Observing with Webster 28" f/2.7
A 28" telescope with a 70" eyepiece height at zenith? If you thought that the big Dob revolution had hit its plateau, wait until you meet the largest, fastest Dob on the planet.
About The Author
For those of you who don't know me, I build large Dobsonian telescopes as a hobby. My definition of large is 24" and up. I teach telescope building classes that emphasize the reasoning behind doing something a certain way, rather than just following a set of plans. I consider myself a more than competent woodworker. I am an AstroMart Moderator, and I currently use a 30" f/5.3 Dobsonian telescope that I designed and built myself. The largest telescope I have built is a 36". I have owned or used almost every brand of Dob in the world, and then some.
Yes, I have been called "nitpicky", and yes, I acknowledge that my reviews are often lengthy. These products are not inexpensive; so I certainly will point out every benefit and flaw I see. My reviews are not length constrained like the 1000 word reviews seen in the glossy magazines, nor do I need to protect advertising revenue, so I try to cover everything with no artificial sweeteners added.
Like gossipy girls in a school yard, many people murmur that if somebody likes a product they review, they are somehow "on the take" or "have a relationship with" a manufacturer. I have no interest in any astro related company (other than giving them much of my income) .
Why Do I Review Telescopes?
Most everything you read on the web forums about large or fast Dobsonian telescopes is simply old wives' tales repeated ad nauseam:
Q: I'm thinking about getting a 36" Dob, what do you suggest?
A: Are your skies dark enough for a 36" Dob? Big Dobs magically gather up light pollution. They only work in the desert, certainly not the Northeast. (Big scopes do not somehow gather more light pollution than small scopes. The larger the scope, the more detail and brightness you see, simple as that).
Q: I'm thinking of getting a 25" f/4 ...
A: Hold on there buddy! Do you have the skill to collimate a f/4? You want all that coma? (All Dobsonian telescopes are collimated the same way, regardless of "speed" or focal ratio. The Paracorr coma corrector has been available for many years).
Q: There is a deal on a 25" f/5 on the club's website...
A: You want to climb a ladder all night long? That's crazy! I like my feet flat on the ground. You would be better off getting a 12" f/5, like me. (Just because one person is afraid to climb a ladder, that does not mean that everyone should be afraid. Real men safely climb ladders all the time, like Firefighters, Electricians, Painters, Orchard Workers….).
Q: I have a 10" Dob now, but I'm thinking about a 30"...
A: You have not even seen everything you can in your 10" yet! Hell, I used a 6" for my first 20 years of observing. You better stick with your current scope until your eyes get older and cloudy. (The skies are not getting any darker and your eyes are not getting any younger. You see more with a big scope, so live it up - now).
Q: I just got my $25,000 32" F/3.6 telescope today...
A: f/3.6 ??? Well, kiss the days of using your $20 Plossl eyepieces goodbye! Hope you have the cash for some Naglers. You know you are now going to have to buy a Paracorr, don't you? Hope you put aside some cash for that, too. (No one is going to use $50 eyepieces on a $20k telescope any more than they are going to use 86 octane gas in their Porsche).
With "advice" like this all over the web ( usually from astronomers who don't even own a scope anywhere near the size being discussed), I figure that a few real "eyes on" reviews are in order.
Is This A Telescope Review?
Not really. I have already reviewed the Webster C28 many years ago ( http://www.astromart.com/articles/article.asp?article_id=443 ).
This is more of an observing report. Probably less than one in a thousand astronomers have ever looked through a f/3.3 telescope, and at the date of this publication, less than 20 worldwide have ever looked through a 28" f/2.7 .
The perception online is that everyone has a big, fast Dob. But the reality is that there are only a handful of sub f/3.3 Dobs, and only one 28" f/2.7 in the entire world.
Spend The Night
The temperature outside had hit a record 100 degrees Fahrenheit and the humidity was so thick your lungs had a full feeling like you had just evolved and took your first steps out of the water. The weather was being described as "truly dangerous" by the media.
I got a phone call from a guy in the club who said he and some other members were going out to Webster's dark site because Webster was testing a C28 f/2.7 telescope. I had never looked through a telescope anywhere near as fast as f/2.7, so of course, I needed to be there, invited or not. I was then told that Webster had no power or phone service (there were rampant power outages across the state due to the insane temperatures), but if the sky was clear, they would be out there.
So with a predicted temperature falling to 94 degrees Fahrenheit by Midnight, it being a weeknight with a 54% moon, a two hour drive, and no way of even verifying that the Webster's would be out there, would it be worth it just to view through a f/2.7 telescope? Hell yes!
I loaded up the van with much liquid refreshment, bug spray, a pair of 120mm Binoculars, a 100 amp hour deep cycle battery (just in case they needed power) and my eyepiece case.
I arrived with plenty of daylight still present because I worried that without functioning traffic lights there might be general mayhem. There was a big grill being manned by a Middle Eastern gentleman named Al. He was cooking Kabobs made from Deer meat and had some handsome looking beef steaks too. I asked him if Deer was Halal and he said everything is fine except Pigs, Eagles, Reptiles and alcohol. That accounts for about half of my daily caloric intake right there, so I simply nodded in agreement that Eagles were not part of my diet either.
Walt Webster said that everything in the now thawing freezer was being cooked, so I better get a plate. He did not have to tell me twice. Al could best Steve Raichlen at the grill any day. It was garlic and lemon heaven.
As more people were arriving, we began to set up the scopes in a semi-shady spot along a tree line. We wanted to keep the scopes from getting hot in the sun and it was certainly cooler outdoors than being enclosed indoors. You always want to keep the Telrad finder out of sunlight, because sunlight can burn the internal target.
Even if A/C was available, when it is hot and humid outdoors and you take a cooler mirror from indoors, condensation immediately forms on the optics. It is the same as when you take a cold beer from the fridge; water vapor from the air condenses on the cold surface and the bottle "sweats".
On the field we helped set up the C28 f/2.7, a C28 f/3.6 in a deep red stain, another C28 f/3.6 in clear finish and a D14 (don't know what f/ratio, but it was f/4 point something) . There were two, fine AP 6" refractors set up also.
None of the scopes were completed. Most needed a light shroud, some had un anodized truss poles or just the wires where a secondary dew heater would be installed. Thankfully, all except the red C28 had functioning tracking and GOTO.
I naturally wanted to collimate the C28 f/2.7 myself, but the secondary had not been centered under a Cheshire yet, and I did not bring one with me that had an opening large enough to take in the whole, monster secondary.
When I say monster, I mean 7" secondary that is 1.5" thick. Monster as in: what you would normally see used as a secondary in a 40" telescope. Monster as in: bigger than most astronomers' primaries...
Eric Webster came over with a extra large Catseye Cheshire, but even that was a close call size wise. If these secondary mirrors get any larger, we are going to need new tools to deal with them. Normally on a 40" telescope the 7" secondary is much farther back from the focuser. On the C28 it is "right in your face". It is hard to convey in words, but the scale of the secondary takes some getting used to. I caught myself taking quick glances at it on more than one occasion.
The C28 f/2.7's primary was made by an optician named Mike Lockwood. From what I can tell, this was the first Lockwood mirror in Michigan. Nobody from either club who was in attendance had ever seen a Lockwood mirror anywhere.
The other C28 optics were from Steve Kennedy and the D14 optics were from Carl Zambuto.
An interesting aside about the Lockwood mirror was that it had the center of the mirror "spotted" with concentric circles directly from the factory. I assume they were cut with a diamond or carbide stylus. Because they were cut while the mirror was still on the machine, they are absolutely true to the center of the mirror; better than any center spotting template could achieve. Other opticians should take note; thumbs up to this innovation.
Actual collimation took about a minute. We carefully collimated the scope with a Glatter Holographic Laser and Glatter BLUG target. Even though this is the fastest telescope I have ever seen, it was NOT any more difficult to collimate than any other Dob.
If you ever read some online "expert" claiming that fast telescopes are more difficult to collimate, you can be sure that they have absolutely no firsthand knowledge of fast scopes at all. Folks, if you have never owned a sub f/4 Dob, DO NOT make some knee-jerk forum post about how hard they are to collimate. You are doing a disservice to our astronomy community, and flaunting your ignorance.
The laser hitting the concentric circles was easiest to see by standing about 24" off axis from the center of the scope. Everyone who tried this off axis stance exclaimed "Oh wow, that makes it easy!" The concentric circles also made a really fine pattern on the BLUG target. I don't know if Webster plans on also placing a Catseye spot on the mirror in addition to the factory circles. There were Catseye "radiation symbols" on all the other mirrors on the field.
It was somehow too hot even for the mosquitoes, because as dusk approached they did not make an appearance. This despite us being only a few dozen yards from an acre sized pond (they call it a pond, honestly it looked like mostly quicksand).
At one point a huge turtle lumbered its way from the woods on one side of the property to the pond. It took it over an hour, and I did not see when it actually got started. It was so hot, I just wanted to say to him "Why not just stay in the pond instead of traipsing all over frigging creation???". Although he probably did not know it, I at least knew he was safe from Al eating him.
Speaking of Al, he brought out what looked to be a Pelican case, but it was a Mems Accelerometer to measure vibration. It was stenciled with "Property of Ford Motor Corporation" and Al said it cost more than any of telescopes. The device has two lines running from it. One line has a kind of solenoid "thumper" to create a repeatable source of vibration, the other has sensors to read the vibrations at different frequencies. The only thing I love as much as food is exotic electronic gear, so Al was quickly becoming my hero.
Al explained that he has been testing scopes for years and can tell you the vibrational characteristics of all the major brands (Obsession, Orion, Meade, Starmaster, Webster (you probably saw that one coming...)). He showed us the difference between the Red C28 that did not have its anti vibration pads installed yet, and the Clear C28 that did.
He also showed us that the C28 f/2.7 vibrated more than the C28 f/3.6. This was exactly the opposite of what I would have guessed, as one would assume the that longer metal truss poles on the f/3.6 would vibrate more. But when tested, he traced the difference to the larger secondary mirror in the f/2.7. He described it as a kind of pendulum effect. The difference was not much at all, but it was an interesting phenomena.
I asked Al for any easy vibration tips for us amateur scope builders at home who do not have access to accelerometers, elastomers or fiber epoxies , and he said "Dissimilar materials. If you have a piece of steel, bolt it to some wood. If you use all one material, you will have frequencies that reinforce and resonate. If you have an aluminum frame, fill it with sand. If you have aluminum sheet, cover it with rubber. Medium Density Fiberboard vibrates less than real wood. Use lead shot rather than solid metal for counterweights. Fill your pier with sand or lead shot." Some great tips, indeed.
Come On Darkness
As it finally became dark enough to see some stars, Al began enunciating the proper pronunciation for them. I don't want to sound like your wife, but however you have been pronouncing their names - you're doing it wrong. As the night went on, the rest of us would unconsciously lower our voice when pronouncing a star's name; not wanting to Al to hear us mutilating the beauty of the Arabic language.
The nighttime temperatures were not going to fall all that much compared to a normal Michigan night. There was a big heavy pressure system of heat upon us and it was not going anywhere, even with a totally clear sky. With no 120v electrical service, the best we had for serious fans were a few 12v, 12" box fans. Although Webster did have some deep cycle batteries already out there, my battery was fully charged and came in handy for the 3 amp load the box fans drew.
The D14 with its thin, Zambuto mirror was at ambient temperature within 20 minutes; said my laser thermometer. The 28" scopes, with their 2" thicknesses took longer, but did get well acclimated in about 2 hours. I was not checking regularly, so I missed the exact time the acclimation occurred.
We started off with the M13 Globular Cluster as it was directly overhead. Jim Webster was hogging the C28 f/2.7 to himself while he was playing with the Paracorr II and trying the widest field eyepiece he had (the 31mm Nagler). After a while, he grunted to himself "Hmmmph, yeah...". Like zombies to a fresh brain, we all silently drifted over. Finally, Jim nodded and waved "Take a look".
Each of us looked into the eyepiece and was surprised. "Where's the coma?", "WOW! M13 at zenith, bright as the sun, and I'm flat footed!", "You have got to be kidding me!", "Two words: GAME - CHANGER", "So great, I might fall off this ladder"; were a few of the remembered comments. There was also much spontaneous laughter, it was an amazing view.
While others were at the C28 f/2.7, I commandeered the clear finished C28 f/3.6 with my own 31mm Nagler and Paracorr. It was also an amazing view, but I wanted to see some flaw or difference between them. Sure, the field of view was wider on the C28 f/2.7, but I was studying the very edge of the view. There was a small amount of coma at the outer edge, but you had to be looking for it. We all started making the trip between the two scopes. Some said that they thought the f/3.6 image was just a tiny bit tighter, but was it really? Or did we just expect it to be? I could not be sure.
