Thursday, December 20, 2012

The Design: Structure

All Systems Go!

A month or so before I left for Australia to work for a while, I placed an order for my primary mirror.  It's a 16" F/4 from Terry Ostahowski which should be ready sometime in March.  With this key decision out of the way, I can pretty much order everything else for the scope as my funds and time allow.

One of the key reasons I decided to build my own telescope was so that I could choose exactly which parts met my particular balance of cost, quality and portability.  I have a good handle on the basic components needed, and some time to figure out exactly which specific part will best serve my needs.  After the mirror, the next thing seemed to be the overall structure... the stuff that would hold all the other stuff together.

The Criteria

Just like the overall criteria for my new scope, the structure itself needs to be portable, and economical, but there are a few more specific requirements:

  • I want it to be as small and light as reasonable to firmly and stiffly support the optical system.  
  • Ideally it will be quick and easy to take apart and put back together.
  • It should have great motion;  Pointing a scope is a big part of using a scope and stiff or irregular movement on either axis can be a frustration.
  • Like most things, being aesthetically pleasing is a plus.
  • Of course it should be as inexpensive as possible while meeting the above criteria.
Any structure will be some compromise of all these competing criteria.  Some of them, like 'great motion' are tricky to evaluate without seeing one in person.  I've already decided that some variation of the Dobsonian mount.  This is mainly due to my desire for ease of use, but also helps a lot with the budget.  An equatorial mount for a 16" telescope would pretty much consume it entirely.

The Options

The first option is to built it all myself.  This sounds like a fun project, I do have some woodworking experience, and there are good plans of various designs available on the Internet.  In theory, it would be the least expensive monetarily, but would take a large amount of time.  Practically, I don't have a wood shop so I would need to purchase quite a number of fairly expensive tools to really do the job.  There is also a good chance I would not get it anywhere near right on the first try, which would mean putting up with something sort of usable, or spending the time and money to re-do it.... maybe more than once!

Although building from scratch was initially appealing, after a bit of thought, the option of a commercial kit seemed like a much better choice.  I'd love to be able to say with pride that I crafted this great telescope by hand, but even if I produced the structure, I knew I was not going to make the mirrors, focuser, cell, or any of the other pieces that go into a working telescope.   Some sort of kit really fit in with my plan for the scope; To assemble it from the specific pieces I feel meet my criteria best.

Besides,  I already had read about a great kit option, so I knew they were out there.  Even though I was pretty excited about the kits, I wanted to see what other options were out there.  My search was not exhaustive, but I came up with a few other options:

  • Obsession Telescopes:  I heard rumors that one could purchase some or all of a kit from Obsession, but I could not really find any information on this.  If they do sell them, I bet they are pretty nice, and rather expensive.  
  • AstroSystems Telekit:  This seems like a nice kit, and it actually comes basically complete with spider for the secondary and a mirror cell.  The cost for a 16" kit is $1670, which after subtracting my budgeted cost for spider ($120) and primary cell ($250) is $1300.
  • Hubble Optics: As indicated in this review Hubble Optics will sell you the structure of their ultra-portable dobs.  The price is listed in the review at $1195, which includes the spider and cell, I assume.  This is a bit better than the AstroSystems, and is very lightweight.  I had researched Hubble Optics as a potential supplier of the entire scope, but it seems there is some work to be done to make their scopes really perform, and I'm looking for something solid, even if it weights a bit more.
  • DobStuff offers kits in a variety of sizes and configurations.  By default it's the structure only, but they also produce mirror cells and sell various lines of parts.  Kits include all the wooden elements, the strut poles, and bearing surfaces (ebony star/teflon) required to build the scope.  All I would have to do is sand, finish, and assemble.  The 13"-16" strut kit is $696.  I saw a few in action at the Golden State Star Party and was impressed.

The Decision

DobStuff kits were high on my list when I started this project.  In a way, it's sort of what inspired it by getting me daydreaming about building a large dob; Knowing I could get the precut parts to assemble made the whole enterprise seem doable.  After exploring the options above, I sent an email to Dennis Steele inquiring about prices and lead time.

He was very helpful and the prices were as quoted on the site.  It also turns out his workshop is near my primary observing locations in Joshua Tree, CA, where the scope would be built and spend most of it's time.  Graciously, he agreed to allow my to pickup the scope from his shop to save some shipping.

I placed an order for a 16" strut kit with the easy transport option for even more portability.  While I was communicating with him I also found that he produced nice aluminum floating mirror cells as well.  I'd already done a fair bit of research on mirror cells, which I'll describe in another post, and I felt his price/quality/design made sense, so I added a mirror cell to the order.

I believe the initial lead time he quoted was something like 4-6 weeks, which seemed fine since my mirror would take four months anyway.  This would still give me plenty of time to work on finishing and assembling the structure before the mirror was ready.  Turns out, he was able to piggy back my order with another 16" kit and cut the parts all at once.  This shortened the lead time to just a week and a half!

On October 20th, Dennis sent me an email with a picture of my completed kit, ready for pickup!

DobStuff 16" kit with mirror cell.  Strut poles are included but not pictured.

It was around this time that I learned I would be going to Australia for several months.  Exciting, but a bit of a bummer at the same time.  I was really looking forward to sanding that bad boy up nicely and figuring out what stain/finish I wanted to use.  When I emailed Dennis to let him know I could not pickup the kit as planned and to arrange for shipping, he kindly offered to hold the kit for me as long as I needed for no additional cost.  That's great customer service!

Current Status

As of now I have almost 2/3rds of a telescope. budget wise at least.  Here is my updated budget with a few the few things I've ordered slotted in with actual pricing.

16" Primary Mirror$2450Terry Ostahowski 16"
Secondary Mirror$220
Mirror Cell$200DobStuff Flotation Cell
Structure$700Dob Stuff 13"-16" Kit

For anyone keeping track, this is about $1200 more than my original budget.  This is pretty much due to my mirror choice.  I had originally planned on going with a more mass produced JMI 16" f/4.5 mirror with secondary for only $1439, which is a very good price.  However this would have made the scope too long and put the eyepiece out of reach for me when pointing towards the top of the sky.

I could have gone with a smaller mirror, and therefore a shorter scope, but once I left the JMI mass produced mirror behind, I was in custom territory and the prices went up considerably even for smaller mirrors.  I ultimately decided to spend more now so I would not be as tempted to upgrade again later or regret that I did not get the scope I really wanted after all was said and done.

So that is where the project stands.  I have a mirror on order, perhaps even being ground by now, a finished DobStuff kit waiting to be picked up, and me out of the country.  I knew waiting would be tough, and being on an overseas adventure of sort has made the time go by more quickly, but I am anxious to get started.  I miss observing in Joshua Tree and knowing I could be working on the scope during the day, and observing at night over the holidays, makes it all the tougher to be away.

I hope the holidays find you in good spirits and provides some wonderful winter observing opportunities.  Clear skies and warm fingers!

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