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Equipment Discussions >> Reflectors

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Project Galileo
scholastic sledgehammer
*****

Reged: 11/14/07

Loc: Jefferson County, Colorado
Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5532699 - 11/21/12 05:28 PM

Beautiful. Just beautiful. Congrats!

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auriga
Pooh-Bah


Reged: 03/02/06

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5532788 - 11/21/12 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


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Bob S.
Carpal Tunnel
*****

Reged: 07/14/05

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: auriga]
      #5532806 - 11/21/12 06:50 PM

Quote:

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


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Bob S.
Carpal Tunnel
*****

Reged: 07/14/05

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5544196 - 11/28/12 04:44 PM Attachment (137 downloads)

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.

Edited by Bob S. (11/28/12 06:13 PM)


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Bob S.
Carpal Tunnel
*****

Reged: 07/14/05

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5544203 - 11/28/12 04:47 PM Attachment (132 downloads)

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.

Edited by Bob S. (11/28/12 04:48 PM)


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Bob S.
Carpal Tunnel
*****

Reged: 07/14/05

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5544313 - 11/28/12 06:00 PM Attachment (101 downloads)

This is a picture of the ring over the schematic of the secondary unit and spider and note the rings connect points coincide with the vanes coming out of the central hub. Because the vanes are not coincident, it provides a bit of a challenge in terms of diffraction issues.

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Mike Lockwood
Vendor, Lockwood Custom Optics
*****

Reged: 10/01/07

Loc: Usually in my optical shop
Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5544326 - 11/28/12 06:11 PM

Quote:

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.



Wow, first we had the flip phone, now we have the flip fan.

These really do work well, even on up to a 32" scope, maybe larger.


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nsldvd
sage


Reged: 10/02/08

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5544451 - 11/28/12 07:53 PM Attachment (77 downloads)

Quote:

This is a picture of the ring over the schematic of the secondary unit and spider and note the rings connect points coincide with the vanes coming out of the central hub. Because the vanes are not coincident, it provides a bit of a challenge in terms of diffraction issues.




Not sure the fan thing is so complicated but good luck and I'm sure it'll work out fine for you...


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Bob S.
Carpal Tunnel
*****

Reged: 07/14/05

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: nsldvd]
      #5544483 - 11/28/12 08:14 PM

Quote:

Quote:

This is a picture of the ring over the schematic of the secondary unit and spider and note the rings connect points coincide with the vanes coming out of the central hub. Because the vanes are not coincident, it provides a bit of a challenge in terms of diffraction issues.




Not sure the fan thing is so complicated but good luck and I'm sure it'll work out fine for you...




On your 32" Webster, the spider vanes are perpendicular. Mine are only perpendicular to each pair neighboring each other. How do you remove your fan for collimation and what gauge/strand count wire did you use?


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nsldvd
sage


Reged: 10/02/08

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5544494 - 11/28/12 08:24 PM Attachment (74 downloads)

Quote:

On your 32" Webster, the spider vanes are perpendicular.



Hi Bob,
I'll get back to you...


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Howie Glatter
Vendor


Reged: 07/04/06

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5544522 - 11/28/12 08:50 PM

Bob, your vanes are perpendicular (at right angles to eachother). They are just not co-linear ; they don't form an X, crossing in the center. Dave's Webster also looks just a little offset (not crossing the center) in his photo.

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Bob S.
Carpal Tunnel
*****

Reged: 07/14/05

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Howie Glatter]
      #5544529 - 11/28/12 08:53 PM

Howie, "co-linear". That is a new catchy buzz word to drop at a cocktail party. I think the spelling is "collinear". It is a shame that I gave up drinking<g>. In Albert Highe's new book ( Engineering, Design and Construction of Portable Newtonian Telescopes 2012) on page 509 he describes his and my spider vanes as "Opposing vanes are not coplaner. However, the angle between adjacent vanes is 90 degrees, making opposing vanes parallel". Now I have two buzz words for that elusive cocktail party. Guess I am going to have to brush up on my geometry skills if I drop those into the conversation. Bob

Edited by Bob S. (11/29/12 06:56 AM)


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nsldvd
sage


Reged: 10/02/08

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5547729 - 11/30/12 07:22 PM Attachment (83 downloads)

Quote:

Quote:

Quote:

This is a picture of the ring over the schematic of the secondary unit and spider and note the rings connect points coincide with the vanes coming out of the central hub. Because the vanes are not coincident, it provides a bit of a challenge in terms of diffraction issues.




Not sure the fan thing is so complicated but good luck and I'm sure it'll work out fine for you...




On your 32" Webster, the spider vanes are perpendicular. Mine are only perpendicular to each pair neighboring each other. How do you remove your fan for collimation and what gauge/strand count wire did you use?




