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Moon shot - Explanation - Clark Vision

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Anonymous
March 17, 2005 12:11:52 PM

Archived from groups: rec.photo.digital (More info?)

Hi there,

Below is an extract from Clark Vision's website regarding a photo of the
moon. Can someone please explain ..... in *simple* English, the section
from " Three raw images ....... "
I lost most of it ( apart from focal lengths, iso, exposure etc ) from
that point onwards ;-)

Thanks

Bernard

The URL is http://clarkvision.com/index.html

"This image of the moon was obtained on January 3, 2005 using a Canon 1D
Mark II 8-megapixel digital camera, a 500 mm f/4 L IS lens with 1.4 and
2x teleconverters. The total focal length is 1400 mm for a full scale of
1.2 arc-seconds per pixel. Three raw images were converted and added to
increase the signal-to-noise, then the image was increased in size by 2
times. The exposure times were 1/125 second at ISO 200, f/11.2 (this is
wide open on the 500 mm f/4 lens with the teleconverters). This larger
image was then sharpened with Adaptive Richardson-Lucey Restoration with
a 11x11 box, 10 iterations, noise level = 2 standard deviations, then a
second pass with a 7x7 box, 10 iterations. Final adjustments included
curves stretch and unsharp mask. For an image with the original camera
resolution, 1.2 arc-seconds per pixel, 1295 x 1829 pixels (260 KBytes),
CLICK HERE. Note: this large image is limited by atmospheric turbulence."
Anonymous
March 17, 2005 12:11:53 PM

Archived from groups: rec.photo.digital (More info?)

Bernard Rother <bprotherREMOVE1@intekom.co.za> wrote:

> Hi there,
>
> Below is an extract from Clark Vision's website regarding a photo of the
> moon. Can someone please explain ..... in *simple* English, the section
> from " Three raw images ....... "
> I lost most of it ( apart from focal lengths, iso, exposure etc ) from
> that point onwards ;-)
>
> Thanks
>
> Bernard
>
> The URL is http://clarkvision.com/index.html

It's actually here:
<http://www.clarkvision.com/galleries/gallery.astrophoto...
3658-60-c-5x-700.html>

And it's pretty impressive.

> "This image of the moon was obtained on January 3, 2005 using a Canon 1D
> Mark II 8-megapixel digital camera, a 500 mm f/4 L IS lens with 1.4 and
> 2x teleconverters. The total focal length is 1400 mm for a full scale of
> 1.2 arc-seconds per pixel. Three raw images were converted and added to
> increase the signal-to-noise,

He took three pictures and added them together, in order to reduce
noise. That doesn't make much sense, though, since adding them together
would just compound the noise from each image. Averaging them would
reduce the noise.

Unless the images were underexposed, in which case you'd have to add
them together to stretch the dynamic range, noise floor be damned.

> then the image was increased in size by 2 imes.

He doubled the size of the picture, probably using interpolation of some
sort, as in Photoshop.

> The exposure times were 1/125 second at ISO 200, f/11.2 (this is wide open
> on the 500 mm f/4 lens with the teleconverters). This larger image was
> then sharpened with Adaptive Richardson-Lucey Restoration with a 11x11
> box, 10 iterations, noise level = 2 standard deviations, then a second
> pass with a 7x7 box, 10 iterations.

He did some math on the image to sharpen it. Twice. There's stuff to
click on to find out how the math works.

> Final adjustments included curves stretch and unsharp mask. For an image
> with the original camera resolution, 1.2 arc-seconds per pixel, 1295 x
> 1829 pixels (260 KBytes), CLICK HERE. Note: this large image is limited by
> atmospheric turbulence."

He's saying that the resolution of the large image is limited by the
effects of the atmosphere on light passing through it. Never mind the
dual teleconverters, fancy math, and double-size interpolation. :-)

I like the final picture, but it does have a very 'enhanced' look,
especially in the large size.
Anonymous
March 17, 2005 12:11:53 PM

Archived from groups: rec.photo.digital (More info?)

