Taming a Tiger
Posted 12 May 2012 - 11:32 AM
By Neil English
Posted 12 May 2012 - 12:59 PM
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!
Posted 12 May 2012 - 02:46 PM
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.
Posted 13 May 2012 - 07:43 AM
Posted 13 May 2012 - 08:50 AM
Posted 13 May 2012 - 09:15 PM
Thanks again for the fine article.
Posted 14 May 2012 - 09:00 AM
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.
Posted 15 May 2012 - 04:29 PM
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,
Posted 15 May 2012 - 05:25 PM
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.
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.
Posted 16 May 2012 - 08:48 PM
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"
Posted 16 May 2012 - 09:33 PM
Also, "RS" may denote Steinheil. "R" could instead denote a Fraunhofer. That, too, would be interesting to know.
Posted 16 May 2012 - 09:58 PM
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.
Posted 17 May 2012 - 03:58 PM
For more information see RC's Yahoo Refractor posts on the following dates:
November 14, 2006
October 16, 2007
February 18, 2008
Posted 18 May 2012 - 11:10 AM
Fraunhofer doublet - the first lens has positive refractive power, the second negative.
So that clears up the mis-information on APM's site.
ps: A sorry to Neil, for waylaying this thread somewhat !
Posted 30 May 2012 - 03:54 PM
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.
Posted 30 May 2012 - 06:11 PM
I also enjoyed Neil's book and his Taming a Tiger report.
Thanks to both of you,
Posted 02 June 2012 - 06:58 AM
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!
Posted 21 September 2012 - 06:20 PM
Resolving magnification: 281 diameters (confirmed at 375x)
One sun atop another; a wee snowman in the dark.
A new record for the Russian glass.
Posted 12 December 2012 - 06:15 PM
Wee hours o’ the morning.
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.
Posted 13 December 2012 - 04:36 PM
Sailing Mare Nostrum, that's all.