reflex finders

(Bobsprit) wrote in message ...
I could cite many
other examples of how to use the Telrad's multi-ring reticle to find
objects which are not visible in even my 8x50 finder, so the

Can you explain how much light the Telrad collects to do this? I've used them,
but I never had the impression that the Telrad collected more light than a 50mm
objective.

Capt RB

The Telrad does *not* collect light. It is a "heads-up" style reticle
projecting finder which projects three dim concentric rings (of
fully-adjustable brightness from bright to dim or even off) on a plate
of glass which you look through to see the sky. The rings are half a
degree, two degrees, and four degrees across. It is the placement of
this pattern on the sky relative to visible stars which helps in
finding things in the main telescope. For one example, put one edge
of the 2 degree ring on Zeta Tauri with the center of the reticle
shifted in the direction of the star Alnath (Beta Aurigae), and the
scope will be pointed towards the Crab Nebula M1. For another
example, put the star Nu Aquarii halfway between the 2 and 4 degree
rings at a point where the center of the reticle is almost due-west of
Nu, and the scope should be pointed towards the "Saturn Nebula" NGC
7009. Most star atlases have Telrad overlays with them which can be
positioned over any object you choose. Once positioned, the stars
around and between the rings of the reticle overlay will be the ones
which will give the visual clues as to where the scope should be
pointed. All the observer has to do is duplicate with the real
reticle on the sky with what is shown on the atlas as far as the
position of the stars and reticle is concerned, and the field where
the object is located should appear in a low-power eyepiece. I use
the software MEGASTAR, and it also has the Telrad reticle built-in, so
I can instantly see what patterns I should make. I can also use the
reticle in extended "star-hopps", to judge precise distances and
directions of travel to go from the stars to the field of the object I
want to find. The observer can also use the "bulls-eye" formation
just to point the telescope at objects which are visible as well as
those which are too faint to see with the unaided eye, using nearby
stars as reference. Examples of this "bulls-eye" method include
putting the center of the reticle a third of the way between Eta and
Zeta Herculis, and the telescope should be pointed at the globular
cluster M13, or putting the center of the reticle just over halfway
between Gamma and Beta Lyrae to locate the Ring Nebula (the outer
edges of the 2-degree circle almost touch both stars). The 3-ring
bulls-eye seems to be more effective at positioning the telescope for
these "point and shoot" finding exercises than the simple "red dot"
finders are. Again, there is nothing wrong with having a good optical
finder (I use both a Telrad *and* an 8x50 finderscope), but the Telrad
is also very useful in getting the telescope pointed at objects which
are invisible both with the unaided eye and in a finderscope. Clear
skies to you.

David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

but the Telrad
is also very useful in getting the telescope pointed at objects which
are invisible both with the unaided eye and in a finderscope. Clear
skies to you.

While I agree that both items are welcome riding the tube, I can't see how he
telrad will do what the original poster was asking. A 50 mm objective with a
mag factor of 8 will collect more light than the human eye, will it not? The
narrower field is a factor, but only relative to finding objects, not actually
seeing them. I always thought a proper finder would be something like 4x90 or
so! Maybe someone will build one.

Capt RB
NY

but the Telrad
is also very useful in getting the telescope pointed at objects which
are invisible both with the unaided eye and in a finderscope. Clear
skies to you.

While I agree that both items are welcome riding the tube, I can't see how he
telrad will do what the original poster was asking. A 50 mm objective with a
mag factor of 8 will collect more light than the human eye, will it not? The
narrower field is a factor, but only relative to finding objects, not actually
seeing them. I always thought a proper finder would be something like 4x90 or
so! Maybe someone will build one.

Capt RB
NY

(Bobsprit) wrote in message ...
but the Telrad
is also very useful in getting the telescope pointed at objects which
are invisible both with the unaided eye and in a finderscope. Clear
skies to you.

While I agree that both items are welcome riding the tube, I can't see how he
telrad will do what the original poster was asking. A 50 mm objective with a
mag factor of 8 will collect more light than the human eye, will it not? The
narrower field is a factor, but only relative to finding objects, not actually
seeing them. I always thought a proper finder would be something like 4x90 or
so! Maybe someone will build one.

Capt RB
NY

The original poster asked:

"I have a 6" dobsonian scope with a 6 X 30 standard finder scope. I
can do fine with this finder on single bright stars and planets but
seem to get lost when looking for dim objects. Should I stick with
this finder until I can use it or consider going to a 0 power reflex
finder of some sort?"


It is obvious from this that he gets lost trying to find dim objects
when using the 6x30 finder. A finder (whether telescopic or reflex)
is for helping to *find* things in the main telescope, and *not*
necessarily for viewing them (viewing is the job of the main
telescope). A Telrad will allow the user to point the telescope to
the location of the dim objects which he wants to see with his 6 inch
Dob. Thus, it *will* be able to do what the original poster wanted.
There are many faint objects like galaxies and planetary nebulae which
are within range of a 6 inch Dob but which a simple 50mm finder will
be completely unable to show. This does not mean that the 50mm finder
is useless for finding things, as it can be of help in pointing the
main scope to the right spot on the sky, but it does mean that the
finder is not necessarily used for viewing them. I can see the large
spiral galaxy M33 in my 8x50 finder, but do I want to view it with
that finder? Nope, the 10 inch main telescope is far more effective
for that. In fact, I won't often use my 8x50 finder to point the
scope at M33. All I have to do is position the center of the Telrad
reticle about halfway between Alpha Triangulae and Tau Piscium (with a
slight northward offset of about one innermost ring width (0.5
degree)), and my 10 inch scope will be pointed at that galaxy. This
is the proper way to use the Telrad, not as a simple "bulls-eye"
pointer, but as a "pattern maker". Those who think the Telrad is only
good for finding things which are visible to the unaided eye don't
really know how to use a Telrad. Clear skies to you.

David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

(Bobsprit) wrote in message ...
but the Telrad
is also very useful in getting the telescope pointed at objects which
are invisible both with the unaided eye and in a finderscope. Clear
skies to you.

While I agree that both items are welcome riding the tube, I can't see how he
telrad will do what the original poster was asking. A 50 mm objective with a
mag factor of 8 will collect more light than the human eye, will it not? The
narrower field is a factor, but only relative to finding objects, not actually
seeing them. I always thought a proper finder would be something like 4x90 or
so! Maybe someone will build one.

Capt RB
NY

The original poster asked:

"I have a 6" dobsonian scope with a 6 X 30 standard finder scope. I
can do fine with this finder on single bright stars and planets but
seem to get lost when looking for dim objects. Should I stick with
this finder until I can use it or consider going to a 0 power reflex
finder of some sort?"


It is obvious from this that he gets lost trying to find dim objects
when using the 6x30 finder. A finder (whether telescopic or reflex)
is for helping to *find* things in the main telescope, and *not*
necessarily for viewing them (viewing is the job of the main
telescope). A Telrad will allow the user to point the telescope to
the location of the dim objects which he wants to see with his 6 inch
Dob. Thus, it *will* be able to do what the original poster wanted.
There are many faint objects like galaxies and planetary nebulae which
are within range of a 6 inch Dob but which a simple 50mm finder will
be completely unable to show. This does not mean that the 50mm finder
is useless for finding things, as it can be of help in pointing the
main scope to the right spot on the sky, but it does mean that the
finder is not necessarily used for viewing them. I can see the large
spiral galaxy M33 in my 8x50 finder, but do I want to view it with
that finder? Nope, the 10 inch main telescope is far more effective
for that. In fact, I won't often use my 8x50 finder to point the
scope at M33. All I have to do is position the center of the Telrad
reticle about halfway between Alpha Triangulae and Tau Piscium (with a
slight northward offset of about one innermost ring width (0.5
degree)), and my 10 inch scope will be pointed at that galaxy. This
is the proper way to use the Telrad, not as a simple "bulls-eye"
pointer, but as a "pattern maker". Those who think the Telrad is only
good for finding things which are visible to the unaided eye don't
really know how to use a Telrad. Clear skies to you.

David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

Those who think the Telrad is only
good for finding things which are visible to the unaided eye don't
really know how to use a Telrad. Clear skies to you.

All excellent points, David. Thank you.

Capt RB

Those who think the Telrad is only
good for finding things which are visible to the unaided eye don't
really know how to use a Telrad. Clear skies to you.

All excellent points, David. Thank you.

Capt RB