"Brutus", my 24" f/4.0 'Ultimate Aperture' Telescope
(William Shakespeare's Julius Caesar, Act 1, scene 2)
In search of "ladder-less big glass"
Having made a foray with my stewardship of "Boris" (Boris) into the world of large-ish (20") aperture slow (f/6.7) Newtonians, I decided that:
1) any jump above my current 16" scopes should be to the 24" level at a minimum (since anything smaller would be a visually insignificant improvement in light grasp), and
2) that such a scope would have to be f/4.5 or faster to be practical for me to use, since I decided 'ladders aren't for me!'
I'd filed this away as an idle realization, when a few weeks later an ad appeared on Astromart offering a 24" f/4.0 Dobsonian telescope. It featured a 2" thick Pyrex primary made by John Hall of Pegasus Optics, who is definitely among the first tier of opticians. The mirror had a nominal peak to valley wavefront rating of between 1/8th and 1/12th wavefront, and a nominal Strehl ratio of 0.95-- both highly respectable for such fast optics. In 1995, when this mirror was made, this was probably one of the 'fastest' large mirrors available to the amateur, and is still on the cutting edge of what is feasible to produce with decent optical quality. (Only Steve Kennedy seems to be breaching the 'f/4 barrier', and that is a recent development.) All this at a price less than ONE-THIRD that of a brand new 24" f/3.7 scope! My dreams of really "big glass" were about to become reality...
Specifications
This primary was mated to a 5" secondary from Galaxy Optics, and mounted by noted Alabama ATM'er Pat Rochford in one of Astrosystems' early vintage "Telekits". It features many Kreige and Berry-style Dob features, including genuine Obsession upper mounting hardware. It features a height to the eyepiece of a scant 91 1/2" (now 90", after all the modifications), which is "two step kitchen stepladder" territory for me! It has a shroud, two fans behind the primary, a Telrad, and was wired for dew heaters. The primary mirror's coating was described as "hazy" but I found the 10-year old QSP coatings to be in surprisingly good shape.
History and Lineage
Pat Rochford kept the scope for nine years after completing it in October 1995, eventually selling it in the fall of 2004 in disgust at the encroaching light pollution that had rendered this scope's aperture superfluous except for the occasional road trip to dark skies. He therefore put it up for sale, and Mark Dearing of Florida bought it. Mark made some modifications- most notably replacing the Astrosystems "Phase 4" focuser (which I dislike) with an older model "Feathertouch" two speed unit (which I've never tried but which is reputed to be the 'gold standard' of focusers). Mark kept the scope for about a year, then realized his interests were shifting from visual observing to imaging. He therefore listed it on Astromart, where it came to my attention.
"Lightning strikes twice"
I was intrigued by the scope, and by the fact that Mark was the seller, since he was the previous owner of my last 'big Dob' Boris! We came to a provisional deal, and I planned to go down to Mark's home in Jacksonville to do a perfunctory star test (pro forma in this case, based on what both Pat Rochford and John Hall had told me about the optics), and pick the scope up. I had a series of family complications that kept me from being able to get away long enough to do this ~24 hour driving odyssey, however, so Mark graciously offered to do what we did the last time around-- meet at the halfway point, at 'South of the Border' (that paragon of kitsch located in South Carolina just below the North Carolina border). We found a window sandwiched between days of bad weather (icy) and Mark and his observing buddy (and scope co-owner) Gary met me there.
First Impressions
The scope was big-- bigger than I'd expected an f/4 to be. It was also heavy-- I didn't think 250 pounds would feel that unwieldy. A big part of it, I believe, are the undersized hard plastic wheels and comparatively short barrow handles, which make the scope a bit tough to move around terrestrially. Celestially, however, the scope handles like a dream. It slews readily in both altitude and azimuth, with a minimum of stiction, and holds its position on any object. Mark removed the finder scope, which affected the balance to the degree that the scope was back-heavy without an eyepiece inserted. Any 2" eyepiece, however, proved enough to balance the scope out, and it holds well without dropping with even a heavy combination such as the Nagler 31/Paracorr. Pat put a handle on the scope, which is handy (glad to know I'm not the only one to add these!), but set the scope up for a left-hander.
Why "Brutus"? There's a story behind this-- see Naming Brutus. Suffice it to say that I needed something to keep my mind occupied on the 402 mile drive back from taking delivery of the scope!
First Light (for me)
The night of 18 December started out very clear if somewhat cold. I collimated the primary and secondary with my Kendrick laser, doing the primary collimation from the mirror box rear using the reflection from the beveled edge of the Kendrick. The Astrosystems secondary holder was a bit tight, but ultimately adjusted well. The relatively short (~62") and thick (1 1/2" outer diameter) truss tubes held the scope in collimation as it was raised and lowered in altitude, despite the comparatively heavy secondary cage.
