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12.5" f/6.5 Teeter Dob with Lockwood glass..

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#26 Ed Wiley

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Posted 16 November 2015 - 10:33 PM

Congrats on your new scope,Dave; its beauty.

 

Ed



#27 JMW

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Posted 16 November 2015 - 10:46 PM

You may want to take some time and read the ServoCAT manual. I was able to improve the backlash and tracking by tuning the settings. The backlash had to be increased and the gear ratios also had to be increased a few percent. I bought my Webster D14 used and didn't read the manual on the ServoCAT for a few years. I wish I took the time when I bought it. It now tracks extremely well and I see the response quickly when I reverse directions when centering on objects. 

 

My scope is only f/4.3 so I don't notice weight changes between my 2+ pounders (31T5, Ethos21, etc...) and my small Nagler Type 6 eyepieces. The altitude cable should be able to be tightened enough to handle imbalance. You may want to get a Televue Equilizer for your 1.25 inch light eyepieces. Try disengaging the ServoCAT and set the balance with your heavier eyepieces. The Equilizer will add some heft to your lighter eyepieces.

 

http://www.televue.c...il#.Vkqio4Rzv8s



#28 Allan Wade

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Posted 17 November 2015 - 04:32 AM

 

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

 

Thanks Dave. I might message Rob sometime and get the finer details.



#29 RobTeeter

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Posted 17 November 2015 - 06:50 AM

 

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

 

You mean Altitude, not azimuth right?

 

Now that you're back I'll send your ServoCat settings file to you by Email. You can fine tune your settings from there to really dial it in to your liking with regard to backlash. 

 

Glad to hear you had some great weather and enjoyed the new scope. 

 

Take care,



#30 RobTeeter

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Posted 17 November 2015 - 07:50 AM

And, for those interested, our DropBox directory of more images of Dave's scope is below (there you can see some additional detail of the mirror cell):

 

https://www.dropbox....6re3AS-Rda?dl=0

 

Thanks,



#31 RobTeeter

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Posted 17 November 2015 - 08:00 AM

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.

 

Allan,

The Dual Boundary Layer Cooling Fans on Dave's scope are controlled with a variable *voltage* (4V-12V) speed controller that we co-designed and collaborated on with Ron Keating (DewBuster fame). We didn't want the typical resistance-controlled speed controller since we felt that would dump too much heat into the mirror box (which you're trying to evacuate from the box!), and that would be wasting battery power. Variable voltage was the way to go. These controllers are now sold through DewBuster's site:

 

http://www.dewbuster...-c-fanctrl.html

 

Ron's build quality is excellent, the board has a small footprint so really fits neatly inside of the mirror box, and we've been using these for about a year now with no hiccups in their operation. Highly recommended!



#32 Chucky

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Posted 17 November 2015 - 08:19 AM

<<  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 >>

 

Simply horrible fuzzballs for me too.  Awful.  As I recall, Friday night had bad seeing as well.  



#33 Allan Wade

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Posted 17 November 2015 - 10:45 PM

 

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.

 

Allan,

The Dual Boundary Layer Cooling Fans on Dave's scope are controlled with a variable *voltage* (4V-12V) speed controller that we co-designed and collaborated on with Ron Keating (DewBuster fame). We didn't want the typical resistance-controlled speed controller since we felt that would dump too much heat into the mirror box (which you're trying to evacuate from the box!), and that would be wasting battery power. Variable voltage was the way to go. These controllers are now sold through DewBuster's site:

 

http://www.dewbuster...-c-fanctrl.html

 

Ron's build quality is excellent, the board has a small footprint so really fits neatly inside of the mirror box, and we've been using these for about a year now with no hiccups in their operation. Highly recommended!

 

Thanks so much Rob. I have searched high and low for exactly that type of controller. I'll be ordering some of those shortly.



#34 Mike Lockwood

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Posted 22 November 2015 - 10:49 PM

Dave, it was good to see you and the telescope at the Chiefland Fall Star Party.

 

I wish I'd gotten to see some of those closer doubles when the seeing got even better than it was when I looked through the scope, but I ended up being quite busy visiting with many people.  It was nice to see so many people on the field, and I was very happy with how the telescope was performing.

 

Stay warm until WSP.



#35 Cotts

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Posted 22 November 2015 - 11:04 PM

Dave, it was good to see you and the telescope at the Chiefland Fall Star Party.

 

I wish I'd gotten to see some of those closer doubles when the seeing got even better than it was when I looked through the scope, but I ended up being quite busy visiting with many people.  It was nice to see so many people on the field, and I was very happy with how the telescope was performing.

 

Stay warm until WSP.

Absotively and posilutely!!!!   

 

The scope will certainly be pointed at some 0.5" and 0.4" pairs at the WSP....  I'll be in Chickee land!!!!  