Hi Bob,
Thanks for your PM and best of hopes with your new scope. With your permission...
I think you're on to something with the boundary layer fan. It may have been about 10 yrs back when I put a similar fan on my 25" Obsession and wired a switch on the UTA that turned the fan "On" and "Off". I recall Sirius in the EP and with the fan off and the mirror only about 60% ambient I could see the star somewhat fuzzy. When I flipped the switch Sirius cleaned up dramatically. Later in the evening when the mirror was more like 85%-95% ambient I repeated the test/experiment but was unable to detect the same or similar result. Over several observing events it became clear the boundary fan was most useful in the early evening and in the later observing period could be turned off and save some battery power. Not every scope needs this type of fan but it does seem to bring the desired observing objective sooner than later. Below is a photo of my old Obsession showing the fan...


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nsldvd
sage


Reged: 10/02/08

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5547743 - 11/30/12 07:30 PM Attachment (66 downloads)

Quote:

Quote:

Quote:

This is a picture of the ring over the schematic of the secondary unit and spider and note the rings connect points coincide with the vanes coming out of the central hub. Because the vanes are not coincident, it provides a bit of a challenge in terms of diffraction issues.




Not sure the fan thing is so complicated but good luck and I'm sure it'll work out fine for you...




On your 32" Webster, the spider vanes are perpendicular. Mine are only perpendicular to each pair neighboring each other. How do you remove your fan for collimation and what gauge/strand count wire did you use?




I also used the "Boundary Layer Fan" on my somewhat modified 22" Starmaster for several years (kinda wish I had that scope back...) with the same positive results. I always turned it off after a couple of hrs as its job was done.

Thanks for your updates on your new (and somewhat amazing) scope. Please continue to share how it works out for you.
Thanks, dave


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Bob S.
Carpal Tunnel
*****

Reged: 07/14/05

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: nsldvd]
      #5548016 - 11/30/12 11:00 PM

Dave, As you can see by the thread that I will not only be utilizing the front boundary layer fan but will have a ducted rear sucking fan operating independently but also in concert with the front fan. What we found preliminarily is that if we only used the rear sucking fan, the image cleaned up almost immediately as you described but after several hours the primary mirror was showing overcorrection which Mike Lockwood attributed to the cooling of the outer circumference of the mirror but not having the center of the mirror cooling at the same rate. Hopefully, with experimentation, we will be able to determine just how much and how long the CBLMS (Comprehensive Boundary Layer Mitigation System) needs to be running and at what speeds are the fans optimal? I appreciate you sharing your empirical data as that will make the implementation of this system all that much smoother knowing what you have experienced in the past.

I talked with John Pratte the builder/designer at JP Astrocraft and he said that using the wire as an electrical conducter did not significantly impact the voltage going to the fan. As you know, we are exclusively using Maglev fans for both vibration reduction over conventional fans and longer fan life. Bob

Edited by Bob S. (11/30/12 11:03 PM)


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Spaced
Post Laureate
*****

Reged: 03/01/05

Loc: Tacoma, Washington, USA
Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5548537 - 12/01/12 10:25 AM

Wow, simply . . . Wow.

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Peter Natscher
professor emeritus


Reged: 03/28/06

Loc: Central Coast California
Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5548760 - 12/01/12 12:58 PM

Hi Bob,

I wish you much observing enjoyment with your new 20" scope. John Pratte surely has done a beautiful job with your new scope. What are the CFM numbers and voltage draw of the MagLev fans on your cooling system -- back-side and front-side? Is the air gap between the primary's front-side baffle and mirror edge tight enough to create an effective venturi so that the front-side airflow against the primary will more effectively travel around the primary and onto the back-side fan for expulsion out the back? You don't want the air movement on the front-side of the primary to just boil and get trapped in a turbulent pattern. It needs to get away from the primary front surface in an orderly fashion for best effect. The moving cooler air needs to travel in a smooth way off of the primary and around the circumference and side of the primary expeditiously by the pull of the backside fan. I was almost there with this system cooling a 24" Starmaster but didn't get the front-side air flow right. None the less, the two backside fans and two side-mounted front-side fans (75 cfm each) had operating halved the cool-down time (vs. no fans) of the 24" f/3.6 primary with 0.75" thickness.

Quote:

Dave, As you can see by the thread that I will not only be utilizing the front boundary layer fan but will have a ducted rear sucking fan operating independently but also in concert with the front fan. What we found preliminarily is that if we only used the rear sucking fan, the image cleaned up almost immediately as you described but after several hours the primary mirror was showing overcorrection which Mike Lockwood attributed to the cooling of the outer circumference of the mirror but not having the center of the mirror cooling at the same rate. Hopefully, with experimentation, we will be able to determine just how much and how long the CBLMS (Comprehensive Boundary Layer Mitigation System) needs to be running and at what speeds are the fans optimal? I appreciate you sharing your empirical data as that will make the implementation of this system all that much smoother knowing what you have experienced in the past.

