Moon shot - Explanation - Clark Vision

Discussion in 'Digital Photography' started by Bernard Rother, Mar 17, 2005.

  1. 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."
     
    Bernard Rother, Mar 17, 2005
    #1
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  2. Bernard Rother

    Paul Mitchum Guest

    Bernard Rother <> 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-1/web/moon-JZ3F
    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.
     
    Paul Mitchum, Mar 17, 2005
    #2
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  3. Bernard Rother

    Ian Mackay Guest

    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" <> wrote in message
    news:d1bakr$p61$...
    > 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."
     
    Ian Mackay, Mar 17, 2005
    #3
  4. Bernard Rother

    Pete D Guest

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

    "Paul Mitchum" <0m> wrote in message
    news:1gtjij6.1kh3vza75scncN%0m...
    > Bernard Rother <> 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-1/web/moon-JZ3F
    > 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.
     
    Pete D, Mar 17, 2005
    #4
  5. Bernard Rother

    PhotoMan Guest

    "Bernard Rother" <> wrote in message
    news:d1bakr$p61$...
    > 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.
     
    PhotoMan, Mar 17, 2005
    #5
  6. Bernard Rother

    YoYo Guest

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

    "Pete D" <> wrote in message
    news:KYa_d.1223$...
    > I have seen as good with a pretty cheap telescope and adapter.
    >
    > "Paul Mitchum" <0m> wrote in message
    > news:1gtjij6.1kh3vza75scncN%0m...
    > > Bernard Rother <> 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-1/web/moon-JZ3F
    > > 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.

    >
    >




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    YoYo, Mar 17, 2005
    #6
  7. 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" <> wrote in message
    > news:KYa_d.1223$...
    >
    >>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
     
    Roger N. Clark (change username to rnclark), Mar 18, 2005
    #7
  8. 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
     
    Roger N. Clark (change username to rnclark), Mar 18, 2005
    #8
  9. Bernard Rother

    Pete D Guest

    "Roger N. Clark (change username to rnclark)" <> wrote in
    message news:...
    > 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" <> wrote in message
    >> news:KYa_d.1223$...
    >>
    >>>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.
     
    Pete D, Mar 18, 2005
    #9
  10. Bernard Rother

    Ken Tough Guest

    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
     
    Ken Tough, Mar 18, 2005
    #10
  11. PhotoMan wrote:
    > "Bernard Rother" <> wrote in message
    > news:d1bakr$p61$...
    >
    >>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
     
    Bernard Rother, Mar 18, 2005
    #11
  12. Bernard Rother

    Colin D Guest

    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
     
    Colin D, Mar 18, 2005
    #12
  13. Bernard Rother

    M-M Guest

    In article <>,
    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)


    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
     
    M-M, Mar 18, 2005
    #13
  14. Bernard Rother

    Ken Tough Guest

    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
     
    Ken Tough, Mar 18, 2005
    #14
  15. 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
     
    mark.worthington, Mar 18, 2005
    #15
  16. Bernard Rother

    Martin Brown Guest

    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
     
    Martin Brown, Mar 18, 2005
    #16
  17. 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
     
    mark.worthington, Mar 18, 2005
    #17
  18. 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
     
    Stephen Poley, Mar 18, 2005
    #18
  19. Bernard Rother

    M-M Guest

    In article <>,
    "mark.worthington" <> 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
     
    M-M, Mar 18, 2005
    #19
  20. 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
     
    Roger N. Clark (change username to rnclark), Mar 19, 2005
    #20
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