Orion ShortTube 4.5 EQ

For Christmas I was given an Orion ShortTube 4.5 EQ Reflector, my first
telescope and I absolutely love it. After reading several articles and
listening to others, I decided to purchase a barlow to go along with the
eyepieces that came with the telescope.

After ordering, but before it arrived, I realized that the ShortTube
already has a built-in barlow. Is it ok to add a second barlow to this?
I've read that stacking barlows will work, with light loss...

Tonight was the first clear night since the arrival of the barlow. I
first directed my attention to Saturn with the barlow and 10mm eyepiece
(200x magnification). I was very impressed with the size, but just
couldn't get it into sharp focus. Same thing with Mars.

I think it was just because of poor seeing, but want to make sure I'm
not trying something stupid by adding a barlow to a ShortTube. Can
anyone comment?

Thank you very much for your input,
EJ

Eric Johnson writes:

After ordering, but before it arrived, I realized that the ShortTube
already has a built-in barlow. Is it ok to add a second barlow to
this? I've read that stacking barlows will work, with light loss...

Yes, you can add a Barlow. However, these "short-tube" reflectors use
a fast spherical primary mirror with a built-in focal corrector. This
corrector extends the focal length (like a Barlow) and also attempts
to correct the sperical aberration (unlike a Barlow). It is not
entirely succesful in this latter function, however, and this type of
telecope is really a compromise between short tubelength and low price
on one side and optical quality on the other. It works reasonably OK
(for the price) if you don't "stress" it too much using too high
magnification or wide-angle eyepieces(*).

Tonight was the first clear night since the arrival of the barlow. I
first directed my attention to Saturn with the barlow and 10mm
eyepiece (200x magnification). I was very impressed with the size,
but just couldn't get it into sharp focus. Same thing with Mars.

200x is pressing this type of telescope a bit. 150x may be a practical
upper limit (very subjective of course). Also, be sure to collimate
the optics as best you can. This telescope is also very sensitive to
careful focusing.

*) Having said that, there is a lot of stuff to see with this
telescope. As a side note, I have been using such a short-tube for CCD
work for almost a year now and, while I hope to replace it with a
better telescope soon, it has enabled me to experience with this
exciting technology and thereby changed my direction in amateur
astronomy forever.

Enjoy your scope!

pej
--
Per Erik Jorde

Eric Johnson writes:

After ordering, but before it arrived, I realized that the ShortTube
already has a built-in barlow. Is it ok to add a second barlow to
this? I've read that stacking barlows will work, with light loss...

Yes, you can add a Barlow. However, these "short-tube" reflectors use
a fast spherical primary mirror with a built-in focal corrector. This
corrector extends the focal length (like a Barlow) and also attempts
to correct the sperical aberration (unlike a Barlow). It is not
entirely succesful in this latter function, however, and this type of
telecope is really a compromise between short tubelength and low price
on one side and optical quality on the other. It works reasonably OK
(for the price) if you don't "stress" it too much using too high
magnification or wide-angle eyepieces(*).

Tonight was the first clear night since the arrival of the barlow. I
first directed my attention to Saturn with the barlow and 10mm
eyepiece (200x magnification). I was very impressed with the size,
but just couldn't get it into sharp focus. Same thing with Mars.

200x is pressing this type of telescope a bit. 150x may be a practical
upper limit (very subjective of course). Also, be sure to collimate
the optics as best you can. This telescope is also very sensitive to
careful focusing.

*) Having said that, there is a lot of stuff to see with this
telescope. As a side note, I have been using such a short-tube for CCD
work for almost a year now and, while I hope to replace it with a
better telescope soon, it has enabled me to experience with this
exciting technology and thereby changed my direction in amateur
astronomy forever.

Enjoy your scope!

pej
--
Per Erik Jorde

Thank you for this information. As I was looking at 200x I had actually
thought 150x may be a better way to go. I'll have to look into
getting another eyepiece.

Thanks again!
EJ

Per Erik Jorde wrote:

Eric Johnson writes:


After ordering, but before it arrived, I realized that the ShortTube
already has a built-in barlow. Is it ok to add a second barlow to
this? I've read that stacking barlows will work, with light loss...


Yes, you can add a Barlow. However, these "short-tube" reflectors use
a fast spherical primary mirror with a built-in focal corrector. This
corrector extends the focal length (like a Barlow) and also attempts
to correct the sperical aberration (unlike a Barlow). It is not
entirely succesful in this latter function, however, and this type of
telecope is really a compromise between short tubelength and low price
on one side and optical quality on the other. It works reasonably OK
(for the price) if you don't "stress" it too much using too high
magnification or wide-angle eyepieces(*).


Tonight was the first clear night since the arrival of the barlow. I
first directed my attention to Saturn with the barlow and 10mm
eyepiece (200x magnification). I was very impressed with the size,
but just couldn't get it into sharp focus. Same thing with Mars.


200x is pressing this type of telescope a bit. 150x may be a practical
upper limit (very subjective of course). Also, be sure to collimate
the optics as best you can. This telescope is also very sensitive to
careful focusing.

