59 replies to this topic

[Cotts]

...is now in the back of my van on the way to Chiefland, FL. for the Fall Star Party..

 

The scope has maple stain/finish with black trim, Wood veneer Upper Tube Assembly, Feathertouch Focuser, ServoCat Jr. via Sky Commander, DewBuster control box, Rigel Quickfinder, secondary dew heater.  The mirror cell is the Whiffle-tree design of JP Astrocraft which is designed to minimize to near-zero any mirror deformation due to pressure on the mirror edge. The Mike Lockwood mirror is quite thin,  3/4" at the edge, if I recall correctly, and will cool easily with falling temperatures.  

 

 There are three fans, one below (behind?) the mirror to gently blow air over the mirror during observing to keep the temperature at ambient and two 'scrubbers' to remove the boundary layer and cool a warm mirror upon set-up.  All three are variable speed.

 

The secondary mirror is 2.12" in diameter for a central obstruction of 16.9% which means the diffraction pattern will be indistinguishable to the eye from that of a fully unobstructed telescope.

 

When I get it set up on Sunday I'll take far too many pictures and post all of them... 

 

First clear night I'll extensively the scope through its paces...

 

Stay tuned.

 

Dave

 

[Jim_Smith]

I'll be tuned!! give us all a full report cotts..Jim S.

[Mike Lockwood]

I have it at 1.1" edge thickness.

 

Looks like clouds Sunday and likely Monday night, but better by Tuesday.

 

Also looks warm, much nicer than the ridiculously frosty ~23F nights at last year's CFSP.  More like 63F instead.

[Allan Wade]

Nice one Dave, you got a killer combination of components. I'd expect your dob to be nothing less than world class. Can't wait to see the photos.

[City Kid]

Sounds like a nice scope. Looking forward to reading the first light report.

[Steve D.]

Dave, I'm curious how you decided on F6.5 for this scope.   Can't wait to see some pictures.

[RobTeeter]

She was certainly a long/tall one to build! We've never done a 12.5" F/6.5 before - so this is an entirely new aperture and focal ratio combination. Balance came out very close to spot-on, considering a unique balance point we've not had to hit yet, along with using a new mirror cell (JP) and its associated hardware that we've not employed before, and our first 12.5" using our new Wood UTA Liner. So a few new variables to consider there. And, with such a long scope, you worry about vibrations and sway, hence we build our scopes a little heavier down at the bottom which helps to dampen vibrations caused by the UTA hanging so far out there from the mirror box, along with a very tall rocker box also adding the potential for some sway.  We only had a couple hours to use the scope here at the shop prior to Dave coming down to get it (we were literally working on it until about 30 minutes to Dave walking through the doors here), so like everyone here I'm also very curious to hear Dave's impressions.  :-)

 

Enjoy the star party, Dave!  Take care,

[Achernar]

I would love to hear how first light goes for you because it sounds like a dream telescope.

 

Taras

[rowdy388]

Dave,
Your new scope sounds like a dream. Can you view at zenith
while standing? Pictures please!!
Dave Y

[CHASLX200]

F6.5 would be great for my needs. No darn Paracorr needed.  It should take 800x with no problem in my steady seeing in my part of FL.  

[Galicapernistein]

A 1.1 inch thick 12" F6.5 Lockwood mirror in a Teeter structure? I would gladly stand on a ladder to look through that.

[Allan Wade]

My guess is you would need a step at zenith to see through the eyepiece. Just going by my 12" f/4.9

[Cotts]

The f/6.5 chose me rather than the other way around.   Mike Lockwood and I were chatting at the Winter Star Party this past February  when he told me he had a nice 12.5" f/6.5 in stock, awaiting coating.  So I committed to that and contacted Rob Teeter shortly thereafter.  John Pratt of JP Astrocraft was brought in on the project to provide the best cell available.

 

Yes, mike, 1.1" - I was operating completely from memory with my first post.....  Still, it will track ambient temperature very well....

 

Rob stepped into unfamiliar territory with the unfamiliar focal ratio and the JP cell but came through with a gorgeous structure.  Just wait to see the pics...

