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" mirror cell

  • Please log in to reply
20 replies to this topic

#1 airbleeder

airbleeder

    Apollo

  • *****
  • topic starter
  • Posts: 1276
  • Joined: 04 Jan 2014
  • Loc: Powder Springs, Georgia

Posted 23 February 2018 - 12:25 AM

   Does anybody have a drawing for a primary cell they wouldn't mind sharing? I have an 8"f6 sonotube dob, 9"ID. If I use a 1" bottom plate mounted to the 4 existing holes on the ota and an 3/4" top plate, I can keep focus where it is and should help with balance. A shop will cut it from aluminum, but I will do the rest. I will appreciate any help I can get. Thanks.

 

Edit: It's a full thickness mirror. 


Edited by airbleeder, 23 February 2018 - 02:56 AM.


#2 Dale Eason

Dale Eason

    Viking 1

  • *****
  • Posts: 832
  • Joined: 24 Nov 2009
  • Loc: Roseville,Mn.

Posted 23 February 2018 - 12:29 AM

Look for the program called PLOP on the net.  It will design the parts for you based on your input.  It runs on windows machines.  If you can not run it or don't understand it then someone could do the design for you.

 

Dale


  • airbleeder and Augustus like this

#3 airbleeder

airbleeder

    Apollo

  • *****
  • topic starter
  • Posts: 1276
  • Joined: 04 Jan 2014
  • Loc: Powder Springs, Georgia

Posted 23 February 2018 - 03:06 AM

   Thanks, I have played around with it some, but it was just play. I will see what I can do with it.



#4 John O'Hara

John O'Hara

    Viking 1

  • *****
  • Posts: 639
  • Joined: 07 Jun 2008
  • Loc: Oil City, PA

Posted 23 February 2018 - 05:54 AM

Here's a simple one from Gary Seronik,  a well known telescope maker and long time columnist for Sky and Telescope:

 

http://garyseronik.c..._making/page/3/


  • airbleeder and Augustus like this

#5 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 21365
  • Joined: 22 Feb 2010
  • Loc: Montclair, NJ

Posted 23 February 2018 - 07:49 AM

   Thanks, I have played around with it some, but it was just play. I will see what I can do with it.

https://www.youtube....xUKvZWWOhqaMXFT


  • airbleeder likes this

#6 airbleeder

airbleeder

    Apollo

  • *****
  • topic starter
  • Posts: 1276
  • Joined: 04 Jan 2014
  • Loc: Powder Springs, Georgia

Posted 23 February 2018 - 08:13 AM

   Thanks Danny. Great video. I couldn't sleep last night, so I will watch it more tomorrow after I've slept tonight. I'm dumb enough with a good night's sleep.



#7 calypsob

calypsob

    Skylab

  • *****
  • Posts: 4160
  • Joined: 20 Apr 2013
  • Loc: Roanoke, Virginia

Posted 23 February 2018 - 03:36 PM

Here's a simple one from Gary Seronik,  a well known telescope maker and long time columnist for Sky and Telescope:

 

http://garyseronik.c..._making/page/3/

is Garys mirror cell suitable for an imaging newtonian?  Ive wondered if it creates a stresspoint in the middle



#8 John O'Hara

John O'Hara

    Viking 1

  • *****
  • Posts: 639
  • Joined: 07 Jun 2008
  • Loc: Oil City, PA

Posted 23 February 2018 - 07:05 PM

 

Here's a simple one from Gary Seronik,  a well known telescope maker and long time columnist for Sky and Telescope:

 

http://garyseronik.c..._making/page/3/

is Garys mirror cell suitable for an imaging newtonian?  Ive wondered if it creates a stresspoint in the middle

 

I'd thought that visual use is even more demanding.  I'm not knowledgeable concerning imaging requirements as I'm strictly a visual observer, so I could be wrong.  