Bernard
The author has added - 'stacked' to use the astronomers term - the images
to, as he says, improve his S/N ratio - the three images are correlated,
the noise isn't - then used a convolution routine to correct for errors in
the optical system. Incidentally, a multi stage Peltier electro cooler good
for perhaps 50 degrees les than ambient is normally used to reduce noise in
astro imaging cameras.

The convolution routine used here is the Lucy-Richardson routine named
after the two mathematicians whose work is used in this algorithm (there are
others including "max entropy") - they are computationally *very* intensive
and normally only used in astronomical image processing packages.

His comments about box size etc are parameters that the user can adjust
during the L-R convolution the procedure is pretty much a 'try it and see'
process for most images.

The comment about arc-seconds per pixel refers to the angular field of view
(expressed in pixels of the imager) this optical setup provided for the shot
(the sky can be divided into degrees, minutes and seconds).

I assume that you are familiar with the unsharp filter and curve stretching
from 'mainstream' image processing?

HTH

Ian



"Bernard Rother" <bprotherREMOVE1@intekom.co.za> wrote in message
news:D 1bakr$p61$1@ctb-nnrp2.saix.net...
> Hi there,
>
> Below is an extract from Clark Vision's website regarding a photo of the
> moon. Can someone please explain ..... in *simple* English, the section
> from " Three raw images ....... "
> I lost most of it ( apart from focal lengths, iso, exposure etc ) from
> that point onwards ;-)
>
> Thanks
>
> Bernard
>
> The URL is http://clarkvision.com/index.html
>
> "This image of the moon was obtained on January 3, 2005 using a Canon 1D
> Mark II 8-megapixel digital camera, a 500 mm f/4 L IS lens with 1.4 and 2x
> teleconverters. The total focal length is 1400 mm for a full scale of 1.2
> arc-seconds per pixel. Three raw images were converted and added to
> increase the signal-to-noise, then the image was increased in size by 2
> times. The exposure times were 1/125 second at ISO 200, f/11.2 (this is
> wide open on the 500 mm f/4 lens with the teleconverters). This larger
> image was then sharpened with Adaptive Richardson-Lucey Restoration with a
> 11x11 box, 10 iterations, noise level = 2 standard deviations, then a
> second pass with a 7x7 box, 10 iterations. Final adjustments included
> curves stretch and unsharp mask. For an image with the original camera
> resolution, 1.2 arc-seconds per pixel, 1295 x 1829 pixels (260 KBytes),
> CLICK HERE. Note: this large image is limited by atmospheric turbulence."
Related resources
Can't find your answer ? Ask !
March 17, 2005 12:11:53 PM

Archived from groups: rec.photo.digital (More info?)

"Bernard Rother" <bprotherREMOVE1@intekom.co.za> wrote in message
news:D 1bakr$p61$1@ctb-nnrp2.saix.net...
> Hi there,
>
> Below is an extract from Clark Vision's website regarding a photo of the
> moon. Can someone please explain ..... in *simple* English, the section
> from " Three raw images ....... "
> I lost most of it ( apart from focal lengths, iso, exposure etc ) from
> that point onwards ;-)

I know you believe you understand what you think he said, but I'm not sure
you realize that what you read is not what he meant.
Anonymous
March 17, 2005 12:11:54 PM

Archived from groups: rec.photo.digital (More info?)

I have seen as good with a pretty cheap telescope and adapter.

