Re: Canon 10D on a telescope

Discussion in 'Digital Photography' started by Bart van der Wolf, Jul 12, 2003.

  1. "Brian McMahon" <> wrote in message
    news:beod8f$fg0$...
    > Hi,
    >
    > I want to try some pictures using a 10D mounted on an astronomical

    telescope
    > using a T mount adaptor.
    >
    > Could anyone help in what setting would be best for stopped down exposure

    ?
    > Or am going to have to estimate it and use a bit of trial and error on
    > manual ?


    It would require knowledge of the telescope's characteristics and the
    magnitude of the celestial objects. Trial and error is cheap with digital,
    go that way...

    Bart
     
    Bart van der Wolf, Jul 12, 2003
    #1
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  2. "Brian McMahon" <> writes:

    >Thanks Lionel and Bart for your replies. I suspected trial and error might
    >be the only way. I was hoping there would be a stopped down auto mode, as
    >there used to be on my old A-1, for stopped down aperture priority
    >automatic, or stopped down manual metering. That was when T mount lenses
    >were still quite common, of course and I found it useful on the lenses of
    >that type that I owned.


    It's strange to hear you talking about "stopped down" in the context of
    astrophotography, because normally there is no aperture diaphragm to
    stop down. In prime focus photography, which is what you use a
    T-adapter for, the telescope objective focuses its image directly onto
    the film or electronic sensor. There's no telescope eyepiece and no
    camera lens in the optical path, and no aperture to stop down.

    Of course, taking aperture equals viewing aperture, so you want to meter
    in the same mode that you'd use with a camera lens stopped down to
    taking aperture. This is probably what you mean.

    >Regrettably, tonight's planned session has been called off, as my friend was
    >rushed off to hospital in a coma, after being attacked and stung repeatedly
    >by a swarm of bees. African bees have a potent sting. He's OK now though and
    >is likely to be discharged this evening. We'll try again another evening in
    >a few days time.


    Ouch.

    Dave
     
    Dave Martindale, Jul 13, 2003
    #2
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  3. Bart van der Wolf

    Mark M Guest


    > I was hoping to take some pictures of Mars, with the assistance of an
    > Astronomer friend of mine. He had calculated that Mars would show a disk
    > larger than the 10D's partial metering circle on the specific telescope to
    > be used, so having the camera do the metering would've been quite handy

    :)

    I wouldn't rely on any camera's meter for this type of work, though the
    10D's meter is a vast improvemetn over it's predacessors (D30/D60). Use the
    histrogram review option to get a good idea of where you are exposure-wise
    in the field.

    > Regrettably, tonight's planned session has been called off, as my friend

    was
    > rushed off to hospital in a coma, after being attacked and stung

    repeatedly
    > by a swarm of bees. African bees have a potent sting.


    I'm sorry to hear about your friend.
    Just for nit-picking's sake... [Someone must carry the torch of nit-picking,
    after all! :) ] -African bee stings are no more potent than our own native
    variety of bee. It's just that they are far more aggressive, and sting in
    larger numbers. More stings equal more damage...but the severity of each
    individual sting is no more severe.

    Class dismissed... :)


    >He's OK now though and
    > is likely to be discharged this evening.


    Glad to hear he's OK.
     
    Mark M, Jul 13, 2003
    #3
  4. "Dave Martindale" <> wrote in message
    news:beq7s5$ne$...
    > "Brian McMahon" <> writes:
    >
    >
    > It's strange to hear you talking about "stopped down" in the context of
    > astrophotography, because normally there is no aperture diaphragm to
    > stop down. In prime focus photography, which is what you use a
    > T-adapter for, the telescope objective focuses its image directly onto
    > the film or electronic sensor. There's no telescope eyepiece and no
    > camera lens in the optical path, and no aperture to stop down.
    >
    > Of course, taking aperture equals viewing aperture, so you want to meter
    > in the same mode that you'd use with a camera lens stopped down to
    > taking aperture. This is probably what you mean.
    >


    > Dave


    Not only telescopes have a fixed aperture. Some photographic lenses do too,
    notably catadioptric types. Since a stopped down metering mode, such as I
    described, takes no notice of any aperture information, as it was designed
    for lenses which could not communicate this information to the camera, the
    meter merely measures the actual light at whatever the taking aperture is
    set to. Thus it doesn't matter whether the lens has a variable aperture or
    not. In the case of a lens, or telescope with a fixed aperture, then it is
    effectively always "stopped down" to the taking aperture, as far as the
    camera and any metering system is concerned.

