#10 Mirror Size

     I mentioned somewhere in an earlier post that if I had easy access to a truly dark sky, I would not require anything larger than an 8" telescope.  To any readers fortunate enough to have that dark sky on demand, along with an 8" scope, you have an ideal situation.  Or not.  It depends on what you are searching for, and how much you hope to see.  You won't be resolving any galaxies into millions of stars with it (nor with any other instrument).  A 6" scope would be quite nice in a great sky if an observer was after only the best and brightest of deep sky objects.  An 8" would be a big bonus for such a project.  For someone enamoured with the whole NGC list, however, a 12" scope in that beautiful dark sky would be darn near perfect.  A 14" objective would be a bonus. 

     I've owned a 3" reflector, a 4.5" reflector, an 8" reflector, and my current 12" Dob reflector.  Going from a 3" reflector to a 12" is not a bad upgrade.  One might think that going from a 3" to a 6" would double the light, and then double it again from a 6" to a 12".  Thus 4x the light gathering power belongs to the owner of a 12" compared to his neighbour with a 3" (refractor or reflector, makes no difference when merely gathering light).  However, this is not the case.

     In actual fact, even though my math is not exact to seventeen decimal points, upgrading to a 6" mirror from a 3" is already an increase of 4x the light-gathering power, not 2x.  7.1" sq. versus 28.3" sq. is 4x the light-gathering power.  Going from a 6" to a 12" increases it again by 4x, from 28.3" sq. to 113" sq. (pardon my non-metric calculations).  In my lifetime, I have increased my light gathering power by a whopping 16x.   I'm still not going to resolve M31 into individual stars with it, but the galaxy sure looks a lot brighter (and I can now see a few globular clusters in it!).

     When I observed with my 8" reflector, I had pre-cut cardboard circles on hand so that I could cover the top of the tube to see what certain objects looked like from a 4" objective and a 6" one.  With the holes cut away, it was also easy to actually see the difference between areas of different sized objectives.  I recently cut a new cardboard aperture to fit over the 12" tube, being 8" (off-centre).  That 8" hole now seems awfully small, with the huge amount of cardboard left over showing the full 12" circle.  Since upgrading from an 8" mirror to a 12", I have increased my light gathering power from roughly 50" sq. to 113" sq., or by about 125%.  It had not really struck me how much bigger that 12" mirror was until the cardboard cover was finished.

 A very rough 8" diameter hole cut from a 12" piece

of thick cardboard.  Black tape hides the bad cutting,
and keeps the circumference roughly even.  Not only
can I now see how objects compare at 8" and 12"

(roughly speaking), but I can really see how much

larger the 12" mirror is (more than 2x, or about 125%).

     We could push this discussion some more, discovering that a 16" mirror has about 201" sq., and a 22" one has around 383" sq.  These scope sizes and larger ones now regularly appear in amateur astronomers' inventories.  How long until we get one big enough to visually resolve Andromeda galaxy at a local star party?  Hmm, that requires around a 200" mirror.  Or maybe several 25" ones spread out and linked by computer on-site.  Maybe that day isn't really too far off after all.

Mapman Mike

#6 My Telescope, Part 2

The fully assembled Orion XX12i, ready for first light.

     As much fun as it was to unpack and assemble the scope, getting it outside at night was the moment I was awaiting.  First light turned into a star party, as I chose to set up on a neighbour's farm.  Randy, Deb and I were the only ones present who had ever looked through a telescope.  We had five others present, and they got quite a show.  I had no idea how to use a Dob, so Randy did the honours, pointing the mirror at showpiece after showpiece.  I was pleased with the views I got (when it was my turn), and knew good things were in store.  The newbie astronomers were blown away by the views they had of the double double in Lyra, Albireo, the Ring Nebula, and various gloriously resolved globular clusters.

     To compensate for losing my equatorial mount, I had ordered a scope with "push to" capability.  It is not a "go to."  You have to physically move the scope from object to object.  A quick and easy two star alignment is required, and then, after following the arrows on the small keypad computer, "voila," the requested object appears in the eyepiece.  As I was convinced that star hopping would prove too difficult, I was planning on using the computer option to navigate the sky.

     I was wrong on the star hopping.  Turns out it is pretty easy after all (see my entries on planning an observing session).  I usually use the computer (which runs on a single 9-volt battery) to get started, then switch to my tried and true method of star hopping.  The scope itself handles like a dream.  It is perfectly balanced at all times and with any eyepiece, something I could never brag about with the old equatorial scope.  Movement of the tube is so smooth that zig-zagging seems like straight motion.  The precision of the 2-speed focusser is one of its best features.