"Paul Mitchum" <usenet@mile23.c0m> wrote in message
news:1gtjij6.1kh3vza75scncN%usenet@mile23.c0m...
> Bernard Rother <bprotherREMOVE1@intekom.co.za> wrote:
>
>> Hi there,
>>
>> Below is an extract from Clark Vision's website regarding a photo of the
>> moon. Can someone please explain ..... in *simple* English, the section
>> from " Three raw images ....... "
>> I lost most of it ( apart from focal lengths, iso, exposure etc ) from
>> that point onwards ;-)
>>
>> Thanks
>>
>> Bernard
>>
>> The URL is http://clarkvision.com/index.html
>
> It's actually here:
> <http://www.clarkvision.com/galleries/gallery.astrophoto...
> 3658-60-c-5x-700.html>
>
> And it's pretty impressive.
>
>> "This image of the moon was obtained on January 3, 2005 using a Canon 1D
>> Mark II 8-megapixel digital camera, a 500 mm f/4 L IS lens with 1.4 and
>> 2x teleconverters. The total focal length is 1400 mm for a full scale of
>> 1.2 arc-seconds per pixel. Three raw images were converted and added to
>> increase the signal-to-noise,
>
> He took three pictures and added them together, in order to reduce
> noise. That doesn't make much sense, though, since adding them together
> would just compound the noise from each image. Averaging them would
> reduce the noise.
>
> Unless the images were underexposed, in which case you'd have to add
> them together to stretch the dynamic range, noise floor be damned.
>
>> then the image was increased in size by 2 imes.
>
> He doubled the size of the picture, probably using interpolation of some
> sort, as in Photoshop.
>
>> The exposure times were 1/125 second at ISO 200, f/11.2 (this is wide
>> open
>> on the 500 mm f/4 lens with the teleconverters). This larger image was
>> then sharpened with Adaptive Richardson-Lucey Restoration with a 11x11
>> box, 10 iterations, noise level = 2 standard deviations, then a second
>> pass with a 7x7 box, 10 iterations.
>
> He did some math on the image to sharpen it. Twice. There's stuff to
> click on to find out how the math works.
>
>> Final adjustments included curves stretch and unsharp mask. For an image
>> with the original camera resolution, 1.2 arc-seconds per pixel, 1295 x
>> 1829 pixels (260 KBytes), CLICK HERE. Note: this large image is limited
>> by
>> atmospheric turbulence."
>
> He's saying that the resolution of the large image is limited by the
> effects of the atmosphere on light passing through it. Never mind the
> dual teleconverters, fancy math, and double-size interpolation. :-)
>
> I like the final picture, but it does have a very 'enhanced' look,
> especially in the large size.
March 17, 2005 12:11:55 PM

Archived from groups: rec.photo.digital (More info?)

Pete so have I, infact I have even seen better! Without using RAW or
without using multiple images stacked & without manipulation.

"Pete D" <no@email.com> wrote in message
news:KYa_d.1223$C7.1097@news-server.bigpond.net.au...
> I have seen as good with a pretty cheap telescope and adapter.
>
> "Paul Mitchum" <usenet@mile23.c0m> wrote in message
> news:1gtjij6.1kh3vza75scncN%usenet@mile23.c0m...
> > Bernard Rother <bprotherREMOVE1@intekom.co.za> wrote:
> >
> >> Hi there,
> >>
> >> Below is an extract from Clark Vision's website regarding a photo of
the
> >> moon. Can someone please explain ..... in *simple* English, the section
> >> from " Three raw images ....... "
> >> I lost most of it ( apart from focal lengths, iso, exposure etc ) from
> >> that point onwards ;-)
> >>
> >> Thanks
> >>
> >> Bernard
> >>
> >> The URL is http://clarkvision.com/index.html
> >
> > It's actually here:
> > <http://www.clarkvision.com/galleries/gallery.astrophoto...
> > 3658-60-c-5x-700.html>
> >
> > And it's pretty impressive.
> >
> >> "This image of the moon was obtained on January 3, 2005 using a Canon
1D
> >> Mark II 8-megapixel digital camera, a 500 mm f/4 L IS lens with 1.4 and
> >> 2x teleconverters. The total focal length is 1400 mm for a full scale
of
> >> 1.2 arc-seconds per pixel. Three raw images were converted and added to
> >> increase the signal-to-noise,
> >
> > He took three pictures and added them together, in order to reduce
> > noise. That doesn't make much sense, though, since adding them together
> > would just compound the noise from each image. Averaging them would
> > reduce the noise.
> >
> > Unless the images were underexposed, in which case you'd have to add
> > them together to stretch the dynamic range, noise floor be damned.
> >
> >> then the image was increased in size by 2 imes.
> >
> > He doubled the size of the picture, probably using interpolation of some
> > sort, as in Photoshop.
> >
> >> The exposure times were 1/125 second at ISO 200, f/11.2 (this is wide
> >> open
> >> on the 500 mm f/4 lens with the teleconverters). This larger image was
> >> then sharpened with Adaptive Richardson-Lucey Restoration with a 11x11
> >> box, 10 iterations, noise level = 2 standard deviations, then a second
> >> pass with a 7x7 box, 10 iterations.
> >
> > He did some math on the image to sharpen it. Twice. There's stuff to
> > click on to find out how the math works.
> >
> >> Final adjustments included curves stretch and unsharp mask. For an
image
> >> with the original camera resolution, 1.2 arc-seconds per pixel, 1295 x
> >> 1829 pixels (260 KBytes), CLICK HERE. Note: this large image is limited
> >> by
> >> atmospheric turbulence."
> >
> > He's saying that the resolution of the large image is limited by the
> > effects of the atmosphere on light passing through it. Never mind the
> > dual teleconverters, fancy math, and double-size interpolation. :-)
> >
> > I like the final picture, but it does have a very 'enhanced' look,
> > especially in the large size.
>
>



