Advice for newbie

I've always been interested in astronomy, and just recently decided to
impulse buy a 4.5" reflector for a local photography store. Its focal
length is 500mm, but bear in mind I knew little or nothing about
apertures/focal lengths at the time I purchase the telescope, i bought
it because it looked good!!

So far, I've been able to get some great views on the moon (when the
clouds cleared after 4 days lol), and I've been able to find saturn
and jupiter. What surprised me how small these objects seemed to me!
Of course I was expecting a full colour view of the rings of saturn
rivalling the HST, such was the limit of my knowledge. In reality they
both looked like small disks, with higher magnification they look
like, well, slightly bigger white disks!

So after my reality check, I can vaguely pick out a few moons around
jupiter, and just about the rings of saturn. Now my question is, what
should I be expecting to see, at what level of detail? Using a 6.5mm
Plossl eyepiece I have worked out should give me 70x magification,
I've seen it written somewhere that a theoretcal limit is 50x aperture
/ inch, so I should be able to achieve 200+ maginication, in reality I
have trouble getting a sharp image of jupiter, and using a barlow 2x
with my 6.5mm eyepiece I find it impossible to get a sharp image. As
the focusser is moved towards getting a sharp image, it defocuses
which is very frustrating because if the image was to come into sharp
focus at that point, it would be an impressive sight as it appears
large and bright, albeit blurry.

So I've heard of this thing called collimation. It seems complicated
to be, could this be the source of the blurry image problem? If I
collimated correctly, would i get a sharp image or have I reached the
limit of what I can achieve? I've been seriously considering
purchasing a 6" cassegrain (perhaps I should have done more
research!), but before I do I need to find out if my disappoiting
images could be improved so that I may not need to spend any more of
my hard earned cash (an avoid an ear bashing from the wife!).

Any advice gratefully received,

Hi Kevin,

Welcome to the real world of amateur Astronomy. You descriptions pretty
much sums up what you can see through a telescope of the size you got if one
limits oneself to a quick look.

The Big Trick for amateurs is to learn how to see faint, low contrast
details. For that, you need to get a book for beginning Astronomers. Look
on the www.skypub.com website for those.

I'm surprised, and surprised myself, at how much you can see through small
telescopes if you take the time to learn and practice. So trundle over to
the site and start your journey!

--- Dave

Oh, and one big piece of advice I can give you; totally FORGET those images
and pictures. Nothing up there looks like it appears on those through any
telescope.


"Kevin" wrote in message
om...
I've always been interested in astronomy, and just recently decided to
impulse buy a 4.5" reflector for a local photography store. Its focal
length is 500mm, but bear in mind I knew little or nothing about
apertures/focal lengths at the time I purchase the telescope, i bought
it because it looked good!!

So far, I've been able to get some great views on the moon (when the
clouds cleared after 4 days lol), and I've been able to find saturn
and jupiter. What surprised me how small these objects seemed to me!
Of course I was expecting a full colour view of the rings of saturn
rivalling the HST, such was the limit of my knowledge. In reality they
both looked like small disks, with higher magnification they look
like, well, slightly bigger white disks!

So after my reality check, I can vaguely pick out a few moons around
jupiter, and just about the rings of saturn. Now my question is, what
should I be expecting to see, at what level of detail? Using a 6.5mm
Plossl eyepiece I have worked out should give me 70x magification,
I've seen it written somewhere that a theoretcal limit is 50x aperture
/ inch, so I should be able to achieve 200+ maginication, in reality I
have trouble getting a sharp image of jupiter, and using a barlow 2x
with my 6.5mm eyepiece I find it impossible to get a sharp image. As
the focusser is moved towards getting a sharp image, it defocuses
which is very frustrating because if the image was to come into sharp
focus at that point, it would be an impressive sight as it appears
large and bright, albeit blurry.

So I've heard of this thing called collimation. It seems complicated
to be, could this be the source of the blurry image problem? If I
collimated correctly, would i get a sharp image or have I reached the
limit of what I can achieve? I've been seriously considering
purchasing a 6" cassegrain (perhaps I should have done more
research!), but before I do I need to find out if my disappoiting
images could be improved so that I may not need to spend any more of
my hard earned cash (an avoid an ear bashing from the wife!).

