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

yet another mirror refiguring question...

  • Please log in to reply
4 replies to this topic

#1 BDS316

BDS316

    Mercury-Atlas

  • -----
  • topic starter
  • Posts: 2,585
  • Joined: 16 Sep 2009
  • Loc: Sol 3

Posted 24 January 2020 - 11:55 AM

After a commercial mirror (Orion, GSO, etc) is refigured, will it still have the same focal length and f/ ratio so it can be put back in the scope without having to change the locations of the diagonal, focuser, etc and with all your eyepieces still coming to focus, as they did previously?

 

Thanks



#2 Mike Lockwood

Mike Lockwood

    Vendor, Lockwood Custom Optics

  • *****
  • Vendors
  • Posts: 1,696
  • Joined: 01 Oct 2007
  • Loc: Usually in my optical shop

Posted 24 January 2020 - 12:07 PM

In most cases, yes.

 

The exception would be if a large amount of polishing was required to remove bad astigmatism or a rolled edge.  In that case the focal length might change by 1/16" or a bit more, but this would be somewhat rare.

 

In the event that a re-grind is required, say in the case of a surface damaged by chemicals, the change could be larger depending on what tooling is available.  Hopefully this is even rarer.


  • Bonco2, happylimpet, Joe1950 and 1 other like this

#3 BDS316

BDS316

    Mercury-Atlas

  • -----
  • topic starter
  • Posts: 2,585
  • Joined: 16 Sep 2009
  • Loc: Sol 3

Posted 24 January 2020 - 12:28 PM

In most cases, yes.

 

The exception would be if a large amount of polishing was required to remove bad astigmatism or a rolled edge.  In that case the focal length might change by 1/16" or a bit more, but this would be somewhat rare.

 

In the event that a re-grind is required, say in the case of a surface damaged by chemicals, the change could be larger depending on what tooling is available.  Hopefully this is even rarer.

Cloudynights is awesome...you ask a question and it gets answered by one of the world's leading authorities on the subject.  Thanks!

 

Next clear night I'll do a star test and report back.  I think I'm dealing with a tad of either under or overcorrection, I don't recall which one.  

 

Which is the one where it's better inside of focus, ie eyepiece closer to OTA?


  • Joe1950 and Dougeo like this

#4 Mike Lockwood

Mike Lockwood

    Vendor, Lockwood Custom Optics

  • *****
  • Vendors
  • Posts: 1,696
  • Joined: 01 Oct 2007
  • Loc: Usually in my optical shop

Posted 24 January 2020 - 12:48 PM

If you see rings (less blurry image) inside of focus but not outside, it is undercorrected.

 

If you see rings outside of focus but not inside, it is overcorrected.  However, this can be caused by cooling a properly corrected mirror, depending on substrate type.

 

http://www.loptics.c...rcorrection.jpg


  • BDS316, Bonco2 and Joe1950 like this

#5 BDS316

BDS316

    Mercury-Atlas

  • -----
  • topic starter
  • Posts: 2,585
  • Joined: 16 Sep 2009
  • Loc: Sol 3

Posted 24 January 2020 - 03:14 PM

If you see rings (less blurry image) inside of focus but not outside, it is undercorrected.

 

If you see rings outside of focus but not inside, it is overcorrected.  However, this can be caused by cooling a properly corrected mirror, depending on substrate type.

 

http://www.loptics.c...rcorrection.jpg

Thanks.  so this picture would be overcorrected since the less blurry rings are outside of focus?




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