----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
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Anonymous
March 17, 2005 11:24:40 PM

Archived from groups: rec.photo.digital (More info?)

YoYo wrote:

> Pete so have I, infact I have even seen better! Without using RAW or
> without using multiple images stacked & without manipulation.
>
> "Pete D" <no@email.com> wrote in message
> news:KYa_d.1223$C7.1097@news-server.bigpond.net.au...
>
>>I have seen as good with a pretty cheap telescope and adapter.

But that wasn't the point. It was done with a telephoto lens,
not a telescope. And in fact a short focus, f/4 telephoto lens.

The image scale is 1.2 arc-seconds per pixel. The diffraction
spot diameter of the 5-inch diameter aperture is 2.2 arc-seconds.
The atmospheric turbulence was about 2-arc-seconds, and the
final resolution is between 2 and 3 arc-seconds. To do better than
this, one needs a larger aperture telescope, like 6 or
8-inches aperture or better and no atmospheric turbulence.
That is not a small telescope.

I have 6, 8, and 12.5-inch aperture telescopes, but chose the telephoto
to see what it could do, not to produce the best ever moon image.

Roger
Anonymous
March 17, 2005 11:30:32 PM

Archived from groups: rec.photo.digital (More info?)

Ian Mackay wrote:

> Bernard
> The author has added - 'stacked' to use the astronomers term - the images
> to, as he says, improve his S/N ratio - the three images are correlated,
> the noise isn't - then used a convolution routine to correct for errors in
> the optical system. Incidentally, a multi stage Peltier electro cooler good
> for perhaps 50 degrees les than ambient is normally used to reduce noise in
> astro imaging cameras.

Cooling applies to long exposure times, not short ones like for the moon (1/125 sec).
My moon images were photon noise limited. So no improvement was possible
except adding/averaging multiple frames. Changing to ISO 100 would
increase the smear due to the earth's rotation.

Actually, it is an error on my web page to say adding. I averaged
3 frames. But in either case, the signal-to-noise ratio is
increased by square root 3.

Roger
Anonymous
March 18, 2005 8:23:01 AM

Archived from groups: rec.photo.digital (More info?)

"Roger N. Clark (change username to rnclark)" <username@qwest.net> wrote in
message news:423A49F8.2010406@qwest.net...
> YoYo wrote:
>
>> Pete so have I, infact I have even seen better! Without using RAW or
>> without using multiple images stacked & without manipulation.
>>
>> "Pete D" <no@email.com> wrote in message
>> news:KYa_d.1223$C7.1097@news-server.bigpond.net.au...
>>
>>>I have seen as good with a pretty cheap telescope and adapter.
>
> But that wasn't the point. It was done with a telephoto lens,
> not a telescope. And in fact a short focus, f/4 telephoto lens.
>
> The image scale is 1.2 arc-seconds per pixel. The diffraction
> spot diameter of the 5-inch diameter aperture is 2.2 arc-seconds.
> The atmospheric turbulence was about 2-arc-seconds, and the
> final resolution is between 2 and 3 arc-seconds. To do better than
> this, one needs a larger aperture telescope, like 6 or
> 8-inches aperture or better and no atmospheric turbulence.
> That is not a small telescope.
>
> I have 6, 8, and 12.5-inch aperture telescopes, but chose the telephoto
> to see what it could do, not to produce the best ever moon image.
>
> Roger

