Zeta Cancri and my NexStar 5i

Finally got a steady night to test my new toy, a NexStar 5i. And
tonight, I just got one of my best views ever of a tight double, Zeta
Cancer (actually a triple). The closest components as far as I know
have a separation of .92 arc-sec. At 250x they appeared as two disks
just touching (like the number 8), with nice concentric diffraction
rings, the atmosphere was very steady. The Dawes limit on my NexStar
5i is .91 arc-sec. So I think I should be pretty happy right? Would
you think this is average for a 5" SCT or did I just have a good night
of seeing or do you think I have a really good scope?
Dave

Dave wrote:
Finally got a steady night to test my new toy, a NexStar 5i. And
tonight, I just got one of my best views ever of a tight double, Zeta
Cancer (actually a triple). The closest components as far as I know
have a separation of .92 arc-sec. At 250x they appeared as two disks
just touching (like the number 8), with nice concentric diffraction
rings, the atmosphere was very steady. The Dawes limit on my NexStar
5i is .91 arc-sec. So I think I should be pretty happy right? Would
you think this is average for a 5" SCT or did I just have a good night
of seeing or do you think I have a really good scope?

Just from that it's a bit hard to tell. The clarity of the image at
the smallest possible level of detail is only one aspect of a telescope's
performance; a more comprehensive measure would consider all sizes of
detail. Of course, just about any telescope, good or bad, will do better
as the details get larger, but *how much better* tells you how good the
scope is.

That's why observing, say, Jupiter is a better test of optical quality,
because Jupiter has oodles of detail of many different sizes. Alas, it's
much harder to say whether a telescope passes this test or not, because
unlike with double stars, one can't simply say you saw something or you
didn't. It takes experience to gauge whether a telescope passes this
test--that and a lot of patience to find the right moment of seeing.

Sorry I couldn't give a more definitive answer.

Brian Tung
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.txt

Sorry I couldn't give a more definitive answer.

Since you have a C5, you might compare this split to ones you have made.

jon

Jon Isaacs wrote:
Since you have a C5, you might compare this split to ones you have made.

Oh, well, it sounds very much like what I would expect. I'm afraid I
don't observe a lot of doubles; I've never looked at zeta Cancri, and
the only one that comes close would be zeta Bootis, which as I recall
is just a bit tighter. It looked very much like what she was describing,
but probably a bit more overlap, too.

Brian Tung
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.txt

(Brian Tung) wrote in message ...
It looked very much like what she was describing,
but probably a bit more overlap, too.

Brian Tung
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.txt

Ms Tung,
I think you mean "he" not "she"
: )

Dave

David wrote:
Ms Tung,
I think you mean "he" not "she"

Doggone it, you're right. I got this poster mixed up with the one with
the unidentified 5-inch SCT. My bad.

Brian Tung
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.txt