cosmologist
member
Reged: 10/01/05
Posts: 33
Loc: Perth, Australia
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I've decided to invest in a 7mm Nagler for my newly purchased 16" LB, but discovered quite a bit of coma the other night while viewing. Reading these forums, it is highly recommended that one buy a Paracorr to reduce the effects of coma. But how will the 7mm perform without a Paracorr, is it essential to buy one down the track? What is more important in your opinion? A Paracorr or a good set of eyepieces?
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David
Lightbridge 16" f/4.5
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F.Meiresonne
Post Laureate
Reged: 12/22/03
Posts: 4136
Loc: Eeklo,Belgium
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An eyepiece has nothing to do with it because the coma is producted by the primary mirror. Eyepieces with longer focal lengths and bigger FOV tend to show the coma better.
I think it is possible in the N7T6 you will not even notice it.
Sometimes i use a MPCC for my Pan 24 or 19 in my OO F/4.5
I never use it with my N13T6 though...
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Freddy
Obsession 18 inch #1638
Orion Optics 8 inch F/4.5 -1/8 wave optics -Vixen GP-E
22x85 Helios Apollo (=GO SS)
15x70 TS Marine (=Obie Ultra)
10x60 Helios Quantum 4(= Obie Mariner)
10x50 Fujinon FMT-SX
10x50,8x40 Helios Nature sport plus
Eyepieces in use :Pan 35,24,19, N13T6, Pentax 10, 7 XW, N9T6, TV2, BGO 12.5, 9 mm
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cosmologist
member
Reged: 10/01/05
Posts: 33
Loc: Perth, Australia
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Quote:
An eyepiece has nothing to do with it because the coma is producted by the primary mirror. Eyepieces with longer focal lengths and bigger FOV tend to show the coma better.
I think it is possible in the N7T6 you will not even notice it.
Sometimes i use a MPCC for my Pan 24 or 19 in my OO F/4.5
I never use it with my N13T6 though...
Thanks for your advice, that makes sense.
In that case I think I can do without a Paracorr for now.
May I ask what a MPCC is?
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David
Lightbridge 16" f/4.5
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V.A.
sage
Reged: 05/14/05
Posts: 281
Loc: Ontario, Canada
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i'm sure you have low power eyepieces as well, so you will need a parrcorr. MPCC is a coma corrector from Baader, less expensive and less convient than a parrcorr, but seems like it introduces more abberiation (spherical) than the coma it corrects.
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10" binocular telescope
Oberwerk 7x50 Mariner
tv 24pans , plossl's and 12mm t4s
6.5 mag. dark skies
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Olivier Biot
Amused
Reged: 04/25/05
Posts: 24589
Loc: 51°N (Belgium)
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Baader MPCC = Multi Purpose Coma Corrector, a coma corrector that you attach to an eyepiece like a filter.
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I think you're worth a double serving of happiness!
Tal-200K (#199) with JMI NGF-Mini2M focuser on GEM3 • Astro-Tech AT80ED • Orion Sirius EQ-G with wireless EQDIRECT • Astro-Tech Voyager • Celestron Regal LX 10x42 • Helios 15x70
ATM projects: 14" f/5 truss Dobson: first light Jul 1, 2011  - currently in 'tweak & widget' mode 
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F.Meiresonne
Post Laureate
Reged: 12/22/03
Posts: 4136
Loc: Eeklo,Belgium
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Quote:
i'm sure you have low power eyepieces as well, so you will need a parrcorr. MPCC is a coma corrector from Baader, less expensive and less convient than a parrcorr, but seems like it introduces more abberiation (spherical) than the coma it corrects.
The spherical abberation is only visible wiht high mag thus with eyepieces with short FL. You can not notice it in a Pan 24. But you right it is not so convenient to use
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Freddy
Obsession 18 inch #1638
Orion Optics 8 inch F/4.5 -1/8 wave optics -Vixen GP-E
22x85 Helios Apollo (=GO SS)
15x70 TS Marine (=Obie Ultra)
10x60 Helios Quantum 4(= Obie Mariner)
10x50 Fujinon FMT-SX
10x50,8x40 Helios Nature sport plus
Eyepieces in use :Pan 35,24,19, N13T6, Pentax 10, 7 XW, N9T6, TV2, BGO 12.5, 9 mm
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V.A.
sage
Reged: 05/14/05
Posts: 281
Loc: Ontario, Canada
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only reason i mentioned that is to let the poster know about it. i've been thinking of buying a MPCC as well, when the time came to buy it, i searched MPCC on CN, and found out about the spherical abberiation, if i had not done that i would have been a little upset right now. Baader should post a warning about it, but they don't!
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10" binocular telescope
Oberwerk 7x50 Mariner
tv 24pans , plossl's and 12mm t4s
6.5 mag. dark skies
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mattz
professor emeritus
Reged: 12/03/06
Posts: 609
Loc: Where is Rescue CA?
