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

Walter Scott Houston's old admonition about barlows, probably outdated

  • Please log in to reply
9 replies to this topic

#1 RichA

RichA

    Surveyor 1

  • *****
  • topic starter
  • Posts: 1,690
  • Joined: 03 Jun 2010
  • Loc: Toronto, Canada

Posted 31 May 2020 - 11:03 PM

That a 2x barlow and an 18mm eyepiece works better than a 9mm eyepiece.  This was based on the premise that eyepieces with physically larger lenses (lower power) were better made than eyepieces with small lenses and that the narrowed light cone coming from the barlow (compared to the scope's normal light cone angle) was "easier" on the eyepiece design, therefore fewer off-axis aberrations.  That's what I remember about it, but he claimed to see more using the barlow-eyepiece combo.

 

 


  • chrysalis, JamesMStephens and mikeDnight like this

#2 RLK1

RLK1

    Mariner 2

  • -----
  • Posts: 268
  • Joined: 19 Apr 2020

Posted 01 June 2020 - 12:25 AM

When I was a kid I used to read his column in Sky & Tel. I got my name in his column for a description of a dark nebula in Sagittarius. Those were the days...


  • chrysalis, happylimpet and JuergenB like this

#3 chrysalis

chrysalis

    ISS

  • *****
  • Posts: 22,082
  • Joined: 10 Aug 2013
  • Loc: North Central NC

Posted 01 June 2020 - 03:42 AM

When I was a kid I used to read his column in Sky & Tel. I got my name in his column for a description of a dark nebula in Sagittarius. Those were the days...

Indeed!! I also used to devour his column in S&T every month. While trying to decide between a career in medicine or astronomy (this must have been 1971 or 1972), I wrote to him to ask his advice on good astronomy colleges. He wrote back with a type-written and hand-signed message that was warm and personal. IIRC, he recommended U of M. I probably still have it somewhere in a memories box... All that to say - they just don't make Walter Scott Houston's anymore.


  • JuergenB and RLK1 like this

#4 russell23

russell23

    Voyager 1

  • *****
  • Posts: 10,848
  • Joined: 31 May 2009
  • Loc: Upstate NY

Posted 01 June 2020 - 05:39 AM

That advice will still hold true for designs similar to those available at the time.  For example a 16mm Brandon x 2 vs an 8mm Brandon.  The minimal glass approach will insist on the 8mm, but the comfort approach would prefer the barlowed 16mm, which also will have better edge performance than the 8mm in many modern scopes.


  • Jon Isaacs, turtle86, RAKing and 3 others like this

#5 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 46,167
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 01 June 2020 - 10:59 AM

That a 2x barlow and an 18mm eyepiece works better than a 9mm eyepiece.  This was based on the premise that eyepieces with physically larger lenses (lower power) were better made than eyepieces with small lenses and that the narrowed light cone coming from the barlow (compared to the scope's normal light cone angle) was "easier" on the eyepiece design, therefore fewer off-axis aberrations.  That's what I remember about it, but he claimed to see more using the barlow-eyepiece combo.

That is sort of true today as well, because telescopes have gotten shorter and eyepiece performance somewhat poorer in the outer field.

A Barlow can help.

Interestingly, many of today's modern eyepiece designs have an internal Barlow lens to accomplish the exact same thing Houston talked about.


  • Jon Isaacs, chrysalis and Spikey131 like this

#6 turtle86

turtle86

    Mr. Coffee

  • *****
  • Posts: 5,501
  • Joined: 09 Oct 2006

Posted 01 June 2020 - 11:25 AM

That advice will still hold true for designs similar to those available at the time.  For example a 16mm Brandon x 2 vs an 8mm Brandon.  The minimal glass approach will insist on the 8mm, but the comfort approach would prefer the barlowed 16mm, which also will have better edge performance than the 8mm in many modern scopes.

+1  The minimum glass approach is overrated IMHO.


  • SteveG, RAKing, Pezdragon and 1 other like this

#7 Michael Covington

Michael Covington

    Author

  • *****
  • Vendors
  • Posts: 5,980
  • Joined: 13 May 2014
  • Loc: Athens, Georgia, USA

Posted 01 June 2020 - 11:35 AM

That a 2x barlow and an 18mm eyepiece works better than a 9mm eyepiece.  This was based on the premise that eyepieces with physically larger lenses (lower power) were better made than eyepieces with small lenses and that the narrowed light cone coming from the barlow (compared to the scope's normal light cone angle) was "easier" on the eyepiece design, therefore fewer off-axis aberrations.  That's what I remember about it, but he claimed to see more using the barlow-eyepiece combo.

It's a great idea, such a great idea that the most modern eyepieces (Nagler, Delite, etc.) are actually an Erfle preceded by a built-in Barlow.

 

In the era of simpler eyepiece designs, that Barlow advice was right on the money.  


  • russell23 likes this

#8 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 46,167
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 01 June 2020 - 11:51 AM

It's a great idea, such a great idea that the most modern eyepieces (Nagler, Delite, etc.) are actually an Erfle preceded by a built-in Barlow.

 

In the era of simpler eyepiece designs, that Barlow advice was right on the money.  

That's a simplification--the upper sections of the eyepieces you mention bear no relationship to the Erfle design,


  • howardcano likes this

#9 Andrekp

Andrekp

    Ranger 4

  • -----
  • Posts: 375
  • Joined: 14 Apr 2020

Posted 01 June 2020 - 01:30 PM

He was writing this (probably) during a very different time.  Eyepieces were simple and had few elements for the most part and often very small lenses.  Barlows were also sometimes different than what you see today.  My ancient Celestron one has a relatively small lens in it, in a long tube.  I have eyepieces with more aperture than this Barlow.  My newer Barlow is as wide as possible in the tube.  Point being, what was true in 1975, may or may not make sense today.

 

that said, modern optical elements are very nice.  Just test things out.  If you think it works fine for you, what’s the difference?  I often use a Barlow and there is no obvious problem with doing so.  That said, I am nowhere near as picky as is the norm around here.


  • BFaucett likes this

#10 RichA

RichA

    Surveyor 1

  • *****
  • topic starter
  • Posts: 1,690
  • Joined: 03 Jun 2010
  • Loc: Toronto, Canada

Posted 02 June 2020 - 06:10 PM

Houston used a long focal length Clark 4" refractor which was probably operating at its full performance level most of the time, not constrained as much by bad seeing as a larger diameter scope and not "trying" for eyepieces like a fast scope of today. 


Edited by RichA, 02 June 2020 - 06:10 PM.



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