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First Light On My 20" f/3 Lockwood/JP Astrocraft

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#1 Bob S.

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Posted 20 November 2012 - 07:25 AM

It is amazing how time flies when you order a new telescope. At first is creeps and then later, it slips from your day-to-day consciousness and suddendly it is found to be nearing completion. This has been the case with my 20" f/3 Lockwood/JP Astrocraft scope. In about 3 weeks, it will have gone through the final completion stage.

We did however get first light in Central Illinois this past weekend when I went up to look at the progress and provide further input into some of the design features. It is so feature laden for visual, astrovideo, binoviewing and DSLR applications that I will save that for another post.

The scope has a Lockwood 20" 1.25" thick Pyrex f/3 primary coupled with a 5" m.a. Lockwood secondary. The JPA custom mirror cell was tested by Lockwood under various bench conditions with the unfinished primary and has been optomized for the thin mirror to operate in all positions. The mirror cell is a work of art all by itself with the use of spherical bearings on each triangle and roller bearings on the lower mirror edge supports. Views of Jupiter's GRS and surrounding ovals at 219x under less than ideal conditions still showed very detailed and colorful images. The unfinished podium on the non-viewing side includes wired and wireless handpands, 12" ultrabook computer, power supplies for the computer and eventually a heated shield that will prevent the computer screen from dewing up. All wiring is internally routed and the entire scope will be powered by one external 12v wire going into the powered ground board.

Mike Lockwood, the optician on this project, is a former electrical engineer/research scientist/ATM that went into the optical business and is building what are arguably some of the finest and most consistent sub f/4 optics on the planet in sizes up to 60" and f ratios as fast as f/2 (he recommends no faster than f/2.75 for Newtonians and I have viewed through one of his 28" f/2.75's that was an absolute stunner). John Pratte, the scope builder, is a chemical engineer, manufacturing executive, former world champion NHRA car tuner/builder, optician, machinist and all around nice guy.

I have included a picture that Mike Lockwood took this weekend as we all experienced a group first light.

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#2 tezster

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Posted 20 November 2012 - 08:23 AM

That is one FINE looking scope! It's hard to imagine it has the same FL as a 10" F6 - comfy seated observing with feet on the ground all the way to the zenith :)

Mind if I ask what the maximum EP height is?

#3 JayinUT

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Posted 20 November 2012 - 08:42 AM

Beautiful scope! Oh the views you are going to have!

#4 Bob S.

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Posted 20 November 2012 - 09:02 AM

That is one FINE looking scope! It's hard to imagine it has the same FL as a 10" F6 - comfy seated observing with feet on the ground all the way to the zenith :)

Mind if I ask what the maximum EP height is?


Maximum ep height is 62" at zenith. John Pratte had to add height to the rocker box feet and make a slightly taller rocker box to get the desired height that I wanted.

#5 Darren Drake

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Posted 20 November 2012 - 09:07 AM

Very nice! What is that thingy above the focuser? It looks like another focuser.....

#6 Bob S.

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Posted 20 November 2012 - 09:09 AM

Very nice! What is that thingy abouve the focuser? It looks like another focuser.....

You can never have enough focusers :lol: Actually it is a 1.25"-2" holster for placement of my Mallincam when it is out of the focuser. The 1.25" portion of the holder is a Baader Clic-Lock device that requires just a slight turn of the knurled nob to secure the camera. You are also probably wondering about the turnbuckle on the front of the rockerbox/mirror box. That is used in conjunction with two sliding bolts on the rear of the mirror box that go into the rocker box to place it in an upright position to simply lean the telescope over and wheel it out to my observing site. The axles have quick release pins that allow the wheels to come off and the axle to be removed. However, you can observe with the wheels attached.

#7 cliff mygatt

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Posted 20 November 2012 - 09:29 AM

It is a lovely scope combined with great optics, one cannot go wrong. Looking forward to see some of those mallincam photos. Good Luck!

#8 Busguy

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Posted 20 November 2012 - 02:16 PM

What a beautiful scope. Craftsmanship looks superb.

Enjoy many nights with it.

Joe

#9 killdabuddha

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Posted 20 November 2012 - 02:53 PM

:drool5: Wow. And how in the world did you get those angle-fitted tube-plug mounting plates?

#10 JimMo

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Posted 20 November 2012 - 02:53 PM

Awesome telescope Bob. I'm sure you'll be thrilled with the views.

#11 auriga

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Posted 20 November 2012 - 04:57 PM

Bob,
Congratulations, a superb scope! You will find it easy and enjoyable to use.

