From: "Herb Kasler" 
To: 
Reply-To: "Herb Kasler" 


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Hello all,

On my last observing session (in the vicinity of Bridgeport, CA),  I was =
looking at M51 with my 16" f/4 newt and thinking "well, that's
pretty = good, but it ain't really knockin' my socks off". I think the
real = thrill of amateur astronomy for me is the idea of looking at some
galaxy = and actually seeing those spiral arms, like in the pictures. Or
clearly = seeing the color in a nebula. Even with my 16" scope, you
need averted = vision to see the arms on almost everything, and only the
brightest = nebulae have any hint of color. Obviously, you can never
actually see = things as well as the cameras can, but ultimately, I think I
can do = better than what I have now. I know that if I got a CCD setup I
could do =
 much better with what I have, but the idea of taking pictures and =
looking at those just desn't put the cheese in my macaroni. After all, =
the HST will always put my measly pictures to shame. But to have those =
photons travel 50 million light years straight into my head, now that's =
groovy. Perhaps this is what they call aperture fever...

Anyhoo, I think I'm eventually going to have to build a bigger scope = than
the one I have in order to be fully self-actualized. I'm thinking = maybe
32-36" would allow me to go to my grave content (I'm not old or =
anything, this is what you'd call a very long-term project). If the =
improvement in what you see is as much as the difference between 8"
and = 16", then I think for me it would ultimately be worth the effort
and = expense.

There are some constraints to my ultimate scope design. For one thing I =
do NOT want to stand on top of a big ladder to look through it. = Therefore
it will have to be a cassegrain of some sort. I think I would = go for a
Nasmyth focus directed out the altitude axis, so that I can = have a
comfortable viewing chair that I can stay in. It does not have to = be
easily portable. It will be in an observatory on my (hypothetical) =
vacation property in the middle of nowhere. It should be relatively =
compact, so that if necessary it can be moved, and so that I don't have =
to build a giant enclosure for it. I also want to be able to use it at =
the lowest practical visual magnification (around 120X, I guess) and for =
rich field photographic applications sometimes (it's not that I *never* =
want to take pictures...). So the primary should be around f/3, for an =
effective ratio of f6-f/8. Full aperture correctors, obviously, are = right
out. So I guess I'm looking at a classical, DK, or RC cassegrain. = Unless
someone has a better idea that will meet those criteria...

So the question is, which of these three designs is the best to pursue? =
Clearly, the DK would be the easiest to make, but can the coma be dealt =
with? Could I get away with making a DK secondary without a 32" Hindle
= sphere? Most importantly, will one of those off-the-shelf coma =
correctors from Televue deal with the coma from an f/8 DK? They're =
supposed to be for f/4, and my understanding is that DK's have around =
twice the coefficient of coma of Newtonians, so does that work out? Or = is
coma not coma? If I were to bite the bullet and somehow make an RC = cass,
would the field corrector for curvature be as big a pain to make = as the
coma corrector for the DK? What would you make if you lusted for = more
aperture, experts? Enquiring minds want to know.

For the forseeable future, the plan would be to build maybe a 12-14" =
aperture scale model of the final scope, with the idea being that that =
would be a considerably more portable option than my current 16" newt.
= The challenge of making that should keep me busy for a couple of years, =
too.

Awaiting your input,


Herb.




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Hello all,
 
On my last observing session (in the =
vicinity of=20
Bridgeport, CA),  I was = looking at M51=20
with my 16" f/4 newt and thinking "well, that's pretty good, but
it = ain't really=20
knockin' my socks off". I think the real thrill of amateur =
astronomy for me=20
is the idea of looking at some galaxy and actually seeing those spiral = arms,=20
like in the pictures. Or clearly seeing the color in a nebula. Even with =
my 16"=20
scope, you need averted vision to see the arms on almost everything, and = only=20
the brightest nebulae have any hint of color. Obviously, you can never = actually=20
see things as well as the cameras can, but ultimately, I think I can do = better=20
than what I have now. I know that if I got a CCD setup I could do  = much=20
better with what I have, but the idea of taking pictures and looking at = those=20
just desn't put the cheese in my macaroni. After all, the HST will = always put my=20
measly pictures to shame. But to have those photons travel 50 million = light=20
years straight into my head, now that's groovy. Perhaps this is what = they call=20
aperture fever...
 
Anyhoo, I think
I'm eventually =
going to have=20
to build a bigger scope than the one I have in order to be fully=20
self-actualized. I'm thinking maybe 32-36" would allow me to go to
my=20 grave content (I'm not old or anything, this is what you'd
call a = very=20
long-term project). If the improvement in what you see is as much as the =

difference between 8" and 16", then I think for me it would
ultimately = be worth=20
the effort and expense.
 
There are some
constraints to my =
ultimate=20
scope design. For one thing I do NOT want to stand on top of a big = ladder to=20
look through it. Therefore it will have to be a cassegrain of some sort. = I think=20
I would go for a Nasmyth focus directed out the altitude axis, so that I = can=20
have a comfortable viewing chair that I can stay in. It does not have to = be=20
easily portable. It will be in an observatory on my (hypothetical) = vacation=20
property in the middle of nowhere. It should be relatively compact, so = that if=20
necessary it can be moved, and so that I don't have to build a giant = enclosure=20
for it. I also want to be able to use it at the lowest practical=20
visual magnification (around 120X, I guess) and for rich field =
photographic=20
applications sometimes (it's not that I *never* want to take = pictures...). So=20
the primary should be around f/3, for an effective ratio of f6-f/8. Full =

aperture correctors, obviously, are right out. So I guess I'm looking at = a=20
classical, DK, or RC cassegrain. Unless someone has a better idea that = will meet=20
those criteria...
 
So the question
is, which of =
these three=20
designs is the best to pursue? Clearly, the DK would be the easiest to = make, but=20
can the coma be dealt with? Could I get away with making a DK secondary = without=20
a 32" Hindle sphere? Most importantly, will one of those off-the-shelf = coma=20
correctors from Televue deal with the coma from an f/8 DK? They're = supposed to=20
be for f/4, and my understanding is that DK's have around twice the = coefficient=20
of coma of Newtonians, so does that work out? Or is coma not coma? If I = were to=20
bite the bullet and somehow make an RC cass, would the field corrector = for=20
curvature be as big a pain to make as the coma corrector for the DK? = What would=20
you make if you lusted for more aperture, experts? Enquiring minds want = to=20
know.
 
For the forseeable future, the plan =
would be to=20
build maybe a 12-14" aperture scale model of the final scope, with the = idea=20
being that that would be a considerably more portable option than = my=20
current 16" newt. The challenge of making that should keep me busy for
a = couple=20
of years, too.
 
Awaiting your
input,
 
 
Herb.
 
 
 
 

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