     The best part of owning this scope is its portability.  I can set it up myself in the field in 15 minutes and be ready to observe.  This includes aligning the finderscope, which must be done each time.  Getting the computer up and running with the two-star alignment takes less than 2 minutes, and getting to the first object of the session requires less than a minute after that.  Taking things apart in the dark is easy, and from observing the night's last object to driving off in my vehicle all packed up takes fifteen minutes.

     The scope came with three eyepieces and a 2x shorty Barlow lens.  The 25mm 1 1/4" Epic 11 ED is actually quite good, giving excellent colour results.  The outside areas of the field are blurry, however.  The 10 mm eyepiece is adequate for now, a mid-range Plossl.  I have already split some mighty close double stars with it.  The 2" eyepiece is very basic, but I like it nonetheless.  It gives 43x, meaning that most of the large clusters fit inside nicely.  However, I mostly use the 25mm (60x/120x) and the 10 mm (150x and 300x), as well as a number of my older eyepieces I had used with the previous scope.  I recently ordered another Epic 11, this time a 15mm which will give me 100x/200x.

     Having used the scope since October 2012, I am now totally comfortable with it and contemplating a long trip, taking it somewhere with a really dark sky.  Below is a link to the scope on the Orion website, if you want a closer look at the stats.  I have no trouble recommending it to anyone looking to bump up from a 6" or 8".  If you already have a 10" and are looking to bump up, then I recommend the 14".  Had I known what I know now about portability, I would have purchased the 14."  The 16" is portable, too, but too much scope for me right now.  Maybe someday. 

Mapman Mike

 http://www.telescope.com/Telescopes/Dobsonian-Telescopes/IntelliScope-Dobsonians/Orion-SkyQuest-XX12i-Dobsonian-Telescope-Shroud-amp-Case-Set/pc/1/c/12/sc/27/p/102024.uts



#5 My Telescope, Part 1

     I have two scopes, actually, but I will talk about the main one today.  After using an equatorial 8" reflector for over 30 years of observing (more to come on that topic), I decided it was time to upgrade.  I made the decision about five years ago, finally getting around to making the purchase last September (2012).  I wanted something notably larger in aperture, so I was not going to get an equatorial mount.  I had put off owning a Dobsonian scope for years, as I preferred star hopping with the equatorial.  North was north, south was south, east was east and west was west.  Period.  None of this zigzag nonsense for me.  Until now.

     The scope had to be portable, within reason.  I own two VWs, and it had to fit in either the Golf hatchback or the Tiguan.  I had to be able to lift all the parts and assemble them myself, sometimes in the dark.  I was looking at a 14" or a 12", eventually deciding on the 12".  Had I known just how portable and easy to assemble the Orion telescopes were, I would have chosen the 14".

     So I am the proud owner of the Orion Skyquest XX12i Dobsonian Telescope.  I also got the shroud, which covers things from the main mirror tube up to the secondary assembly.  It helps keep out stray light and blowing dust.  And I purchased the storage bags to pack everything for traveling.  All in all, a pretty good deal.

     It arrived in three boxes, and one fine Saturday afternoon my wife, best friend and I got down to work setting it up.

Christmas in September!  Deb opens Box #1.  First came the great unpacking project, using a long checklist to make certain each part had arrived.  According to the instructions (below), some assembly was required.

Despite the rather intimidating diagram, putting the base together wasn't all that difficult.  Once the base is assembled, it stays assembled.  It fits nicely into the back of either of our vehicles.

Phase One was to put the Dobsonian base together.  Though this posed few difficulties, adding the "push to" components was tricky, not helped overly by the instructions.  A few phone calls to the Orion help line on a Saturday afternoon helped us get the results we needed.

Phase One is nearly complete!  Because of some problems adding the push-to components, it took a couple of hours.

 The completion of Phase One was a suitable time for a coffee and tea break.  Mapman Mike triumphantly holds onto the assembled base.  Randy seems relieved.  First light cannot be far off now!

Unwrapping the 12" mirror was an exciting moment.  How often does one get to see a brand new telescope mirror suddenly appear in one's home?

     The mirror came with a free blemish (not the central dot, which is for mirror alignment purposes).  Randy patiently removed a small, sticky spot, carefully using wet and then dry Q Tips.  Afterwards, the mirror was as good as new.  The rest of the assembly was easy.  The entire project took about 5 hours, including unpacking and itemizing everything.  Needless to say it was cloudy that night (and for many nights afterwards (and since).

Continued in Part 2...