My 12" Dob

[SAB]

My 12" truss dob, with primary mirror figured by a local amatuer and ASV club president.

I already own a 10" GSO dobsonian reflector which has wonderful optics and is joy to view the night sky with. If I had a girlfriend/wife, I would certainly get the "Honey, why do you need to buy a slightly larger telescope than the perfectly good one you have now?" "Well sweetheart, basically for the same reason you need 8 pairs of black shoes".

Yes, my 10" GSO is a nice scope, so my hypothetical spouse has a point! So why did I buy a 12" dob you ask? One night of browsing the astro classifieds, I came across a second hand 12" (304mm) truss tube dobsonian complete with Televue barlow, plossl eyepiece, Lumicon UHC filter and a whole collection of other goodies for a price that was almost too good to be true. So what do you do? That's right. You buy it! There's no "hmmm should I or shouldn't I" and certainly no "Honey, I found this amazing deal on a......"! It is not often that a deal like this comes up, and it was not something I could let get away. So, If I were hitched, I would've consulted the spouse AFTER I bought the scope, sure, there

would've been trememdous rage and relentless lecturing, but hey, that'll last an hour, whereas the scope will last a lifetime

Recently, a gentleman came over to purchase an eyepiece off me and he has connections to the previous owner and actually knows this scope. During conversation, this scope came up, and he pointed out my 10" GSO, stating that "That's a Hyundai, the 12 incher you bought is a Ferrari"!

Ok, was it worth the $600 I spent? Short answer: Yes,

The Package

In a nutshell it is a 304mm diameter truss dobsonian with a 1415mm focal length, making it an F4.65. The primary mirror is a high-quality hand figured product, which was figured by a well regarded member of the Astonomical Society of Victoria. The scope features 8 inter-connected truss poles lined with a black foam and has a lightshroud.

The stuff included in the AU $600 asking price include:

- The scope itself

- Telrad and 50mm finder

- Televue 3x Barlow

- Kendrick dew heater for secondary mirror

- Televue 32mm Plossl

- Lumicon UHC filter

- Light shroud

- Accessory box

- Tools for collimation

- Sky Atlas 2000.0 field edition

- Herald Bobroff Atlas

- Nortons 2000 book

- A pack of 10 tissues!

The Telescope

The scope itself is a solidly built, robust product. It has been heavily used over several years prior to coming under my wing and consequently shows some wear and tear. The paint on the UTA and rocker looks like a drought ravaged lake-bed, the secondary spider has some rust, the rocker has numerous dings and rough spots, the finder tube and rings could do with a re-paint.....BUT it is a perfectly workable product and performs just as well as if it were plated with 24 carat gold ;-). The primary mirror has a few marks, mostly near its center so these are largely hidden by the secondary. Now that being said, all visual imperfections were well advertised and photographed in the ad.

Features

The scope comes with an Astro Systems 2-inch "Phase 3" focuser, which has smooth motion and no image shift. Also included is a Telrad and 50mm finderscope with interchangable 1.25" eyepieces. Apparently, this finder is infact half a binocular with a 1.25" diagonal fitted. The eyepieces are focused by sliding them in and out of the focuser. The finder comes with an old 30mm plossl eyepiece with a nail potruding from the chrome barrel to assist in lining up on targets. I'm not sure of the finder's F/L, however it's 160mm from the objective to the mirror diagnal and the 30mm eyepiece seems to give a magnification around 5x. I have used my other plossls, including a 9mm, 12mm 15mm and 18mm to vary the finder's magnification up to a maximum of 18x or so. This is handy for locating smaller/fainter DSOs. As a matter of fact, I found the Eta Carinae region quite lovely observing thru the finder!

Collimation

The primary mirror is collimated via 3 large bolts which can be manipulated with a spanner or socket wrench. The secondary has 4 small hex bolts which are adjusted using an allen key. The primary mirror springs are massive, probably a good 3-4mm thick, if not more. Early on, I found that collimation shifted as I moved the scope in altitude, so after a bit of sleuthing, I tracked the problem to the primary being too loosely supported on its sides. I solved this by shimming it by sliding in small squares of paper between the primary edge and two of the silicon blobs supporting it. This has greatly reduced the movement and works well as an interim measure.

Getting Started

First things first, one must take this beast from house to backyard! It is large and is awkward to handle fully assembled so I drag it to the back door on a rug and then lift it partially assembled and carry it to the observing area. Make no mistake, this thing could eat my 10" dob for breakfast! Lifting it up and lowering it back down requires a posture that is akin to someone taking a dump in a squat toilet! I set up by removing the UTA and just lifting the rocker with the poles attached. Once I made it through my dog infested deck, around all the garden furniture and down the 5 steps without falling over and killinng myself, or worse yet, the scope, I set the half assembled rig down and re-attach the UTA. Setting up the scope from scratch is also easy once you get the hang of it. This is my first truss scope and the first few nights were a learning process, but now I can get it assembled in perhaps less than 5 minutes. No tools are required for set-up and takedown of the instrument. Tools are required only for collimation, which were included with the scope.

