Hi Kevin,
Before I bought my 16" NSS, I was going to build the 16"er myself.
Even though the folks at Protostar don't recommend it, they will make a 3
vane spider to fit your scope. A 3 vane spider will produce less diffraction
energy resulting in smaller spikes.
You will see 6 spikes using a 3 vane spider, and because a 4 vane spider
actually produces 8 diffraction spikes, but you only see 4 because they
overlap, the bugaboo is they almost never overlap each other perfectly. So
since it's almost impossible to get the 4 vanes perfectly aligned with each
other, the resulting diffraction spikes will often look twice as thick as
they would were they aligned spot on.
Now don't get me wrong, I am perfectly happy with the views I get using a 4
vane spider. But if I were building the perfect scope, one that I would want
to keep for a long time, I would put a Feathertouch focuser on it rather
than a JMI. It's not that there is anything wrong with the JMI, it's just
not a Feathertouch. :-) And to my mind the same thing holds true with the
choice of any component you put on your scope.
I don't remember who it was, but while at Lake San Antonio last year I ran
into an observer with a 18" scope. He had a 3 vane Protostar spider in his
scope. The views were very nice, and I saw no added vibration when I tapped
the side of the UCA. The owner said that the setup was problem free.
The curved spider vanes I've seen were made from a much thicker piece of
metal. Made that way I assume to prevent flexure. The views had a little
less contrast on bright objects, but no difference was seen on DSO's
Just my 2 cents...
Rashad
----- Original Message -----
From: "Mark Wagner" <mgwagner@resource-intl.com>
To: "The Astronomy Connection" <sf-bay-tac@seds.org>
Sent: Friday, April 30, 2004 9:35 AM
Subject: Re: [TAC] Spiders (on topic)
> At 4/30/2004, grimly_fiendish@comcast.net wrote:
>
> >I came across the curved vane spider and was wondering if anyone has used
> >one and if the claims are true. I would appreciate any advice, please
> >reply to me off list.
>
> Kevin,
>
> I'd like to see replies on-list, if people wouldn't mind. I've heard that
> the curved spiders "soften" diffraction spike, I've heard they eliminate
> them. But I haven't seen any side-by-side comparisons. So, I too would
be
> interested in other's actual experiences.
>
> Mark
>
>
Received on Fri Apr 30 19:51:27 2004