How I avoided aperature fever

I've had a number of small scopes, both astronomical and terrestrial in the 60mm to 150mm category. Considering that I got introduced to this hobby by some folks with 16" Starmasters and Starsplitters, it's both funny and pathetic that to date my "big" scopes have been a 6" Mak and a 5" Mak newt, (Oh, and a 6" truss tube clockwork reflector that never even saw starlight, for a variety of reasons.)

Anyway, I've always fancied that I really wanted a nice premium grade truss tube DOB in the 12-16" range. But every time I looked at the increasing cost of those fine instruments, reality got in the way. So, I was pretty sure that I was the perfect target market for a nice 10"-13" sonotube tube.

I was prepared to order either one of the new Discovery 13" DOBs, or maybe even one of the lesser Asian 10" DOBs. I squandered who knows how many hours pouring over all the different specs, options, models and brands. It all sounded pretty good, and started to make lots of sense to me. The Discovery 13 struck me as a heck of a bargain, and the new crop of Taiwanese metal tube 10" DOBs struck me as bargain basement gold. Then I did a very simple experiment that completely changed my thinking.

I put 55lbs of freeweights in the bottom of a 6g. bucket. Then I duct-taped another 6g bucket on top of that, and duct-taped (2) more 5g. buckets on top of that. That all resulted in a 64" tall realistic replication of what either a 10" metal or 13" sonotube DOB might actually represent. Then I carried it up the stairs, through a couple doors, and out of the basement to "set it up" in the yard. That was it. It was that simple.

That easy experiment convinced me beyond any doubt that a 50-something pound, rather clumsy OTA was more than I'd actually be willing to observe with on a regular basis. Sure, I can do it, but I know myself well enough to know that I often wouldn't; particularly during those frequently unplanned observing sessions when I'm outside only because I'm awake. Obviously, not everybody has the same set of limitations and same personality. But, it was sure an eyeopener for me.

Comparitively an 8" DOB tube can weigh in at just 20lbs. and can come in much shorter lengths depending on focal ratio. With that in mind, I didn't hesitate any longer to order a cheap $300 8" reflector. It's not the scope of my dreams, but I'll get to see if it's the scope of my reality. If it lets me observe while sitting in a chair, and if it is easy enough to actually use on a regular basis, then who knows? It may actually allow me some actual observing time that I probably wouldn't indulge in with a "better" instrument. If it works out for me, then I may even consider a "premium" 8" DOB, but I'm fairly sure that unless my situation changes dramatically, I probably won't be in the larger market any time soon. We'll see. That's the current thinking, anyway.

Mike Swaim (reserving the right to change my mind at any and all times ;-)

I'm with you Mike. I love my 8" dob. I can pick the whole thing up and carry it outside and across the street (dirt road really) about 200 steps, no problem, it seems to need very minor adjustments in collimation about once or twice a year. I use it all the time. Some people do the same sort of thing with a 10", and it may work fine, but I'm happy right where I am.

That 14 inch T scope is pertty tempting, but I suspect it would be a once or twice a month instrument, so I think that my daughter's wish for a pony comes first.

I know that for me an 8" Orion or Discovery dob is the limit in both physical size and financially. I bought an 8" Orion XT8 used back in March and after replacing the secondary (it gave astigmatic images) I really like the scope. The OTA of the 10" is 15 pounds heaver and an increase of that amount would just be too much for me.

Warren Boyles

Mike:

Your test is a good one for the 12.5 inch and larger size scopes but not for the current 10 inch F5 batch of Asian scopes.

Due to unforseen luck, I am the proud owner of an Orion XT-8, a OPT StarHunter 10 inch F5 GS scope and a 12.5 inch F4.1 Discovery DOB. The 10 inch DOB is much closer in size to the XT-8 and quite portable, the OTA is only 48 inches long and weighs about 35lbs. When Orion originally designed the XT-10, I think they were quite wise in keeping the OTA length to a minimum. While a longer OTA would have some advantages, that 48 inch tube is quite easy to move about and fits nicely in most cars, even small cars.

I have included a JPG of these three scopes, I call em "The Three Bears." It is pretty clear I think how much larger the 12.5 incher is even though it is only F4.1 An F4.7 or F5 scope of course is much longer and even more awkward to move about.

Of the two, the XT-8 and the Starhunter 10, I much prefer the Starhunter 10, the added aperture provides a noticeable increase in brightness and resolution without making the scope unmanageable.

The way I have avoided Aperture fever is to realize that anything larger than my 12.5 inch scope will be awkward and time consuming to set up. I like the fact that the 12.5 inch scope can be hauled in the back of my Ford Escort and be setup within 2 minutes of arriving at a dark sky spot. Add, the fact that I am a real cheapskate and that the added hassle of going to a 15 inch scope would only buy me about 44% more light, I am happy where I am.

Of course if a 16 inch Truss DOB showed up locally for under a $1000, I would be first to buy.

jon

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I remember years back when dobsonians were just being interduced, I build a 16". (sonotube not truss! At least at first!!! :-))

On one observing night clouds came over near midnight so we all decided to pack up. 4 People helped me with my heavyweight. One other guy had a 6" f/5 dob that I had built for him. He put the tube under one arm and the mount onder the other, and cheerfully said "See you later guys!", and happily walked off. That set back large dobs for years in Western Australia!! Is was not long after that, I changed the 16" to a truss-tube design.

Cheers,

Maurice

I agree with you! There is now way under heaven, or on earth, that I would haul a 13" sonotube out of the basement to observe with it.

A few points here.

Unless your local temps are virtually the same, day and night, this sized scope will not be a "quick-look" scope anyway. Therefore, if the basement is the _only_ place you could store such a scope, then a truss type is the way to go. The optics can be cooling as you set up.

There is a significant differance between an 8" and a 13"(+/-) scope. Optically there is really no contest.

For a solid tube scope this big physically, it is necessary to take realistic countermeasures. Store the scope somewhere else. Make it egonomically useable. Or, as you have correctly deduced, it won't get used.

If you want one (and you would love it!), then reprioritize your floor space options. Store the scope within one doorway of the outdoors. Be it in a breezeway, porch, garage, den, livingroom or whatever. Pick the biggest, accessible doorway you can, and make a minor adjustment in floor plan, that will yield a major adjustment in your night sky viewing. The folks tooling around the sky with the big SCT's do this same thing.

john

Couldn't resist jumping in on this to brag about my 14" split-tube scope. About a year ago I sawed my 87-pound, 14" Discovery in half. Attached a couple of aluminum bars; now the two halves snap together in a few seconds, no collimation needed. Granded, the lower half is still hefty at 67 pounds but it's an awful lot easier to handle than the original tube. I can load it in my car without lifting the weight of the mirror (see photo). I also built an equatorial mount; the original cradle is on wheels and is used now only for storing the scope and wheeling it around the garage and driveway.

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