Jump to content


Photo

A 2" Diagonal?

  • Please log in to reply
5 replies to this topic

#1 Douglas729

Douglas729

    Vostok 1

  • *****
  • Posts: 198
  • Joined: 25 Dec 2010
  • Loc: Clarksville Mo.

Posted 17 February 2013 - 02:58 AM

“a 2" diagonal to support 2" eyepieces will make it impossible to maintain a back focus below 200mm...”

Why? The 2” eyepiece holder.

The GSO Dielectric Diagonal optical path:
1. 12mm SCT visual back.
2. 52mm diagonal.
3. 40mm removable eyepiece holder.

This 104mm diagonal plus a 110mm binoviewer will create a 214mm optical path.

How to quickly swap between 2” eyepieces and a binoviewer:

Unscrew the 2” eyepiece holder, fit it with an interior ring to secure the 1.25” binoviewer nosepiece tightly. Whittle, file, hacksaw and glue a 10mm binoviewer/diagonal adapter together with threads on both ends.

Now you have either a standard 2” diagonal with the purchase of a new threaded eyepiece holder OR a binoviewer and 2” diagonal adapter with a 184mm optical path.

Attached Files



#2 mhilscher

mhilscher

    Vostok 1

  • *****
  • Posts: 128
  • Joined: 13 Jul 2011
  • Loc: Cologne, Germany

Posted 18 February 2013 - 10:30 AM

thank you

#3 mhilscher

mhilscher

    Vostok 1

  • *****
  • Posts: 128
  • Joined: 13 Jul 2011
  • Loc: Cologne, Germany

Posted 18 February 2013 - 10:30 AM

thank you

#4 ohioalfa64

ohioalfa64

    Mariner 2

  • -----
  • Posts: 201
  • Joined: 16 Aug 2012
  • Loc: Ohio (NW)

Posted 02 March 2013 - 05:30 PM

Can you further explain this?

#5 Eddgie

Eddgie

    Voyager 1

  • *****
  • Posts: 12975
  • Joined: 01 Feb 2006

Posted 05 March 2013 - 01:13 PM

Are you asking Douglas to explain what he did and why?

Douglas modified a 2" diagonal by removing the normal 2" eyepeice holder and replaceing it with a threaded connector that would allow him to connect the binoviewer directly to the top of a 2" diagonal.

This reduces the light path length making it easier to reach focus in refractors (though doubtful that most refractirs would still reach focus with a 2" diagonal and binoviewer, but it might lower the amount of GPC or OCS power, resulting in a wider true field capability).

Douglas was saying that he was able to get the back focus down below 200mm, which is just about impossible when using a standard 2" diagonal.

Of course an easier way to do it would be using a 1.25" diagonal, or better yet, a setup like the Baader Maxbright with a 1.25" diagonal that attaches directly to the front of the binoviewer in the same way as Douglas's picture shows.

With this method the light path is only about 150mm.. Many refractors will reach focus even with binoviewers using this configuration.


It is also beneficial to reduce the light path for binoviewing SCTs because it keeps the focal lenght shorter, and many SCTs will start to suffer aperture reduction if the back focus is allowed to go past 200mm

Not sure what you were asking though, but hopefully this covers it.

Post was edited. I said "Reflectors" and of meant "refractors."

#6 ohioalfa64

ohioalfa64

    Mariner 2

  • -----
  • Posts: 201
  • Joined: 16 Aug 2012
  • Loc: Ohio (NW)

Posted 07 March 2013 - 09:45 PM

You did nicely. Thank you.






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics