Your opinions, please...

"Alan W. Craft" wrote in message
...

I'm considering a Parks classic Newtonian,
and to mount on a Vixen GP-DX equatorial
mount. While their 8" f3.5 seems to be just
a wee bit too fast, and their 8" f6 a tad too
slow for DSO's and the like(not to mention
the tube length), I've looked into the
possibility of an 8" f5 custom-made by
Parks and sold via Scope City...

Check out the recent issue of Sky and Telescope about observing DSOs
and the merits of high or low magnification. "Slow" scopes are fine for
many such objects. The conventional wisdom dictating fast scopes simply
doesn't hold up in practice, once the other variable of vision and observing
are factored in.

Cheers,
Larry G.

LarryG wrote:
"Alan W. Craft" wrote in message
...

I'm considering a Parks classic Newtonian,
and to mount on a Vixen GP-DX equatorial
mount. While their 8" f3.5 seems to be just
a wee bit too fast, and their 8" f6 a tad too
slow for DSO's and the like(not to mention
the tube length), I've looked into the
possibility of an 8" f5 custom-made by
Parks and sold via Scope City...

Check out the recent issue of Sky and Telescope about observing DSOs
and the merits of high or low magnification. "Slow" scopes are fine for
many such objects. The conventional wisdom dictating fast scopes simply
doesn't hold up in practice, once the other variable of vision and observing
are factored in.

Not to mention that f/6 is not really all that slow. On an 8" one could
get about 2 degrees out of a 35 mm Panoptic.

--
Bill

************************************************** *************************
A conscience is what hurts when all your other parts feel so good.
---------------------------------------------------------------------------
Home page - http://www.gl.umbc.edu/~wmchal1
************************************************** *************************

The 8" f/6 is not too slow for deep sky objects. In fact, it is perfect and
the tube is not really that long. You want a 5mm to 6mm exit pupil which
translates to a 30mm to 35mm focal length eyepiece. I would suggest 2-inch
eyepieces for wide fields and there are several reasonably priced selections
on the market. The classical 7mm exit pupil is too big but even that is in
reach with a 40mm eyepiece.

A big advantage of f/6 is that you can get by without a coma corrector. At
f/5 or faster you have to start thinking about buying a corrector. Stay
away from the f/3.5! Way too much coma and it will not correct well with a
coma corrector.

Del Johnson




"Alan W. Craft" wrote in message
...

I'm considering a Parks classic Newtonian,
and to mount on a Vixen GP-DX equatorial
mount. While their 8" f3.5 seems to be just
a wee bit too fast, and their 8" f6 a tad too
slow for DSO's and the like(not to mention
the tube length), I've looked into the
possibility of an 8" f5 custom-made by
Parks and sold via Scope City...


Alan

Alan W. Craft wrote in message . ..
I'm considering a Parks classic Newtonian,
and to mount on a Vixen GP-DX equatorial
mount. While their 8" f3.5 seems to be just
a wee bit too fast, and their 8" f6 a tad too
slow for DSO's and the like(not to mention
the tube length), I've looked into the
possibility of an 8" f5 custom-made by
Parks and sold via Scope City...

"Thank you for contacting Scope City.
I have reviewed your request for
information on the Parks Optical tube
for telescopes. Based on the information
provided ( 8 inch - f/5 - F=1000, Newtonian)
you would need a 9 3/8th ID 9 3/4 OD
diameter tube, all we need to know from
you is the length you would like to purchase.
You can see a complete listing of all the
tubes Parks offers. We have many in
stock, custom order usually take a
few months."

"...the length I would like to purchase."?

Wouldn't the focal ratio determine that,
or am I missing something?

Substantially, yes, but I suppose you might want a bit longer tube
to cut down on stray light or drop the primary down a bit for some
close-to-the-tube focuser/smaller diagonal combination.


Also, please comment on the focal
ratio I've indicated...advantages...
disadvantages?

All opinions, good or bad, are most
welcome.

