Jump to content


Photo

Taming a Tiger

  • Please log in to reply
23 replies to this topic

#1 Charlie Hein

Charlie Hein

    Voyager 1

  • *****
  • Administrators
  • Posts: 12307
  • Joined: 02 Nov 2003
  • Loc: 26.06.08N, +80.23.08W

Posted 12 May 2012 - 11:32 AM

Taming a Tiger - My experiences with a Tal 125R achromat.

By Neil English

#2 7331Peg

7331Peg

    Sirius Observer

  • *****
  • Posts: 1930
  • Joined: 31 Aug 2008
  • Loc: North coast of Oregon

Posted 12 May 2012 - 12:59 PM

Excellent review, Neil, of an excellent refractor. Certainly enough details there to chew over for anyone thinking seriously of a five inch achromat.

It really is a shame that achromats of this aperture have become hard to find these days. I've got a Meade AR-5 that I will never part with -- it's split more than it's share of double stars, and feasted many a night on the brighter galaxies and globulars. Five inches of glass is a very satisfying alternative to a larger and heavier six inch refractor.

Thanks for the addition to the literature! :bow: :bow: :bow:


John :refractor:

#3 jrbarnett

jrbarnett

    Eyepiece Hooligan

  • *****
  • Posts: 19883
  • Joined: 28 Feb 2006
  • Loc: Petaluma, CA

Posted 12 May 2012 - 02:46 PM

Thoughtful and well written, as always, Neil.

APM have the TAL 100RS in stock for not too much dosh. I am tempted...Hell, I even have a (faux) fur bomber hat that would fit thematically with the scope!

Thank you, Comrade English. :grin:

- Jim

#4 Ed Holland

Ed Holland

    Vanguard

  • -----
  • Posts: 2093
  • Joined: 16 Jun 2010
  • Loc: San Jose, CA and Oxford, UK

Posted 13 May 2012 - 07:43 AM

Excellent subject matter and superb presentation. I really enjoyed reading this article. The author's adventure with the Tal 'scope shares some plot elements (pun intended) with my acquisition of a Meade AR5. That scope has become a "keeper" and I find myself a firm fan of the venerable achromatic doublet.

Ed

#5 Scott in NC

Scott in NC

    80mm Refractor Fanatic

  • *****
  • Administrators
  • Posts: 15104
  • Joined: 05 Mar 2005
  • Loc: NC

Posted 13 May 2012 - 08:50 AM

An excellent read, Neil! :bow: Glad you were able to get "Tonya" tuned up to spec!

#6 paul m schofield

paul m schofield

    Explorer 1

  • -----
  • Posts: 65
  • Joined: 23 May 2010
  • Loc: Western North Carolina, USA

Posted 13 May 2012 - 09:15 PM

Superbly written article, Neil; like reading fine classic literature. And thank you for confirming what I've felt all along about my LXD75AR5. The f/9.3 provides stunning views with great contrast and the whole setup is not too heavy with only one ten pound counterweight. Like you, I use a TV Everbrite diagonal and a 40mm Antares erfle. But my favorite eyepiece with this scope is my 24mm Panoptic... outstanding.
Thanks again for the fine article.

Paul

#7 Jeff Morgan

Jeff Morgan

    Fly Me to the Moon

  • *****
  • Posts: 5597
  • Joined: 28 Sep 2003
  • Loc: Prescott, AZ

Posted 14 May 2012 - 09:00 AM

Another entertaining and imaginative read from Neil English.

Perhaps Mr. English should apply his formidable literary talents to writing a monthly observers column? I would think he would have a large following almost immediately.

#8 Andy Howie

Andy Howie

    Mariner 2

  • *****
  • Posts: 207
  • Joined: 10 Sep 2005
  • Loc: Paisley, Scotland

Posted 15 May 2012 - 04:29 PM

I second what Jeff said above. Another enjoyable read, Neil!!

I have to admit, a few months back, when I read of the previous owners terrible dissapointment with this 125R, it did make me scratch my head and wonder what could be wrong. It just contrasted with what I'd read regarding the optics on this frac.

All the best,
Andy.

