Jupiter

Troy Piggins wrote:
* Jeff R. wrote :
Cooled camera?

Nope. This one:
http://www.theimagingsource.com/en_U...yer/dbk21au04/

I'm considering (don't tell my wife) a cooled CCD for longer
exposure, deep sky stuff. They're the duck's nuts. But won't be
getting the top of the line ones. They go for $10k or multiples
thereof. Reckon something like this will do me:

http://web.aanet.com.au/~gama/QHY8.html

Long time since I knew much about them things.
ISTR colour didn't exist, and you had to use filters and three exposures
with a mono unit.
I have patience, but not that much.

Waddy'a reckon that unit would retail for?
(Any point in asking if you've tried a DSLR ?)

Hand or auto-guided?

No guiding. Not for 90 secs or so. Mount was just tracking
sidereal rate on its own.

Fairy nuff.


This sort of stuff it's more about atmospheric conditions, the
jetstream, and scope focus and collimation. I have yet to come
to terms with tweaking all that.

Even with all that, don't neglect widefield stuff.
Point your camera somewhere around Crux, and do a wide-angle shot for a few
minutes (piggy-backed, of course) and the results will astound!

I couldn't believe how much I could see in a short exposure, even here in
the 'burbs where the clouds light up like fireworks from the streetlights.


(fun, idd'n it!)

Oh, ya!

:-)

--
Jeff R.

Troy Piggins wrote:
The astrophotography has been keeping me occupied lately. This
is my first attempt at planetary imaging. Lots to learn, I know.
Don't see much astrophotography here so thought I'd share.

Taken with a 8" f/10 scope with a 2.5x powermate (like a
teleconvertor) giving it an equivalent focal length of around
5000mm. Camera was a DBK21 CCD camera.

The dark spot is the shadow of one of the moons, and you can just
make out the Great Red Spot at the top.

http://piggo.com/~troy/photos/2009/2...er091023_1.jpg

Pretty nice for an 8" scope. Single shot or composite?

--
Ray Fischer

On Sat, 24 Oct 2009 07:21:39 +1000, Troy Piggins
wrote:



How does one stop down the aperture of a fixed aperture scope?
The bare scope is f/10. With the 2.5x powermate it becomes an
equivalent f/25. I haven't heard of people using those masks
you're referring to. I'll look into it. Thanks.

A simple round hole cut into some opaque plastic, cardboard, or thin
aluminum sheeting will suffice. Placed over the opening of your telescope.
For a refractor this is easy (no central obstruction). Just place it
concentric with the optical axis.

For a reflector the choice is not so easy. The secondary mirror's size is
optimized for the light path and f/ratio.

Larger reflector telescopes can use an aperture mask offset to one side, so
as to use an unobstructed region of the mirror between the outside diameter
of the primary and the outside diameter of the secondary, and situated
between the spider-vanes. Consider too the number of spider-vanes you have.
If 4 vanes you will have to cut your mask smaller so its diameter fits
within an open quadrant between any two spider-vanes.

The huge plus of this for planetary imaging is that now you have an
obstruction-free telescope. Of reduced aperture but for bright subjects and
due to "seeing" problems this can be a huge plus too. Many people buy 12"
or larger reflectors with the intent to only use it as a stopped-down
off-axis planetary imager. (8"-10" telescopes too, but you then start to
lose resolution due to primary size alone when stopped-down off-axis.)
There is a huge cost-savings in buying pre-fabricated easy to make
manufactured telescopes much greater than the size needed, as opposed to
buying or building an off-axis (asymmetric) reflecting telescope design
(see below), or prohibitively expensive refractor of those diameters which
is now fraught with CA problems.

With the aperture offset you are no longer plagued with diffraction from
secondary mirror and its spider supports. Since this is a reflector, you
now have a telescope that is free of all chromatic-aberration, making it
much better than a refractor of the same size (large and astronomically
expensive refractors bought with planetary imaging in mind). Special
asymmetric reflector telescopes are designed this way, but grinding and
figuring the offset curvatures are extremely difficult and many ingenious
methods were tried and found to try to circumvent this fabrication problem.
One of the more ingenious is to grind an achromat corrective lens for use
with a standard parabolic mirror set at an angle. This achromat ground to
the proper figure by using a creative method found for the home telescope
builder, but then you introduce CA problems. Often, to simplify things,
they'll just buy a much larger pre-figured mirror and then cut it up into 2
or 3 smaller offset-telescope primaries. (I don't think I could bring
myself to do that, even though I have the means. It would be like cutting a
favorite child into 2's or 3's.)

By using an offset aperture mask on a large telescope you now have the best
of 3 worlds. An exceptional planetary imager (the same as a prohibitively
expensive asymmetric reflector telescope), no CA problems as exists in all
refractors, and when the mask is removed you now have a very very nice
deep-sky light-bucket.

Aside: This is precisely why I chose the size telescope I now have (16"
dia.). The 16" also not chosen arbitrarily due to costs nor other issues.
When researching I found that due to even the most pristine seeing
conditions (unless I am on a mountain-peak), that without adaptive optics
the resolution of this size telescope is the same as that of Mt. Palomar's
200" telescope. The weakest link now being caused by the atmosphere itself.
There was no appreciable gain in resolution by buying larger. Light-grasp
yes, resolution no. (Keep in mind too, this was before image-stacking
became popularized to increase resolution. And since I was going to
primarily use it for visual astronomy this didn't enter into my
decision-making equations. Then, nor now.)

Another plus to an offset mask is that you can rotate the aperture-mask to
find a "sweet spot" of your mirror where the figure is the most pristine.
This can greatly improve on its 1/8th to 1/20th wavelength of light
tolerance across its whole surface.

For smaller telescopes you can try an aperture reducing mask placed
concentric with the axis of the telescope, but then the smaller you stop
down the aperture the more that diffraction becomes an issue due to the
larger percentage of central obstruction vs. the useful light path.

Experiment.

On Sat, 24 Oct 2009 07:30:59 +1000, Troy Piggins
wrote:

* Rich wrote :
On Oct 23, 11:43*am, Troy Piggins wrote:
[---=| Quote block shrinked by t-prot: 14 lines snipped |=---]
tweaking of the collimation which should give a sharper image.
Will have to try that next time, haven't done it before.

You need at least 25,000mm to really shoot Jupiter. Nice shot at
5000mm though.

Anthony Wesley, the guy who discovered the that most recent
impact scar on Jupiter, takes these sort of shots with an
effective focal length of around 9000mm.

http://www.iceinspace.com.au/forum/a...4&d=1256210105

I'd be extremely happy if I can get anywhere near as good as
that. Have you ever tried to image with something of the sort of
focal lengths you're suggesting with back-yard amatuer gear? I'd
love to see examples.

Don't mind Rich, he's just a troll that regurgitates what he's read other
trolls invent, or he himself invents. He doesn't even own a camera, much
less a telescope. Proved many times by many people. He's only here to play
"pretend" with his role-play life, using bits and snippets of info that he
happens to find anywhere on the net. He believes anything he reads on the
net, with no real-life experience to know the difference of when he's being
bull****ted.

On Sat, 24 Oct 2009 22:17:05 +1000, Noons wrote:

Goos stuff as usual, Piggo. Pity you can't move all that gear 300 miles inland,
eh?

Inland is worse, but then you'd know this if you knew the least bit about
photography and astronomy. Another **** poor attempt of yours to try to
look like you knew something. Trolls never do.

Troy Piggins wrote,on my timestamp of 24/10/2009 7:21 AM:
* Damn 35 F Rain - Staying Warm Inside Is Winning Today wrote :
* Troy Piggins wrote :

[---=| Quote block shrinked by t-prot: 11 lines snipped |=---]
http://piggo.com/~troy/photos/2009/2...er091023_1.jpg


Goos stuff as usual, Piggo. Pity you can't move all that gear 300 miles inland,
eh?
Sometimes I wish I could retire in a place like Maree or Oodnadatta and enjoy
clear, cloudless skyes all year round. I do recall reading a newspaper in the
campsite by starlight alone, no moon! Beer (Red Back) ain't half bad over there
either...


Yes, this image was stacked from around 2500 frames of an avi
file using Registax. Suspect that's the technique you're
referring to.

Did you get that size image from the 8" scope and sensor alone or did you add a
converter and/or digital resize?

I'm toying around with the idea of a 8" or 10" dobsonian, want to get a feel for
what's possible and what's needed. Kids have been bugging me to get back into
this stuff...

* Jeff R. wrote :
Troy Piggins wrote:
* Jeff R. wrote :
Cooled camera?

Nope. This one:
http://www.theimagingsource.com/en_U...yer/dbk21au04/

I'm considering (don't tell my wife) a cooled CCD for longer
exposure, deep sky stuff. They're the duck's nuts. But won't be
getting the top of the line ones. They go for $10k or multiples
thereof. Reckon something like this will do me:

http://web.aanet.com.au/~gama/QHY8.html

Long time since I knew much about them things.
ISTR colour didn't exist, and you had to use filters and three exposures
with a mono unit.
I have patience, but not that much.

All of the high end, top astro imagers still use the mono sensor
cameras with filters - the cameras are much more sensitive
because each pixel is really a pixel, instead of divided into
RGGB.

Waddy'a reckon that unit would retail for?

It's around $3k for the one I want.

(Any point in asking if you've tried a DSLR ?)

I've been using a 40D for deep sky stuff to date - galaxies,
nebulae, globular and open star clusters. Much cheaper
alternative to the above CCDs, but don't have the quantum
efficiency, well depth, sensitivity, antiblooming, etc bells and
whistles that the CCDs do. But coming from a photography
background, much easier to translate over.

My 40D is modified - they remove the UV/IR filter off the sensor
and replace it with clear glass. Makes it much more sensitive to
IR light spectrum which is what a lot of deep sky, esp nebulae,
emit.

If I get a chance to process and upload some of my deep sky
images, I'll post links taken with 40D.

That DBK21 camera I took Jupiter with, would never use it for
deep sky stuff, only planetary or using it as a guide camera.

Hand or auto-guided?

No guiding. Not for 90 secs or so. Mount was just tracking
sidereal rate on its own.

Fairy nuff.

This sort of stuff it's more about atmospheric conditions, the
jetstream, and scope focus and collimation. I have yet to come
to terms with tweaking all that.

Even with all that, don't neglect widefield stuff.
Point your camera somewhere around Crux, and do a wide-angle shot for a few
minutes (piggy-backed, of course) and the results will astound!

I couldn't believe how much I could see in a short exposure, even here in
the 'burbs where the clouds light up like fireworks from the streetlights.

I've got some narrowband filters - Ha, OIII, SII (these refer to
narrow bands of wavelengths of light emitted from certain
nebulae). They cut out heaps of the light pollution because they
only let extremely narrow band of wavelengths of light through.

My intention is to shoot planetary or narrow band shots from home
here, and when I get to "dark" sites (remote and no light
pollution) I'll do the colour imaging.

--
Troy Piggins

* Noons wrote :
Troy Piggins wrote,on my timestamp of 24/10/2009 7:21 AM:
* Damn 35 F Rain - Staying Warm Inside Is Winning Today wrote :
* Troy Piggins wrote :

[---=| Quote block shrinked by t-prot: 11 lines snipped |=---]
http://piggo.com/~troy/photos/2009/2...er091023_1.jpg

Goos stuff as usual, Piggo. Pity you can't move all that gear
300 miles inland, eh?
Sometimes I wish I could retire in a place like Maree or
Oodnadatta and enjoy clear, cloudless skyes all year round. I
do recall reading a
newspaper in the campsite by starlight alone, no moon! Beer
(Red Back) ain't half bad over there
either...

I've been to a few dark sites this last year, at new moon, not a
cloud in the sky. Got a sore neck from constantly gazing up at
the sky.

Yes, this image was stacked from around 2500 frames of an avi
file using Registax. Suspect that's the technique you're
referring to.

Did you get that size image from the 8" scope and sensor alone
or did you add a converter and/or digital resize?

The C8 8" f/10 schmidt cassegrain I have had a 2.5x powermate
(like a teleconvertor) on it, which gave focal length of around
5000mm. Plus the image was slightly cropped to square it up from
the sensor size of 640x480.

I'm toying around with the idea of a 8" or 10" dobsonian, want
to get a feel for what's possible and what's needed. Kids have
been bugging me to get back into
this stuff...

"Aperture rules" - 10" lets in almost twice the amount of light
the 8" does

Do you want it for visual observing or taking photos? If visual,
all good. If photos, slippery slope. Dobs/Newtonians might be
fine for planetary imaging, but no good unless you mount them on
equatorial mount for deep sky, long exposure shots.

If you're really keen, email me for more chats.

--
Troy Piggins

* Ray Fischer wrote :
Troy Piggins wrote:
[---=| Quote block shrinked by t-prot: 7 lines snipped |=---]

The dark spot is the shadow of one of the moons, and you can just
make out the Great Red Spot at the top.

http://piggo.com/~troy/photos/2009/2...er091023_1.jpg

Pretty nice for an 8" scope. Single shot or composite?

It's a stacked image from the best of around 2500 frames taken
from a 90 second avi file. Not an easy answer

--
Troy Piggins

Outing Trolls wrote,on my timestamp of 24/10/2009 9:24 PM:
On Sat, 24 Oct 2009 22:17:05 +1000, Noons wrote:

Goos stuff as usual, Piggo. Pity you can't move all that gear 300 miles inland,
eh?

Inland is worse, but then you'd know this if you knew the least bit about
photography and astronomy. Another **** poor attempt of yours to try to
look like you knew something. Trolls never do.


What an idiot...