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| paracorr & EP combos for widefield on f/4 Webster scopes? http://webstertelescopes.com/forum/viewtopic.php?f=7&t=587 |
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| Author: | jonW [ Sat Feb 19, 2011 6:33 pm ] |
| Post subject: | paracorr & EP combos for widefield on f/4 Webster scopes? |
I currently use Paracorr I + Nagler 26T5 on an f/4.7 scope, with good results. But on an f/4 Webster scope I'm thinking the combo of Paracorr II + 21mm Ethos will substantially pull ahead, both for coma correction and contrast. Any thoughts or experiences on this ? I find the sky background to be noticably grey with a 26mm eyepiece at f/4.7. So at f/4 I guess it will be worse still, due to larger exit pupil. |
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| Author: | jimwebster [ Mon Feb 21, 2011 6:46 pm ] |
| Post subject: | Re: paracorr & EP combos for widefield on f/4 Webster scopes |
Both the 26mm Nag and the 21mm Ethos yield exit pupils under 6mm when used with the Paracorr, so if your eye is truly dark adapted, either eyepiece should give great results. With the club we have done a few tests between both eyepieces designs, and so far it seems the Naglers have slightly more contrast at a given magnification. http://televue.com/engine/TV3_page.asp?NoBack=True&id=89&plain=TRUE&focal_length=&fl_unit=mm&aperture=22&a_unit=in.&fratio=4&_2in=yes¶corr=yes&Ethos=TRUE&Nagler=TRUE&sortby=SortTrueField&title=&SUBMIT1=CALCULATE#results |
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| Author: | jonW [ Mon Feb 21, 2011 8:17 pm ] |
| Post subject: | Re: paracorr & EP combos for widefield on f/4 Webster scopes |
Naglers pulling ahead of Ethos on contrast at equivalent magnification- that's really interesting. So the 21mm Ethos isnt necessarily the holy grail of eyepieces for fast dobs. The paracorr II is going to cause some folk to scratch their heads who already have version I. At < f/4 type II is a no brainer to buy I guess. But there is a twilight zone between f/4.5 and f/4 where Televue say either is OK. Some ppl have noticed superior performance of Paracorr II at f/4 though. Guess it boils down to personal tolerance of residual coma..... |
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| Author: | jimwebster [ Mon Feb 21, 2011 8:59 pm ] |
| Post subject: | Re: paracorr & EP combos for widefield on f/4 Webster scopes |
Eric has been using a type I Paracorr on his f/3.3 scope and it works just fine. Everyone assumes it is a type II, and is surprised when they find how good the view is through the old one. If you already have the type I, at f/4 I'd just keep it and never look back. Same thing with eyepieces. Kennedy said that one customer was angry because if the customer cocked his head all the way sideways, he could see some artifact at the very edge of the field on the 21mm Ethos at f/3.3. He wanted a whole new mirror made at f/4. Now, you have to ask yourself about the logic of throwing out an entire mirror because of a view through a single eyepiece (let alone that you need to really strain to see the "problem"). There will always be better eyepieces as time goes on. No eyepiece should be considered the be all end all. |
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