Although I know that collimation is critical on a fast scope like this-- which is why I'll be adding a "Cat's Eye" triangle and using that and the autocollimator-- my rough and ready laser collimation produced admirable results. Stars were crisp and tight when viewed through the Nagler 31 with Paracorr.
 |
I started out on Mars, and was rewarded with a good 54 arc-minute view at 90X. |
|
M57 was nice, but frankly not much more impressive than through my 16" scopes |
|
The Double Cluster was nice, showing as much detail in my streetlit Christmas light festooned neighborhood as the 16" scopes do under dark skies. |
|
M31, M32, and M110 were impressive. I saw much more extent to M31 than usual, plus a dust lane on the side facing M110. Easily the most impressive sight of the night. |
|
By the time M42 rose enough to be seen, the transparency had deteriorated markedly. Despite this, I was able see as much or more nebular detail than I usual get from the 16" scopes. I was able to see the "E" and "F" stars in the Trapezium using the Nagler 31. |
The upshot is that this scope renders very good images-- even when I know I can do better on its collimation, is remarkably portable for its aperture, and is quite usable "as is". All in all, a gem of a telescope, and one that I could foresee owning 'forever'.
Second Light Observing Report: Brutus impresses a tough crowd
Tonight Brutus faced an audience that is probably harder to impress than the judges at the Stellafane ATM competition. I'm referring to my family, who normally tolerate-- but don't participate in-- my astronomy sessions, which they consider "Dad's foible". Tonight's views of M-42, in particular, won the coveted "Oh wow!" remark from all four of my teenaged children, as well as the even more precious and seldom awarded Spousal Approval of a Telescope. <g> All commented on how much they could see in the scope, how crisp the images were, and how easily they could move the scope despite its bulk. I told them what a rarity it was for them to be observing through a 24" scope with both feet planted firmly on the ground, which all were able to do for M-42.
I also showed them the Double Cluster, Betelgeuse (for which they nearly needed sunglasses), and Mars. I looked at M-31/32/110 before inviting them outside; the transparency rendered it less impressive than on my last viewing session, so I didn't share the views. M-42, on the other hand, showed definite purple and reddish hues in addition to the greens I customarily see in my 16" instruments. I also tried my binoviewers on Mars, with OK results. (I think the binoviewers are heavy enough that they pull themselves off-axis slightly; the Feathertouch focuser just doesn't offer the support and gripping power of the Clement focuser on Natasha.)
I was impressed again at how good the collimation of this scope was simply after using the Kendrick laser. I know it could be done more precisely, but was surprised at how these results seemed to confound the reputation of f/4 scopes as hyper-finicky on collimation. The plastic wheels, meanwhile, continued to annoy me, both when transporting the 'scope and when trying to observe with the handles in place. Once my fans and flocking paper arrive, I'll take a day and tackle a slew of ATM tweaks.
Third Light: a Christmas Present
Early Christmas morning (a bit after midnight), "the children were nestled all snug in their beds" (NOT! they're teenagers, with vampire like sleep schedules!) but that didn't stop me from wheeling Brutus down the driveway for a short cruise through the Messier objects. The transparency was so-so, but nonetheless I took in M1, M35, M36, M37, M38, M42, M43, M51, M78, M81, M82, M97, and M108. The most impressive views of the night were of M35-- this much aperture really makes the better clusters come alive-- M82, and M51, which managed to show a hint of structure despite being a scant 25 degrees above the horizon and located nearly in line with my local streetlight. This session gives me a pleasant foretaste of what kind of performance I can expect from this scope on Deep Sky Objects under truly dark skies. Quite a Christmas present!
Modifications
However, as with any Richberg scope, there are a number of things I'll tweak and modify. See Mods to Brutus for details-- some of these are pretty cool, I think! As tweaks go, virtually all of these changes are more in the nature of customizing the scope to my observing style and preferences than "fixing it", reflecting the fact that this is already a great scope that provides impressive views. The only "must do" mods were upgrading the wheels and the ramps, which were needed to allow the scope to be safely and readily transported to darker skies.
Update: after using the scope more extensively-- including at the Winter Star Party-- I came up with an additional set of modifications. Brutus Mods Round 2 With those completed, about the only conceivable thing the scope lacks is "go to" and tracking-- nice to have (especially for planetary observing), but not necessities for the Deep Sky Objects that are the raison d'etre of a large Dob such as this.
FINAL UPDATE: Yes, I did some more mods. (content coming...) Brutus Mods Rd 3
Brutus and Natasha from the side
Front view-- Natasha looks downright puny compared to Brutus' impressive
aperture!
Despite the coatings being 10 years old, the surface is in much better shape than I expected.
Standing with Brutus you can see how I could observe to nearly 45 degrees elevation flat-footed.
Leaning on Brutus' handle
Reaching zenith with a two-step kitchen stepladder (you sub-six footers are in trouble, though!)
Observing seated with my "Cat's Perch Pro" chair, I can see to within ~8" or zenith, which gets me to ~65 degrees elevation