Observing

This scope has premium hand figured optics with proven optical quality. After a few nights out, the performance of this scope certainly did not dissappoint. The focal length enables me to sit regardless of tube orientation, a huge bonus. The following descriptions are based on observations from my suburban home in Melbourne, Australia, with typical seeing conditions (4-7/10). Rather than make brief statements on the scope's performance, such as "M11 was breathtaking", I like to go a bit more indepth using examples from each class of object to give a better perception of the instrument's capabilities to the reader.

Saturn

The only planet I've observed with this scope so far. I was impressed with the sharpness of the view, even at 272x with typical seeing and with Saturn being only 40º above the horizon. The crepe ring is easily shown with good contrast, as is the Cassini division, which during moments of good seeing could be seen to extend over halfway from the rings ansae to the globe. Even at 353x a single split second bout of steady seeing bought a memorable view. I must say I am impressed. It became evident that the hand figured mirror is no lemon, but a quality piece of glass.

Bright Nebulae

If you've ever stuck an OIII filter into a 12" scope or larger, armed with a low-power widefield eyepiece, swept up the Eta Carina Nebula and haven't wet yourself, then you're not true-blue ;-) Seriously, using an 83x and OIII filter on Eta Carina on this scope is a memorable experience. Even with a rising 3rd quarter moon, the sheer contrast of the nebula, its pitch black bays, inlets, lanes and "lakes" are incredible. I decided to see what higher mags would do, a filtered view at 217x shows marvellous texture and detail. Without the filter, the central parts of the nebula are still bright and many of the dark features stand out well. The Homunculus nebula is superb in good seeing. Using mags in the high 200 to low 300's range, the lobes are noticably uneven in both brightness and definition. Both lateral jets sticking out of the star Eta Carina can be seen, as can a small starlike point located in the fainter lobe tucked in amongst Eta Carinae. The nebula is very much brighter than in my 10", a profound and surprising difference.

M42 is a somewhat different specimen in this scope when compared to the 10". Immediately I could see more detail in the core at moderate powers, and all 6 trap stars were resolved at 83x. It reminded me of a view I had in an 18" Obsession, with outragous detail visible in the core!

Other large, faint extended nebulae, including CED 122, IC2948, GUM 39 and GUM 41 are visible, especially with a UHC or OIII. These objects are noticibly easier to see than with the 10".

Planetary Nebulae

Once you get into 300mm+ size range, Planetaries become interesting targets. I have only observed the Ghost of Jupiter and the Eight Burst Planetary, plus an obscure object called PK 288+0.1 near the Eta Carina Nebula. The Ghost of Jupiter shows its famous structure well and the Eight Burst is clearly seen as an elongated C-shape ring with an uneven brightness interior. My sketch of PK 288+0.1 through this scope exactly matches an amatuer photo I found on the net. Basically what I mean by that is that it was the telescope showing me the detail, not my imagination! I have also viewed NGC 3918, the Blue Planetary and it was a beautiful aqua coloured orb at 442x. I pushed the mag to over 500x and I suspected uneveness in this orb but couldn't confirm.

Globular Clusters

I have only viewed Omega Centauri through this scope at 442x - yeah basically it was mindblowing. How does a carpet of innumerable pinpricks covering the entire field sound?

Galaxies

Only had a limited run with galaxies but I was pleased with the results from my suburban location. The Leo triplet is nice, the two M galaxies show their individual shape and the dust lane in NGC3628 is visible. All 3 members of the M105 group in Leo show their size and shape well. The dust lane in the Sombrero was clearly visible at all magnifications under 3rd quarter moonlight. No doubt that under clear, dark skies, this will be an excellent instrument for serious galaxy hunting.

Conclusions/Summary

This telescope was definately a great buy. Quality optics, smooth movement and great all-round performance that can be enjoyed while fully seated. The scope can handle high magnifications if required, notably for small high surface brightness PN's, I estimate on an excellent night that she'll b able to pull in excess of 700x based on my current high-mag observations under good (but not great!) seeing.

Review by Sab.

[Solar B]

Great Job and Report

Brian

[Casus belli]

Excellent report. To move your scope couldnt you harness all those dogs, somewhat akin to huskies, to drag the scope out for you?

Just a thought. (Ok probably not one of my more sane ones)

It really sounds as you have a fantastic scope there. Happy viewing

[centroid]

A very interesting and comprehensive report, thanks for taking the time to write it.

Dave