 

Dave



#36 Allan Wade

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Posted 23 November 2015 - 07:10 AM

 

Dave, it was good to see you and the telescope at the Chiefland Fall Star Party.

 

I wish I'd gotten to see some of those closer doubles when the seeing got even better than it was when I looked through the scope, but I ended up being quite busy visiting with many people.  It was nice to see so many people on the field, and I was very happy with how the telescope was performing.

 

Stay warm until WSP.

Absotively and posilutely!!!!   

 

The scope will certainly be pointed at some 0.5" and 0.4" pairs at the WSP....  I'll be in Chickee land!!!!  

 

Dave

 

You're going to the WSP, that's great. I'm going to track you down for a look through your dob.



#37 Cotts

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Posted 23 November 2015 - 09:00 AM

All are welcome to visit and steal a few photons.  I will be in Chickee 'La Palma' to the west of the vendors area...  I always fly a Canadian flag so i won't be hard to find.

 

Allan, is this your first time at WSP?

 

Dave



#38 Allan Wade

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Posted 23 November 2015 - 07:55 PM

Dave, yes first WSP. I'm in Galileo Chickee, if that means anything to you.

 

I thought I better come along and meet all the famous people of astronomy.  :grin:  But I'm really looking forward to observing with some of the big dobs, as I get ready for mine next year. Plus putting some faces to all the names.



#39 GeneT

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Posted 24 November 2015 - 01:16 PM

Teeter just seems to making his telescopes better and better.  :waytogo:



#40 Cotts

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Posted 24 November 2015 - 04:44 PM

Dave, yes first WSP. I'm in Galileo Chickee, if that means anything to you.

 

I thought I better come along and meet all the famous people of astronomy.  :grin:  But I'm really looking forward to observing with some of the big dobs, as I get ready for mine next year. Plus putting some faces to all the names.

Allan, your chickee is less than 100 feet from mine.  We couldn't possibly miss each other...

 

Dave



#41 Allan Wade

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Posted 24 November 2015 - 06:34 PM

 

Dave, yes first WSP. I'm in Galileo Chickee, if that means anything to you.

 

I thought I better come along and meet all the famous people of astronomy.  :grin:  But I'm really looking forward to observing with some of the big dobs, as I get ready for mine next year. Plus putting some faces to all the names.

Allan, your chickee is less than 100 feet from mine.  We couldn't possibly miss each other...

 

Dave

 

That's great, see you there.



#42 CHASLX200

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Posted 24 November 2015 - 07:14 PM

 

Dave, yes first WSP. I'm in Galileo Chickee, if that means anything to you.

 

I thought I better come along and meet all the famous people of astronomy.  :grin:  But I'm really looking forward to observing with some of the big dobs, as I get ready for mine next year. Plus putting some faces to all the names.

Allan, your chickee is less than 100 feet from mine.  We couldn't possibly miss each other...

 

Dave

 

Stop by my house on the way down. I would love to see what that scope can do in my steady seeing right on the gulf.



#43 ed_turco

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Posted 26 November 2015 - 11:18 AM

F/6.5 is the ideal f/ratio to render invisible the last teeny bit of coma at the edge with a 68* APOV 40mm eyepiece.  Astro Tech and Paragon come to mind...

 

Also, as my eyes' pupils don't open as wide as they once did, the extra magnification tends to alleviate that problem.  Of course, one could go to an Astro Tech 30mm eyepiece (Astronomics!) and avoid all the fuss.   My problem is that I already have a 40mm and hope to make an f/7 to suit the occasion -- that depends on my helpmate joining me in the project, as I am too crippled to do the job alone, even if it is a 4.25" Newt like the one listed below in my signature.  But as I wrote in a story a fair time ago, my helpmate made a telescope of her own before I married her!

 

 

Ed



#44 Mark Harry

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Posted 29 November 2015 - 07:11 AM

Rob did some beautiful work on the scope, and all indications are the optics are right up to snuff. F/6.5 was a darn good choice.

Congrats, Dave
Regards,
M.



#45 Mark Harry

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Posted 02 December 2015 - 07:03 AM

Had one other question-
***
 How much did this scope weigh ?

M.



#46 Cotts

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Posted 02 December 2015 - 07:22 AM

Mark, I don't know the total assembled weight.  Maybe Rob T. knows???  The mirror/rocker combo with mirror in is too heavy to be easily lifted by me and my bad back.   I ordered the wheelbarrow handles and roll it up and down the ramps into the van...

 

Dave



#47 Peter Natscher

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Posted 06 December 2015 - 09:06 PM

 

Dave, it was good to see you and the telescope at the Chiefland Fall Star Party.

 

I wish I'd gotten to see some of those closer doubles when the seeing got even better than it was when I looked through the scope, but I ended up being quite busy visiting with many people.  It was nice to see so many people on the field, and I was very happy with how the telescope was performing.

