Jupiter

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

All up I'm pretty happy with it. Suspect the scope needs some
tweaking of the collimation which should give a sharper image.
Will have to try that next time, haven't done it before.

--
Troy Piggins

On Sat, 24 Oct 2009 01:43:38 +1000, 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

All up I'm pretty happy with it. Suspect the scope needs some
tweaking of the collimation which should give a sharper image.
Will have to try that next time, haven't done it before.

Much depends too on "seeing" conditions. The atmospheric stability. Most
times you just have to wait and hope for the best days. The very same
perfectly collimated optics can provide a draw-dropping 3D-looking view of
Saturn one day, and an irregular mushy blob the next. Look into the
sharpening techniques that web-cam astrophotographers use, by combining
details from many many frames to virtually look through the turbulent
atmosphere, capturing and combining those bits of each image that are
stable and sharp.

You might also try stopping down the aperture of your telescope during bad
seeing conditions. A larger aperture means that your telescope is trying to
image through larger lower-frequency areas of atmospheric turbulence. If
the turbulence that night is mostly of the lower-frequency variety it will
help to filter it out. I keep a 6" mask handy for those times to put on my
16" scope. Apodizing masks also cure things on some days for planetary
imaging.

* 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

All up I'm pretty happy with it. Suspect the scope needs some
tweaking of the collimation which should give a sharper image.
Will have to try that next time, haven't done it before.

Much depends too on "seeing" conditions. The atmospheric stability. Most
times you just have to wait and hope for the best days. The very same
perfectly collimated optics can provide a draw-dropping 3D-looking view of
Saturn one day, and an irregular mushy blob the next. Look into the
sharpening techniques that web-cam astrophotographers use, by combining
details from many many frames to virtually look through the turbulent
atmosphere, capturing and combining those bits of each image that are
stable and sharp.

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

You might also try stopping down the aperture of your telescope during bad
seeing conditions. A larger aperture means that your telescope is trying to
image through larger lower-frequency areas of atmospheric turbulence. If
the turbulence that night is mostly of the lower-frequency variety it will
help to filter it out. I keep a 6" mask handy for those times to put on my
16" scope. Apodizing masks also cure things on some days for planetary
imaging.

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.

--
Troy Piggins

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.

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...

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.

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...

* 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

Troy Piggins wrote,on my timestamp of 24/10/2009 11:06 PM:


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.

The dry air inland makes quite a difference: very little haze.
Never cease to be amazed how clear the sky is in the desert: I've got photos of
Mt Connor at nearly 30Ks that look like the blessed thing is just 5 away.


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.

Cool. Good luck with convincing the other half for the better camera!


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

Yeah, I know. But it also increases the size and weight of the thing a lot!



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.


Mostly visual to start with: can't afford all the imaging stuff at the moment.
There are a few suppliers of eq mounts I can use later on once I can afford the
photography side. Figured the Dobsonians are a good priced entry point for wide
aperture visual and can be used as a base for more advanced stuff.
Thanks, I'll definitely ping you later on.

(silly typo correction)

On Sat, 24 Oct 2009 01:43:38 +1000, 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

All up I'm pretty happy with it. Suspect the scope needs some
tweaking of the collimation which should give a sharper image.
Will have to try that next time, haven't done it before.

Much depends too on "seeing" conditions. The atmospheric stability. Most
times you just have to wait and hope for the best days. The very same
perfectly collimated optics can provide a jaw-dropping 3D-looking view of
Saturn one day, and an irregular mushy blob the next. Look into the
sharpening techniques that web-cam astrophotographers use, by combining
details from many many frames to virtually look through the turbulent
atmosphere, capturing and combining those bits of each image that are
stable and sharp.

You might also try stopping down the aperture of your telescope during bad
seeing conditions. A larger aperture means that your telescope is trying to
image through larger lower-frequency areas of atmospheric turbulence. If
the turbulence that night is mostly of the lower-frequency variety it will
help to filter it out. I keep a 6" mask handy for those times to put on my
16" scope. Apodizing masks also cure things on some days for planetary
imaging.