Alan

Like some others have said, there's nothing really wrong with an f/6
for most DSOs, IMO. FWIW.

Regards,
Russell

I'm considering a Parks classic Newtonian,
and to mount on a Vixen GP-DX equatorial
mount. While their 8" f3.5 seems to be just
a wee bit too fast, and their 8" f6 a tad too

Hi:

Well...Parks has made some nice optics over the years--if sometimes not as good
as you'd expect--but...you know, lots of Synta and Guan Sheng 8 inch f/5s are
testing out at 1/8 wave...and you can get a whole OTA for a song.

Just a thought...

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

On Thu, 24 Jul 2003 14:14:36 GMT, "Del Johnson" ...reflected:

The 8" f/6 is not too slow for deep sky objects. In fact, it is perfect and
the tube is not really that long.

I agree, and would LOVE to have the 8" f6, but
wouldn't the tube overwhelm a GP-DX mount, let
alone a standard GP? As it is, I'm thinking that
the f5 would be a bit cumbersome in its own
right, but certainly less than the f6.

I've seen the pictures. Parks places the 8" f6
on either their 'Precision,' or, more appropriately,
on their 'Superior' equatorial mounting, and not
at all onto their 'Astrolight' which bears enough
of a resemblance to either the GP or GP-DX
as to preclude their collective considerations.

You want a 5mm to 6mm exit pupil which
translates to a 30mm to 35mm focal length eyepiece. I would suggest 2-inch
eyepieces for wide fields and there are several reasonably priced selections
on the market. The classical 7mm exit pupil is too big but even that is in
reach with a 40mm eyepiece.

A big advantage of f/6 is that you can get by without a coma corrector. At
f/5 or faster you have to start thinking about buying a corrector. Stay
away from the f/3.5!

I'll take that advice, but I'm SOOOOOOOOOO
leaning towards that 8" f5. It would be, perhaps,
the ideal compromise between an f3.5 and an f6.

Way too much coma and it will not correct well with a
coma corrector.

Del Johnson

Thank you, Del.

Alan

On Thu, 24 Jul 2003 08:40:04 +0000 (UTC), William Mc Hale ...reflected:

LarryG wrote:
"Alan W. Craft" wrote in message
...

I'm considering a Parks classic Newtonian,
and to mount on a Vixen GP-DX equatorial
mount. While their 8" f3.5 seems to be just
a wee bit too fast, and their 8" f6 a tad too
slow for DSO's and the like(not to mention
the tube length), I've looked into the
possibility of an 8" f5 custom-made by
Parks and sold via Scope City...

Check out the recent issue of Sky and Telescope about observing DSOs
and the merits of high or low magnification. "Slow" scopes are fine for
many such objects. The conventional wisdom dictating fast scopes simply
doesn't hold up in practice, once the other variable of vision and observing
are factored in.

Not to mention that f/6 is not really all that slow. On an 8" one could
get about 2 degrees out of a 35 mm Panoptic.

Correct me if I'm wrong, but shouldn't the focal length of the telescope
in conjunction with the f.l. of the eyepiece, that is, the magnification,
determine whether or not a telescope is fast or slow?

While an 8" f6 would be considered fast when compared to an 8" f10,
the same 8" f6 would at the same time be equitable in "speed" to a 4" f12,
and therefore considered slow.

Such slowness is precisely what I am trying so desperately to avoid,
and in order to use the telescope for comet-hunting and widefield DSO
observation, while at the same avoiding glaring instances of coma
and exacting collimations.

Please excuse my ignorance on the matter if I've overlooked something.

Alan

On 24 Jul 2003 12:23:57 -0700, (Russell Martin) ...reflected:

Alan W. Craft wrote in message . ..
I'm considering a Parks classic Newtonian,
and to mount on a Vixen GP-DX equatorial
mount. While their 8" f3.5 seems to be just
a wee bit too fast, and their 8" f6 a tad too
slow for DSO's and the like(not to mention
the tube length), I've looked into the
possibility of an 8" f5 custom-made by
Parks and sold via Scope City...

