Autore: pat69
Data: 12-22-05 15:08
L'estrazione pupillare dovrebbe essere di 11mm (17 per il T4), il peso
sui 600 gr (480 per il T4), il field stop immagino sia simile.
Per l'acquisto dipende molto dal prezzo e stato dello stesso, oltre agli
oculari che già hai ed ovviamente per un uso deep-sky (per il planetario è sprecato e non ottimale).
Personalmente ho preso un Pentax XL 10.5 usato su tale focale, dato che ho un 17T4 ed anche per risparmiare qualcosa; per il 17mm trovo molto utile la presenza dell'Instadjust, anche se il meccanismo dei Pentax
mi sembra un pò migliore.
Qui trovi alcuni commenti sul Type2:
http://www.excelsis.com/1.0/entryvotes.php?sectionid=22&entryid=9
Un commento di Ed Ting:
Ed Ting - TeleVue Nagler 12 mm
(Type 2, $375 list, about $300 street)
The first of the Type 2 Naglers, the 12 mm continues the tradition of optical excellence in the Nagler line. The Type 2 eyepieces contain 8 elements instead of 7, and do not suffer from the Kidney Bean Effect. However, some of the eye relief went away (check one out beforehand if you wear glasses while observing) and some observers feel (myself included) that the Type 2 Naglers are somewhat less sharp than their Type 1 counterparts.
The compromise in design arose out of necessity. The 13 mm Nagler is about the largest eyepiece one can build. To achieve longer focal lengths, the eyepieces would have to be huge. According to Rutten and van Venrooij, a 25 mm Nagler would measure 5 inches in diameter and weight close to 25 pounds! Hence, the re-design, and a few sacrifices, with the Type 2 Naglers.
Still, the 12 mm is a superb eyepiece. It is a pefectly acceptable substitute for the 13 mm (well, now you don't have a choice...) and may even be preferred, if the Kidney Bean Effect annoys you. Like the 13 mm, the 12 mm has a 1.25" barrel, with a 2" skirt around the outside.
Patrizio
Celestron CGE 1400 XLT, Meade LX90 EMC
42°19'N, 13°19'E (AQ)
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