Thats fine but seems a lot of work for the result, I do admit that the
photos I have seen were with film not digital. And I do actually find this
sort of thing interesting, I am playing around at the other end and am
waiting for adapters and tubes for some macro fun. Cheers.
Anonymous
March 18, 2005 11:57:49 AM

Archived from groups: rec.photo.digital (More info?)

Roger N. Clark wrote:

>The image scale is 1.2 arc-seconds per pixel.

Do you have any idea what that worked out to as a linear distance
on the moon surface? (I know, I could work it out, but then the
earth-moon distance does vary some)

--
Ken Tough
Anonymous
March 18, 2005 12:27:56 PM

Archived from groups: rec.photo.digital (More info?)

PhotoMan wrote:
> "Bernard Rother" <bprotherREMOVE1@intekom.co.za> wrote in message
> news:D 1bakr$p61$1@ctb-nnrp2.saix.net...
>
>>Hi there,
>>
>>Below is an extract from Clark Vision's website regarding a photo of the
>>moon. Can someone please explain ..... in *simple* English, the section
>>from " Three raw images ....... "
>>I lost most of it ( apart from focal lengths, iso, exposure etc ) from
>>that point onwards ;-)
>
>
> I know you believe you understand what you think he said, but I'm not sure
> you realize that what you read is not what he meant.
>
>
It all just sounded very interesting and the fact that Roger used a
camera & tele lens got me to thinking maybe I could try something
similar. All I have in my arsenal for that type of shot is a 400 mirror
lens, 2x converter, a tripod, clear sky ( live at the coast away from
big lights ) and of course, the D70. The closest I'll ever get to
Peltier cooling is drilling a hole in the body for air cooling ;-)
Bernard
Anonymous
March 18, 2005 3:47:22 PM

Archived from groups: rec.photo.digital (More info?)

In article <vt6o3ZBtvnOCFwUs@objectech.co.uk>,
Ken Tough <ken@objectech.co.uk> wrote:

> Roger N. Clark wrote:
>
> >The image scale is 1.2 arc-seconds per pixel.
>
> Do you have any idea what that worked out to as a linear distance
> on the moon surface? (I know, I could work it out, but then the
> earth-moon distance does vary some)

The smallest craters that you see are about 5 miles across, according to
information I picked up somewhere a while ago.

How's that for citing a reference?

m-m
Anonymous
March 18, 2005 6:52:59 PM

Archived from groups: rec.photo.digital (More info?)

Colin D <ColinD@killspam.127.0.0.1> wrote:

>Ken Tough wrote:
>> Do you have any idea what that worked out to as a linear distance
>> on the moon surface? (I know, I could work it out, but then the
>> earth-moon distance does vary some)

>I figure about 2.24 kilometres per pixel, and about 1560 pixels to cover
>the moon's diameter. That's taking the earth-moon distance as 385,000
>km, which is the average.

Yup, looks like a good calculation. I see its diameter is 3,476 km,
so 2230 metres per pixel. No hope of seeing a spacecraft, then.
Maybe on the next (IMO, useless) moon landing they could bring along
Christo to do some art installation visible from earth..


--
Ken Tough
Anonymous
March 18, 2005 6:53:22 PM

Archived from groups: rec.photo.digital (More info?)

What I find interesting is one of the other images with Saturn in the
background. A 500mm lens with 1.4X teleconverter giving 700mm is I think
equiv to approx 14x magnification compared to the human eye. I have looked at
Saturn through a spotting scope with a 15-45x range and it certainly did not
show resolved rings at 15x mag.
Is it possible, without the original image being resolved, to magnify in
photoshop to show a resolved image? I would have thought it unlikely since
you would be simply magnifying a small oval shaped blob into a bigger one.

Mark

Ken Tough wrote:

> Colin D <ColinD@killspam.127.0.0.1> wrote:
>
> >Ken Tough wrote:
> >> Do you have any idea what that worked out to as a linear distance
> >> on the moon surface? (I know, I could work it out, but then the
> >> earth-moon distance does vary some)
>
> >I figure about 2.24 kilometres per pixel, and about 1560 pixels to cover
> >the moon's diameter. That's taking the earth-moon distance as 385,000
> >km, which is the average.
>
> Yup, looks like a good calculation. I see its diameter is 3,476 km,
> so 2230 metres per pixel. No hope of seeing a spacecraft, then.
> Maybe on the next (IMO, useless) moon landing they could bring along
> Christo to do some art installation visible from earth..
>
> --
> Ken Tough
Anonymous
March 18, 2005 7:04:21 PM

Archived from groups: rec.photo.digital (More info?)

mark.worthington wrote:

> What I find interesting is one of the other images with Saturn in the
> background. A 500mm lens with 1.4X teleconverter giving 700mm is I think
> equiv to approx 14x magnification compared to the human eye. I have looked at
> Saturn through a spotting scope with a 15-45x range and it certainly did not
> show resolved rings at 15x mag.

A very good spotting scope will show Saturn as clearly oval at about
20x. Some people with very acute eyesight can see it with less.

> Is it possible, without the original image being resolved, to magnify in
> photoshop to show a resolved image? I would have thought it unlikely since
> you would be simply magnifying a small oval shaped blob into a bigger one.

But an f4 500mm lens in good focus is the functional equivalent of a 5"
telescope and that will have no difficulty at all in resolving Saturns
rings. The compromises in fast camera lenses probably give an image
quality roughly comparable with the view through a 3" telescope.

Where telescopes are concerned aperture determines maximum resolution. A
high quality APO for planetary work would normally be about f8.

Regards,
Martin Brown
Anonymous
March 18, 2005 7:17:24 PM

Archived from groups: rec.photo.digital (More info?)

HI Martin,

So in effect are you saying that the 500mm lenses is actually resolving the rings
albeit too small to see through the camera at the time, then when put through
photoshop and enlarged the resolution is clearly seen?

Regards

Mark

Martin Brown wrote:

> mark.worthington wrote:
>
> > What I find interesting is one of the other images with Saturn in the
> > background. A 500mm lens with 1.4X teleconverter giving 700mm is I think
> > equiv to approx 14x magnification compared to the human eye. I have looked at
> > Saturn through a spotting scope with a 15-45x range and it certainly did not
> > show resolved rings at 15x mag.
>
> A very good spotting scope will show Saturn as clearly oval at about
> 20x. Some people with very acute eyesight can see it with less.
>
> > Is it possible, without the original image being resolved, to magnify in
> > photoshop to show a resolved image? I would have thought it unlikely since
> > you would be simply magnifying a small oval shaped blob into a bigger one.
>
> But an f4 500mm lens in good focus is the functional equivalent of a 5"
> telescope and that will have no difficulty at all in resolving Saturns
> rings. The compromises in fast camera lenses probably give an image
> quality roughly comparable with the view through a 3" telescope.
>
> Where telescopes are concerned aperture determines maximum resolution. A
> high quality APO for planetary work would normally be about f8.
>
> Regards,
> Martin Brown
Anonymous
March 18, 2005 9:11:59 PM

Archived from groups: rec.photo.digital (More info?)

On Fri, 18 Mar 2005 16:04:21 +0000, Martin Brown
<|||newspam|||@nezumi.demon.co.uk> wrote:

>mark.worthington wrote:
>
>> What I find interesting is one of the other images with Saturn in the
>> background. A 500mm lens with 1.4X teleconverter giving 700mm is I think
>> equiv to approx 14x magnification compared to the human eye. I have looked at
>> Saturn through a spotting scope with a 15-45x range and it certainly did not
>> show resolved rings at 15x mag.
>
>A very good spotting scope will show Saturn as clearly oval at about
>20x. Some people with very acute eyesight can see it with less.