 

I have a Catsperch Classic chair coming that will get my eye up to about 77" but the eyepiece height of my new scope is about 80" at the zenith so a ladder will be needed.  I may try to borrow one at Chiefland or just look at stuff below about 70 degrees altitude. (I have a ladder at home).....

 

I will take copious notes and post a report here, eventually.

 

Here I sit in a motel in Chiefland on what appears to be a perfectly clear and warm night.   Waiting until Tuesday for the next clear night will be excruciating!!!

 

Dave

[CHASLX200]

The f/6.5 chose me rather than the other way around.   Mike Lockwood and I were chatting at the Winter Star Party this past February  when he told me he had a nice 12.5" f/6.5 in stock, awaiting coating.  So I committed to that and contacted Rob Teeter shortly thereafter.  John Pratt of JP Astrocraft was brought in on the project to provide the best cell available.

 

Yes, mike, 1.1" - I was operating completely from memory with my first post.....  Still, it will track ambient temperature very well....

 

Rob stepped into unfamiliar territory with the unfamiliar focal ratio and the JP cell but came through with a gorgeous structure.  Just wait to see the pics...

 

I have a Catsperch Classic chair coming that will get my eye up to about 77" but the eyepiece height of my new scope is about 80" at the zenith so a ladder will be needed.  I may try to borrow one at Chiefland or just look at stuff below about 70 degrees altitude. (I have a ladder at home).....

 

I will take copious notes and post a report here, eventually.

 

Here I sit in a motel in Chiefland on what appears to be a perfectly clear and warm night.   Waiting until Tuesday for the next clear night will be excruciating!!!

 

Dave

If that mirror is as good as my OMI and Zambuto 12.5" optics were you will have a true winner, plus no need for a Paracorr to boot.  I could take them mirrors up to 800x on my best nites on the planets.

[SkyRanger]

I am very impressed with the design of the JPA mirror cell and looking forward to hearing how it works.

GG

Edited by SkyRanger, 09 November 2015 - 08:16 AM.

[Cotts]

Brief first light report.  

 

Through haze and sucker holes last night we got a look at Albireo, DoubleDouble, Double Cluster, Pleiades.  Mirror appears perfect.  Diffraction pattern clearly visible at about 600x.

 

No wifi at Chiefland so pics will have to wait.  I'm at the library in town for wifi.

 

Patience, campers!

 

Dave

[Cotts]

Pics!!!!

 

With the 'wheelbarrow handles' for loading, unloading etc.

 

Two fans for 'scrubbing' the mirror and cooling it to ambient.  These are variable speed and 100% silent!!  There is another fan underneath for ongoing cooling.  Forgot to take a pic, though...

 

Dew Controller is on the opposite side from the fans.  Dew Buster brand...

 

Mirror cover and the truss ring - the truss ring allows quick removal of the trusses and Upper Tube Assembly in one piece - good for a sudden storm....

 

The stalk for the Sky Commander and Stellar Cat drive...

 

Dave

[Cotts]

Truss poles are joined in pairs.  Bottom ends have the Moonlite 'ball and socket' attachment.  Upper ends (by aurora Precision) have nice registering pins for very repeatable collimation..

 

Assembled with shroud in place

 

12.5" f/6.5 makes for a taaaaaalllll telescope!  Consider my height is 6'6"...

 

Dave

[JMW]

The good news is the planets don't hang out at the zenith so you can do a lot of your high powered viewing without a ladder. This is the tallest 12.5 inch truss Dob I have ever seen. Good looking scope.

[charotarguy]

Beautiful scope.

[Kunama]

Very nice looking scope Dave,  decent height too.  

I find I hardly ever have the scope pointed to zenith, most of the interesting stuff seems to roll by between 45 and 75 degrees.  Hopefully you won't experience the wrath of the Rain and Cloud Gods as I have since building my big scope.

[Cotts]

Visual report  on the 12.5” f/6.5 Teeter Dob with Mike Lockwood mirror.

