope and their skills match up to reveal the ultimate in deep sky detail, or when their observing acuity keeps up with that of their neighbors.

Through long experience, I have learned that:

1) The best equipment does not lead to enjoyment of the night sky. That enjoyment is innate, or does not exist, and only you know which it is. I started my observing with my bare eye and I still do a lot of observing that way, because I love the sky – equipment not needed.

2) The quest for best equipment can interfere with the enjoyment of the night sky if it is not kept in proper balance – the ends must justify the means. If you find yourself under the sky doing star testing or comparing two different brands of eyepiece more often than you find yourself actually looking at or imaging the sky, then perhaps your interest in equipment is interfering with the enjoyment of a superior mistress – only you can decide if that is so, but you should think about it.

3) The best equipped amateur astronomers do not appear to have more fun than I do while observing. I know how much fun I have, but I don’t detect as many people with $30,000 kits smiling as I should.

4) Some of the best equipped amateur astronomers are among the least capable and least knowledgeable observers - and vice-versa. There are a whole bunch of perfectly respectable reasons for this – for example, people who can afford good telescopes tend to be diligent hard workers and successful wage earners, which proscribes their leisure time and prevents them practicing their observing skills as much as they might want. But some others are just pretentious middle-class show-offs who think a telescope worth a few grand is a status symbol worth putting on parade. My philosophy says it is not that, it’s a tool, and just as middle management is not to be trusted with a jackhammer....

So, here’s my prescription. Get a decent telescope. Make sure it is well built enough that it will be usable and not frustrate you, and make sure it is optically good enough to satisfy you. Make sure it is a fairly good match for your observing interests. By all means use reviews to help you select a likely model; temper this with your own critical attentions by going to an astronomy club star party or two and checking out what is there. And don't be too discouraged if you roll your first couple telescopes over on the used market because they weren't a good fit - the early days are full of learning experiences.

Once you have found the right tools, stick with them. If you have a 4" telescope, it will take you ten or twenty years to exhaust its potential – plenty of time to have a lot of fun, and really hone your observing skills. If you have a bigger telescope, you have even more time to kill before you’ve seen it all. Many years before you get to the bottom of your last possible observing list, you will realize that you’ve acquired a good deal of familiarity with the sky and with how your equipment works. Once you are at the top of your game with your chosen telescope, you will know it – and you will be well ready for whatever is next.

By that time, all curiosity about what equipment I use will have dissipated, and you wouldn’t have bothered to read to the end of this essay!


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