*) Having said that, there is a lot of stuff to see with this
telescope. As a side note, I have been using such a short-tube for CCD
work for almost a year now and, while I hope to replace it with a
better telescope soon, it has enabled me to experience with this
exciting technology and thereby changed my direction in amateur
astronomy forever.

Enjoy your scope!

pej

Thank you for this information. As I was looking at 200x I had actually
thought 150x may be a better way to go. I'll have to look into
getting another eyepiece.

Thanks again!
EJ

Per Erik Jorde wrote:

Eric Johnson writes:


After ordering, but before it arrived, I realized that the ShortTube
already has a built-in barlow. Is it ok to add a second barlow to
this? I've read that stacking barlows will work, with light loss...


Yes, you can add a Barlow. However, these "short-tube" reflectors use
a fast spherical primary mirror with a built-in focal corrector. This
corrector extends the focal length (like a Barlow) and also attempts
to correct the sperical aberration (unlike a Barlow). It is not
entirely succesful in this latter function, however, and this type of
telecope is really a compromise between short tubelength and low price
on one side and optical quality on the other. It works reasonably OK
(for the price) if you don't "stress" it too much using too high
magnification or wide-angle eyepieces(*).


Tonight was the first clear night since the arrival of the barlow. I
first directed my attention to Saturn with the barlow and 10mm
eyepiece (200x magnification). I was very impressed with the size,
but just couldn't get it into sharp focus. Same thing with Mars.


200x is pressing this type of telescope a bit. 150x may be a practical
upper limit (very subjective of course). Also, be sure to collimate
the optics as best you can. This telescope is also very sensitive to
careful focusing.

*) Having said that, there is a lot of stuff to see with this
telescope. As a side note, I have been using such a short-tube for CCD
work for almost a year now and, while I hope to replace it with a
better telescope soon, it has enabled me to experience with this
exciting technology and thereby changed my direction in amateur
astronomy forever.

Enjoy your scope!

pej

Thank you for this information. As I was looking at 200x I had actually
thought 150x may be a better way to go. I'll have to look into
getting another eyepiece.

Thanks again!
EJ

One to consider: The www.scopestuff.com 15mm Widefield. In you ShortTube 4.5
EQ that would give you something 67x and 133X with the barlow, both very useful
magnfications. The eyepieces are $39 shipped and have a 66 degree FOV. They
offer Plossl like performance sharpness wise but a bigger FOV.

I had a scope similar to the your ST 4.5 EQ. Not a planet or double star
killer but I had many many memorable times with that scope.

Jon

Thank you for this information. As I was looking at 200x I had actually
thought 150x may be a better way to go. I'll have to look into
getting another eyepiece.

Thanks again!
EJ

One to consider: The www.scopestuff.com 15mm Widefield. In you ShortTube 4.5
EQ that would give you something 67x and 133X with the barlow, both very useful
magnfications. The eyepieces are $39 shipped and have a 66 degree FOV. They
offer Plossl like performance sharpness wise but a bigger FOV.

I had a scope similar to the your ST 4.5 EQ. Not a planet or double star
killer but I had many many memorable times with that scope.

Jon

Great that sounds like it's exactly what I need.

Now that you mention it, what is it about reflectors versus refractors
that makes the one better than the other for viewing planets? With your
ST, what kind of views of the planets were you able to get?

EJ


Jon Isaacs wrote:

Thank you for this information. As I was looking at 200x I had actually
thought 150x may be a better way to go. I'll have to look into
getting another eyepiece.

Thanks again!
EJ


One to consider: The www.scopestuff.com 15mm Widefield. In you ShortTube 4.5
EQ that would give you something 67x and 133X with the barlow, both very useful
magnfications. The eyepieces are $39 shipped and have a 66 degree FOV. They
offer Plossl like performance sharpness wise but a bigger FOV.

I had a scope similar to the your ST 4.5 EQ. Not a planet or double star
killer but I had many many memorable times with that scope.

Jon

Great that sounds like it's exactly what I need.

Now that you mention it, what is it about reflectors versus refractors
that makes the one better than the other for viewing planets? With your
ST, what kind of views of the planets were you able to get?

EJ


Jon Isaacs wrote:

Thank you for this information. As I was looking at 200x I had actually
thought 150x may be a better way to go. I'll have to look into
getting another eyepiece.

Thanks again!
EJ


One to consider: The www.scopestuff.com 15mm Widefield. In you ShortTube 4.5
EQ that would give you something 67x and 133X with the barlow, both very useful
magnfications. The eyepieces are $39 shipped and have a 66 degree FOV. They
offer Plossl like performance sharpness wise but a bigger FOV.

I had a scope similar to the your ST 4.5 EQ. Not a planet or double star
killer but I had many many memorable times with that scope.

Jon

Now that you mention it, what is it about reflectors versus refractors
that makes the one better than the other for viewing planets? With your
ST, what kind of views of the planets were you able to get?

EJ

Reflectors can give better planetary views than refractors of the planets
simply because they are generally bigger. But everything needs to be aligned,
the scope, the "seeiing", the planets.

The Short tube newtonian I had would show the rings of Saturn, a few moons, the
moons of Jupiter, the cloud belts, never saw a shadow transit with it.

jon