"Thank you for contacting Scope City.
I have reviewed your request for
information on the Parks Optical tube
for telescopes. Based on the information
provided ( 8 inch - f/5 - F=1000, Newtonian)
you would need a 9 3/8th ID 9 3/4 OD
diameter tube, all we need to know from
you is the length you would like to purchase.
You can see a complete listing of all the
tubes Parks offers. We have many in
stock, custom order usually take a
few months."

"...the length I would like to purchase."?

Wouldn't the focal ratio determine that,
or am I missing something?

Substantially, yes, but I suppose you might want a bit longer tube
to cut down on stray light or drop the primary down a bit for some
close-to-the-tube focuser/smaller diagonal combination.

Are you suggesting a "low-profile" or helical focusser?

Though, I didn't understand what you meant when you wrote,
"drop the primary down a bit."

In any case, I would want the telescope to be arranged
and constructed just like the readily-available ones, but an f5
instead of an f6.

Also, please comment on the focal
ratio I've indicated...advantages...
disadvantages?

All opinions, good or bad, are most
welcome.

Alan

Like some others have said, there's nothing really wrong with an f/6
for most DSOs, IMO. FWIW.

I have this "brain cramp" that keeps telling me that you
need low, and even very low, magnification to see most
DSO's, but that's not necessarily true, is it?

Of course, you wouldn't want to use a 5mm on a galaxy.

Regards,
Russell

Alan

On 24 Jul 2003 21:36:43 GMT, (Rod Mollise) ...reflected:

I'm considering a Parks classic Newtonian,
and to mount on a Vixen GP-DX equatorial
mount. While their 8" f3.5 seems to be just
a wee bit too fast, and their 8" f6 a tad too

Hi:

Well...Parks has made some nice optics over the years--if sometimes not as good
as you'd expect--but...you know, lots of Synta and Guan Sheng 8 inch f/5s are
testing out at 1/8 wave...and you can get a whole OTA for a song.

Just a thought...

I'm intrigued. I went and looked at the "Skywatcher" 's,
and will look again, but I couldn't be assured of receiving
a primary and secondary of such a tolerance, not to
mention the Parks-like tube and component qualities.

But, no, I really couldn't count on that mirror tolerance
with Parks, either.

Also, and perhaps a minor point, the Parks mirrors are of
Pyrex. I didn't see that the Synta's were, but I didn't
research them extensively...yet.

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

Alan

"Alan W. Craft" wrote in message
...
On Thu, 24 Jul 2003 08:40:04 +0000 (UTC), William Mc Hale
...reflected:

Not to mention that f/6 is not really all that slow. On an 8" one could
get about 2 degrees out of a 35 mm Panoptic.

Correct me if I'm wrong, but shouldn't the focal length of the
telescope
in conjunction with the f.l. of the eyepiece, that is, the magnification,
determine whether or not a telescope is fast or slow?

"Fast" and "slow" are borrowed from the world of photography
in which the speed of a lens (the amount of time it takes to record
an image of proper exposure) is determined entirely by its f/number
(assuming there isn't a filter or obstruction in the light path.)



While an 8" f6 would be considered fast when compared to an 8" f10,
the same 8" f6 would at the same time be equitable in "speed" to a 4" f12,
and therefore considered slow.

No. Exactly the opposite. Speed relates to how much light a lens/mirror
can pour into a given small area at the image plane. An 8" would be able
to put four times the amount of light that a 4" could deliver into the same
area.



Such slowness is precisely what I am trying so desperately to avoid,
and in order to use the telescope for comet-hunting and widefield DSO
observation, while at the same avoiding glaring instances of coma
and exacting collimations.

Please excuse my ignorance on the matter if I've overlooked
something.

Alan


Again, please find and read the Sky and Telescope article. There are many
other
factors than just scope speed.

Cheers,
Larry G.