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Main
Date: 26 Jun 2007 01:13:48
From: craig510a3
Subject: 8" Meade SN Question
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Just picked one up used. Should I see a dim dark area in my field of
view? Do you normally see the secondary mirror in Newtonians?
New to the SN, other scope is a LX200 12".
Thanks,
Craig
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Date: 26 Jun 2007 11:13:24
From: craig510a3
Subject: Re: 8" Meade SN Question
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On Jun 25, 9:37 pm, Chris L Peterson <c...@alumni.caltech.edu > wrote:
> On Tue, 26 Jun 2007 01:13:48 -0000, craig510a3 <craigberk...@gmail.com>
> wrote:
>
> >Just picked one up used. Should I see a dim dark area in my field of
> >view? Do you normally see the secondary mirror in Newtonians?
>
> >New to the SN, other scope is a LX200 12".
>
> In an occluded scope, you don't get a solid cylinder of rays exiting the
> eyepiece, but an annular cylinder. If your eye's pupil is constricted
> (as is typical in the daytime), it can be of similar size or smaller
> than the shadowed center of the exit rays. In that case, you will see a
> central dark area, or even be able to find an eye location where you see
> nothing at all. The effect is worse with SCTs than Newts because they
> have larger central obstructions. But you shouldn't see this at
> nighttime unless your pupils are permanently constricted due to some
> disease or injury.
>
> _________________________________________________
>
> Chris L Peterson
> Cloudbait Observatoryhttp://www.cloudbait.com
Thank you!
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Date: 26 Jun 2007 11:13:06
From: craig510a3
Subject: Re: 8" Meade SN Question
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On Jun 25, 9:18 pm, "Curtis Croulet" <calypte@_NO_SPAM_verizon.net >
wrote:
> > Just picked one up used. Should I see a dim dark area in my field of
> > view? Do you normally see the secondary mirror in Newtonians?
>
> > New to the SN, other scope is a LX200 12".
>
> You're looking in the daytime, right? The shadow of the diagonal is norm=
al
> in this circumstance. It will be invisible at night. You should be able=
to
> see the secondary of your SCT under similar conditions.
> --
> Curtis Croulet
> Temecula, California
> 33=B027'59"N, 117=B005'53"W
I was.
Thank you for the info.
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Date: 26 Jun 2007 01:37:54
From: Chris L Peterson
Subject: Re: 8" Meade SN Question
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On Tue, 26 Jun 2007 01:13:48 -0000, craig510a3 <craigberkley@gmail.com >
wrote:
>Just picked one up used. Should I see a dim dark area in my field of
>view? Do you normally see the secondary mirror in Newtonians?
>
>New to the SN, other scope is a LX200 12".
In an occluded scope, you don't get a solid cylinder of rays exiting the
eyepiece, but an annular cylinder. If your eye's pupil is constricted
(as is typical in the daytime), it can be of similar size or smaller
than the shadowed center of the exit rays. In that case, you will see a
central dark area, or even be able to find an eye location where you see
nothing at all. The effect is worse with SCTs than Newts because they
have larger central obstructions. But you shouldn't see this at
nighttime unless your pupils are permanently constricted due to some
disease or injury.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 26 Jun 2007 01:18:47
From: Curtis Croulet
Subject: Re: 8" Meade SN Question
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> Just picked one up used. Should I see a dim dark area in my field of
> view? Do you normally see the secondary mirror in Newtonians?
>
> New to the SN, other scope is a LX200 12".
You're looking in the daytime, right? The shadow of the diagonal is normal
in this circumstance. It will be invisible at night. You should be able to
see the secondary of your SCT under similar conditions.
--
Curtis Croulet
Temecula, California
33°27'59"N, 117°05'53"W
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