Cherokee #2 Pronto and Lyra

You can avoid the need for a compass if you learn how to spot Polaris.
(The North Star)

If you look at your star charts, you'll find two of the stars in the big
dipper define a line that points right at Polaris.

On M57, you'll probably need about 60 power to see the hole in the
donut. I typically observe it at about 90 power in my 4.5" refractor.

If you pick up a 9 mm eyepiece, you'll have 53.33 power without your
barlow, and 106.66 with it.

Cherokee wrote:

Ed,

How did you get the magnification numbers? I'd like to calculate those
for my Pronto.

Ed, Brian,

What eyepiece should I buy to be able to split these 2? If I need
higher magnifications for certain objects, I best buy it right away so
I don't have to skip viewing them.


The usual rule of thumb says you can make use of 2X per millimetre of
aperture under excellent conditions. So for the maximum useful
magnification you want an EP that can deliver something like 120X -
150X -- depending on how optimistic you are. Dividing that into the
focal length of your objective, which Ed said is 480 mm, gives a
range of 3.2 mm (somewhat optimistic) - 4 mm (more conservative), but
considering that you already have a 2X Barlow you can combine that
with an EP of twice the FL for the same result. For example a 7.5-mm
eyepiece will give you 480/7.5 = 64X alone, or 128X with the Barlow.

--
Odysseus

Chuck,

Thanks. It was a great time - I felt like a kid again.

peace,
Cherokee

Mark,

ahhhhh - find the North star and North and South are immediatly
apparent. OK, I have the summer triangle and the North Star to look
for. You guys are coming up with some great tips!

peace,
Cherokee

Ed,

A very useful website. I spent around 30 minutes playing around with
the simulator. Can you take a moment and explain to me what FOV is all
about? I liked the FOV setting at it's widest. What FOV does my 24mm
Konig have?

Also, if I need 100x to split Epsilon-Lyra, then I need a 4.8mm
eyepiece. OK, which eyepiece should I get and from where? I'm eager
to order what I need so I can split it. I hate to leave loose
ends......

peace,
Cherokee

Odysseus,

Since I have a 24mm Konig and an Ultima Barlow, this gives me a 24mm
eyepiece and a 12mm eyepiece, right? Per my other post, it appears I
would next get a 4.8mm eyepiece for 100x????

peace,
Cherokee

"Cherokee" wrote in message
ups.com...
Ed,

A very useful website. I spent around 30 minutes playing around with
the simulator. Can you take a moment and explain to me what FOV is all
about? I liked the FOV setting at it's widest. What FOV does my 24mm
Konig have?



When considering FOV, you have two types to consider.

The Apparent Field of View (AFOV) is determined by the eyepiece design.
Your Konig has a 60 degree AFOV. An unrestricted AFOV is 360 degrees, but
when looking through an eyepiece your view is limited to ~30-90 degrees by
the eyepiece. You can look through an eyepiece without a telescope and see
the limits of the field and estimate the AFOV.

The True Field of View (TFOV) is determined by the eyepiece/telescope
combination and describes how much of the night sky fits into the field of
view. For example if the full moon fills the field of view of an eyepiece
it has a TFOV of ~1/2 degree.

True Field of View = Apparent Field of View / Magnification. There are
some eyepiece distortions that make this equation less than accurate but for
now don't worry about that.

Lets take our moon example again. If you are using your 60 degree AFOV
Konig at 20x, you'll see about 3 degrees of sky (~6 lunar diameters).

Ed T.

Using the barlow, you could get a 9mm eyepiece. That would put you a little
over the 100x, but that's okay too.


"Cherokee" wrote in message
oups.com...
Odysseus,

Since I have a 24mm Konig and an Ultima Barlow, this gives me a 24mm
eyepiece and a 12mm eyepiece, right? Per my other post, it appears I
would next get a 4.8mm eyepiece for 100x????

peace,
Cherokee

Cherokee wrote:

Since I have a 24mm Konig and an Ultima Barlow, this gives me a 24mm
eyepiece and a 12mm eyepiece, right? Per my other post, it appears I
would next get a 4.8mm eyepiece for 100x????


You certainly could (or something close to it), but a 9.6-mm you
could use with the Barlow for 100X would also give you the option of
50X when used alone, giving you in all a choice of 20X, 40X, 50X, &
100X. There wouldn't be any point to using a 4.8-mm EP with the
Barlow, because at 200X you'd be 'overdriving' your aperture.

OTOH with some 'scope-EP combinations a Barlow can create
difficulties in focusing: if a given EP requires the focuser to be
racked nearly all the way in, with a Barlow it'll likely 'bottom out'
before the view gets sharp. Since your current EP works with your
Barlow, if you can find a(n approximately) 9.6mm that's parfocal with
the 24mm you can be sure it'll be similarly compatible.

--
Odysseus

Since I have a 24mm Konig and an Ultima Barlow, this gives me a 24mm
eyepiece and a 12mm eyepiece, right? Per my other post, it appears I
would next get a 4.8mm eyepiece for 100x????

I own the Ranger, which has identical optics to the Pronto
but uses a 1.25-inch focuser instead of a 2-inch focuster.
I also have an 8-24mm zoom eyepiece which, in combination
with a Barlow, lets me "dial in" pretty much any magnification
I want.

Your 24mm eyepiece should be just great for general low-
magnification browsing. Eventually, you may want to supplement
it with a 2-inch eyepiece to give you a *really* low power
and correspondingly vast field of view. When all is said
and done, that is the Pronto's greatest strength; few other
scopes on the market can touch it for low-power work.

For closeup views of deep-sky objects, I usually like to
use a magnification of around 50X - 60X on my Ranger,
meaning an eyepiece in the 8mm - 9.6mm range. I betcha
you would see M57 as a ring at 60X, where it might be
much harder at 40X.

For planets, I usually like at least 100X, and often higher.
Tight double stars and the Moon often profit from 150X,
although the marginal gain above 120X is fairly small.
Anyway, all these magnifications are best achieved with
the aid of a Barlow, because the eye relief of a standard,
moderately priced 3mm - 5mm eyepiece is painfully short.
In other words, to see the entire field, you nearly have
to press your eyeball against the glass.

- Tony Flanders