Expert: Tom Whiting - 2/22/2004

Question
I am planning to reenter the hobby of astronomy after many years.  I had just a very basic reflector scope and now I am checking out various items on Astromart.  Many terms confuse me.  Could you explain them?
diagonal
wedge  super wedge
dovetail
Losmandy dovetail
plate
the various mounts (I ma interested in a scope with the goto feature)
visual back
1/7 wave
hand paddle

Thanks for all your help.
Casey

Answer
Casey,
would have answered this last night, but the allexperts
website was down....could not access it...
tw



Casey,
I've found that its much better to take 6 months or so,
and learn the naked-eye night sky, and avoid the so-called "goto" features, and use the extra money to buy high quality optics, or even a bigger aperture.

It's really not that hard....constellations (as you probably
know) are just area's of the sky....if you can memorize the
4 adjoining states PA, OHIO, IND, ILLINOIS, then you can
also learn and memorize Gemini, Cancer, Leo, and Virgo....
4 adjoining constellations.

Also, have you as yet had enough astronomical experience
to decide on what you want to specialize in?....DSO's
(Deep Sky Objects), lunar/planetary detail, comet hunting,
variable stars, splitting double/multiple stars, asteroid
viewing/hunting, etc etc. There is just too much not
to specialize....and depending on what you decide, will determine what kind of scope you want. There is a scope that maximizes each of those above activities.....all planes fly, but you don't send a bomber to do a fighters job,
and vice-versa, and scopes are almost the same way.

Another thing...join a local astronomy club for additional
advice and help...this way, you can check out the other
members scopes, and see how they feel about it.

But to your question...some of which I am not that familar
with because I am strictly eyeball to the eyepiece, and I
am my own finder and my own goto, and my own clockdrive....
ie...strictly manual operation.

1. Diagonal...any small mirror/prism that directs the light
at a 90 degree angle...examples are the secondary mirror
of our Newtonian reflectors...that is called the diagonal
mirror. Other examples are the 90 degree device on the
end of a refractor telescope that allows for eye and head
comfort when a refractor is pointing high in the sky, so
the observer does not have to lay on the ground looking
thru the scope. Term is also used for right angle finder
scopes, but I don't like them.

2. Wedge...the plate you mount a scope that allows it to
perform as an equatorially mounted scope as opposed to
alt-azimuth; the wedge angle from the horizon will be
the same as your latitude, so your polar axis points to
the North Celestial Pole (near Polaris) as it has to for
an equatorial mount to work properly.

3. Dovetail...the "V" shaped mount that holds a visual
finder scope on the main scope...dovetail holders allow
you to remove and mount your visual finderscope very easily.

4. Losmandy mount and plate....(?)..sorry, I have no idea...
I don't do photography or have clock-drive on my scopes, so
perhaps those terms relate to those activities.

5. Various Mounts...well, there is the basic equatorial where only one motion will follow the night sky. There
is also the alt-azimuth, including DOB (Dobsonian) mounts
which are the simplest, but require two motions....up/down
and left/right to maintain the image in the eyepiece.
Which to use depends on what you want, and in a way, how
big or small your scope is (?). This is where experience
comes in, and attendance at those club star parties that you
will be invited to.

6. Visual back...simply an eyepiece holder that holds a
visual eyepiece, as opposed to a camera, spectroscope,
photometer, or other piece of auxiliary equipment.

7. Hand paddle...not sure, as I have no electrical equipment on my scopes, but I believe that is the control device on
a "goto" scope, called the hand paddle.

8. 1/7 wave....an expression, or amount, of quality of
your optics. All telescopes must meet the criteria of
a certain fraction of a wavelength of light which is about
16 millionth of an inch...the poorer ground and polished
surfaces are 1/4 wavelength, or about 4 millionths of an
inch from perfection, both in parabolic shape for the mirror and the smoothness of the glass.
This is a bare minimum! Anything worse, is a piece of junk,
as are so called 'department store' telescopes. Your equipment must meet the 1/4 wavelength criteria!

Most of us amateur astronomers want much better images and
thus better optics, and generally will not accept anything
less than 1/8 or even 1/10 wave....2 millionths of an
inch or better. The better the grind and figure on a glass,
the better the image, thus you can go to higher magnifications without much degradation of the image, which you cannot do with worse than 1/4 wave, or presumably, anything less than 1/8 wave....thus I would not purchase something advertised at 1/7 wave, which is worse than 1/8 wave.

This is the real reason that our mirrors are so expensive;
you are paying for that exquisite grind, polish, and figure
on your mirror surfaces (or lens if refractor)....and its
darn well worth it, IF you really want to go into this
hobby in the proper way....who wants a crappy image?
No one. So good telescopes are so costly, just like
H-D motorcycles, boats, and airplanes....which need maintenance, insurance, license, registration, gasoline,
storage facility, did I mention maintenance?
We need none of that.
All we need is a few extra eyepieces and a good star atlas.

So you cost-average our hobby over a 20 year period,
and really it isn't so bad, is it?

Also, I don't know where you are from, but here in Erie, PA
boats and motorcycles are in storage all winter long...but
not my scope....I can use it year round.

Hope all this helps,
Clear Skies,
Tom Whiting
Pres...ECMOG
Please visit our club website at:
http://www.velocity.net/~bwhiting/


FOLLOW UP:
Casey,
I just remembered; I had a 24 inch portable DOB truss-type
for sale on Astromart a few months ago...didn't sell,
so I still have it (it was replaced by my 30 inch
portable).  Can be seen on our website under the photo
section....if you, or anyone else is interested,
contact me at 814-864-9203 as it is still available.
Asking $5295 for it...Nova optics to 1/10 wave...
Or at bwhiting@velocity.net
Thanks, and Clear Skies,
Tom Whiting
Erie, PA