Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

8 inch F/7 CHIEF group build

ATM
  • Please log in to reply
387 replies to this topic

#1 Ed Jones

Ed Jones

    Skylab

  • *****
  • topic starter
  • Posts: 4,095
  • Joined: 06 Apr 2004
  • Loc: Sin-sin-atti

Posted 14 August 2020 - 08:28 AM

This thread will be on making an 8 inch F/7 Chief using all optics that can be purchased.
First I'll post the design in the optical designs.
 

Edit: Moved from the other Chief topic:

 

I got a quote for a lens needed to make an 8 inch F/7 Chief. For 10 plano-concave lenses the price is $59 coated, (not a COTS lens). It will mate with a plano-convex Newport or OptoSigma lens. Discovery optics sells an 8 inch F/7 primary so all the optics could be purchased to make a high performance unobstructed Chief (better than any APO).
 


Edited by cuzimthedad, 14 August 2020 - 12:38 PM.

  • mark cowan, SteveV, kfrederick and 9 others like this

#2 gatorengineer

gatorengineer

    Mercury-Atlas

  • *****
  • Posts: 2,961
  • Joined: 28 Feb 2005
  • Loc: Hellertown, PA

Posted 14 August 2020 - 09:39 AM

I have a couple of 3d Printers, I would volunteer to print the lens holders in PETG + Carbon Fiber,  for the cost of filament, (possibly nylon + Carbon Fiber (on my list to run but havent done it yet), I have done PETG plus CF.

 

My 3d cad skills are still evolving but I can probably do it.


  • Dave O likes this

#3 jtsenghas

jtsenghas

    Fly Me to the Moon

  • *****
  • Posts: 5,234
  • Joined: 14 Sep 2014
  • Loc: The flatlands of Northwest Ohio 41.11N --Bloomdale

Posted 14 August 2020 - 09:52 AM

Nice, Ed! That quantity of 10 brings that down to COTS prices! Did Newport quote those? 

 

We could print lens cells similarly to the f/12 and f/10.8 cells I made for us this spring. That makes a Chief only a modest step above a Newt for ATM work! 

 

20200110_101901_compress35.jpg

 

I personally wouldn't bite until at least after I get my first Chief built, but that appeals to me. 

 

Discovery Optics may be willing to provide a price break too if they get an order for a similar quantity of 8" f/7, or hold off until such a quantity of orders accumulate.  When I inquired more than a year ago they had a couple 8" f/8 in the shelf, but no f/7s.

 

You would need only one participant willing and able to do the 3d printing of the lens cells. 

 

(Edited after being moved from another thread) 

 

 


Edited by jtsenghas, 14 August 2020 - 12:49 PM.

  • Dave O likes this

#4 steveastrouk

steveastrouk

    Apollo

  • *****
  • Vendors
  • Posts: 1,166
  • Joined: 01 Aug 2013
  • Loc: State College, Pa.

Posted 14 August 2020 - 10:04 AM

If the group is not too big, I'd happily mill and turn a suitable lens cell. 


  • kfrederick, Oberon and davidc135 like this

#5 mark cowan

mark cowan

    Vendor (Veritas Optics)

  • *****
  • Vendors
  • Posts: 9,689
  • Joined: 03 Jun 2005
  • Loc: salem, OR

Posted 14 August 2020 - 10:53 AM

I'd be totally in for a group purchase for that 8" f/7 corrector element Ed mentions.  This is something I've had an itch to do for a long time.

 

Hope it's not too much digression, but an 8" Scheifspiegler is the only same aperture reflector I've ever seen beat my 8" f/6 Newt.  bounce.gif  


  • kfrederick, Dave O and Augustus like this

#6 kfrederick

kfrederick

    Skylab

  • *****
  • Posts: 4,055
  • Joined: 01 Feb 2008

Posted 14 August 2020 - 11:15 AM

Let Ed show us the way he knows best .The 20 corrector cell is all wood and after 11 years it works fine. Do not over think this . Fine to chat on this thread  or start a new one might get more views . 


  • Dave O likes this

#7 Ed Jones

Ed Jones

    Skylab

  • *****
  • topic starter
  • Posts: 4,095
  • Joined: 06 Apr 2004
  • Loc: Sin-sin-atti

Posted 14 August 2020 - 12:09 PM

Did Newport quote those?

 

No from China but more than likely that where Newport and others get their optics.  I still to discuss some things with them.

I'll need to design a lens cell that can be 3D printed but I'll post the design on the optical design thread and yes this should be a new thread.


Edited by Ed Jones, 14 August 2020 - 12:12 PM.

  • kfrederick and Dave O like this

#8 ccaissie

ccaissie

    Surveyor 1

  • *****
  • Posts: 1,964
  • Joined: 13 Sep 2010
  • Loc: Whitefield, Maine

Posted 14 August 2020 - 12:28 PM

All ears!  I have a couple of nice 8f7 mirrors.



#9 jtsenghas

jtsenghas

    Fly Me to the Moon

  • *****
  • Posts: 5,234
  • Joined: 14 Sep 2014
  • Loc: The flatlands of Northwest Ohio 41.11N --Bloomdale

Posted 14 August 2020 - 12:43 PM

I just reached out with an email to Discovery Optics asking for inventory levels and lead times on their 8" f/7 primaries.  I also asked if a price break might be available if they got a significant order or group of orders to crank out at least 10.

 

A year ago when I was considering making an 8" f/8 Chief they didn't have the f/7 in stock at the time. 

 

The f/7 could be configured to a sweet viewing angle at a reasonable height. 


Edited by jtsenghas, 14 August 2020 - 12:47 PM.


#10 cuzimthedad

cuzimthedad

    Just Be Cuz

  • *****
  • Moderators
  • Posts: 7,281
  • Joined: 09 Apr 2006
  • Loc: Nampa, ID

Posted 14 August 2020 - 12:45 PM

Posts concerning the group build in the other Chief topic have been moved to this thread. If I missed any, please let me know and I'll move them here pronto. Also left a link there about this topic.


  • Dave O and jtsenghas like this

#11 davidc135

davidc135

    Apollo

  • -----
  • Posts: 1,205
  • Joined: 28 May 2014
  • Loc: Wales, UK

Posted 14 August 2020 - 01:44 PM

I'd be in for a pair of corrector lenses.  David


  • Dave O likes this

#12 jtsenghas

jtsenghas

    Fly Me to the Moon

  • *****
  • Posts: 5,234
  • Joined: 14 Sep 2014
  • Loc: The flatlands of Northwest Ohio 41.11N --Bloomdale

Posted 14 August 2020 - 01:55 PM

It's small enough to be closed tube, too, with the improved bafflng that provides. One could upsize the tube or flex a 10" metal tube into an elliptical section with a few elliptical wooden hoops.


  • Dave O and Oberon like this

#13 Oberon

Oberon

    Gemini

  • -----
  • Posts: 3,469
  • Joined: 24 Feb 2013
  • Loc: Hunter Valley NSW Australia

Posted 14 August 2020 - 03:33 PM

Hi Ed, count me in. I have an 8” F/6.9 that is begging for it.


  • Dave O likes this

#14 Ed Jones

Ed Jones

    Skylab

  • *****
  • topic starter
  • Posts: 4,095
  • Joined: 06 Apr 2004
  • Loc: Sin-sin-atti

Posted 14 August 2020 - 04:02 PM

Well I wouldn't start buying stuff just yet, I've never bought from this company or know anything about them.  Also I need to design the lens cell.  I use Solidworks so infrequently that I almost have to relearn it each time I do.  


  • PrestonE, Dave O and Matthew Paul like this

#15 LarsMalmgren

LarsMalmgren

    Messenger

  • *****
  • Posts: 407
  • Joined: 22 Jan 2010
  • Loc: Denmark

Posted 14 August 2020 - 04:50 PM

I'm interested in the lenses also.

 

I will make the mirror myself or buy one here in Europe though smile.gif

 

 

Ed, when you get around to it, how relaxed is the tolerance on the mirror focal length ?


Edited by LarsMalmgren, 14 August 2020 - 04:51 PM.


#16 Ed Jones

Ed Jones

    Skylab

  • *****
  • topic starter
  • Posts: 4,095
  • Joined: 06 Apr 2004
  • Loc: Sin-sin-atti

Posted 14 August 2020 - 05:56 PM

 

how relaxed is the tolerance on the mirror focal length ?

It's fairly loose but Mike Jones has offered to do some tolerancing and give us some numbers.

 

If you noticed this Chief had about 1.8 degrees image tilt, pretty small as TCTs go.


  • LarsMalmgren and Dave O like this

#17 steveastrouk

steveastrouk

    Apollo

  • *****
  • Vendors
  • Posts: 1,166
  • Joined: 01 Aug 2013
  • Loc: State College, Pa.

Posted 14 August 2020 - 06:21 PM

Well I wouldn't start buying stuff just yet, I've never bought from this company or know anything about them.  Also I need to design the lens cell.  I use Solidworks so infrequently that I almost have to relearn it each time I do.  

If you want to sketch it on paper, I can do it for you, in SW or someother package


  • Dave O likes this

#18 jtsenghas

jtsenghas

    Fly Me to the Moon

  • *****
  • Posts: 5,234
  • Joined: 14 Sep 2014
  • Loc: The flatlands of Northwest Ohio 41.11N --Bloomdale

Posted 14 August 2020 - 06:39 PM

If you want to sketch it on paper, I can do it for you, in SW or someother package

Actually, Ed did a good job on such lens cells in Solidworks this past winter for his f/12 and my f/10.8.  He used an older version of Solidworks and I converted the files to a .stl (stereo lithography) format for a 3d printer. 

 

He and I haven't yet built with these lens cells. You might find a read of my thread on this starting about here to be worthwhile on the topic.  If you go back to previous pages in that thread, you'll see I even visited him personally. 

 

You'll see that in PLA I had to print at about 101.5% size to get a satisfactorily loose fit, but the lens angle came out beautifully as verified with a CMM.

 

Centration and relative angles of the lenses are what matter the most here. Even the distance between them is fairly forgiving in his tolerance analysis. They can be tilted as an assembly in such a cell for fine tuning. 


Edited by jtsenghas, 14 August 2020 - 07:07 PM.

  • Dave O likes this

#19 gatorengineer

gatorengineer

    Mercury-Atlas

  • *****
  • Posts: 2,961
  • Joined: 28 Feb 2005
  • Loc: Hellertown, PA

Posted 14 August 2020 - 07:51 PM

Ed,

 

About 10 years ago you ran an 8 F7 with OTS lenses in spiderless, if you still have the archive, I think a bunch of work was done there.    You even had lens numbers (I may still even have the lenses somewhere).



#20 jtsenghas

jtsenghas

    Fly Me to the Moon

  • *****
  • Posts: 5,234
  • Joined: 14 Sep 2014
  • Loc: The flatlands of Northwest Ohio 41.11N --Bloomdale

Posted 14 August 2020 - 08:18 PM

Note that for sufficiently long focal ratios that the two lenses can be the very same radius as each other, just positive and negative.  The f/12 versions made with such matching lenses will have fantastically tight spot diagrams across the visual spectrum.  Married together they make an optical window since the opposite faces are planar and the glass types are also the same.  They can be inspected against each other for fringes this way. 

 

As the focal ratios get faster, the concave lens needs a longer radius than the convex lens.  In exchange for my printing lens cells, and because Ed Jones is a heck of a guy anyway, Ed reworked my concave lens from Newport to be about 0.6" longer in radius to optimize it for my 8" f/10.8 primary. 

 

A lot of these Chiefs could use commercial, off the shelf lenses of the same radii as each other and still be better than achromats on axis and at least comparable or sometimes still slightly better 0.25 degrees off axis. It all depends on your chosen tolerances and range of frequencies considered. 

 

With a slight increase of the radius of the concave lens, they can do even better for any focal ratio, and much better for sub f/8 primaries.

 

I applaud Ed for working on an 8" f/7 version here with custom concave lenses (coated, even!) that are competitive for cost with COTS choices. 8" f/7 gets down to simple ergonomic designs that can use standard elliptical secondary mirrors since the focuser can reasonably be placed close to perpendicular to the optical axis of the primary.  I expect the tiny amount of lateral color due to the different radii will be negligible.  On axis, this appears to be a fantastic prescription. 

 

Go, Ed!


Edited by jtsenghas, 14 August 2020 - 09:35 PM.

  • Dave O likes this

#21 mark cowan

mark cowan

    Vendor (Veritas Optics)

  • *****
  • Vendors
  • Posts: 9,689
  • Joined: 03 Jun 2005
  • Loc: salem, OR

Posted 15 August 2020 - 12:57 AM

It's small enough to be closed tube, too, with the improved bafflng that provides. One could upsize the tube or flex a 10" metal tube into an elliptical section with a few elliptical wooden hoops.

Definitely that.  Provide a housing as needed to attach, or, a sonotube could be flexed as well (ask me how I know ;) ).



#22 jgraham

jgraham

    ISS

  • *****
  • Posts: 21,292
  • Joined: 02 Dec 2004
  • Loc: Miami Valley Astronomical Society

Posted 15 August 2020 - 08:45 AM

I'm interested in a mirror & lens set. Sounds like a neat project and would pair well with my 4" Kutter Schiefspiegler project.

 

Neat stuff.


  • Dave O likes this

#23 Ed Jones

Ed Jones

    Skylab

  • *****
  • topic starter
  • Posts: 4,095
  • Joined: 06 Apr 2004
  • Loc: Sin-sin-atti

Posted 15 August 2020 - 10:46 AM

  Well I'm surprised and pleased at the interest.  Before I lose track of whose interested I'm starting a list of those who want a lens so PM me to verify that you're on the list.  I'm still negotiating specs. lens thickness and price. the price might possibly change but I'll try to hold it.  I am only buying/supplying the concave lens.  The primary you can make or buy from Discovery for $299, the convex lens from Newport is KPX205 which is $75 and a 2 inch diagonal or 2.14 will work from a number of sources but I wouldn't buy anything yet until I actually have lenses in hand and check them out.  Their delivery is 4 to 5 seeks.

  Check out my videos on building a Chief, this one should be similar. 


  • tim53, LarsMalmgren and Dave O like this

#24 jtsenghas

jtsenghas

    Fly Me to the Moon

  • *****
  • Posts: 5,234
  • Joined: 14 Sep 2014
  • Loc: The flatlands of Northwest Ohio 41.11N --Bloomdale

Posted 15 August 2020 - 11:00 AM

I've left an email and voice message to Discovery asking for inventory levels on 8" f/7 mirrors and warning them that they may see orders of a significant number at that size.  

 

For what it's worth I also inquired if there might be a price break if they got a minimum order, or group of orders in a short time. At $299 each, though, they may not want to budge. 

 

I'm not among those of you looking to buy. I've still got more mirrors than scopes, but I'm trying to help this along. 

 

I think it would be fun to see various mechanical designs to Ed's optical design, especially since secondary tilt angles are entirely at the discretion of the builder. 



#25 RajG

RajG

    Vostok 1

  • -----
  • Posts: 141
  • Joined: 11 Mar 2020
  • Loc: Noo Joisey, aka the Armpit of America

Posted 15 August 2020 - 11:37 AM

That's a great design. If you use a 6inch f/9.3 mirror with identical radii and spacings in that design, you can afford to have the mirror be spherical and it is still diffraction limited on axis. Also since it is slower, the coma is much lower and the diffraction-limited image size is much larger. That might an easier/cheaper option for those who prefer to grind their own mirror.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics





Also tagged with one or more of these keywords: ATM



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics