Why can't I see Jupiters moons ?

Discussion in 'Digital Cameras' started by Guest, May 22, 2005.

  1. Guest

    Guest Guest

    I am able to see jupiters moon with my x7 binoculars, but why
    can't I see them when I take a picture of Jupiter with my
    Olympus 2020 zoom. I used the full zoom (x3) plus the digital
    zoom (2.5), but nothing, i.e. only jupiter ???
    Guest, May 22, 2005
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  2. Guest

    ASAAR Guest

    Two reasons I can think of, but they're only guesses. First, is
    Jupiter brighter than its moons? If you're not sure, maybe there
    are some astronomical albedo tables that you could search for. You
    might try increasing the exposure time, unless you're already using
    the max. allowed by your camera. I hope you're using a really solid

    Second, even at full zoom (and I doubt that the digital zoom would
    help) jupiter itself is probably a pretty small part of the image.
    If you greatly magnify the image on your computer you could probably
    count how many pixels wide it is. Divide the number of pixels by
    the ratio of Jupiter's diameter to its moon's diameter. This will
    tell you how wide the moon should be, in pixels. If the result
    isn't at least 2, you're unlikely to notice any moons in the
    picture. If it's in the range of 2 to 4, any motion at all, such as
    vibration transferred through the ground is likely to contribute
    enough blur to make the moons difficult to see.
    ASAAR, May 22, 2005
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  3. Guest

    Matt Ion Guest

    That's true only for 35mm film and/or digitals with the same size sensor.

    A more accurate rule of thumb would be 1X magnification is focal length
    divided by diagonal size of film frame or sensor. A 35mm film frame is
    about 63mm diagonally, but 50 will give you a close enough approximation
    to remember easily. f=126mm would give you about 2X magnification,
    f=189mm would be 3X, and so on.

    With a smaller sensor, the corresponding focal length needed gets smaller.

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  4. olivia wrote:
    : I am able to see jupiters moon with my x7 binoculars, but why
    : can't I see them when I take a picture of Jupiter with my
    : Olympus 2020 zoom. I used the full zoom (x3) plus the digital
    : zoom (2.5), but nothing, i.e. only jupiter ???

    You have already received info on the difference in how binocs and cameras
    use the term X. And you got info on exposure based on the moon instead of
    Jupiter itself. But one other thing to consider. In your calculations, use
    only the Optical zoom number. Digital zoom will not help in this case. A
    digital zoom just takes the data from a small part of the largest optical
    image and multiplies it to fill the image. So this does not increase the
    details available, just makes the details already available larger (and
    fuzzier). I know that this description is very inacurate and there will be
    others who may give long math rich explainations of the process of Digital
    Zoom, but for the newcomer to the concept it will get the idea across.

    So between your 105mm max optical zoom (roughly equal to 2x binocs), and
    the blurring of the digital zoom you will not come anywhere close to the
    resolution of your 7x binocs. At best you are getting 2x.

    To match your 7x binocs you would need a 350mm lens (aprox) and you would
    have to meter the exposure to the brightness of the moons. If the metering
    is done on Jupiter itself, the moons would be so under exposed as to be
    nearly (or completely) invisible. The best way to get a photo of
    astronomical objects may be to use a regular astronomical telescope and a
    camera adapter to replace the eyepiece of the telescope.


    Randy Berbaum
    Champaign, IL
    Randy Berbaum, May 22, 2005
  5. Guest

    Deep Reset Guest

    A more accurate diagonal length of a 35mm frame (36mm * 24mm) would be
    more like 43mm. (Pythagorus)

    Deep Reset, May 22, 2005
  6. Guest

    Darrell Guest

    I have really good 7x50 binoculars but I am not convinced they have enough
    power to see Jupiter, let alone it's moons.
    Darrell, May 22, 2005
  7. Guest

    Ron Hunter Guest

    Probably not. My brother used to have a pair of 16x50 that did a good
    job on both Jupiter, and Saturn. I could clearly see the 4 major moons.
    Of course, his 6" reflector did even better!
    Ron Hunter, May 22, 2005
  8. Guest

    Nostrobino Guest

    That's true.

    So far, so good.


    You can easily prove to yourself that this is wrong. Take a 50mm lens which
    can be removed from the camera with the diaphragm wide open. (Screw-mount
    SLR lenses generally are this way, while many others, eg. Minolta AF bayonet
    mount, stop down all the way when removed from the body unless the
    activating pin is held in the full open position.)

    Now hold that lens over a page of typescript and vary the distance until
    it's in focus. You will see that the typescript is *considerably* magnified,
    which of course would not be the case if it had "a magnifying power of 1x,"
    which would be no magnification at all. The 50mm lens will in fact magnify
    the image about 5x.

    The magnifying power of a lens is traditionally taken to be 250 divided by
    the focal length of the lens in mm. In other words, it is exactly the
    *reverse* of your idea; magnifying power *decreases* with longer focal
    length, it does not increase.

    This too you can easily prove to yourself. Take a strong magnifier or loupe,
    say 10x or more, and see how short its focal length is by projecting the
    image of a distant subject onto some suitable surface, such as a piece of
    paper. Compare this with a relatively weak magnifying glass of 2x or 3x,
    which you will find has a much longer focal length.

    Similarly, anyone who uses a microscope would (or should) be able to tell
    you that higher power eyepieces have shorter focal lengths than lower power
    ones do. (The eyepiece lens magnifies the virtual image formed by the
    microscope's objective lens.) The same thing is true of binoculars and other
    telescopes, for that matter; shorter f.l. eyepieces give proportionally
    greater magnification, though in the case of binoculars you generally don't
    know what the eyepiece f.l. is.

    The problem here is that "magnification" has effectively different meanings
    in different applications. Yes, 7x binoculars magnify the image 7 times
    compared to the unaided eye, and a 20x spotting scope magnifies the image 20
    times compared to the unaided eye. And yes, a 200mm lens magnifies an image
    4x IN THE CAMERA, COMPARED TO a 50mm lens. But outside of that specific
    comparison it is meaningless to say that a 200mm lens has a magnification of
    4x. That has no relationship whatever to the magnification of a telescope or
    binoculars, just as neither has any direct relationship to the power of a
    magnifying glass or loupe.

    Nostrobino, May 22, 2005
  9. Guest

    Bubbabob Guest

    Jupiter is one of the brightest objects in the sky. I knew a 10 year old
    kid once who couldd see all four of Jupiter's moons naked-eye. Amazing what
    you can see before the lens of the eyes starts to become fibrous with age.

    I have seen the planet Uranus without any optical aid at all.
    Bubbabob, May 22, 2005
  10. Guest

    Guest Guest

    : I am able to see jupiters moon with my x7 binoculars, but why
    You can see Jupiter just with your eyes, after the moon it is the 2nd
    brightest object in the night sky. 4 moon are barely visible with x7.
    I can almost guarantee you won't see any moons with x16 because
    of the shake, unless you have some form of tripod arrangement.
    Guest, May 22, 2005
  11. I got a long way down the path toward a career in astronomy because,
    as a kid, I aimed 7x50 binocs at Jupiter one night and saw Jupiter's
    disk (obviously not a star), and 4 bright stars nearby, all more or
    less in a line. I didn't know what it was, so I recorded the positions
    of the stars. They were quite bright and quite a distance from

    The binocs were top quality USNavy issue. It helped to steady the
    heavy binocs against something.

    The next night I looked at it again, and the nearby "stars" had moved!
    But they were still more or less in a line. I recorded the positions
    every clear night for a month or so. Of course many times I could see
    less than 4. I finally made it to a library (this was in the early
    60's), and compared my charts with with diagrams in Sky & Telescope,
    learned I had been looking at Jupiter, and figured out which moon was
    which. I was hooked.

    I still use the binocs for looking at the (luckily) dark night sky.

    Duncan Chesley, May 22, 2005
  12. Guest

    Ron Hunter Guest

    Elbows braced on the roof of a car works...
    Ron Hunter, May 22, 2005
  13. On Sun, 22 May 2005 11:22:56 -0400, in rec.photo.digital , "Darrell"

    I have seen Jupiter, unaided, in New York City. It is pretty bright.

    Matt Silberstein

    All in all, if I could be any animal, I would want to be
    a duck or a goose. They can fly, walk, and swim. Plus,
    there there is a certain satisfaction knowing that at the
    end of your life you will taste good with an orange sauce
    or, in the case of a goose, a chestnut stuffing.
    Matt Silberstein, May 23, 2005
  14. Guest

    Darrell Guest

    I can see the bright object, I know it's Jupiter. But with my 7x50 I still
    see a star like object, and I don't see it's satellites. On Friday Jupiter
    was in the sky near the moon. I will correct my earlier statement I doubt I
    can see it's moons through my 7x50's I am skeptical people can resolve
    enough detail to see the moons un-aided.
    Darrell, May 23, 2005
  15. Guest

    Bubbabob Guest

    Most people can't but I saw a kid do it once. He was able to describe the
    positions of all of the moons. It takes young, perfect eyes and a
    transparent, steady sky.

    If you can't see a small disk with your 7X50's either something is wrong
    with them or something is wrong with your eyes. Try focusing better. The
    moons should be readily visible as well, even in a trashed out city sky.
    Bubbabob, May 23, 2005
  16. Guest

    ASAAR Guest

    And not all people's vision is limited to 20/20. Whenever I had
    my vision tested in school, reading succesive lines of progressively
    smaller letters on the eye chart, they always had me stop reading
    letters when I could have gone several lines beyond. And I guess
    you're right about youthful eyes having advantages. When my parents
    were fairly young (about 30, and possessing good vision themselves),
    I could always read highway road signs long before the car got close
    enough for them to make out what was on the signs. Now that I think
    of it, they didn't exactly encourage my assistance. :)
    ASAAR, May 23, 2005
  17. On Mon, 23 May 2005 05:21:05 -0000, Bubbabob

    Right. But remember that the moons move from night to night. Often all
    four won't be visible. Occasionally none will be visible because they
    will be either in front of Jupiter, behind it, or in its shadow.

    Duncan Chesley, May 23, 2005
  18. Guest

    Nostrobino Guest

    You may be just exchanging that ball of wax for a can of worms. ;-)

    Nostrobino, May 23, 2005
  19. Guest

    Darrell Guest

    I have seen camera store clerks describe a 10X (10:1 zoom ratio) as being
    more powerful than 7X binoculars, and he tried to correct the customer who
    said, "I think that's wrong"
    Darrell, May 23, 2005
  20. Guest

    Nostrobino Guest


    Now there's a clerk who's in the wrong line of work.

    Nostrobino, May 23, 2005
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