 

Stay warm until WSP.

Absotively and posilutely!!!!   

 

The scope will certainly be pointed at some 0.5" and 0.4" pairs at the WSP....  I'll be in Chickee land!!!!  

 

Dave

 

Dave,

 

Will this telescope's longer focal length and smaller CO give you any advantage over a f/4.5-5 Dob observing the Moon, double stars, or planets from your Toronto location that doesn't have the better seeing of the south east U.S.? Does 12.5" f/7-8 operate better than f/4-5 from your poorer home environment?  Is a smaller CO more forgiving in poorer seeing?  I've never observed with anything longer than f/5.2 in a Dob so I don't now what a f/6.5 will do more of.  In my 25 years of observing with different types of telescopes of different apertures from f/3.3 to f/14.6, I think planetary observing is mainly all about seeing and your observing location and not necessarity the type of telescope you use given the optics and system are operating decently.  That's why observers will travel 1,000's of miles just to get better views bringing what ever they have to observe with perfect or not.  I've had stupendous planetary views with f/3.3, 3.6, 4.3 Dobs as well as a f/14.6 Mak only from better locations out here in the west and only during times of better seeing.  Even Mr. Lockwood in Illinois occassionally gets great planetary views with his super fast f/3.0 Dob after traveling to WSP and Okie Tex star parties.  Bob Schilling's 20" f/3 Dob gave him superior views from air-steady Florida.  Neither could do the same way up in the turbulent jet stream north east with any telescope. Just my thoughts.


Edited by Peter Natscher, 06 December 2015 - 09:21 PM.


#48 Tyson M

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Posted 09 December 2015 - 12:36 PM

Gorgeous teeter scope. Love these planet killer designs.

#49 Cotts

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Posted 09 December 2015 - 05:43 PM

Peter, the biggest advantage of the longer f/ratio Newtonian is that its contrast transfer is somewhat better than the "shorties".  A 35% central obstruction will throw quite a bit more light from the central disc of the diffraction pattern into the rings, reducing high resolution contrast (planetary especially), than a 17% central obstruction, all else being equal...  (field contrast between stars in wider views is NOT affected much, if at all.  Blackness of sky background is mostly due to cleanliness and good baffling of stray light and  the exit pupil being used...)

 

Additional advantages of longer Newts:

 --less coma

---able to use longer eyepieces with their greater eye-relief for the same magnification

--simpler eyepiece designs - kellner, plossl, ortho - are happier in a longer scope.

 

The elephant in the room is seeing, as you point out.  If the seeing is mediocre there may may be no discernible difference between a 12.5" f/ 3.0 and a 12.5" f/6.5.  But in those moments of seeing that are Pickering 8-10 I would think there is a difference in favour of the longer scope for high resolution planetary viewing.

 

Ease of focus?  I have heard that the 'sweet spot' is a bit smaller in the shorter scope due to the greater convergence angle of the light cone but with a quality focuser in either scope I don't think this is a big deal....

 

Downside of f/6.5?  A TALL telescope, ladders, etc.  Greater weight for the aperture...

 

As in so many dilemmas, many factors must be weighed and there is no telescope that is not a compromise.

 

Dave



#50 Mike Lockwood

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Posted 09 December 2015 - 08:22 PM

Peter, the biggest advantage of the longer f/ratio Newtonian is that its contrast transfer is somewhat better than the "shorties".  A 35% central obstruction will throw quite a bit more light from the central disc of the diffraction pattern into the rings, reducing high resolution contrast (planetary especially), than a 17% central obstruction, all else being equal...  (field contrast between stars in wider views is NOT affected much, if at all.  Blackness of sky background is mostly due to cleanliness and good baffling of stray light and  the exit pupil being used...)

 

Additional advantages of longer Newts:

 --less coma

---able to use longer eyepieces with their greater eye-relief for the same magnification

--simpler eyepiece designs - kellner, plossl, ortho - are happier in a longer scope.

 

The elephant in the room is seeing, as you point out.  If the seeing is mediocre there may may be no discernible difference between a 12.5" f/ 3.0 and a 12.5" f/6.5.  But in those moments of seeing that are Pickering 8-10 I would think there is a difference in favour of the longer scope for high resolution planetary viewing.

 

FYI, a 25" f/3.0 has a 6" m.a. flat, and that is only a 24% obstruction.  A 20" f/3.0 might get by with a 4.5" m.a. flat (23%), but a 5" flat is often easier to use (25%).

 

Those values are quite different from 35%.

 

However, smaller telescopes do have a bit larger obstruction because the fixed length of the focuser takes up a larger fraction of the focal length.


Edited by Mike Lockwood, 09 December 2015 - 08:25 PM.



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