I am not at all surprised at how good it is, since I have the 16"f/4 version, the "sweet sixteen' pictured on John Pratte's web site. It's a beauty and a great pleasure to use. I have had no trouble with it at all. Easy to collimate, retains object when I change eyepieces, moves easily but stays where I put it. Very solid construction, very rigid, goes together easily and disassembles easily. I have a Wessling mirror, one of the last ones he made rather than a Lockwood but I think they would be equivalent. I notice you have chosen the same wood stain I did. Looks great.

Let us know your experiences with the 20" f/3 once it is delivered and you have a chance to do some more observing with it. You are one of the most experienced posters with a variety of scopes so it will be good to hear your take on this one.

Bill Meyers

#12 Bob S.

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Posted 20 November 2012 - 06:13 PM

Bob,
Congratulations, a superb scope! You will find it easy and enjoyable to use.

I am not at all surprised at how good it is, since I have the 16"f/4 version, the "sweet sixteen' pictured on John Pratte's web site. It's a beauty and a great pleasure to use. I have had no trouble with it at all. Easy to collimate, retains object when I change eyepieces, moves easily but stays where I put it. Very solid construction, very rigid, goes together easily and disassembles easily. I have a Wessling mirror, one of the last ones he made rather than a Lockwood but I think they would be equivalent. I notice you have chosen the same wood stain I did. Looks great.

Let us know your experiences with the 20" f/3 once it is delivered and you have a chance to do some more observing with it. You are one of the most experienced posters with a variety of scopes so it will be good to hear your take on this one.

Bill Meyers


Thanks Bill. I too had a 18" f/4.5 Wessling mirror in a beautiful structure whos name escapes me for the moment. It was an absolutely superb mirror. Dick was one of the handful of very good opticians. John Pratte has some of his mirrors and at least one or two for sale I think.

John as you know has been absolutely wonderful to work with. He is extremely meticulous and thinks things through before charging ahead. I could not ask for a better build.
Bob

#13 Mike Lockwood

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Posted 20 November 2012 - 06:31 PM

:drool5: Wow. And how in the world did you get those angle-fitted tube-plug mounting plates?

Well, John made them, of course.

While using this scope, I found myself repeatedly asking for the observing chair - my back was hurting from having to stoop over at the eyepiece of what is very clearly a telescope that should be used while seated.

#14 Jarad

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Posted 20 November 2012 - 08:06 PM

Glad to see it finally arrived, Bob! I'm sure you'll enjoy it under those nice steady Florida skies.

Be sure to bring it to PSSG next year!

Jarad

#15 Bob S.

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Posted 20 November 2012 - 08:38 PM

Glad to see it finally arrived, Bob! I'm sure you'll enjoy it under those nice steady Florida skies.

Be sure to bring it to PSSG next year!

Jarad


Jarad, It has not "arrived" yet but is getting within three weeks of arrival.

Here is a picture of the custom-machined billet aluminum offset spider hub, collimation screws, tilt plate and vanes that John Pratte manufactured. You will also notice that the UTA has two flat sides that allow it to nest better in the mirror box if that is desired.

You will also notice that the spider vanes are indeed parallel (opposing vanes) and perpendicular (neighboring
vanes), but they are not coincident, or on the same line.

The purpose of this vane's orientation was to prevent the 5" secondary from experiencing rotational torque generally associated with larger secondaries. You see people using wheel weights to prevent the rotation. John Pratte as an engineer (with the concurrence of Mike Lockwood) couldn't live with that and made them so there is virtually no rotational torquing of the secondary. The diffraction spikes are just four but behave a bit differently when you defocus on a star seperating in a horizontal fashion. The spider vanes also have their own dedicated uprights on the UTA that are primary support for the vanes and secondarily for the UTA rings that have other supports. The vertical slots in the billet center hub are reportedly for receiving transmissions from outer space. I am thinking of also using this as a SETI instrument :roflmao:

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#16 mtb54703

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Posted 21 November 2012 - 10:20 AM

The purpose of this vane's orientation was to prevent the 5" secondary from experiencing rotational torque generally associated with larger secondaries.


Interesting... It's not just that its a larger secondary, it's the greater secondary offset that's required for a faster mirror that is responsible for the greater rotational torque...

:scratchhead:

Awesomely nice looking scope!

#17 jim molinari

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Posted 21 November 2012 - 02:54 PM

Bob ...
Very well thought out with top quality optics and structure. I like your Watec Monitor and Mallincam mount ... clever! I will be interested to hear how the cooling/airflow system performs. I hope you get a chance to bring it out West where I can see it in action. Congrats and enjoy!
Jim

#18 Jarad

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Posted 21 November 2012 - 03:12 PM

Jarad, It has not "arrived" yet but is getting within three weeks of arrival.



