Request for opinions on telescope parts

I'm going to be sending my newly polished mirror out for coating shortly,
and I wanted to get some feedback from the group about the parts I'm
planning on using to build my scope.

I'm not an engineer, and I don't have any kind of useful toolshop, so making
a focuser, spider, or mirror cell is not an option.

Cash is a definite concern. I want to keep the prices down, but still get
decent equipment.

For coating the mirror, I'm planning on going with L&L Optical, as that's
the coater that Bob Royce uses.

For the focuser, I'm planning on using JMI's RCF-1 kit with the 1.25"
eyepiece adapter.
http://www.jimsmobile.com/rcf_data.htm

For the spider, I'm going with Gary Wolanski's spider with the offset spider
vanes. The offset vanes should eliminate the possibility of the spider
rotating at all.
http://www3.bc.sympatico.ca/gwolanski/SPIDERS.HTM

For the mirror cell, I'm getting a University Optics cell.
www.universityoptics.com/moreATM.htm

For the secondary, I'm going to go with one from Antares Optical
http://www.antaresoptics.com/SecEM.html

I have some questions about the size of my diagonal. I've been working with
Newt 2.5 to try and figure out the size diagonal to get. I'm planning on
using my scope for everything from planetary and lunar work to deep sky.

The three standard sizes of diagonals that I'm considering are as follows:

1.3". Angular view for 100% illuminated are is 0.13 degrees. For the 75%
area is 0.81 degrees. 16% obstruction.
1.52". Angular view for 100% illuminated are is 0.40 degrees. For the 75%
area is 1.06 degrees. 19% obstruction
1.83". Angular view for 100% illuminated are is 0.69 degrees. For the 75%
area is 1.43 degrees. 23% obstruction

What would you suggest, and why?

Thanks.

Clear Skies!

Tom Karpf

What diameter primary ? and what focal length ?
jc

--
http://mysite.wanadoo-members.co.uk/jc_atm/

PS, try Woden Optics diagonal calc.

--
http://mysite.wanadoo-members.co.uk/jc_atm/

What diameter primary ? and what focal length ?

A couple of years ago I built a plywood and sonotube
Dob for my Mum, and while I used commercial optics,
I made the mirror cell myself from a design Gary
Seronik published in Sky & Telescope (May 2002).
Hacked it out on the kitchen table with a jigsaw
and a hand drill. Ugly as hell (my fault, not Gary's),
but works like a charm.

Laura Halliday VE7LDH "Que les nuages soient notre
Grid: CN89mg pied a terre..."
ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte

It's an 8", f/6.8. 1380mm focal length.


"John Carruthers" wrote in message
...
What diameter primary ? and what focal length ?
jc

--
http://mysite.wanadoo-members.co.uk/jc_atm/

wrote in message
om...
I'm going to be sending my newly polished mirror out for coating
shortly,
and I wanted to get some feedback from the group about the parts I'm
planning on using to build my scope.

I'm not an engineer, and I don't have any kind of useful toolshop, so
making
a focuser, spider, or mirror cell is not an option.

Cash is a definite concern. I want to keep the prices down, but still
get
decent equipment.

For coating the mirror, I'm planning on going with L&L Optical, as
that's
the coater that Bob Royce uses.

For the focuser, I'm planning on using JMI's RCF-1 kit with the 1.25"
eyepiece adapter.
http://www.jimsmobile.com/rcf_data.htm

For the spider, I'm going with Gary Wolanski's spider with the offset
spider
vanes. The offset vanes should eliminate the possibility of the spider
rotating at all.
http://www3.bc.sympatico.ca/gwolanski/SPIDERS.HTM

For the mirror cell, I'm getting a University Optics cell.
www.universityoptics.com/moreATM.htm

For the secondary, I'm going to go with one from Antares Optical
http://www.antaresoptics.com/SecEM.html

I have some questions about the size of my diagonal. I've been working
with
Newt 2.5 to try and figure out the size diagonal to get. I'm planning
on
using my scope for everything from planetary and lunar work to deep sky.

The three standard sizes of diagonals that I'm considering are as
follows:

1.3". Angular view for 100% illuminated are is 0.13 degrees. For the
75%
area is 0.81 degrees. 16% obstruction.
1.52". Angular view for 100% illuminated are is 0.40 degrees. For the
75%
area is 1.06 degrees. 19% obstruction
1.83". Angular view for 100% illuminated are is 0.69 degrees. For the
75%
area is 1.43 degrees. 23% obstruction

What would you suggest, and why?

Personally, I'd go with the 1.52 secondary. It's a good compromise for
excellent images on all the objects you mention. You could go up or down,
if you wanted to specifically explore the planets, or just do DSO's, but
for all-around performance, the 1.52" is hard to beat...

I like your choices otherwise, except, perhaps, the UO primary cell. It
will be OK (and they also have a new one for which I have no data), but I
might choose a DAR primary cell, myself. You'll do fine with the UO, but
I think you'd will like the DAR better over the long haul...
http://www.oneilphoto.on.ca/oneilatm.htm

Jan Owen


Thanks.

Clear Skies!

Tom Karpf

It's an 8", f/6.8. 1380mm focal length.

To fully illuminate the field you'd need a 2.33" (minor axis) mirror.
I think this a little on the large side, it's the same as my 10" F6.1,
so you could get away with 1.75" , losing some of your hard won
photons but decreasing the central obstruction. It's swings and
roundabouts, I tried mine with a 1 1/8" but it was just too much.
jc

from the Woden optics calculator;
Field Radius %Illumination Magnitude Drop
0.50 100.00% 0.000
0.55 98.22% 0.019
0.60 95.19% 0.054
0.65 91.52% 0.096
0.70 87.46% 0.145
0.75 83.14% 0.201
0.80 78.63% 0.261
0.85 74.00% 0.327
0.90 69.31% 0.398
0.95 64.57% 0.475
1.00 59.84% 0.558




--
http://mysite.wanadoo-members.co.uk/jc_atm/

For the focuser, I'm planning on using JMI's RCF-1 kit with the 1.25"

eyepiece adapter.
http://www.jimsmobile.com/rcf_data.htm

Hi:

I'm probably better known as an amateur telescope _buyer_ than an
amateur telescope _maker_, but I've built a couple over the years, and
even done 3.5 mirrors (it's a long story) ;-)

I can at least offer my experience witht the JMI focuser.

I put this very focuser on the 6 inch dob Pat Rochford and I (mainly
Pat Rochford ;-)) built for my daugher. Works great...just about as
good as their DX3 in my opininion. You _will_ have to take some time to
adjust it to get the right feel. Also, JMI seems to have a bad habit of
leaving parts out the kit. That happened on the kit I bought for
Elizabeth's scope, and, considerably later, on one Pat bought. When the
kit arrives, check carefully for parts and make sure all holes have
been drilled as they should be.

Peace,
Rod Mollise
Author of:_Choosing and Using a Schmidt Cassegrain Telescope_
http://members.aol.com/RMOLLISE/index.html

"Jan Owen" wrote

Personally, I'd go with the 1.52 secondary. It's a good compromise for
excellent images on all the objects you mention. You could go up or down,
if you wanted to specifically explore the planets, or just do DSO's, but
for all-around performance, the 1.52" is hard to beat...

I like your choices otherwise, except, perhaps, the UO primary cell. It
will be OK (and they also have a new one for which I have no data), but I
might choose a DAR primary cell, myself. You'll do fine with the UO, but
I think you'd will like the DAR better over the long haul...
http://www.oneilphoto.on.ca/oneilatm.htm

I agree with Jan all the way. The DAR cells are excellent, and are custom
sized for the I.D. of your tube. As for the secondary size, I'm using a
1.52" in my 8" f/6, and I believe the 100% illuminated field on mine is
about 0.40". That's plenty. Your system at f/6.8 is even longer, and the
longer the f/l of the primary, the smaller the secondary you need for the
same size 100% illuminated field. If you design your system such that your
focal plane is set 1/2" above the focuser's minimum height, you'll do fine
with 1.52", even on deep sky, and have a 19% obstruction. Good luck with it.

Howard Lester

"DustyMars" wrote in message
.. .
In article ,
says...

"Jan Owen" wrote

Personally, I'd go with the 1.52 secondary. It's a good compromise
for
excellent images on all the objects you mention. You could go up or
down,
if you wanted to specifically explore the planets, or just do DSO's,
but
for all-around performance, the 1.52" is hard to beat...

I like your choices otherwise, except, perhaps, the UO primary cell.
It
will be OK (and they also have a new one for which I have no data),
but I
might choose a DAR primary cell, myself. You'll do fine with the
UO, but
I think you'd will like the DAR better over the long haul...
http://www.oneilphoto.on.ca/oneilatm.htm

I agree with Jan all the way. The DAR cells are excellent, and are
custom
sized for the I.D. of your tube. As for the secondary size, I'm using
a
1.52" in my 8" f/6, and I believe the 100% illuminated field on mine
is
about 0.40". That's plenty. Your system at f/6.8 is even longer, and
the
longer the f/l of the primary, the smaller the secondary you need for
the
same size 100% illuminated field. If you design your system such that
your
focal plane is set 1/2" above the focuser's minimum height, you'll do
fine
with 1.52", even on deep sky, and have a 19% obstruction. Good luck
with it.

Howard Lester



You're right if this is to be used mostly for DSO's. I would go to
either 1.33" or 1.25" for mostly planetary work. Would be plenty of
field (0.25" and 0.34" respectively) for most eyepieces
--

But the OP specifically spelled out that he plans to use the scope for
EVERYTHING from lunar/planetary to DSO's. So installing a small secondary
in that sense, while it WILL work, is not optimal for the DSO side of his
equation... A 1.52" will deliver a great all around scope in his context.

However, he's certainly free to use any secondary mirror size he wishes.

Incidentally, I have owned an 8" f/6 for over 20 years, and have had 1.3",
1.52", and 1.83" secondaries in it at different times over the years. I
even had the scope set up for a (relatively) quick change-over from one
size to another, for a while. But I long ago settled on the 1.52" for all
uses, and have been happy with that choice everafter...

Your mileage may vary...

Jan Owen