New focuser or not?

I use a Meade Starfinder 16" dob that I've had nearly 10 years now, I
guess. In all that time, I've made many modifications to the scope to
improve its ease of use, but one part is still the original stock
equipment - the 1 1/4" rack-and-pinion focuser that came with the unit.


I've never replaced the focuser because I've never felt strongly
compelled to do so. It has always worked well - never slips or binds,
doesn't image shift, and causes me no grief, particularly since I only
observe visually through it. I've always resisted replacing it as my
own personal astro anti-snob symbol. The only real benefit I see from
going to an NGF or similar would be finer focusing control, but that
seems a pretty small gain for the money. I have no 2" exclusive
eyepieces - all of my Naglers are dual fit units. Replacing it would
only start me down the slippery slope of justifying $300-$400 2"
eyepieces to fill the bigger hole in the focuser.

I guess my question is to ask if anyone can convince me otherwise.
Have I talked myself out of substantial benefits of which I might not
be aware? Are there hidden factors that scream "replace it" that I've
missed? I can see some situations where such a change is surely
justified - I can't stand the built-in focuser on my LX90, f'r
instance. Am I missing something here? Just about every single
mid-size dob I've ever seen in the field has a better focuser, but I
don't just want to succumb to pointless equipment envy.

BTW - anyone going to the Oregon Start Party this year? Been there
every year since about '94. I can't wait for my annual dose of reddish
dust in every crack and crevice of my equipment and vehicle.

Restricting yourself to 1.25" eyepieces makes it impossible to use the
full field of view in your scope. Even a 16mm Nagler (the largest 1.25"
Nagler I believe) only has a field stop of 22mm (or thereabouts), while
a 31mm Nagler has a field stop of 42mm or almost double the field size
and 4 times the visible field!

It is correct to say that the only reason to get a 2" focuser is if you
are going to get some 2" eyepieces. However, the views of these monster
EPs is so awesome that the view alone justify the expense (at least for
me). In fact, In my EP collection I only have 1 ((out of 6) operating
eyepiece that only fits in a 1.25" barrel (the 7mm Nagler) and the 2"
powermate to enable use of these at higher powers.

On to the focuser: I think the planetary (fine focus) controls are
worth the cost of the high dollar NGF and StarLight focusers. You can
make increadably fine adjustments without inducing vibrations into the
scope.

But if you never want to see the whole of M31, then just continue on
with your current focuser.

Hi, Mitch has summed it up quite well, and there's not much I can add
to Mitch's good explanation.

Surprising that this 16" Reflector originally came with only a 1-1/4"
Focuser, but I'll take your word for it.

If you should decide to take the eventual plunge to 2" Oculars, I would
imagine that there are other 2" Focuser options you could persue, from
perhaps other people, no doubt including Meade themselves.

Perhaps people like University Optics, Apogee, and no doubt a number of
others (Parks?)which could possibly provide a good solid sound 2"
Focuser without all the bells, and whistles.

The Feathertouch is virtually without peer, other than Van Slyke
Engineering, but both with set you back some dinero.

After almost a year of use, my friend decided to upgrade his Intes MN-61
Mak-Newtonian from a standard Intes "Horrible Helical" to a 2" Starlight
Feathertouch Focuser. IMO, it was the best thing he could ever do to
that particular scope. It was an absolute joy to use after this
upgrade.

As Mitch explains, you are missing much wide field, low power capability
with your 16". The choice must ultimately be yours, Yep, eyepiece
collections alone sometimes can exceed the investment of the Telescope
itself. Mark

I put the $165 moonlite on my 8" reflector----It's beautiful. But for me,
crappy mechanics distracts from viewing because I feel like I can't get
things exactly right. The smoothness of the new focuser is like driving a
fine car---I enjoy the ride more. If you're only looking to go from here to
there---why bother?

Doink
"Mark D" wrote in message
...
Hi, Mitch has summed it up quite well, and there's not much I can add
to Mitch's good explanation.

Surprising that this 16" Reflector originally came with only a 1-1/4"
Focuser, but I'll take your word for it.

If you should decide to take the eventual plunge to 2" Oculars, I would
imagine that there are other 2" Focuser options you could persue, from
perhaps other people, no doubt including Meade themselves.

Perhaps people like University Optics, Apogee, and no doubt a number of
others (Parks?)which could possibly provide a good solid sound 2"
Focuser without all the bells, and whistles.

The Feathertouch is virtually without peer, other than Van Slyke
Engineering, but both with set you back some dinero.

After almost a year of use, my friend decided to upgrade his Intes MN-61
Mak-Newtonian from a standard Intes "Horrible Helical" to a 2" Starlight
Feathertouch Focuser. IMO, it was the best thing he could ever do to
that particular scope. It was an absolute joy to use after this
upgrade.

As Mitch explains, you are missing much wide field, low power capability
with your 16". The choice must ultimately be yours, Yep, eyepiece
collections alone sometimes can exceed the investment of the Telescope
itself. Mark

I put the $165 moonlite on my 8" reflector----It's beautiful. But for
me, crappy mechanics distracts from viewing because I feel like I can't
get things exactly right. The smoothness of the new focuser is like
driving a fine car---I enjoy the ride more. If you're only looking to go
from here to there---why bother?
Doink
======================================

I understand exactly where you're coming from Doink. Pretty much, a 2"
Focuser that will be compatible for a 16" Reflector (Probably has at
least a 17"-18" Tube, will set you back about $100-$125. So the slight
increase in $$$ to perhaps go the Moonlite route wouldn't be too much of
an increase in price.(Depends what a compatible Focuser base mount would
cost)

I haven't pulled up current exact costs for the Starlight Feathertouch
for a Newtonian with a needed compatible base, (there are a few
different drawtube lengths available) but it's probably getting near
double what the Moonlight cost.

The 2-speed option on these focusers make them a real joy to use, and
really facilitate nailing down precise focus, especially with fast FL
Scopes.

I have a new design Feathertouch on my Celestron C-14, with a Starlight
custom adapter which couples the FT directly to the large rear 3.16"
port on the C-14. They have the capability to handle large eyepieces,
heavy diagonals, bino-viewers, and imaging equipment with ease.

The original poster may be seeking a more ecomonical alternative though,
and that's why I mentioned other options-focusers, that he could perhaps
persue-look into should he choose. Mark

wrote in message
oups.com...

I guess my question is to ask if anyone can convince me otherwise.
Have I talked myself out of substantial benefits of which I might not
be aware?

The ability to get a larger field of view.

True field of view
= field stop of eyepiece
/ focal length of telescope
* 57.3

A 1.25" focuser allows for an eyepiece with a 27mm field stop.

A 2" focuser allows for an eyepiece with a 46mm field stop.

Your scope has a focal length of 1827mm. Your maximum field of view would be
(47mm / 1827mm * 57.3) 1.5 degrees. Although realistically, because of the
following formula, you will be limited 32mm and smaller eyepieces.

Exit pupil
= focal length of eyepiece
/ f-ratio of scope

Maximum exit pupil of 7mm in a F4.5 = 7 * 4.5, or 31.5mm focal length
eyepiece

You could add a 2" focuser and spend $90 on a 30mm WideScan clone which will
provide about 1.3 degrees. This is nearly a half degree more than what you
can get with the largest field stop in a 1.25" eyepiece. However, the
performance of these eyepieces is pretty bad for a large area of the outer
edge.

You could spend roughly $600 and get the 31mm Nagler T5, which will be much
better corrected for edge of field performance. But to truly get the most
out of it, you will want to add the ParaCorr to get rid of the coma inherent
in the paraboloidal primary mirror, which then increases the focal length of
your telescope by 15%, or in your case, to 2100mm. This then has the effect
of decreasing the field of view by 15%, or in the case of the aforementioned
eyepieces, to 1.1 degrees (you lose nearly 1/4 degree, half the width of the
full moon).

I'm not going to make the value judgement for you of its worth, but there
you have it.

Personally, I have a Meade Starfinder 12.5" and rarely use my only 2"
eyepiece, a 35mm Panoptic. I do have a Paracorr and a 24mm Panoptic (a 1.25"
eyepiece with the largest possible field stop of 27mm). In my scope that all
works out to a tack sharp 0.88 degree field of view. That's only a little
larger (although quite a bit sharper across the field) than what you can get
out of your scope without a Paracorr, and with a 32mm Plossl, or a 24mm
Panoptic.

In the final analysis, I find that the primary value of my 2" focuser, is
that it allows me to use the ParaCorr.

-Stephen Paul

Stephen Paul wrote:
wrote in message
oups.com...

I guess my question is to ask if anyone can convince me otherwise.
Have I talked myself out of substantial benefits of which I might not
be aware?

The ability to get a larger field of view.

True field of view
= field stop of eyepiece
/ focal length of telescope
* 57.3

A 1.25" focuser allows for an eyepiece with a 27mm field stop.

A 2" focuser allows for an eyepiece with a 46mm field stop.

Your scope has a focal length of 1827mm. Your maximum field of view would be
(47mm / 1827mm * 57.3) 1.5 degrees. Although realistically, because of the
following formula, you will be limited 32mm and smaller eyepieces.

Exit pupil
= focal length of eyepiece
/ f-ratio of scope

Maximum exit pupil of 7mm in a F4.5 = 7 * 4.5, or 31.5mm focal length
eyepiece

Correct, which is why the lowest magnification eyepiece I typically use
is a 32mm Televue Plossl, which with an apparent FOV of 65 degrees
provides a view of roughly 1.1 degrees at 57x. Not the theoretical
maximum perhaps, but perfectly reasonable. I can use a 40mm, but the
lost light and secondary shadow mean that I typically don't. The view
with the Plossl is sharp all the way to the edge, which is definitely
NOT the case with the 12mm Nagler T2 I often use (as you note in your
discussion about the ParaCorr). For high-mag, my Radians do a great
job at inch-and-a-quarter.

You could spend roughly $600 and get the 31mm Nagler T5, which will be much
better corrected for edge of field performance. But to truly get the most
out of it, you will want to add the ParaCorr to get rid of the coma inherent
in the paraboloidal primary mirror,

So now we're talking nearly $1000 for a focuser, eyepiece, and
ParaCorr. I know that no one else can make a value jugdement for me,
but that pushes the envelope of my incremental cost of improvement
threshold.

Personally, I have a Meade Starfinder 12.5" and rarely use my only 2"
eyepiece, a 35mm Panoptic. I do have a Paracorr and a 24mm Panoptic (a 1.25"
eyepiece with the largest possible field stop of 27mm). In my scope that all
works out to a tack sharp 0.88 degree field of view. That's only a little
larger (although quite a bit sharper across the field) than what you can get
out of your scope without a Paracorr, and with a 32mm Plossl, or a 24mm
Panoptic.

In the final analysis, I find that the primary value of my 2" focuser, is
that it allows me to use the ParaCorr.

Actually, that last statement is the kind of insight I was looking for.
Coma is definitely noticeable at f4.5, and does degrade the image in
my scope. I've never been able to get my hands on a ParaCorr to
experiment with, but that might be justification enough in the long
run.