It varies according to the position of Saturn in its orbit and
consequently the angle of the rings. When they are edge-on you need an
enormous telescope to see them. Just at the moment (I happened to take a
look last weeekend) they are at a large angle and at their easiest to
see. Well worth a look for anyone who hasn't done so recently.

--
Stephen Poley
Anonymous
March 18, 2005 9:49:24 PM

Archived from groups: rec.photo.digital (More info?)

mark.worthington wrote:
> HI Martin,
>
> So in effect are you saying that the 500mm lenses is actually resolving the rings
> albeit too small to see through the camera at the time, then when put through
> photoshop and enlarged the resolution is clearly seen?

Mark,
I know if I zoom in with the camera zoom functions, I can see
Saturn's rings with a 500 mm lens on the LCD. I can't remember if I
can see the rings in the viewfinder. I know I can see the rings
visually in the viewfinder when I have a 2x extender on the
500 mm. If have a magnifier on your camera viewfinder, like the
Canon right angle finder C for Canon DSLRs, you can probably
see the rings with a 500mm telephoto.

Here is Saturn with a 500mm lens plus extenders:
http://clarkvision.com/astro/saturn.03.02.2004

Again, this is not the greatest Saturn image in the world,
but it was not done with a telescope. It is a telephoto
lens. I do much better with Cassini and about the
same aperture lens ;-) !

Roger
Anonymous
March 18, 2005 10:10:00 PM

Archived from groups: rec.photo.digital (More info?)

M-M wrote:

> In article <vt6o3ZBtvnOCFwUs@objectech.co.uk>,
> Ken Tough <ken@objectech.co.uk> wrote:
>
>
>>Roger N. Clark wrote:
>>
>>
>>>The image scale is 1.2 arc-seconds per pixel.
>>
>>Do you have any idea what that worked out to as a linear distance
>>on the moon surface? (I know, I could work it out, but then the
>>earth-moon distance does vary some)
>
>
> The smallest craters that you see are about 5 miles across, according to
> information I picked up somewhere a while ago.
>
> How's that for citing a reference?
>
> m-m

The smallest craters in my moon image at
http://clarkvision.com/galleries/gallery.astrophoto-1/w...
that really look like craters are 4 pixels. At 1.2 arc-seconds
per pixel, or 2.2 kilometers/pixel, that would be about 9 km
for a 4-pixel crater, or 5.5 miles. Smaller spots 3 pixels across
are craters but you couldn't prove it from that image alone; those
are less than 4 miles across.

Amateur telescopes can do much better, probably at 4 to 6 times better,
so under a mile. The best amateurs can probably do 3 or so times better
than that with image stacking methods.

But that is not the smallest craters one can see. I have seen detail on
the moon around 0.05 arc-second through an 88-inch aperture telescope
(Clark, R.N., Perfect Seeing, Sky and Telescope, page 103, July, 1997).
That corresponds to about 0.1 km, or a little more than a football field.
I bet other astronomers have done better.

Roger
Anonymous
March 19, 2005 1:33:01 AM

Archived from groups: rec.photo.digital (More info?)

In article <41FCBDAF.753E05EA@ntlworld.com>,
"mark.worthington" <mark.worthington@ntlworld.com> wrote:

> I have looked at
> Saturn through a spotting scope with a 15-45x range and it certainly did not
> show resolved rings at 15x mag.

You need 60x or 4000mm to see the rings on Saturn clearly.

m-m
Anonymous
March 19, 2005 2:39:49 AM

Archived from groups: rec.photo.digital (More info?)

Ken Tough wrote:
>
> Roger N. Clark wrote:
>
> >The image scale is 1.2 arc-seconds per pixel.
>
> Do you have any idea what that worked out to as a linear distance
> on the moon surface? (I know, I could work it out, but then the
> earth-moon distance does vary some)
>
> --
> Ken Tough

I figure about 2.24 kilometres per pixel, and about 1560 pixels to cover
the moon's diameter. That's taking the earth-moon distance as 385,000
km, which is the average.

Colin
!