    As in my previous email, Canon used to provide such a mode and it was called
    "stopped down" metering. It was designed for any kind of lens which could
    not communicate it's aperture to the camera., including any fixed aperture
    type.

    Regards,
    Brian
     
    Brian McMahon, Jul 14, 2003
    #4
  5. "Mark M" <> wrote in message
    news:cQ6Qa.3772$Bp2.2437@fed1read07...
    >
    >
    > I wouldn't rely on any camera's meter for this type of work, though the
    > 10D's meter is a vast improvemetn over it's predacessors (D30/D60). Use

    the
    > histrogram review option to get a good idea of where you are exposure-wise
    > in the field.
    >


    Thanks, that's a useful tool to use.


    >
    > I'm sorry to hear about your friend.
    > Just for nit-picking's sake... [Someone must carry the torch of

    nit-picking,
    > after all! :) ] -African bee stings are no more potent than our own

    native
    > variety of bee. It's just that they are far more aggressive, and sting in
    > larger numbers. More stings equal more damage...but the severity of each
    > individual sting is no more severe.
    >
    > Class dismissed... :)
    >
    >


    Certainly getting in the way of a swarm of African bees, or disturbing a
    nest will cause a greater reaction, resulting in multiple stings.

    Most stings, however, are from single bees and are accidental and not
    related to mass attacks, which are extremely rare. Note that I am referring
    to African bees living in Africa, not the infamous hybrids occurring in
    parts of America, or the wild stories that have arisen as a result. The
    sting certainly appears to create a much higher level of subsequent allergy
    than bees in other parts of the world and a further sting, at some future
    time, appears to result in allergic symptoms, which are taken very seriously
    by the medical profession here.

    It is quite normal to have bees as visitors at the table, when eating
    outdoors, but whilst everyone is wary of them, they are, after all, a part
    of life here and you just have to be careful not to trap one accidentally,
    or take a drink from a soft drink can, without checking first for the
    presence of a bee. Yes, stings in the mouth are the most common ones. I've
    never heard of any bee stings being initiated by aggressive bees, apart from
    disturbed nests or swarms ( rare enough not to be any concern). I've also
    never heard of a bee that has been attacked by a human, accidentally or
    otherwise, going off to find a gang of his mates to come back and
    aggressively seek out and inflict multiple stings on the perceived attacker.
    An accidental sting is taken seriously here and usually medical attention is
    sought, just in case.

    In the case of my friend, he had been stung before and was indeed allergic,
    the allergy having developed as a result of the first sting, as opposed to
    an existing allergy. He found this out the next time he was stung. He is,
    however, an amateur bee keeper and has no intention of giving up his hobby,
    eccentric scientist that he is. The weekend accident was due to his desire
    to move a new swarm that had arrived in the guest area of the game reserve
    and whilst he was donning protective clothing, another group of staff
    started spraying the nest with insecticide, which rather annoyed the bees.
    He was stung three times and was immediately taken to hospital by a
    colleague, who was with him at the time. Nobody else was stung, as they
    already had protective gear on. It took an hour to get to the hospital, from
    the game reserve he is based at, by which time he was in coma. He's fine now
    though and back at work.

    So, whilst we don't consider bees to be any kind of major hazard, compared
    to others (like eating the wrong kind of food and dying of heart attack), we
    do have some respect for them :)

    Regards,
    Brian
    In sunny South Africa
     
    Brian McMahon, Jul 14, 2003
    #5
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