  • calypsob likes this

#9 John O'Hara

John O'Hara

    Viking 1

  • *****
  • Posts: 639
  • Joined: 07 Jun 2008
  • Loc: Oil City, PA

Posted 23 February 2018 - 07:09 PM

Giving it some thought, where imaging may be more demanding is in the need to maintain focus for a prolonged period while CCD exposures are being made.  A wooden cell may be more subject to expansion and contraction than a metal cell, causing focus shift.  This would not be important visually.  As far as stress on the mirror, I'm not sure why imaging would be more affected by stress induced aberrations than would the visual image. 

 

Maybe someone with imaging experience can chime in.


Edited by John O'Hara, 23 February 2018 - 07:25 PM.


#10 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 21365
  • Joined: 22 Feb 2010
  • Loc: Montclair, NJ

Posted 23 February 2018 - 07:13 PM

here's my 8in cell for my f.35

 

8in cell.JPG

 

https://www.youtube....8rBwA&index=100


  • calypsob and airbleeder like this

#11 calypsob

calypsob

    Skylab

  • *****
  • Posts: 4160
  • Joined: 20 Apr 2013
  • Loc: Roanoke, Virginia

Posted 23 February 2018 - 07:18 PM

Giving it some thought, where imaging may be more demanding is in the need to maintain focus for a prolonged period while CCD exposures are being made.  A wooden cell may be more subject to expansion and contraction than a metal cell, causing focus shift.  This would not be important visually.  As far as stress on the mirror, I'm not sure why imaging would be more affected by such inducted aberrations than would the visual image. 

 

Maybe someone with imaging experience can chime in.

The star field has to be flat and round for a camera sensor, aberration correction is extremely critical with astrophotography if you are sampling the pixels properly.  If undersampling, there is a small amount of leway.  Focus shift could be an issue, it depends on how lucidly it occurs.  With short exposures it may not be a problem at all.   I have been wanting to try Garys design on a small astrograph which is why I wanted to ask.  I am thinking that I might be able to use a larger sphere on the back and create a less localized point of pressure. 


Edited by calypsob, 23 February 2018 - 07:20 PM.

  • John O'Hara likes this

#12 John O'Hara

John O'Hara

    Viking 1

  • *****
  • Posts: 639
  • Joined: 07 Jun 2008
  • Loc: Oil City, PA

Posted 23 February 2018 - 07:25 PM

 

Giving it some thought, where imaging may be more demanding is in the need to maintain focus for a prolonged period while CCD exposures are being made.  A wooden cell may be more subject to expansion and contraction than a metal cell, causing focus shift.  This would not be important visually.  As far as stress on the mirror, I'm not sure why imaging would be more affected by such inducted aberrations than would the visual image. 

 

Maybe someone with imaging experience can chime in.

The star field has to be flat and round for a camera sensor, aberration correction is extremely critical with astrophotography if you are sampling the pixels properly.  If undersampling, there is a small amount of leway.  Focus shift could be an issue, it depends on how lucidly it occurs.  With short exposures it may not be a problem at all.   I have been wanting to try Garys design on a small astrograph which is why I wanted to ask.  I am thinking that I might be able to use a larger sphere on the back and create a less localized point of pressure. 

 

Makes sense.



#13 airbleeder

airbleeder

    Apollo

  • *****
  • topic starter
  • Posts: 1276
  • Joined: 04 Jan 2014
  • Loc: Powder Springs, Georgia

Posted 24 February 2018 - 09:57 AM

here's my 8in cell for my f.35

 

attachicon.gif 8in cell.JPG

 

https://www.youtube....8rBwA&index=100

   I like that cell. I could probably have it cut from aluminum stock. Would it need to be 6point or would a 3point be sufficient for an 8" f6? Do you allow any clearance between the back plate and inside of OTA or is a snug fit best? Thanks. That's very helpful.


Edited by airbleeder, 24 February 2018 - 10:00 AM.


#14 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 21365
  • Joined: 22 Feb 2010
  • Loc: Montclair, NJ

Posted 24 February 2018 - 10:30 AM

imagine this with 1/4" alum plate instead of 1/2" ply

 

gallery_106859_3508_13403.jpg

 

 

6 is always way better than 3, but oddly enough its also better than 9.

