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Main
Date: 18 Nov 2006 16:03:16
From: Sixtus
Subject: widest FOW eyepiece on C5 w/o Redu.Cor. ?
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We would like to get the widest possible field of view on our C5, in night-
as well as in daytime.
The Celestron 6.3 r/c is impossible to use in daytime (vignetting, black
spots etc.), for instance with the 30 mm Ultima.
The latter gives 1,2 degrees at f/10, but with a little hard-to-hold
eyepoint/-relief.
Is that to be expected of every such 30-35 mm eyepiece ?
We will stick to the 1 1/4 size, so who are the competitors outthere ?
Are the 65-70 deg. field-of-view eyepieces the answers ? Will any have an
"easier" eye relief than the Ultima ?
Regards
Carl
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Date: 18 Nov 2006 11:01:07
From: William Hamblen
Subject: Re: widest FOW eyepiece on C5 w/o Redu.Cor. ?
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On Sat, 18 Nov 2006 16:03:16 +0100, "Sixtus" <pegoo@yahoo.uk > wrote:
>We would like to get the widest possible field of view on our C5, in night-
>as well as in daytime.
>
>The Celestron 6.3 r/c is impossible to use in daytime (vignetting, black
>spots etc.), for instance with the 30 mm Ultima.
>
>The latter gives 1,2 degrees at f/10, but with a little hard-to-hold
>eyepoint/-relief.
>
>Is that to be expected of every such 30-35 mm eyepiece ?
>
>We will stick to the 1 1/4 size, so who are the competitors outthere ?
>
>Are the 65-70 deg. field-of-view eyepieces the answers ? Will any have an
>"easier" eye relief than the Ultima ?
The Tele Vue eyepiece calculator shows that their 40 mm Ploessl, 32 mm
Ploessl and 24 mm Panoptic all have a 1.2 degree true field with a
focal length of 1270 mm. The 24 mm Panoptic is pricey.
Bud
--
The night is just the shadow of the Earth.
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Date: 18 Nov 2006 08:15:04
From: Brian Tung
Subject: Re: widest FOW eyepiece on C5 w/o Redu.Cor. ?
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Sixtus wrote:
> We would like to get the widest possible field of view on our C5, in night-
> as well as in daytime.
>
> The Celestron 6.3 r/c is impossible to use in daytime (vignetting, black
> spots etc.), for instance with the 30 mm Ultima.
The black spot is an issue relating to the central obstruction and the
constriction of your eye's pupil, which is unavoidable during the day.
The vignetting does result from the the reducer-corrector in conjunction
with the narrow rear port opening, but you'd have the same problem if
you tried to use 2-inch eyepieces--possibly worse.
The C5 simply isn't equipped to yield very wide fields during the day.
Your eye's pupil is about 2 mm across at those times, which equates to
about 60x. Any less than that, and the black spot will begin rearing
its ugly little head. It becomes objectionable at powers below maybe
40x or 50x. (Your mileage may vary, of course.)
> We will stick to the 1 1/4 size, so who are the competitors outthere ?
Tele Vue's 32 mm Plossl. Orion has a 32 mm Plossl, too, I think. But
they'll all have the same problems.
> Are the 65-70 deg. field-of-view eyepieces the answers ? Will any have an
> "easier" eye relief than the Ultima ?
Not significantly different, I'm afraid.
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
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Date: 18 Nov 2006 16:17:04
From: Willie R. Meghar
Subject: Re: widest FOW eyepiece on C5 w/o Redu.Cor. ?
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"Sixtus" <pegoo@yahoo.uk > wrote:
>We would like to get the widest possible field of view on our C5, in night-
>as well as in daytime.
The ideal way of doing this would be to match the eyepiece's exit
pupil size with the observer's pupil size -- under the conditions in
which the scope will be used. This means one magnification for night
use, and a higher magnification for day use. In both instances, an
eyepiece with a wide apparent field would be desirable.
>The Celestron 6.3 r/c is impossible to use in daytime (vignetting, black
>spots etc.), for instance with the 30 mm Ultima.
As Brian Tung correctly explained, this is to be expected.
Willie R. Meghar
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