Any advice gratefully received,

Hi Kevin,

I'd start at http://skyandtelescope.com/howto/sco...icle_787_1.asp and
get it properly collimated. Then you need to give it an hour outside to
cooldown to the air temperature. After that, you'll get your best
performance out of the scope.

However, even then, the 50x per inch requires fairly good optics. You may
find you top out at 20-25x per inch. Of course, with good collimation, you
may go quite a bit higher. You'll never know until you get it collimated and
have a good night.

The other advice I'd give you is to go to a local astro club. You'll be able
to find someone who will check your collimation and help you get that last
tweak just right. You'll also get to look through a lot of scopes as well as
learn your way around the sky.

I also noticed .uk in your email addy. You may find someone near you through
uk.sci.astronomy.

Let us know how it works out!

Clear Skies

Chuck Taylor
Do you observe the moon?
Try the Lunar Observing Group
http://groups.yahoo.com/group/lunar-observing/
Lunar Picture of the Day http://www.lpod.org/
************************************

"Kevin" wrote in message
om...
I've always been interested in astronomy, and just recently decided to
impulse buy a 4.5" reflector for a local photography store. Its focal
length is 500mm, but bear in mind I knew little or nothing about
apertures/focal lengths at the time I purchase the telescope, i bought
it because it looked good!!

So far, I've been able to get some great views on the moon (when the
clouds cleared after 4 days lol), and I've been able to find saturn
and jupiter. What surprised me how small these objects seemed to me!
Of course I was expecting a full colour view of the rings of saturn
rivalling the HST, such was the limit of my knowledge. In reality they
both looked like small disks, with higher magnification they look
like, well, slightly bigger white disks!

So after my reality check, I can vaguely pick out a few moons around
jupiter, and just about the rings of saturn. Now my question is, what
should I be expecting to see, at what level of detail? Using a 6.5mm
Plossl eyepiece I have worked out should give me 70x magification,
I've seen it written somewhere that a theoretcal limit is 50x aperture
/ inch, so I should be able to achieve 200+ maginication, in reality I
have trouble getting a sharp image of jupiter, and using a barlow 2x
with my 6.5mm eyepiece I find it impossible to get a sharp image. As
the focusser is moved towards getting a sharp image, it defocuses
which is very frustrating because if the image was to come into sharp
focus at that point, it would be an impressive sight as it appears
large and bright, albeit blurry.

So I've heard of this thing called collimation. It seems complicated
to be, could this be the source of the blurry image problem? If I
collimated correctly, would i get a sharp image or have I reached the
limit of what I can achieve? I've been seriously considering
purchasing a 6" cassegrain (perhaps I should have done more
research!), but before I do I need to find out if my disappoiting
images could be improved so that I may not need to spend any more of
my hard earned cash (an avoid an ear bashing from the wife!).

Any advice gratefully received,

I'll also note that in addition to what has been said, many of the really
cheap telescopes use a spherical mirror rather than a parabolic one.
This means that the focus will never be quite there as the light isn't being
focused as well as it should be.
It is nice that the reflector telescope is being sold more and more than the
little 50 and 60mm refractors as the reflector will provide a better image
brightness and field of view than the little refractors but the scope is
really too short for good viewing of planets and will have trouble getting
the good focus that is needed for that job.
The 500mm focal length will mean that you need a very short focal length
eyepiece to obtain the high power and when you go to the very short FL EPs
then you end up having a lot of trouble seeing anything through them. I
generally consider that a 9mm EP to be the shortest that I'd consider for
any viewing due to the image problems with anything shorter.
In all, the scope is a nice one to use to see large objects at low power
like the various nebulae and so forth that are in the sky but not for the
high power viewing of the planets.
--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink less.
Works every time it is tried!

Hi Kevin-

I also started out with a 4.5", though mine had a longer focal length
and so somewhat higher magnification per eyepiece focal length. But, at
the same time, back then the eyepieces I used were dismal, so I got
larger blurry images (smile).