The 31mm Nagler is not the best eyepiece for really fast scopes like these because the exit pupil is too large; so some of the light is wasted and not sent through the eye's pupil to the retina. Between all of us we did not have two 26mm Naglers (What the hell; you guys call yourselves astronomers?), so we went with the 21mm Ethos next.
Here, neither scope was totally corrected to the edge, but the image was brighter. Now we were seeing the full ability of these 28" mirrors. Bright images, maybe even whiter images. If you turned your head uncomfortably sideways to see the very edge, you could see where the eyepiece and Paracorr ran out of steam in the outer 5% FOV on the f/2.7 and outer 2% on the f/3.6 . The effect was more pronounced in the C28 f/2.7 to be sure. But to be totally honest, I never observe with my head sideways looking at the very edge of an Ethos, and I doubt many other astronomers do either. Using the eyepiece in a normal, relaxed, on-axis fashion gave simply pleasing views. The scopes were performing well, so we went next to the 17mm Nagler.
The 17mm Nagler is the workhorse of the Televue line. I probably use it more than the 13mm Nagler that is most people's first choice. Many experienced observers state that the 17 Nagler has more contrast than the 17mm Ethos. I think I can agree with that; maybe because it has less glass in the lightpath. We hopped over to the M92 Globular Cluster, also placed well in the sky. Again, the view was great and unless you were actively looking for edge artifacts, you would be simply lost in the beauty of the view.
If any of you have read my review of the new Paracorr II ( http://www.astromart.com/articles/article.asp?article_id=799 ) , you might remember that it was unusable with the king of all binoviewers - the Denk 2s. The front end of the Denk 2s have an OCS (Optical Corrector System) that lets it come to focus with Dobsonians and acts as a coma corrector too. Most other binoviewers (cough, cough...Televue), simply don't work at all with any of the Dobs I own.
So the Denks were going to have to go it alone, without the assistance of the Paracorr. We each loaded our Denks with a pair of 24mm Panoptic eyepieces and stuck them into the f/2.7 and the f/3.6 scopes. I have to admit at this point that I had already looked through a C22 f/3.3 with the Denks, so I knew that f/3.6 was going to be fine, but f/2.7 is way outside of anything that was around when the Denk 2s were designed.
The Denks have a "Power Switch" that let you cycle through three levels of magnification without switching eyepieces. I went for the highest power right off the bat on the f/3.6 and M13 almost filled the eyepiece completely with a blazing 3D view. I cycled through the other magnifications, but left it at high power for the others to coo over.
When I got my turn at the f/2.7, I had the biggest surprise of the night. The image held up! It was simply a great view. I know, it should not be possible, but if you were not going out of your way looking for trouble (like us reviewers like to do), you could just take it all in without complaint. Perfect? No. Serviceable? Yes, absolutely. I just shrugged and shook my head in disbelief.
I had been told that when enough demand occurs, Russ Lederman at Denkmeier is going to redesign the OCS for faster scopes. I hope he does not view with a f/2.7 scope beforehand, because he might not bother.
By this point the moon had risen to an acceptable height in the sky. Although many observers hate the moon, I like it and it makes a great, high contrast target. I like to test the "snap" of a telescope on the moon. When a mirror is really well made, it will snap into focus. The snap has to be experienced to appreciate, but I'll try to describe it here.
A mediocre mirror will not give you the confidence that you are in absolute focus on the moon. You will think that you are in focus while you are looking at one feature, but as you eye wanders across to another, you will instinctually reach for the focuser and try to get another, better focus point. I've seen people buy motor driven focusers thinking that they need "finer" focus control to see consistent sharp images, but what they really need is a new mirror.
A great mirror instantly snaps into focus, and as your eye wonders over to other features, you don't reach for the focuser, because you absolutely know you are in razor sharp focus. You don't want to touch the focuser, because you know you could only make it worse. Again, snap is hard to describe, but once you experience it, you'll know it.
We cruised along the moon's terminator at different magnification settings on the binoviewers. Contrast was good on both scopes.
