Copernicus crater

Here's a shot of Copernicus, taken under good seeing conditions...

http://www.digitalsky.org.uk/lunar/c...-04_Red_cn.jpg
--
Pete Lawrence
[Registered users can see links. ]

On Wed, 24 Sep 2008 11:54:48 +0100, Pete Lawrence
<[Registered users can see links. ].uk> wrote:


Hi Pete-

Both images are excellent. A few questions: are these single shots, or
did you use some lucky imaging? What was the exposure time? From the
file names, I'm guessing you've isolated the red channel? Is that to
control atmospheric dispersion?
_________________________________________________

Chris L Peterson
Cloudbait Observatory
[Registered users can see links. ]

On Sep 24, 12:54*pm, Pete Lawrence <[Registered users can see links. ].uk> wrote:


Blimey! That's so sharp you can still see the builder's footprints all
around the edges!

Sorry, Pete. :-)

Superb shot!

On Wed, 24 Sep 2008 09:05:47 -0600, Chris L Peterson
<[Registered users can see links. ]> wrote:


Hi Chris,

Same technique used for both images. A high frame-rate camera
(Lumenera SKYnyx 2-0M) to grab multiple frames and then processed
through Registax before assembly. Indivudual frame exposure time was
30ms for both images. I use a red filter to reduce the effects of
atmospheric seeing.
--
Pete Lawrence
[Registered users can see links. ]

What number red filter?

I use a red filter to reduce the effects of

On Thu, 25 Sep 2008 15:09:53 GMT, "MAT" <[Registered users can see links. ]> wrote:


An Astronomik Type 2 red filter.
--
Pete Lawrence
[Registered users can see links. ]

Nice image for sure, but.......

Seeing is still the #1 factor to getting good images. It took me several
years and thousands of $$ to realize this fact. There is a certain
advertising "hype" that a firewire so-called "fast" multiple frame grabbing
camera will defeat poor seeing conditions but this is definitely not the
case. I spent much time researching these cameras and in fact tested
several of them, but I found CCD S/N ratio sensitivity insufficient for the
truly rapid frame captures needed to overcome poor seeing conditions.

In the coming years, there may be several options and that is what I am
waiting for. One option is that CCD's are constantly improving so
sensitivity may allow say 1/100 sec exposure at 60 fps for Jupiter, but I
think that is a long way off yet. Another is a technique similar to
adaptive optics in some ways and different in other ways.... I once
"borrowed" four C-8's, set them up within 10 feet of one another and aimed
them at Jupiter. Then, using software, webcam movies were captured all at
the same instant for one minute. The results were significantly better than
if a single telescope had been used because essentially you had 4 frames per
instant time to choose from as being "good" or "bad" for stacking purposes.
The final experiment was conducted among a dozen amateurs with twelve scopes
in the 8- 12" range aimed at Saturn. A technique called "match and freeze"
was used to literally freeze the effects of the jetstream making Saturn
independent of it. This required using scope hand controllers to
stop-go-stop again (to help defeat a fast jetstream) and the frames were
captured at a certain point in the process. Extremely tedious, but the
image of Saturn was not unlike those of folks who are blessed with
constantly good seeing. So there are ways with current technology to defeat
even a fast jetstream, but the process is far from cheap unless you can find
enough volunteers.

Cheers,
Al



"Pete Lawrence" <[Registered users can see links. ].uk> wrote in message
news:[Registered users can see links. ]...

On Thu, 25 Sep 2008 13:35:33 -0400, "Albert Maxwell" <[Registered users can see links. ]>
wrote:


I assume you mean high resolution images. Certainly, in the absence of
equipment problems (and assuming reasonable aperture), seeing is what
ultimately limits resolution.


In this you are very much mistaken. There is no doubt at all that
capturing and combining many short exposure images, especially when
images are selected for quality (lucky imaging) can significantly reduce
the effects of seeing. At my observatory, I never have better than 3
arcsec FWHM stars in a 10-second exposure, but I can get subarcsecond
resolution capturing planets with video. This is an extremely valuable
tool.


S/N is only part of the picture. You can have poor S/N and still have
high resolution. Also, S/N is dependent on aperture. The larger the
aperture, the more photons you'll receive, and the better your S/N. So
you can't really generalize about cameras alone, you have to consider
the entire setup.



I normally shoot Jupiter with a simple webcam, with 1/100 second
exposure and 15 fps. With a 12" aperture, I am not particularly limited
by S/N issues. That is, at 1/100 second the brightest regions of Jupiter
are nearing saturation on the sensor, so readout noise (and photon
statistics) are all I need to consider.

CCDs already have excellent quantum efficiency, typically recording
about 50% of the photons that reach them. So there is little room for
improvement there. For short exposure imaging, readout noise is the
primary problem. I expect this will be largely eliminated in the near
future. I already have a zero readout noise camera, and it can capture
images with exposures of only about a millisecond, with no noise
penalty. You simply collect enough that the photon noise reaches an
acceptably low level. There are also people working around the readout
noise problem by using image intensifiers.

But these tricks to deal with readout noise are for getting high
resolution on DSOs and other dim objects. They are not required for the
Sun, Moon, and bright planets, all of which can be imaged with very
ordinary video equipment (including webcams), at subarcsecond resolution
even under marginal seeing, and with extremely high S/N in the final
stacked images.
_________________________________________________

Chris L Peterson
Cloudbait Observatory
[Registered users can see links. ]

On Thu, 25 Sep 2008 13:35:33 -0400, "Albert Maxwell" <[Registered users can see links. ]>
wrote:


Not too sure what the "but" is for? I never said that seeing wasn't
the most important factor.


--
Pete Lawrence
[Registered users can see links. ]

"Chris L Peterson" <[Registered users can see links. ]> wrote in message
news:[Registered users can see links. ]...

Yes, high resolution imagery.


Do you have a high resolution image to show then, like those coming from
Peach and others? You're talking about reducing the effects of turbulence
and the technique you describe does do that to a certain extent, but not
high resolution with low noise unless the atmospheric conditions are
favorable.


Ok, technically, yes but the image will be far from presentable.

Also, S/N is dependent on aperture. The larger the

True, the larger the scope, the more light reaches the CCD, but then again
larger scopes are more susceptible to atmospherics. A catch 22 so to speak.

I should have mentioned "planetary high resolution" in my initial response
as the discussion is getting away from that realm. It does no good to
capture at those settings or even aperture- for the purpose of high
resolution, low noise planetary imaging- if seeing conditions are not good.


Ah, image intensifiers. It is worth experimenting with those further.


You can image a planet under any conditions ending up with the results you
speak of. However, if atmospheric conditions are poor to average will you
end up with a very high resolution, low noise and presentable solar system
object type image, based on the best amateur equipment available today?

The aforementioned question or "challenge" so to speak was what prompted me
to conduct my research. These essentially "glorified" webcams were being
marketed (still are) for greater than $1K amounts in some cases with users
being quite disappointed when they failed to meet the resolution of the guy
near the equator or in an excellent seeing location. As of 2007, I had not
yet found a single camera with a CCD capable of achieving truly high
planetary resolution in poor to average seeing conditions with low noise and
an aesthetic result after stacking and processing. Not a single camera, but
as I mentioned before, the volunteer and several scopes approach did begin
to achieve such results.

The bottom line is that I guess it all depends on what you seek. I want
high resolution, low noise planetary images taken under 5/10 or less seeing
conditions. And, yes, I'm looking at this primarily from an aesthetic and
not a scientific, data-based point of view, although one must include such
data for a realistic image.

Al
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