#9 ukcanuck

ukcanuck

    Vendor (Skylight Telescopes)

  • *****
  • Vendors
  • Posts: 1411
  • Joined: 07 Nov 2006
  • Loc: London, UK

Posted 15 May 2012 - 05:25 PM

Another nice job Neil, well done. It's surprising why this highly desirable Tal refractor hasn't made it into full-time import into the UK. :rainbow:

#10 Andy Howie

Andy Howie

    Mariner 2

  • *****
  • Posts: 207
  • Joined: 10 Sep 2005
  • Loc: Paisley, Scotland

Posted 15 May 2012 - 06:59 PM

Another nice job Neil, well done. It's surprising why this highly desirable Tal refractor hasn't made it into full-time import into the UK. :rainbow:


Agreed!
If I had a few pennies spare, I'd seriously consider buying a 125R lens cell and one of their 2" crayfords, then build an ota around them. Wouldn't have that lovely 'old school' flared tube, but it would save on the high shipping costs(for heavy gear.) from deepest, darkest, Novosibirsk.

Andy.

#11 astroneil

astroneil

    Surveyor 1

  • *****
  • Posts: 1757
  • Joined: 28 Jul 2009
  • Loc: res publica caledoniae

Posted 16 May 2012 - 02:39 PM

Thanks very much guys.

All the best.

Neil.

#12 Andy Howie

Andy Howie

    Mariner 2

  • *****
  • Posts: 207
  • Joined: 10 Sep 2005
  • Loc: Paisley, Scotland

Posted 16 May 2012 - 08:48 PM

Useless information alert .........Noticed on APM Germany's site, that the 100RS is described as a Steinheil doublet rather than the Fraunhofer doublet. I would then presume that the 125R and 75R are too?

From Wikipedia...

"Steinheil doublet

The Steinheil doublet, devised by Carl August von Steinheil, is a flint-first doublet. In contrast to the Fraunhofer doublet, it has a negative lens first followed by a positive lens. It needs stronger curvature than the Fraunhofer doublet"

#13 jrbarnett

jrbarnett

    Eyepiece Hooligan

  • *****
  • Posts: 19883
  • Joined: 28 Feb 2006
  • Loc: Petaluma, CA

Posted 16 May 2012 - 09:33 PM

Useless or not, it's still pretty damned interesting. Thanks for sharing it. Now I'm wondering *why* one would implement a Steinheil over a Fraunhofer...:thinking:

Also, "RS" may denote Steinheil. "R" could instead denote a Fraunhofer. That, too, would be interesting to know.

Regards,

Jim

#14 Andy Howie

Andy Howie

    Mariner 2

  • *****
  • Posts: 207
  • Joined: 10 Sep 2005
  • Loc: Paisley, Scotland

Posted 16 May 2012 - 09:58 PM

http://www.myoptics....as/doublet.html
Quote from the 2nd paragraph....
"The Steinheil, or „flint-in-front“, objective is less used because of the greater suscepttibility of the flint glass (less stable than crown glass) to atmospheric attack. The Steinheil objective is also used when offers better correction of aberrations. However, because it has stronger curves, it is seldom used unless necessary."


I've sent off a mail to the factory(Tal) asking what lens design they use in their 75, 100 and 125 fracs.

As for the letters. I've always presumed the S was added to differentuate(sp?) between two models. At one time 2 4"F10's were produced alongside each other. The original with a basic r&p focuser with very limited travel, then the 2" focuser version.
The 100R has been discontinued for some time and now all fracs and the apo's now use a crayford of Tal's own make.

I must admit this is the first I've heard of the 100RS possibly being of a different lens design. I'll report back when I get a response.

Andy.

#15 Jeff Morgan

Jeff Morgan

    Fly Me to the Moon

  • *****
  • Posts: 5597
  • Joined: 28 Sep 2003
  • Loc: Prescott, AZ

Posted 17 May 2012 - 03:58 PM

I was researching my own Astro-Physics Star12 (also a Steinheil design) and came across several informative posts by Roland Christen on this configuration. It's advantages are that it less sensitive to decentering and has fewer cool down issues. He also claims the steeper curves are actually easier to make with smoother surfaces than the shallow Frauhhofer curves! And in case of the Star12, it also protects the expensive ED element by placing it on the inside.

For more information see RC's Yahoo Refractor posts on the following dates:

November 14, 2006
October 16, 2007
February 18, 2008

#16 Andy Howie

Andy Howie

    Mariner 2

  • *****
  • Posts: 207
  • Joined: 10 Sep 2005
  • Loc: Paisley, Scotland

Posted 18 May 2012 - 11:10 AM

I got the following reply today, straight from 'the horses mouth'..............

Fraunhofer doublet - the first lens has positive refractive power, the second negative.

Anatoly





So that clears up the mis-information on APM's site.

Andy.

ps: A sorry to Neil, for waylaying this thread somewhat !