This is going to sound funny, but you had to be seated at the C28 f/2.7 to comfortably observe. Think about this for a second: the moon up at 45 degrees, you are using a 28" telescope, and you are sitting down comfortably taking it all in. This would be simply inconceivable even a few weeks ago.
Here on the moon I could finally see some difference between the two 28" mirrors. Not a huge difference, but a repeatable one. The f/3.6 had just slightly more snap. I know it is not a fair fight, and it is probably just the difference in focal length, but it the f/2.7 was just the tiniest bit more fidgety finding the perfect focus (but once you found it, you had it over the entire image, no problem).
I say it is the focal length because a well made f/7 telescope has a huge "depth" to its focal point. You can be slightly above or below it and the image is still razor sharp. Not so with the fast scopes, you have to dial the focus point exactly in.
A guy named Ken (sorry, I did not get your last name) pointed out that the D14 Zambuto mirrored scope, although it did not have as much detail as the 28" scopes, had slightly blacker blacks along the terminator. We mostly agreed that indeed that was the case. Theories were introduced that maybe the smaller optic scattered less light, maybe Zambuto had a smoother polish, maybe our eyes were blown out by the brightness, exit pupils were too different, or maybe the standard aluminum coatings on the Zambuto introduced less scatter than the enhanced coatings on the Kennedy and Lockwood 28s. In the end, the only thing we agreed upon is this subject is certainly in need of further study.
Everyone did their own thing on all of the scopes on the field, until it was quite late and Jupiter was high in the sky. This would be the ultimate test, high power viewing on the gas giant. We double checked collimation (it never hurts to check when the scope is as cold as it is going to get in the night), and let 'em loose.
We found excellent performance all the way around, but I honestly expected that because the moon looked so good. Jupiter had gobs of detail that went in and out with the seeing and we of course observed with and without Neutral Density Filters to cut down on the brightness. We also tried to observe with and without the Paracorr. Without, you were bombarded with coma around the edges (picture that half second before going into hyperspace in Star Wars, and you have a pretty accurate image). The center 60% of the view was fine, but the outer 40% was too distracting at f/2.7. On the f/3.6 you could observe without the Paracorr, at least at higher powers.
One bit of comical relief came when a gentleman (I'm not outing him) who was first looking through one of the AP refractors and then the C28 f/2.7 said:
Guy: You know the big dobs really are not as good on the planets!
Me: Really? I was at the refractors a few minutes ago and the view was nice, but not as detailed as this.
Guy: Yeah but Jupiter's moons are perfect points of light on the refractors. They are just not as sharp on the big scopes, they look almost like discs.
Crowd: They ARE discs! (in almost perfect unison).
Crowd: (much laughter)
We beat him down and threw him in the swamp (no, of course not, the turtle did not deserve that). Actually, we explained how larger scopes can see not only discs, but pointed out the different colors on the moons. Really the 28" scopes clobbered the poor refractors, not that it was a fair fight, but you know how sometimes the refractor-heads like to drone on. I wish they all could have been out with us this night.
We all learned quite a bit from this observing session.
For those who just looked at the pictures and skimmed down to the bottom, here is a summary of sorts:
1. The Paracorr 2 has no problem fixing the coma on a f/2.7 telescope.
2. If secondary mirrors get any larger, we are going to need new tools to align them.
3. The underdog, Mike Lockwood, made a great mirror that ran almost neck and neck vs. the more experienced Kennedy. A shoot out at the exact same focal length would be of much interest. (Hint, hint - Webster)
4. Vibration can be reliably measured and its causes identified by expensive equipment.
5. You are pronouncing the names of all of the stars incorrectly.
6. The Denk 2 binoviewers work admirably even at crazy fast focal ratios.
7. Seated observing with a 28" telescope is suddenly a reality.
8. 28" telescopes give great performances on Jupiter.
9. Large, high quality and very fast mirrors can snap into focus. Do not accept mush under the guise of it being a large mirror.
10. Practicing Muslims and Roman Catholics do not eat eagles - ever.
11. Flat footed observing with a 28" telescope. Wow, just wow.
Webster did say that they were adding the C28 f/2.7 to their regular line up. They did not have it up yet on their site as I was finishing this report, but I assume it will be up by the time you are reading this.
As someone exclaimed in the dark, the C28 f/2.7 is indeed a serious Game Changer.
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