Sunday, January 09, 2011

 

Uncle Rod’s Telescope Academy: How Big?


Did you receive your first telescope this Christmas? Or are you planning on buying that first (or second, or third) scope after the holidays, maybe in time for the spring observing season? Whether you have a scope now and are thinking of a new “better” one, or you’re after your first, the big question is, well, “How big; how much aperture do I need?”

Yep, aperture, not aperature as some tenderfeet like to call it, is the defining characteristic of a telescope and a very important consideration. In fact, if you’ve been hanging out with the veteran amateurs at your club, or at least listening to what us curmudgeons say, you may have heard us bandying about an aphorism that goes: “Aperture Always Wins.”

And that is true, all things being equal. A larger aperture telescope, a telescope with a larger objective lens or mirror, will always show more. Of everything. Some people just ain’t convinced of that cold, hard, fact, of course. They hope there’s a way to beat the merciless and immutable laws of physics. That somehow, someway that beautiful 4-inch APO refractor should be able to perform visually at the level its price would indicate.

Over the years, I’ve heard two “theories” as to why smaller is really better: “If your seeing, your atmospheric steadiness, is not good, a smaller telescope will show more than a bigger one,” and “If you live where it’s light polluted, a larger aperture telescope will pick-up more sky glow as well as more light from the target, and you won’t see any more than you would with a smaller instrument.” True? There’s a grain of truth in both these hypotheses, but only a grain.

Let’s take the old saw about seeing first. Yes, it’s true the larger the telescope, the larger the column of atmosphere it must peer up through. Take a look through a bigun and a littleun under adverse seeing conditions, and, yeah, the smaller scope’s image looks “better.” I think it would indeed be fair to say that in poor seeing a smaller scope throws up a more aesthetically pleasing image than a larger instrument. B-U-T…

No matter how bad the seeing in any location, it always settles down for at least a brief spell. Keep looking at Jupiter with large aperture telescope and, by the end of the evening, you will have seen considerably more detail that you would have through a small one. Just don’t like the look of a big dog’s planets under poor seeing? You can always stop down the offending aperture with a cardboard mask, making your big dog into a high focal ratio puppy. But how you gonna aperture up a smaller instrument?

Then there's light pollution’s supposed impact on a big(ger) gun. The simplest way to disprove this one is with a field test. Set up a small telescope next to a larger one in your bright backyard, a significantly larger telescope—I like to pit a 12-inch against a 6-inch—and point both at, say, M13 (globular clusters are effective demonstration tools). Insert eyepieces into the telescopes that yield roughly the same magnifications. Have a look.

What will you see/say? “Unk, M13 looks like a great big ball of stars in the 12-inch; it’s just a smudge in the 6-inch. It’s a bright smudge, but it’s just a smudge.” The supposed too bright sky background in the larger telescope? If you find the background in any scope offensively bright, pump up the magnification; that will spread out and help suppress the background glow of your city’s lights.

Ground truth? In light pollution, always go for as much aperture as you can muster. The aperture advantage of a larger scope is actually more keenly felt in light pollution than it is under a pristine sky. Under a dark sky, the 6-inch will resolve plenty of stars in M13. The Great Glob won’t be as rich a ball of stars as it is in the 12, but will look real sweet nonetheless. The 6-inch will keep up with the 12-inch a lot better under dark skies--on many objects.

So aperture does always win? Yes, all things being equal, but all things are rarely equal. What’s not equal? You. Your observing interests. Your home and domestic situation. Your vehicle. There are some things not directly related to raw performance that must be considered if you and the new telescope are to have a long and productive relationship.

The most important thing I can communicate to newbies is: TELESCOPES ALWAYS LOOK SMALLER IN MAGAZINE ADS. Before deciding you’ll be happier with a 12-inch SCT than an 8 or 10 or 11 because you can afford it, and, afterall, aperture does always win, hie thee to the local club and have a look at one in person. Don’t just look through it or at it as it sits on its tripod, though. Observe its owner remove it from their vehicle, get it on the tripod, and reverse the process after midnight.

The same goes for every other telescope of any design larger than about 10-inches in aperture. Do not buy unless you can see the scope in person. And you almost always can, or at least a similar scope. If not at the club dark site, at a local dealer (if you are lucky enough to have such a thing) or at a regional or national star party.

First concern if you are contemplating a large aperture telescope? Weight. The above mentioned 12-inch SCT’s weight is close to 75-pounds, which you must lift to mount on the tripod. Which means you must heft the scope at least waist high. And lift it off that tripod on a dark, dewy field in the wee hours when you are bone tired. That’s to set the LX200 up in alt-azimuth mode. Put the 12-inch on a wedge for astrophotography all by yourself? I DON’T THEENK SO, LUCY!

My Celestron NexStar 11, which I love, and which is somewhat lighter than Meade’s 12-inch, is, I am sorry to say, year-by-year, becoming too much for me to handle, at least in the role of portable telescope. I can see that before too much longer I will be endangering myself and the NS11 every time I get her out of her case. Yes, if you are (unlike Unk), young and strong, you may laugh at even 100-pounds. But that will not last, muchachos.

After the first exciting months with a big SCT (or RC or refractor or anything), even manly men may stop laughing about “a little weight. When it comes time to set the scope up in the backyard for a quick Monday night run, suddenly it’s “too cold” or “too much light pollution” or “something good on TV” or “not much to see right now, anyway.”

While I’ve used my favorite sort of scope, the SCT, as the example so far, “heavy” is hardly confined to big CATs. Any telescope larger than 12-inches aperture is likely too heavy for most folks to want to fool with more than occasionally. Yeah, I know about the dodges: wheely bars, pneumatic lifts, engine hoists, yadda, yadda, yadda. Most of these things are not convenient to use on a regular basis and are potentially detrimental to you or your scope’s safety.

Raw weight is probably the number one thing that bites uninformed telescope buyers in their nether regions, but the telescope’s overall size, its bulk, is a close second. Even if not overly heavy, scopes that are large and inconvenient to move and/or assemble are just a hassle.

I have a beautiful 12.5-inch truss tube Dobsonian. It was handcrafted by a man I consider one of the nation’s premier ATMs. He built it for me out of an humble Meade StarFinder Dob. You know, one of them Dobs from the decade before last that look a lot like hot-water heaters: great big white Sonotube tube and a minimalist particleboard mount. It is now a wonderful scope. But one I rarely use.

Why? Too much HASSLE. Yes, it breaks into pieces, and I really have to break it into pieces even to get it in the backyard. And therein lies the problem. The scope, Old Betsy by name, was no lightweight when she was in her Meade body, but her Hassle Factor was low. I could have her in the backyard and ready to go in five minutes or less. Tote her rocker-box out and plunk it down. Take a deep breath and manhandle her tube out the door and into the rocker-box and I was ready to observe.

The truss version of Betsy? I have to take the rocker-box, the mirror-box, the upper cage, and the truss tubes out separately and assemble them into a telescope. Yes, it would be possible to put the scope on wheels of some kind, but then she wouldn’t fit through some of Chaos Manor South’s doorways.

Betsy is still a great scope, and I can now fit her in my vehicles and haul her to dark sites where she can really strut her stuff, but if she were my only telescope I wouldn’t be observing often. One thing’s sure: she gets far less (if any) use in the backyard now than she did in her original, simpler form.

Smaller truss tube reflectors? Like the Meade 8-inch and 10-inch Lightbridges? The Hassle Factor for most trusses goes up exponentially with aperture; an 8-inch or 10-inch truss tube scope can be hauled into the backyard with the tube fully assembled just like my old StarFinder. A 12-inch? Not by me. A standard design 16-inch? Fuhgeddabout it for just about anybody.

The Hassle Factor doesn’t just apply to solid tube vice truss tube Dobsonians. And it is not just the result of aperture, though that is the main thing that determines how painful a scope will be to deal with. A 6-inch of almost any configuration can be hauled out in one or two pieces and plunked down. Nevertheless, the Hassle Factor can affect even small scopes if their combination of tube and mount is fussy and complicated enough.

Be careful when evaluating a proposed telescope’s Hassle Factor. Yes, a GEM mount, a German equatorial mount, can make very large SCTs, for example, manageable. Unlike a fork SCT, you can break a GEM mounted telescope into several (more) manageable pieces. Some people will not have a problem separating the telescope into tripod, mount, tube, and weights and carrying those pieces out separately for assembly. You will most assuredly find it easier to set up a 12 or 14-inch GEM SCT than a fork of equivalent aperture. BUT MOST OF US WILL STILL NOT WANT TO DO IT OFTEN. Not over the long run, and your once wonderful telescope will be in danger of becoming a hangar queen.

The questions to ask yourself before you pull the trigger on a larger-than-8-inch? Do I have a place to store this thing without causing undue domestic conflict? Will it fit through the doors? Can I get it outside or to the car without doing major damage to woodwork and furniture and getting yelled at like Li’l Rod’s Mama used to yell at him when he was maneuvering his Palomar Junior into the back forty? Will I really be willing to wrestle with it often? Will it fit in the car?

Unless you’ve a pristine backyard, you’ll want to carry your scope to the club site or star parties frequently, so the telescope must fit in your vehicle. For me that is not a major limitation, since my scope-design of choice, the SCT, is very vehicle friendly. Hell, you can load a C14 and its GEM in a cotton-picking VW Beetle. But if you are a Dobsonian fancier, it will be an entirely different can of worms. I don’t know about you, but I do not want my choice of telescope and telescope aperture to dictate my choice of vehicle.

Today, thankfully, this is not the problem it was when all Dobs came in solid tubes, or when truss tube Dobbies had mirror boxes the size of hot tubs. Today you can get “ultra light” Dobsonians like those pioneered by ATMs and, commercially, by Obsession Telescopes, in apertures up to 18-inches (or even larger) that will fit derned near any vee-hickle. But these big, light scopes demand compromises and are not for everybody.

Shorter, faster Dobs in the f/3 range are now coming into vogue, but they don’t do much for transport and storage problems. Oh, they are easier to handle when setup—no big ladders—but their mirror boxes and upper cages usually take up just as much room in the truck as those of their longer cousins.

Finally, there is expense. If you want to go big, you gotta be prepared to pay for it. Tops in the SCT game, Celestron’s C14 Edge HD Pro and Meade’s 16-inch fork mount ACF CAT, go for 10K and 16K respectively. A bigdob? A basic 20-inch will cost about the same as the Celestron, and a 20 with everything on it including go-to will equal the price of the Meade SCT.

It is RAT CHEER that it would profit some folks to stop, let the emotion drain away, and seriously consider how much aperture they really need and can afford. If you are a dyed-in-the-wool deep sky visual observer with a dark sky at home or access to a dark sky nearby, yes, by all means, turn over 10 or 20K to Dave Kriege or Rick Singmaster or the boys at Celestron or Meade. IF, after reviewing all of the above, you believe you will use the thing enough to make you and your banker feel good about the purchase.

You think not? Just because you don’t have a 14-inch SCT or a 20-inch Newtonian don’t mean you won’t see a lot and have a lot of fun. The old cliché, “The Best Telescope is the One that Gets Used” still applies. The amateurs of the 1960s and 1950s saw a lot and had a lot of fun, even though a 6-inch f/8 Newtonian was all most of ‘em could aspire to. Ever. There are also the technological gimcracks we have available, equalizers like video and CCD cameras and uber-super eyepieces that make big aperture less necessary for some people and some observing programs than it once was.

Beyond silly stuff like engine hoists, is there anything that will let you break the aperture barrier imposed by your living situation? To peacefully coexist with a telescope that should be too big? If you are an SCT owner, one thing I can heartily recommend besides eschewing forks for GEMs is a good case with WHEELS. My wheeled JMI case has allowed me to use my NS11 more frequently with less pain than I initially thought possible. Yes, I still have to maneuver the case into and out of my Toyota sedan, but a wheeled case at least lessens the pain.

A big Dob? If you’ve a place to store one at home with appropriately wide doorways, like a garage, a pair of “wheelbarrow” handles with wheels on ‘em may make getting the 20-inch into the backyard as easy as grabbing a StarBlast. Wheel the scope out fully assembled and, if your storage area is unheated, you are looking at the sky in just a few minutes. With all that aperture.

If you don’t have such a setup at home, don’t have a big pickup or SUV to haul it in, but still want a big Dobsonian? Many big gun owners rely on trailers. With a good, weather-proof trailer the scope can be left assembled, ready to be towed to the dark site at a moment’s notice. Not that I think this is an overly good solution—at least for frequent use. You, like me, may not enjoy pulling a trailer. And it might not make the telescope very happy, either. Even the best trailers will give your baby a comparatively bumpy ride, maybe to the point where hardware—bolts and screws—starts backing out. Still, lots of folks do trailers, and for the biggest of the big a trailer is the only practical solution.

The best dodge? Own a smaller scope, too. A grab ‘n go scope that supplements the bigun. Reconcile yourself to the fact that the 14 or 20 or 30 will only be used on special occasions. No, the grab ‘n go will not (always) show as much as the big dog, but you will nevertheless still see more of the heavens than you would sitting in front of the consarned TV watching music videos—though Unk does hear tell Lady Gaga’s bod is pretty “heavenly.”

Yes, you’ve got a 25-inch Starmaster, but most of the time you’ll use a Celestron C8, or an Orion 10-inch Dobsonian, or, if you are as lazy as your ol’ Unk, a 4.5-inch StarBlast mini-Dob. As I have said before, over the course of our buggy, damp, hotter than hell summers if I didn’t have the StarBlast and my beloved pair of Burgess 15x70 binoculars, I probably wouldn’t see much. But I see a lot with my little scope and so can you. In fact, the best view I have ever had of the Veil Nebula has been with the StarBlast. The man or woman behind the eyepiece is still more important than the pedigree or aperture of the telescope.

What’s for you? I won’t presume to say. That’s for you to decide. But here’re some rough ideas of what might appeal.

If you are apartment dweller who must haul the scope down several floors via stairs or elevator.

If you have an area nearby where you can observe, an 8-inch or even 10-inch solid tube Dobsonian can work. Since you are likely dealing with mucho light pollution, I don’t normally recommend less than 8-inches. What would I choose? Orion’s Intelliscope 8 or 10 or maybe even their new go-to Dob.

If the stairs are brutal or many obstacles have to be negotiated or it’s vital to get everything down in one go, it is probably best to back off my “8-inch” rule to something like the 4.5-inch or 6-inch StarBlast or a nice, small, short refractor.

You are an apartment dweller or other urban resident without an observing area nearby?

You might as well bump it up to an 8 or 10-inch SCT in a nice, wheeled case. You’ll need to disassemble the telescope for transport, but you’ll need to do that to get it in the car, anyway.

If you are an apartment dweller who must observe from a balcony.

The only limitation is the size of the balcony and your ability to move the telescope onto that balcony (I do not advise leaving a scope outside, even with a decent cover, due to bugs and moisture). Push-to and go-to mounts? Will you be able to get at sufficient alignment stars? If you have a 180 degree swath of sky before you, a digital setting circle computer like the Sky Commander will work, and so will a go-to scope that only needs a 2-star alignment to get going—like a fork mount SCT. This can really make your observing more productive, since the typical urban/suburban sky is difficult for starhopping.

You are an apartment dweller who has access to the building’s roof?

Whatever you can get up there. If you have elevator access, anything you can maneuver into the elevator. Stairs/ladder? A nice StarBlast is the top end of the curve; better is a small refractor or binoculars

You are a suburbanite with a backyard.

The limit is what you will be able to get outside, and, most importantly, what you will be willing to get outside. Even if your skies are good and the weather sweet for observing year-round, ask yourself whether you will be willing to mess with a 20-inch telescope, even if all you have to do is wheel it out, on a Monday night after a hard day at the office. Plan on having a grab ‘n go to at least supplement a larger telescope. For use at home, an 8-inch Dob is a very good thing to have.

If you are a suburbanite who plans to do most serious observing from a remote dark site.

Get that big compact Dob, a C14, or a big trailer and as big a Dobsonian as you want. As above, though, plan on getting yourself some kind of a home-use instrument. And understand going in that the big, expensive telescope will only get used a dozen times a year or FEWER.

You are a country dweller with a superior sky.

The sky is the limit. As long as, AGAIN, you have a place to store the scope and are sure you’ll be willing to set it up frequently. Even the best skies are no antidote for a Too Much Trouble telescope. You, like the suburbanite, will still want a handier scope no matter how monstrous your Primary Instrument.

The ultimate solution for everybody? Is simple. If you can build an observatory, your problems are over. Certainly, not everybody can due to zoning rules/covenants, expense, and a lack of a suitable and secure area to build one. But if you can do an observatory, “how big” is no longer a problem or question. The answer is “big as you want/can afford.”

Even amateurs who live in light polluted areas will find an observatory of some kind a big improvement. Maybe even a bigger improvement than for country folk. A domed observatory or a Skyshed Pod will block a lot of the ambient light that devils you. Course, you’ll want to own a “travel telescope” as well if you don’t want to go to the trouble of removing the main instrument from the observatory. And so it goes…so many telescopes to buy…so few dollars.

In the final analysis? Don’t worry, be happy. Yeah, if you live in a fourth floor walkup, you should probably forget about 25-inchers, but even an 80mm refractor, IF YOU USE IT A LOT, will show you a huge amount of wonders, is nothing to be sneezed at, and will, yes, make you a REAL amateur astronomer.

Next Time: Unk had planned to get out to the dark site this past Saturday evening, even though there was a small Moon in the sky, and even if only with his little girlfriend Charity Hope Valentine, the ETX. Alas, I awoke Saturday a.m. with laryngitis and the feel that I was near-about in the grip of a nasty cold. So I wimped out.

What, then? Have you visited your astronomy club lately? Yep, Unk’s semi-regular epistle as to why you should still, even in the days of Cloudy Nights’ and Astromart’s forums, belong to a good, old NON-VIRTUAL astronomy club. See y’all then.

Comments:
Once again, an excellent topic with expert advice. When I made what I thought to be my first educated purchase, I chose the Meade SN8. As far as portability goes....it is great! What i did not consider was hardware such as the stock focuser. Someday, I will be swapping it out for something better. But in hindsight, I wish I would have taken care of that detail at time of purchase.

Thanks again Uncle Rod. Your blog makes the hobby that much more enjoyable!
 
Tis the season to help friends-of-friends with their new purchases.... tonight a little achromat (not)goto and soon a little (unmotorised)GEM newtonian. Showing people M42 for the first time, or M31.... the response says it all.... a BIG scope may show it a bit bigger (but still green and fuzzy), but a small scope will still show SOMETHING! Seeing a planet or nebula or galaxy with their own eyes and all those crisp little stars.... makes the last month of cloud worth it!

PEter
PS Get well soon
 
You really nailed it when you said "But how you gonna aperture up a smaller instrument?". Loving my C8 and Mak 127 now and for a long time to come.
 
When it comes time to set the scope up in the backyard for a quick Monday night run, suddenly it’s “too cold” or “too much light pollution” or “something good on TV” or “not much to see right now, anyway.”

It seems you did observe me for years! ;-)
Thats exactly the way it goes unfortunately.
Wolfgang from Germany

lx90 12" Lightbridge 12"
 
Hi Unk,

Well, I ended up going with the Big'un, a C14. I dragged it out to the yard on a number of occasions, but in the back of my mind, I knew I was going to build a permanent setup, even in the Chicago 'burbs where I live. And that's what I did. Extended out my deck a bit, and put in a pier that I built, and mounted the telescope on that. Rather than go with pretty expensive storage like a dome, I ended up using a Rubbermaid outdoor storage closet, which ends up being a perfect fit for the scope. So far, it's been through a number of fall storms and winter snows, with no leakage to speak of. Takes about 5 minutes to move the cabinet out of the way (I added some framing on the bottom and put on rollers), and I'm pretty much ready to go. It's still a work in progress, but I think it's a winner.
 
RonG - I was looking at the big Rubbermaid options the last tiem I was at the builder's supply store thinking about doing the same thing - do you you have any photos you could share?
 
Hi Bret,

I've only got a couple of pics right now, but I'd be happy to share them. Just not sure how to do it here.

Basically this is the 6' tall model with the double doors in front. I built a 2x4 frame to reinforce the floor and added 6 rollers to it. The frame also supports the slot I cut into the floor to make room for the pier. When the cabinet is close, I have an additional piece of wood I put across the front of the slot next to the pier, which pretty much locks it in place. In the spring, I'm going to modify that a bit to block vertical movement as well, just in case of really high winds, although I think it's pretty safe now. I also added a lock bracket to the doors to replace that little plastic piece that the cabinet comes with. One more thing if you decide to try something like this setup. The walls of the Rubber maid unit are actually thin double-walls. In order to attach the 2x4 frame, I also made a matching 1x4 frame for inside the cabinet, giving me someplace to attach the bolts without worrying about just ripping through the doublewall. In the spring, I'll be starting up a new website with more pictures. I'll probably call it something like "Dirty Skies Observatory" because I'm in the burbs outside of Chicago. In the meantime, if you want to see the other pics, we can ask Unk if there's a way to do that here, or I can just email them to you.
 
Unk,

I like your comment "TELESCOPES ALWAYS LOOK SMALLER IN MAGAZINE ADS." I recently upgraded from a cheap 3 inch Celestron Firstscope. Not bad for a beginners scope, but now I had more money and wanted something better. I also wanted something small, light, easy to transport, setup and takedown. I live in a suburban house with a garage now, but I move every few years. I may be in a small apartment next time I move.

I considered the 4.5 and 6 inch Starblast reflectors as well as the Skyquest 4.5 inch. I'm not sure where I'll be living in 3 years, so I didn't want a big heavy scope to hassle with. Both the Starblast 6 and Skyquest 4.5 were bigger, heavier and looked like more hassle to setup and store. That's why I decided on the Starblast 4.5 instead.

In the picture the Starblast 4.5 looks almost the same size as the Celestron Firstscope 3 inch. After all,the objective mirror is only 1.5 inches bigger, so how much bigger could it be? Right?

When the Starblast 4.5 came in the mail, the box was 3 times bigger than I expected. Holy Cow! This telescope is WAY bigger than it looked in the picture. It's a good thing I didn't order one of the bigger, bulkier,heavier telescopes! I setup this telescope whenever there is a clear night, maybe 2 or 3 times a week. A bigger heavier telescope would be too much hassle and probably just sit in the garage all the time.
 
Hey Rod,
zhanks a lot! i was hanging in-between 8,10, and 12 inch GEQ newtons... i'll settle for the smallest :)
 
They are definitely bigger in person... I was looking at an 8" Dob, but they were out of stock so I bought the 10" figuring it's not too big. The thing is the tube is 2" larger in diameter than the mirror. So it's a 12" tube and 22" base. I like it though. It's a Zhumell Z10. Thanks for all the info.
 
Rod, we are planning a mobile observatory as a shared resource for communities living in a dark sky reserve here in SW Ireland. Would you mind if I emailed you? John Griffin. kerrygathering@gmail.com
 
Certainly you may.
 
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