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Don't underestimate how much a Paracorr helps even at shorter FLs. I was surprised how much better the view was using my 9T6 with the Paracorr. Stars that stayed split all the way to the edge with the Paracorr were smudges once past 30 percent of FOV without the Paracorr. I've revamped my EP lineup to work more easily with the Paracorr, it stays in the whole time now.
I have the 5 and 7 coming (I was a victim of the sale) and I'll post results with those EPs with and without a Paracorr.
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Matt
Orion XT10i with Feather Touch and Paracorr
26T5 17T4
9, 7, & 5T6
Either 12T4 or 13T6, we'll see after the death match.
One homeless SV80S
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V.A.
sage
Reged: 05/14/05
Posts: 281
Loc: Ontario, Canada
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that's exactly why i went with the parrcorr, so i can use it past the low power range.
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10" binocular telescope
Oberwerk 7x50 Mariner
tv 24pans , plossl's and 12mm t4s
6.5 mag. dark skies
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Bill Weir
Carpal Tunnel
Reged: 06/01/04
Posts: 2166
Loc: Metchosin (Victoria), Canada
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Dude you are doomed. Now that you have noticed the coma it will eat you up. Get the Paracorr then just leave it in the focuser at all times when observing. That Baader thing will need to be changed fron eyepiece to eyepiece. How convenient is that? Even with my 5mm T6 Nagler I can tell the difference when it's not in the Paracorr.
Bill
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6'' Orion SkyQuest
f/5 12.5" Astrotel truss dob
f/3.3 20" Super FXQ Starmaster
William Optics 80mm ZenithStar ED II
1591/2500
Observing sessions grand total for 2012, 47.
So far in 2013, 7.
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astrodon
Carpal Tunnel
Reged: 04/07/05
Posts: 2552
Loc: Portland, OR, USA
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Hate to derail the thread, but does anyone have trouble with the 1.25" to 2" adapter (taking it out and putting it in)?
The Paracorr works wonders with the coma on short f/ratio reflectors.
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Eager to get the Cave 6" f/4 out with some 'high' (medium in this scope) power eyepieces!
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walt r
Post Laureate
Reged: 02/13/07
Posts: 3611
Loc: Doylestown, PA
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If you are asking about the adapter that comes with the Paracorr, then yes. I have so much trouble with it I never use it. The combination of of under cut with the compression ring must be Al's biggest follies. Oh well. The Paracorr is definitly a winner and mine also stays in the focuser.
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Walt
Obsession 18" f/4.45 #1370 AN/SC
MK67 Deluxe 6" f/12 Mak-Cass, Super Polaris GEM, JMI MicroMax DSC
DIY 60mm f/6 Achromat
Cookbook 245 CCD
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V.A.
sage
Reged: 05/14/05
Posts: 281
Loc: Ontario, Canada
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yes , i have not one but two paracorrs on order. i find coma is a problem with plossls at f/6, it's time for some coma correction since i'm moving up to 2" focusers. the paracorr is new to me as i come from a refractor telescope past, so i'm learning as i go along. the paracorr will be a built-in ,non-removable , non-visible part of the scope, with a suitable focuser fixed to where the tunable top is, basically i will toss out the tunable top in favor of a focuser, of course the main focuser on the telescope will no longer be needed. as any form of corrector lens it should be a built-in part of the telescope.
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10" binocular telescope
Oberwerk 7x50 Mariner
tv 24pans , plossl's and 12mm t4s
6.5 mag. dark skies
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astrodon
Carpal Tunnel
Reged: 04/07/05
Posts: 2552
Loc: Portland, OR, USA
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Quote:
yes , i have not one but two paracorrs on order.
explained by in your sig; 10" binocular telescope..
I see the light! 
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Eager to get the Cave 6" f/4 out with some 'high' (medium in this scope) power eyepieces!
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Bolsermatic
member
Reged: 06/16/06
Posts: 20
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Quote:
the paracorr will be a built-in ,non-removable , non-visible part of the scope, with a suitable focuser fixed to where the tunable top is, basically i will toss out the tunable top in favor of a focuser, of course the main focuser on the telescope will no longer be needed. as any form of corrector lens it should be a built-in part of the telescope.
I agree completely with this concept and have been working toward a similar solution. Two things to be aware of:
1) if the primary mirror is moved up or down from successive collimation adjustments, the position of the paracorr lense will need to be moved as well to retain it's optimum position as a coma corrector.
2) If the tuneable top is replaced with a focuser you will need to be careful when adjusting so as not to hit the paracorr lense with the bottom of an eyepiece, barlow, or filter. This can be an issure sometimes even when the tuneable top is used.
Do you have any pictures of your 10" binocular build you could share?
Steve
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