 

my 6in cell up close an personal

 

https://www.youtube....h?v=NT525eWG-ek


Edited by Pinbout, 24 February 2018 - 10:32 AM.

  • plyscope, John O'Hara and airbleeder like this

#15 airbleeder

airbleeder

    Apollo

  • *****
  • topic starter
  • Posts: 1276
  • Joined: 04 Jan 2014
  • Loc: Powder Springs, Georgia

Posted 24 February 2018 - 12:07 PM

    You have a point there. I was planning to use thicker stock for added weight to lower the eyepiece height, so I can observe seated if possible, but using 1/4 would allow me some room for cell location since I will need to drill a couple more holes into the OTA anyhow (4 to 3).

   Should my edge supports work out well on the angles I use for the clips? Maybe use nylon screws to attach the clips and also serve as edge supports?

   In your picture, I'm also guessing those are nylon capheads you used for pads? I believe that cell is perfect if I can get all the dimensions straight in my head so I can get it drawn for cutting and do my part correctly. You always do some fine work. It must be nice.

   Once I get the plans to my man it will probably take him a while to cut, so I will try to build a ply mounting plate for use while I wait on him.

   Edit: Don't know what I was thinking in that second sentence.


Edited by airbleeder, 24 February 2018 - 11:11 PM.


#16 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 21365
  • Joined: 22 Feb 2010
  • Loc: Montclair, NJ

Posted 24 February 2018 - 12:12 PM

Should my edge supports work out well on the angles I use for the clips? Maybe use nylon screws to attach the clips and also serve as edge supports?

 

si

si



#17 NHRob

NHRob

    Fly Me to the Moon

  • *****
  • Posts: 7221
  • Joined: 27 Aug 2004
  • Loc: Southern Cloud-Hampshire

Posted 24 February 2018 - 07:07 PM

1/4"is pretty thin stock.  Do you find it is thick enough to avoid any flexure?



#18 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 21365
  • Joined: 22 Feb 2010
  • Loc: Montclair, NJ

Posted 24 February 2018 - 09:47 PM

1/4" looks pretty thick to me. how much does the mirror weigh? not that much and the 3 bars are out of 1/8"

 

but if you have to 3/8" would be better than 1/2". 1/2" is where I'd start using tube.

 

http://www.aurorap.c... sheet rev4.pdf

 

the brackets are drawn ~ same as the plate...those brackets are 1/4" thk


  • airbleeder likes this

#19 airbleeder

airbleeder

    Apollo

  • *****
  • topic starter
  • Posts: 1276
  • Joined: 04 Jan 2014
  • Loc: Powder Springs, Georgia

Posted 24 February 2018 - 11:49 PM

   I don't know what weighs, no scale but it's 1.25" thick. I'll probably go with the 1/4" stock then. No doubt you know more than I do.

   I hope I can get the drawings to him this week, but there's no telling when he will cut it because he only does bigger contract work. Doing me a favor so I'll just take it to him and get it whenever.



#20 Pinbout

Pinbout

    ISS

  • *****
  • Posts: 21365
  • Joined: 22 Feb 2010
  • Loc: Montclair, NJ

Posted 25 February 2018 - 09:41 AM

just cut it with a jig saw, the only real critical parts of a cell are the hole locations and even then only the mirror supports are critical...kind of.

 

print it out and spray mount the drawing to the alum. leave center marks for the holes and center punch them before you drill them.

 

you don't even need a drill press. but a bandsaw helps.


  • airbleeder likes this

#21 airbleeder

airbleeder

    Apollo

  • *****
  • topic starter
  • Posts: 1276
  • Joined: 04 Jan 2014
  • Loc: Powder Springs, Georgia

Posted 25 February 2018 - 10:32 AM

    Wouldn't hurt to try it. I have a jig saw and drill press I picked up at yard sales. They aren't the best, but they operate ok. Do a practice run with some ply and existing back plate, see how that goes. 


  • Pinbout likes this


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






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics