Stacking Question...

I have an 8"f6 Dob and a scopetronics setup for my digital camera. I am
able to take 1/30 second shots of say Jupiter and Saturn. Unfortunately I
do not have a guiding system to track so stacking multiple images becomes a
problem.

There are fantastic images taken by others where a 1000 images are stacked
and the detail is incredible.

I have tried to stack multiples of the same image with little luck in
obtaining anything but an over exposed image. A couple of image stacks may
bring out some detail. I understand that multiple images can reduce
background noise and grabbing a group of saved images during a window of
great seeing can also help.

For me to try stacking do I set the shutter speed to say 1/250 sec and
although the image, when dumped to the computer, is very faint would I then
stack 100 copies to grab the detail and increase the brightness?

Not sure if I have worded my question correctly but I am hoping someone will
know what I mean.

Regards
Brian

It sounds like you are summing while stacking instead of averaging. I
suggest you download the free ware Registax. It not only averages the
stack but also sorts the image out according to quality by determining
the FFT of a given spot. Hope this helps

wrote in message
ps.com...
It sounds like you are summing while stacking instead of averaging. I
suggest you download the free ware Registax. It not only averages the
stack but also sorts the image out according to quality by determining
the FFT of a given spot. Hope this helps


I think you are correct about the summing. I do have Registax. I will have
to spend more time learning it.

On 3 Mar 2005 15:18:38 -0800, wrote:

It sounds like you are summing while stacking instead of averaging. I
suggest you download the free ware Registax. It not only averages the
stack but also sorts the image out according to quality by determining
the FFT of a given spot. Hope this helps

Averaging is probably the last thing you want to do when working with
the 8-bit data you get from most webcams and digicams. Summing is the
proper technique- and it is what most programs (including Registax) do.
The summed images may be normalized back down to an 8-bit space when
processing is complete, but you don't want to do anything sophisticated
like frequency space processing on 8-bit data.

Of course, if you just add your 8-bit images directly into 8-bit
resulting images you'll get in trouble, and you might well be right that
this is what the OP is doing.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Amyotte:
I have an 8"f6 Dob and a scopetronics setup for my digital camera. I am
able to take 1/30 second shots of say Jupiter and Saturn. Unfortunately I
do not have a guiding system to track so stacking multiple images becomes a
problem.

There are fantastic images taken by others where a 1000 images are stacked
and the detail is incredible.

I have tried to stack multiples of the same image with little luck in
obtaining anything but an over exposed image. A couple of image stacks may
bring out some detail. I understand that multiple images can reduce
background noise and grabbing a group of saved images during a window of
great seeing can also help.

For me to try stacking do I set the shutter speed to say 1/250 sec and
although the image, when dumped to the computer, is very faint would I then
stack 100 copies to grab the detail and increase the brightness?

Not sure if I have worded my question correctly but I am hoping someone will
know what I mean.

Generally speaking, "stacked" lunar and planetary images are not a
stack of photos from a digital camera (though they could be); they are
QT or AVI videos of a certain duration (i.e., a certain number of
frames) captured with a webcam and a computer. "Stacking" software such
as Registax or Keith's Image Stacker permits the imager to select the
best of the individual frames, align them, and combine ("stack") them
into a final image that is higher in quality than any of the individual
frames; it is often quite amazing how good the end result appears
compared to how poor the individual video frames appear.

Stacking individual images from a still digital camera also works. In
the case of a planet where rotation over a relatively short period of
time is an issue you would do well to take the images in as rapid a
succession as you can carefully do. It doesn't matter that you don't
have a guiding system, because you're going to visually put the
planetary image somewhere in the frame (accuracy isn't important so
long as you capture the entire planetary disc). The accurate alignment
will be done in software. The rule of thumb is the more frames the
better; Daniele Gasparri says that his recent image of Saturn was made
of 1,500 frames from a Philips webcam
http://www.marcofazzoli.com/danielegasparri/html_eng/saturn_050302.htm.
Nonetheless, you can make very good images with half a dozen
still-camera frames if they are focused and exposed with care -- and
with a decent sky and a bit of practice. You should be able to capture
Saturn or Jupiter with shutter speeds slower than 1/250, but I'm a bit
too lazy to calculate the minimum speed that you need with an unguided
'scope. Patient experimentation with note-taking as to what you did
during each imaging session is the key. After a successful session you
consult your notes and do the same thing at the next session. If that
session also succeeds, you have your technique and the rest is
gathering experiencing and refinement of the technique.

Davoud

succession as you can carefully do. It doesn't matter that you don't
have a guiding system, because you're going to visually put the
planetary image somewhere in the frame (accuracy isn't important so
long as you capture the entire planetary disc). The accurate alignment
will be done in software.

I have tried stacking a couple of frames but the image is rather small to
pick up on a particular detail.

I current use a 9mm Super-Wide Knight Owl EP that doesn't barlow well on the
planets and a Knight Owl MC series 25mm for lunar.


The rule of thumb is the more frames the
better; Daniele Gasparri says that his recent image of Saturn was made
of 1,500 frames from a Philips webcam
http://www.marcofazzoli.com/danielegasparri/html_eng/saturn_050302.htm.

Fantastic shot!!!

Nonetheless, you can make very good images with half a dozen
still-camera frames if they are focused and exposed with care -- and
with a decent sky and a bit of practice. You should be able to capture
Saturn or Jupiter with shutter speeds slower than 1/250, but I'm a bit
too lazy to calculate the minimum speed that you need with an unguided
'scope. Patient experimentation with note-taking as to what you did
during each imaging session is the key. After a successful session you
consult your notes and do the same thing at the next session. If that
session also succeeds, you have your technique and the rest is
gathering experiencing and refinement of the technique.


I haven't been taking too many notes although I do check the EXIF of
previous successful shots as a starting point.

I have uploaded a couple of the recent pictures onto
alt.binaries.pictures.astro.


Thanks Davoud

Brian

Overall, I think you need to read more on the subject of taking images of
planets and how to do stacking, but here's a short answer.

First, it sounds like you're summing the images together, not stacking in the
sense that those planet imagers, including myself, do with programs like
Registax.

Second, to reduce noise significantly, you need to get hundreds of images.
Reducing noise is a statistical thing, and in statistics you need to have many
samples or images in order to get any significant effects. 30 samples is sort
of a Rule of Thumb minimal number in order to get meaningful results. You can
do this with a digital camera, but a better way is to use a webcam. It's a
question of time really. In the time you can take a dozen or so images with a
digital camera, you can take hundreds of images with a webcam. But the Big
Problem is the lack of tracking. This severely limits your ability on planets
when it comes to taking a lot of images. One solution is to get an equatorial
tracking platform for Dobs - look on the web for these. I think in the long run
you're going to find it too frustrating to do it with your current setup.

Third, use a program like Registax, which can automatically select the best
frames, align them, and stack them for you once you learn how to use it.
--
Sincerely,
--- Dave
----------------------------------------------------------------------
It don't mean a thing
unless it has that certain "je ne sais quoi"
Duke Ellington
----------------------------------------------------------------------

"Amyotte" wrote in message
...
I have an 8"f6 Dob and a scopetronics setup for my digital camera. I am able
to take 1/30 second shots of say Jupiter and Saturn. Unfortunately I do not
have a guiding system to track so stacking multiple images becomes a problem.

There are fantastic images taken by others where a 1000 images are stacked and
the detail is incredible.

I have tried to stack multiples of the same image with little luck in
obtaining anything but an over exposed image. A couple of image stacks may
bring out some detail. I understand that multiple images can reduce
background noise and grabbing a group of saved images during a window of great
seeing can also help.

For me to try stacking do I set the shutter speed to say 1/250 sec and
although the image, when dumped to the computer, is very faint would I then
stack 100 copies to grab the detail and increase the brightness?

Not sure if I have worded my question correctly but I am hoping someone will
know what I mean.

Regards
Brian

Third, use a program like Registax, which can automatically select the
best frames, align them, and stack them for you once you learn how to use
it.
--
I have been playing with Registax but do need to learn it better

Brian

"Amyotte" wrote in message
...
I have an 8"f6 Dob and a scopetronics setup for my digital camera. I am
able to take 1/30 second shots of say Jupiter and Saturn. Unfortunately I
do not have a guiding system to track so stacking multiple images becomes
a
problem.

There are fantastic images taken by others where a 1000 images are stacked
and the detail is incredible.

I have tried to stack multiples of the same image with little luck in
obtaining anything but an over exposed image. A couple of image stacks
may
bring out some detail. I understand that multiple images can reduce
background noise and grabbing a group of saved images during a window of
great seeing can also help.

For me to try stacking do I set the shutter speed to say 1/250 sec and
although the image, when dumped to the computer, is very faint would I
then
stack 100 copies to grab the detail and increase the brightness?

Not sure if I have worded my question correctly but I am hoping someone
will
know what I mean.

Regards
Brian


Hi Brian,

I think unfortunately the bad news is that you're going to need a tracking
mount. With webcams, your best images usually result between F20-F35. That
means that at F6, you're going to need something like a 5x Powermate to get
to F30. At this F ratio, planets move incredibly fast through the field of
view and are nearly impossible to track manually. You can try, but I think
you'll be disappointed.

You want to try to stick with 1/33 sec or greater with planets at preferably
10 fps. Anything slower is prone to atmospheric smearing generally, and
anything faster is usually flooded with noise except on bright targets like
the moon.

For your lack of motorized mount, you don't need anything special... just
something that "generally" tracks. With a dual drive corrector, you'll be
able to make up for any differences in planetary movements caused either by
mount error or inadequate polar alignment. A good, decent cost mount for
you might be the Orion Atlas. It should easily handle your OTA and if you
watch the "2nd hand" portion of their website, you can sometimes find a
really good price. I found mine that way for under $650 a couple of years
back. It includes the polar alignment scope and dual axis corrector. I
know that might seem expensive, especially considering the price of your Dob
to begin with, but you won't regret the upgrade.

You can always take images at either prime focus or, say, at F12 with a 2x
barlow, but these focal lengths are generally an inadequate "match" for a
webcam's CCD, which expects more than that. As a result, pictures lack the
details they should have. Exceptions would be bright, large detailed
objects such as the moon and filtered sun, which will continue to reveal
detail at prime focus.

Good luck with whatever you decide.

Best,
John Anderson

Hi Brian,

I think unfortunately the bad news is that you're going to need a tracking
mount. With webcams, your best images usually result between F20-F35.
That
means that at F6, you're going to need something like a 5x Powermate to
get
to F30. At this F ratio, planets move incredibly fast through the field
of
view and are nearly impossible to track manually. You can try, but I
think
you'll be disappointed.

You want to try to stick with 1/33 sec or greater with planets at
preferably
10 fps. Anything slower is prone to atmospheric smearing generally, and
anything faster is usually flooded with noise except on bright targets
like
the moon.

For your lack of motorized mount, you don't need anything special... just
something that "generally" tracks. With a dual drive corrector, you'll be
able to make up for any differences in planetary movements caused either
by
mount error or inadequate polar alignment. A good, decent cost mount for
you might be the Orion Atlas. It should easily handle your OTA and if you
watch the "2nd hand" portion of their website, you can sometimes find a
really good price. I found mine that way for under $650 a couple of years
back. It includes the polar alignment scope and dual axis corrector. I
know that might seem expensive, especially considering the price of your
Dob
to begin with, but you won't regret the upgrade.

You can always take images at either prime focus or, say, at F12 with a 2x
barlow, but these focal lengths are generally an inadequate "match" for a
webcam's CCD, which expects more than that. As a result, pictures lack
the
details they should have. Exceptions would be bright, large detailed
objects such as the moon and filtered sun, which will continue to reveal
detail at prime focus.

Good luck with whatever you decide.

Best,
John Anderson


Thanks John

I will keep my eye open for a mount. I currently enjoy the grab and go DOB
mount. I can be up and running in minutes from where I store the scope to
the deck. Add in cool down time of course.

I have uploaded a couple of the recent pictures onto
alt.binaries.pictures.astro.

Brian