Hey, no fair! You can't title your thread "First light" until you get the scope and get first light! :foreheadslap:

Now I can't be jealous for 3 more weeks!

Jarad

#19 David Castillo

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Posted 21 November 2012 - 03:33 PM

Looks like the best thing to cure a back ache.
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#20 Bob S.

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Posted 21 November 2012 - 04:13 PM

Bob ...
Very well thought out with top quality optics and structure. I like your Watec Monitor and Mallincam mount ... clever! I will be interested to hear how the cooling/airflow system performs. I hope you get a chance to bring it out West where I can see it in action. Congrats and enjoy!
Jim


Jim, The cooling system is a combination of proven technologies used by two different astronomers and many others I am sure. BTW, we sure had some beautiful views through your 20" scope, Chris Ford's 24" and Nick Tsakoyias TEC 180 FL scope at the Golden State Star Party this year. Joe Wambo with his 32" f/3.7 Lockwood/Webster placed a fan above his primary mirror scrubing off the boundary layer. I also talked with Jimmy Lowery who has a 48" f/4 telescope out in Texas and we were discussing cooling strategies for mirrors and he mentioned that he uses 10 Maglev (magnetic levitation) fans in an enclosed rear mirror cell for his behemoth scope.

What John Pratte operationalized was an enclosure for the rear of the telescope that has at the center a Maglev fan (the fans are inherently more vibration free than a conventional motored fan) mounted in Sorbothane and fastened with a sandwiched support plate to the rear aluminum enclosed back. The fan has a potentiometer to control fan speed/air flow and there is an annulus above the primary that creates a venturi effect that sucks the air off the mirror face and out the back of the scope. On the front of the mirror about a foot above the primary will be a smaller Maglev fan suspended by thin but sturdy wires that will also be a variable speed device and blow air away from the center of the mirror. The fan will be able to rotate out of the way to collimate the scope.

The combination of the blowing/sucking system we have termed the Comprehensive Boundary Layer Mitigation System or CBLMS for short. The CBLMS should accomplish several things: 1. It should scrub the boundary layer off the surface of the primary 2. It should provide for more rapid equilibration of the primary and uniformally accomplish this with the combined fan systems. Again, these technologies have been used seperately but to my knowledge not quite in the way that we are going about it.

In Joe Wambo's scope at this years Winter Star Party in the Florida Keys, we were looking at Mars at 950x with "etched" views of the Martian atmosphere and planets surface. We could see very distinctly defined clouds above the Martian surface. Now, my little 20" will not produce those kind of views with eyepieces but it sure will with my Mallincam Extreme astrovideo camera. Bob

#21 Project Galileo

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Posted 21 November 2012 - 05:28 PM

Beautiful. Just beautiful. Congrats!

#22 auriga

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Posted 21 November 2012 - 06:35 PM

Bob,
I am interested to see that you have adopted the Dick Wessling/John Pratte/Ross Sackett wheel arrangement, which I have found to be excellent on my scope.

See:
http://stardazed.com/CaptainNemo.html

and jpastrocraft.com

Jon Isaacs has used this design as well.

I too have found that John Pratte is an excellent person to work with, as well as being a fine craftsman with the insight of an engineer.

Bill

#23 Bob S.

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Posted 21 November 2012 - 06:50 PM

Bob,
I am interested to see that you have adopted the Dick Wessling/John Pratte/Ross Sackett wheel arrangement, which I have found to be excellent on my scope.

See:
http://stardazed.com/CaptainNemo.html

and jpastrocraft.com

Jon Isaacs has used this design as well.

I too have found that John Pratte is an excellent person to work with, as well as being a fine craftsman with the insight of an engineer.

Bill


Bill, It is neat how scope builders stand on the shoulders of those that came before them. John Pratte is also integrating the axle/tires on the front of the rocker box to work with supplied wheelbarrow handles so that I can roll the scope up a ramp if I choose to. Bob

#24 Bob S.

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Posted 28 November 2012 - 04:44 PM

Well, progress continues on the JPA. As part of the CBLMS (Comprehensive Boundary Layer Mitigation System), John Pratte has been doing his engineering homework to produce the frontal magnetic levitation fan that will be hidden in the shadow of the secondary mirror and blow on the primary. I have included a couple of pictures of this work in progress that will be suspended by very thin 12v current conducting wires.

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#25 Bob S.

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Posted 28 November 2012 - 04:47 PM

Here is a picture of the forward fan in the up position so that I will be able to collimate the telescope. We are also considering the placement of the wires to add as little diffraction spike input as possible. You will notice that the ring is not round. It mimics the .42" offset of the secondary mirror.

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