 

My eyepiece 'fleet' with the 12.5":

31mm  Nagler 67x 

24 mm Explore Sci  86x

17.3mm Delos  119x

12mm Delos 172x

8mm Delos 258x

5mm Nagler 413x

6-3mm Nagler Zoom 344x to 688x 

 

The first two nights (Tuesday and Wednesday) of observation were very foggy and absolutely dew-drenched - the most dew I have ever seen.  Both nights the main mirror dewed up just after midnight - the joys of a thin 1.1” mirror which tracks ambient temperature very well, I suppose….

 

Along with the dew was some of the best atmospheric steadiness I have ever experienced.  I would place the seeing at 9 to 9.5 (pickering) out of 10.  With a 3mm eyepiece (688x) on a 4th mag star near the zenith, the full diffraction pattern was stable and almost unmoving.  Unfortunately the transparency was mediocre and, towards midnight, increasingly poor….

The third night (Thursday) was very transparent and drier, with much more manageable dew but the seeing was extremely poor.  The close pairs of Epsilon Lyrae were two touching fuzzballs (the night before you could have driven a HumVee through the blackness between…)

 

I looked at a bunch of double stars the first night…  I used my Nagler 6mm - 3mm zoom which gives magnifications from 344x to 688x.   Close pairs seen were:

 

STF 186: sep. 0.8”, mags 6.79/6.84
wide, dark sky split. The dark space was equal in width to the central discs of both components.  very delicate first rings  were present at all times…

A 1504: sep. 0.6”, mags 8.84/8.92
darkline split.  Central discs ‘kissing’…  first rings were pretty much too faint to see…

BU 525:  sep. 0.5”,  mags 7.45/7.47
very deep notch.  a black or grey line seemed visible at times..

STF 346 AB  sep.0.5”  mags 6.19/6.21  This is triple star 52 Arietis.  The ABxC pair is at 5” separation…   Very nice to see three stars here.  The AB pair was a deep notch, again with fleeting glimpses of a line between…

 

Uranus and Neptune

 

Uranus showed a perfect, sharp-edged blue-green ball.  No albedo features were visible.   I was thrilled to see the limb-darkening better than I have ever seen it before.  I’m pretty sure I saw two moons, Titania (mag 13.9) and Oberon (mag 14.1), which I determined after making a sketch and comparing to Sky Safari….  Never seen them before!!!

 

Neptune was equally sharp but half the size and some fainter.  Triton (mag 13.8) was dead easy with direct vision…

The rest of the night became too foggy for any success…

Wednesday night I tried to obtain some video lucky imaging of some double stars with varying success.  I’m going to process those and put the images up in the double star forum…

 

Deep sky with good transparency and horrible seeing:  Thursday night and Friday night…

 

A few Planetary Nebulae

 

IC 1295: 1.7’ x 1.4’,  11.7mag - amorphous, round glow, faint, no central *  172x

Sharpless 2-71:  1.1’ , 13.2mag. - ex. faint.  only visible with averted vision…

NGC 6751: 21”x21” - bright, easy, best with 258x.  round featureless disc.

NGC 6765:  38” 13.1mag - very much like an elongated galaxy. 258x showed it well

NGC 6778:  25”x19”, mag 12.3, bright, small, oval.  best with 258x

Eskimo and the  Blinking Planetaries were spectacular!!  Words fail!!

 

Some Galaxies:  (these are part of my test for before/after lens replacement in my eyes.  Surgery is next week(!)  Mags and Surface Brightnesses from Clark’s Visual Astronomy of the Deep Sky.

NGC 7814:  v mag 12.0 S.B. 22.4, 119x, easy, elongated, 172x shows stellar nucleus

NGC 128:  v mag 12.8, S.B. 21.3,  much fainter than previous, 172x shows it well, though..  oval.  In the field were NGC 126 and 125 which were both smaller and fainter;  126 needed averted vision….

NGC 147:  v mag 12.1, S.B. 24.2, large, very faint, low surface brightness.  119x best

NGC 185:  v mag 11.8, S.B. 22.9, large, brighter than 147..  again 119x best

NGC 253:  Fabulous!  A wealth of detail.  Used powers from 67x to 172x.  

NGC 278:  v mag 11.6, S.B. 20.6, Stellar nucleus, bright and easy at 119x and 172x

IC 1613:  v mag 12.0, S.B. 25.6, invisible despite a 30-minute search….

NGC 428:  v mag 11.7, S.B. 23.2, Extremely faint. only visible with averted vision…

NGC 628:  v mag 9.0, S.B. 22.4, V. faint, barely visible with direct vision, 172x

NGC 672: v mag 11.6, S.B. 22.4,  A very pretty open cluster, Collinder 21 is in the field but I never saw a galaxy…

NGC 891:  v mag 12.2,  S.B. 23.5,  This is a larger galaxy but very faint and ghostly.  At 172x a hint of the dark lane was visible with averted vision…

NGC 972:  v mag 12.3, S.B. 22.0, Never found it…

NGC 1023:  v mag 11.0, S.B. 21.5, elongated with 119x and 172x.  Central bright star-like nucleus

NGC 1055: v mag 12.0, S.B. 23.6,  Extremely faint.  Barely visible with direct vision.  A bit better  with averted vision.

 

General mirror impression.

  At f/6.5 there is only noticeable coma in the outer half of the field of the 31mm Nagler and the 24 mm ES, both 82-degree eyepieces.   My ‘Workhorse’ 17.3 Delos shows a tiny bit of coma at the outer edge of the field.   With any shorter eyepieces there is no coma.

 

With the superb seeing of Tuesday and Wednesday night I was able to carefully examine the diffraction pattern at 688x.  It is perfectly circular, with no ‘hair’ or other distortions.  The first diffraction ring is delicate and thin and, again, perfectly circular.  With a 16.9% central obstruction the very great majority of the magic 84% figure (the light in the central disc as opposed to the rings) falls where it should.  I have no idea of the Strehl ratio but it is most likely very, very close to 1.0…..
Thanks, Mike.  Too bad you won’t be making ‘small’ mirrors like this any more…

 

Dave

[Allan Wade]

Beautiful dob Dave, and I'm betting it will be a very good planetary scope at that f/ratio.

 

Would you mind telling me a bit about the 2 scrubbing fans you have. What brand are they and how are they mounted to avoid vibration transfer. Also, about the rotary fan switch. What brand is that and does it rotate around to a fully off position.

 

That would be very useful stuff.

[Cotts]

Mechanical report on the structure.

 

Rob Teeter's structure is of the highest quality.  Very solid, orthogonal with simple ergonomics.  The fans (2 side fans for scrubbing and one below for temperature control throughout the night)  All three fans are variable speed and 100% silent.  

 

His unique truss ring system allows quick removal of the truss rods and upper tube all in one piece.  I used it Saturday night when threatening weather  quickly turned into a noachic deluge.  I grabbed the upper part of the scope and put it in the van in about 1 minute...

 

I like the truss rods in pairs.  The upper part has registering pins which, when seated, make for a very sturdy and repeatable attachment of the upper tube.  It is a lot easier to put the UTA on four things instead of eight....

 

The aesthetic look of Maple with black trim is certainly striking. The fit and finish are top notch.  Well done, Rob! 

 

One thing I will have to keep an eye on is balance.  The scope is very long.  The resulting moment-arm  is significant.  Switching between heavy and light eyepieces may require an after-market adjustable balancing effort.   

 

I had to tweak the tension in the Stellar Cat's Azimuth drive.  (Thanks Charlie Starks and Vic Menard!!!)  The drive, at 30 degrees elevation, could  not lift the scope with a 31mm Nagler......    I will have to get used to the backlash in the drive, too....   It's the nature of the beast with a dob drive.....

 

I'm a happy camper!

 

Dave

[Cotts]

Beautiful dob Dave, and I'm betting it will be a very good planetary scope at that f/ratio.

 

Would you mind telling me a bit about the 2 scrubbing fans you have. What brand are they <don't know.  Maybe Rob T. can tell us...>and how are they mounted to avoid vibration transfer. <the under fan is suspended on elastic rubber bands - not sure about the scrubbers...>  Also, about the rotary fan switch. What brand is that and does it rotate around to a fully off position.  Yes.  Click on/off with rotation to control speed..

 

 

 

 

Dave