I talked with John Pratte the builder/designer at JP Astrocraft and he said that using the wire as an electrical conducter did not significantly impact the voltage going to the fan. As you know, we are exclusively using Maglev fans for both vibration reduction over conventional fans and longer fan life. Bob




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Peter Natscher
professor emeritus


Reged: 03/28/06

Loc: Central Coast California
Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5548853 - 12/01/12 02:01 PM

Bob,

How will the front-fan wiring affect your setup and breakdown assembly routines? Will it add time to an already simple observing routine? Of course, if you are only going to roll this baby out of your garage to observe and video, then it's a no brainer. Buy if this scope is one that will be transported, assembled, and disassembled at a remote site, how will you design the fan's wire suspension attachments to the trusses (or mirror box?) to retain easy setup, especially in the dark at 3am? The suspension wires must be easy attached and tight. I do all my observing at remote darker sites, and so I'm a *fan* of an uncomplicated telescope.

Quote:

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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Bob S.
Carpal Tunnel
*****

Reged: 07/14/05

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Peter Natscher]
      #5548899 - 12/01/12 02:32 PM Attachment (67 downloads)

Quote:

Bob,

How will the front-fan wiring affect your setup and breakdown assembly routines? Will it add time to an already simple observing routine? Of course, if you are only going to roll this baby out of your garage to observe and video, then it's a no brainer. Buy if this scope is one that will be transported, assembled, and disassembled at a remote site, how will you design the fan's wire suspension attachments to the trusses (or mirror box?) to retain easy setup, especially in the dark at 3am? The suspension wires must be easy attached and tight. I do all my observing at remote darker sites, and so I'm a *fan* of an uncomplicated telescope.

Quote:

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.







Peter, John has ingeniously designed the front mirror fan so that the suspension system is secured by 4 little turn paddles similar to Starmaster mirror clips and when rotated out of the way and when disconnected from the power source that is built into the top of the mirror box, the entire unit can be lifted out in seconds. I doubt that I will need to do that but it can be done. John has also crafted the mirror cover to sit above the fan unit and be locked in conveniently with the same type of "mirror clip" pieces but just higher so that it does not touch the fan system. I have included a picture of the lift off front fan assembly.

Edited by Bob S. (12/01/12 02:35 PM)


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Bob S.
Carpal Tunnel
*****

Reged: 07/14/05

Re: First Light On My 20" f/3 Lockwood/JP Astrocraft new [Re: Bob S.]
      #5549855 - 12/02/12 06:49 AM Attachment (56 downloads)

Quote:

Quote:

Bob,

How will the front-fan wiring affect your setup and breakdown assembly routines? Will it add time to an already simple observing routine? Of course, if you are only going to roll this baby out of your garage to observe and video, then it's a no brainer. Buy if this scope is one that will be transported, assembled, and disassembled at a remote site, how will you design the fan's wire suspension attachments to the trusses (or mirror box?) to retain easy setup, especially in the dark at 3am? The suspension wires must be easy attached and tight. I do all my observing at remote darker sites, and so I'm a *fan* of an uncomplicated telescope.

Quote:

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.







Peter, John has ingeniously designed the front mirror fan so that the suspension system is secured by 4 little turn paddles similar to Starmaster mirror clips and when rotated out of the way and when disconnected from the power source that is built into the top of the mirror box, the entire unit can be lifted out in seconds. I doubt that I will need to do that but it can be done. John has also crafted the mirror cover to sit above the fan unit and be locked in conveniently with the same type of "mirror clip" pieces but just higher so that it does not touch the fan system. I have included a picture of the lift off front fan assembly.




Peter, Something that I had not noticed myself until I studied the picture John sent me of the fan system was that he made accomodations for my concerns about adding diffraction spikes with the fan support wires because we are not using coplanar/collinear secondary spider vanes. If you look closely you will notice that the fan support wires utilize the same strategy that was used for rotational stability of the secondary mirror/holder on the wire support scheme of the frontal fan. The neighboring support wires are perpendicular to each other but not coincident but parallel to the support wire on the other side of the fan. When I saw John's drafting plans for the build of the UTA and his utilization of those plans for the frontal fan, I failed to initially realize that he has been able to maintain the same obstruction scheme thereby eliminating additional sources of diffraction spikes that had been a concern of mine.

Without sounding like an ad for John Pratte of JP Astrocraft which would be better served in the Vendor section, I am simply amazed at his forward thinking throughout the build process of this very custom scope. I was discussing studying Albert Highe's new book about the design and construction of Newtonian telescopes and Pratte had advised me that he had already gotten a copy and was reading many sections of the new book and was able to discuss specific chapters. Sheesh, I feel like one of the luckiest guys on the planet for having taken Mike Lockwood's suggestion to run the build requirements by John and see what he thought? Not to mention that a 20" f/3 1.25" thick Lockwood primary and 5" Lockwood secondary are not exactly chopped liver Bob


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