You don't mention what brand your scope is, and that might tell us a
little about the quality of the mirror, but assuming it's a good one
(and most are these days), your problem is almost certainly collimation.
It seems complicated, but there are places on the web that will walk you
through it, and after a while it will become pretty easy. But having the
mirrors lined up is of *paramount* importance, especially given the
comparatively short focal ratio of your new scope.

As CLT suggests, the problem might also have to do with cool down. I
notice improvement in images over a period of about 2 hours with my 8".
Your cool down time might not be as long, but you should still give it
at least an hour or so before trying to collimate it on a star.

You might also find a local astronomy group in your town. That way, you
can have somebody help you line up your mirrors, and you can see what
things look like through other peoples' scopes too. And realize also
that learning to see through a telescope is indeed that - *learning* to
see. Over time your eye will begin to pick things out that it didn't
notice before. And turbulence in the atmosphere (bad seeing conditions)
can also wipe out seeing any planetary detail.

Welcome, and good luck -
Chris




Kevin wrote:
I've always been interested in astronomy, and just recently decided to
impulse buy a 4.5" reflector for a local photography store. Its focal
length is 500mm, but bear in mind I knew little or nothing about
apertures/focal lengths at the time I purchase the telescope, i bought
it because it looked good!!

So far, I've been able to get some great views on the moon (when the
clouds cleared after 4 days lol), and I've been able to find saturn
and jupiter. What surprised me how small these objects seemed to me!
Of course I was expecting a full colour view of the rings of saturn
rivalling the HST, such was the limit of my knowledge. In reality they
both looked like small disks, with higher magnification they look
like, well, slightly bigger white disks!

So after my reality check, I can vaguely pick out a few moons around
jupiter, and just about the rings of saturn. Now my question is, what
should I be expecting to see, at what level of detail? Using a 6.5mm
Plossl eyepiece I have worked out should give me 70x magification,
I've seen it written somewhere that a theoretcal limit is 50x aperture
/ inch, so I should be able to achieve 200+ maginication, in reality I
have trouble getting a sharp image of jupiter, and using a barlow 2x
with my 6.5mm eyepiece I find it impossible to get a sharp image. As
the focusser is moved towards getting a sharp image, it defocuses
which is very frustrating because if the image was to come into sharp
focus at that point, it would be an impressive sight as it appears
large and bright, albeit blurry.

So I've heard of this thing called collimation. It seems complicated
to be, could this be the source of the blurry image problem? If I
collimated correctly, would i get a sharp image or have I reached the
limit of what I can achieve? I've been seriously considering
purchasing a 6" cassegrain (perhaps I should have done more
research!), but before I do I need to find out if my disappoiting
images could be improved so that I may not need to spend any more of
my hard earned cash (an avoid an ear bashing from the wife!).

Any advice gratefully received,

I think a nice 5" refractor like the Orion 120 on their Skyview Pro mount
is a good beginner's scope. I know everyone says go dob, but with a
refractor there's no collimation issues, planetary views should be good
(with a minus violet filter) and double stars should look wonderful and M42,
M31 and the rest of the brighter Messier objects should also be easy and
pleasing to see.

"Bob May" wrote in message
...
I'll also note that in addition to what has been said, many of the really
cheap telescopes use a spherical mirror rather than a parabolic one.
This means that the focus will never be quite there as the light isn't
being
focused as well as it should be.
It is nice that the reflector telescope is being sold more and more than
the
little 50 and 60mm refractors as the reflector will provide a better image
brightness and field of view than the little refractors but the scope is
really too short for good viewing of planets and will have trouble getting
the good focus that is needed for that job.
The 500mm focal length will mean that you need a very short focal length
eyepiece to obtain the high power and when you go to the very short FL EPs
then you end up having a lot of trouble seeing anything through them. I
generally consider that a 9mm EP to be the shortest that I'd consider for
any viewing due to the image problems with anything shorter.
In all, the scope is a nice one to use to see large objects at low power
like the various nebulae and so forth that are in the sky but not for the
high power viewing of the planets.
--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink
less.
Works every time it is tried!

Thanks for all your advice guys, it was all very useful. The site
descibing how to collimate the scope was especially useful, I'm off to
get myself a cheshire

The manufacturer of the scope is 'Arena' I tried looking them up on
the web but haven't found anything so far, but I can say its pretty
robustly built and has an equatorial mount which is quite heavy and
doesnt shake around at all, and the eyepieces seem pretty good to me I
have a 25mm and 6.5mm, plus 2 barlows 1.5x and 2x (although these are
plastic and doent seem as well made as the eyepeices which are made
from metal)

So, from what I can figure is I need to collimate the scope first,
then learn to see more detail in these small images. But would getting
another scope with a larger aperture benefit me? The way I look at it,
I paid £150 for my scope which included a pretty good mount and a
couple of good eyepieces, which I could re-use and just pay for a new
'telescope' bit. Bearing in mind, at some time in the future I wouldnt
mind giving astrophotography a go, which would seem pretty pointless
with a 4.5" unless its pictures of the moon!

As for joining a local club, that's one for the future, my wife
already thinks I spend too much time enjoying myself as it is!


Cheers,





starburst wrote in message ...
Hi Kevin-

I also started out with a 4.5", though mine had a longer focal length
and so somewhat higher magnification per eyepiece focal length. But, at
the same time, back then the eyepieces I used were dismal, so I got
larger blurry images (smile).

You don't mention what brand your scope is, and that might tell us a
little about the quality of the mirror, but assuming it's a good one
(and most are these days), your problem is almost certainly collimation.
It seems complicated, but there are places on the web that will walk you
through it, and after a while it will become pretty easy. But having the
mirrors lined up is of *paramount* importance, especially given the
comparatively short focal ratio of your new scope.

As CLT suggests, the problem might also have to do with cool down. I
notice improvement in images over a period of about 2 hours with my 8".
Your cool down time might not be as long, but you should still give it
at least an hour or so before trying to collimate it on a star.

You might also find a local astronomy group in your town. That way, you
can have somebody help you line up your mirrors, and you can see what
things look like through other peoples' scopes too. And realize also
that learning to see through a telescope is indeed that - *learning* to
see. Over time your eye will begin to pick things out that it didn't
notice before. And turbulence in the atmosphere (bad seeing conditions)
can also wipe out seeing any planetary detail.

Welcome, and good luck -
Chris




Kevin wrote:
I've always been interested in astronomy, and just recently decided to
impulse buy a 4.5" reflector for a local photography store. Its focal
length is 500mm, but bear in mind I knew little or nothing about
apertures/focal lengths at the time I purchase the telescope, i bought
it because it looked good!!

So far, I've been able to get some great views on the moon (when the
clouds cleared after 4 days lol), and I've been able to find saturn
and jupiter. What surprised me how small these objects seemed to me!
Of course I was expecting a full colour view of the rings of saturn
rivalling the HST, such was the limit of my knowledge. In reality they
both looked like small disks, with higher magnification they look
like, well, slightly bigger white disks!

So after my reality check, I can vaguely pick out a few moons around
jupiter, and just about the rings of saturn. Now my question is, what
should I be expecting to see, at what level of detail? Using a 6.5mm
Plossl eyepiece I have worked out should give me 70x magification,
I've seen it written somewhere that a theoretcal limit is 50x aperture
/ inch, so I should be able to achieve 200+ maginication, in reality I
have trouble getting a sharp image of jupiter, and using a barlow 2x
with my 6.5mm eyepiece I find it impossible to get a sharp image. As
the focusser is moved towards getting a sharp image, it defocuses
which is very frustrating because if the image was to come into sharp
focus at that point, it would be an impressive sight as it appears
large and bright, albeit blurry.

So I've heard of this thing called collimation. It seems complicated
to be, could this be the source of the blurry image problem? If I
collimated correctly, would i get a sharp image or have I reached the
limit of what I can achieve? I've been seriously considering
purchasing a 6" cassegrain (perhaps I should have done more
research!), but before I do I need to find out if my disappoiting
images could be improved so that I may not need to spend any more of
my hard earned cash (an avoid an ear bashing from the wife!).

Any advice gratefully received,