#17 JimP

JimP

    Surveyor 1

  • -----
  • Posts: 1519
  • Joined: 22 Apr 2003
  • Loc: South Carolina

Posted 30 May 2012 - 03:54 PM

Wonderful article Neil. I just finished your book on refractors and I must say it is Excellent. I highly recommend it!
Just to answer your question, and Not to toot my own horn, I have discovered a number of new/uncatalogued Lunar Domes both visually and by imaging, with apochromatic refractors starting with an AP 6" F/12 many years ago. All are being cataloged by the GLR (Geologic Research Groups) headed by Raf Lena in Italy. We have a book on lunar domes coming out in November, published by Springer.
Back to your 5" achromat. What a beautiful telescope! A true work of art! I like very much your comments regarding contact with previous astronomers who used achromatic refractors. My first refractor was an 8" R.E. Brandt doublet mounted in an irrigation pipe.

best,

JimP

Attached Files



#18 astrogeezer41

astrogeezer41

    Vostok 1

  • *****
  • Posts: 102
  • Joined: 27 Aug 2010

Posted 30 May 2012 - 06:11 PM

I enjoyed your post JimP. Congratulations on your lunar dome work.

I also enjoyed Neil's book and his Taming a Tiger report.

Thanks to both of you,
Robert

#19 astroneil

astroneil

    Surveyor 1

  • *****
  • Posts: 1757
  • Joined: 28 Jul 2009
  • Loc: res publica caledoniae

Posted 02 June 2012 - 06:58 AM

Jim & Robert,

I appreciate your comments.

I have fought many battles, endured many a campaign.

I have learned a great deal about telescopes in the process but much more so concerning human nature.

Let goodwill and commonsense prevail!

Sincerely,

Neil English. ;)

#20 astroneil

astroneil

    Surveyor 1

  • *****
  • Posts: 1757
  • Joined: 28 Jul 2009
  • Loc: res publica caledoniae

Posted 21 September 2012 - 06:20 PM

Tonight; 23:00h local time, my 125R managed a clean split of 36 Andromedae. Magnitudes 6/6.5 separation ~1.0". Ambient temperature 4C.
Resolving magnification: 281 diameters (confirmed at 375x)

One sun atop another; a wee snowman in the dark.

A new record for the Russian glass.

Tonya; Olympian!

Attached Files



#21 astroneil

astroneil

    Surveyor 1

  • *****
  • Posts: 1757
  • Joined: 28 Jul 2009
  • Loc: res publica caledoniae

Posted 12 December 2012 - 06:15 PM

December 11, 2012;

Wee hours o’ the morning.
Temperature -6C
Seeing excellent.

52 Orionis: classic Dawes pair; both components magnitude +6, separation 1” with secondary to the southwest of the primary; split by a hair at 281x

32 Orionis: 1.3” separation, magnitude differential 1.3, secondary well resolved at 281x north east of the primary.

Eta Geminorum (Propus); enjoyed best ever view of secondary. Employed the Baader fringe killer to reduce glare of the bright, red giant primary. 1.6” separation, magnitude delta between components ~ 2.65. Beautifully resolved @281 diameters west of primary; definite bluish tint in secondary.

Theta Aurigae; components separated by 3.8” but huge magnitude differential(~4.5). A 7th magnitude spark well resolved just northwest of primary.

Lamda Cygni: 0.9” magnitude delta between components ~1.8. Pair unresolved at all magnifications (up to 350x). Classic figure 8 morphology orientated north to south.

Achromatic telescope resolves to theoretical limits with my average eyes.

Tonya; Triumphator!

Attached Files



#22 7331Peg

7331Peg

    Sirius Observer

  • *****
  • Posts: 1930
  • Joined: 31 Aug 2008
  • Loc: North coast of Oregon

Posted 13 December 2012 - 01:23 AM

Sensational shooting, I should say, Neil!

The Reverend Dawes would no doubt be thrilled from one end of his 96.5mm f/15.8 Dolland to the other . :grin:


John :refractor:

#23 astroneil

astroneil

    Surveyor 1

  • *****
  • Posts: 1757
  • Joined: 28 Jul 2009
  • Loc: res publica caledoniae

Posted 13 December 2012 - 04:36 PM

Hiho Admiral,

Sailing Mare Nostrum, that's all.

Regards,

Neil. ;)

#24 starrancher

starrancher

    Mercury-Atlas

  • *****
  • Posts: 2960
  • Joined: 09 Jun 2009
  • Loc: Northern Arizona

Posted 20 August 2013 - 04:43 PM

Excellent !






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics