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Re: [Wanna be Astronomers] low magnification astronomy

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  • Ronald Scratch
    Most of those magnifications fall around binocular strength or lower power eyepieces, depending on what type of scope you use them with. Usually these are
    Message 1 of 8 , Sep 25, 2008
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      Most of those magnifications fall around binocular strength or lower power eyepieces, depending on what type of scope you use them with.

      Usually these are wider fields, which are good for:
      Open Star clusters. Ex: M45
      Some Nebulae. Ex: Orion Nebula
      Moon. Ex: Lunar Maria
      Wide field views of the Milky-way.


      Ron


      --- On Thu, 9/25/08, ali <ak666666@...> wrote:

      > From: ali <ak666666@...>
      > Subject: [Wanna be Astronomers] low magnification astronomy
      > To: wannabeastronomers@yahoogroups.com
      > Date: Thursday, September 25, 2008, 11:08 AM
      > Hello
      >
      > How much astronomy can be done with following
      > magnifications:
      >
      > 10X
      > 20X
      > 30X
      > 40X
      >
      >
      >
      >
      > Thanks
      >
      >
      >
      > Ali
    • John
      Ali: Actually, I do quite a bit of observing at 37.5X -- which in my 8 Dob that has a 1200mm focal length, using a 32mm plossl is a field of view that is 70.5
      Message 2 of 8 , Sep 26, 2008
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        Ali:

        Actually, I do quite a bit of observing at 37.5X -- which in my 8" Dob
        that has a 1200mm focal length, using a 32mm plossl is a field of view
        that is 70.5 arc-minutes, or a little over 1 degree.

        I find that this is a great magnification to use with my 8" Dob, and
        the field of view is perfect for most deep sky objects. The field of
        view is a little restricted for finding some objects. Also, it is a
        little restrictive for the Andromeda galaxy. To solve those problems I
        have a 38mm Erfle eyepiece (2" eyepiece), which is 31X magnification,
        with a field of view that is 114 arc-minutes, or almost 2 degrees,
        which makes for very comfortable viewing from an 8" scope.

        I rarely go much over 50X for any of my deep-space observing. I will
        creep the magnification up to 200X on some objects, but this is rarely
        warranted. I live in an area that has a limiting magnitude of over +7
        on almost any moonless night, and very steady seeing, so I can push
        the magnification on my 8" past 250X on objects like M57, M27, M51,
        and almost any of the globular clusters, but again, I rarely do. 99%
        of my viewing is done at under 40X.

        John, east central Nevada
      • ali
        John: Your reply was most informative. I was thinking of making a small refractor working at these magnifications. Your account has made me thinking that a f6
        Message 3 of 8 , Sep 26, 2008
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          John:
           
          Your reply was most informative.
          I was thinking of making a small refractor working at these magnifications.
          Your account has made me thinking that a f6 8" scope is a great instrument.
          Over +7 limiting mag means you have great skies!
          Do you take photographs too from your scope?
           
           
          Ali, Lahore Pakistan
           
           
        • John
          Ali, Not a problem. I am limited on the pictures that I can take with my scope -- it is only on a Dobsonian mount -- however, I have taken some good pics of
          Message 4 of 8 , Sep 28, 2008
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            Ali,

            Not a problem. I am limited on the pictures that I can take with my
            scope -- it is only on a Dobsonian mount -- however, I have taken some
            good pics of the moon. In my opinion, the 8" Dobsonian is one of the
            best scopes to start doing serious visual observations. I will say,
            however, that even an 8" reflector is limited by sky conditions more
            so than even a 6" reflector. I am a major proponent of the reflector
            telescope. I may be a little bias. When you look at the fact that an
            8" reflector here is states sells for around $300 dollars and will
            give views as good as a 6"-7" refractor that sells for 10X as much,
            and without the problems of chromatic aberration that refractors suffer.


            Yes, Ali, I am blessed with very clear skies here. I am in the high
            desert of Nevada. Where I live is at over 7000' above sea level, my
            main observing site is at over 9600' above sea level. My humidity is
            almost always below 15% and it does not rain here often (less than 10"
            per year). The only problem is that once winter comes, which is very
            soon here, I will not be able to get to my main observing site. That
            is alright though, since my back yard almost always has a limiting
            magnitude of around +6. The only problem is that we see minus 40-50
            below zero Fahrenheit here in the winter, but there is such a
            temperature swing from day to night that we may see 20 degrees above
            zero in the day. I have seen as much as an 80 degree temperature
            difference from day to night here, and as much as a 30 degree
            difference in one hour after sunrise or sunset! Crazy, I know!


            There is one thing that I was going to add, but forgot: When trying to
            figure out what your lowest magnification should be for the telescope
            that you want to use; you simply divide your eyepiece focal length by
            the F ratio of the telescope, this will give you the exit pupil
            diameter. For an adult over about 30 years-old I would go with an exit
            pupil of about 6-6.5, since this is about the maximum diameter that
            your dark-adapted pupil will dilate to anyway.

            John
          • ali
            John, Please send one of your moon pictures if possible. Regards Ali ... From: John To: wannabeastronomers@yahoogroups.com Sent: Sunday, September 28, 2008 9:7
            Message 5 of 8 , Sep 29, 2008
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              John,
               
              Please send one of your moon pictures if possible.
               
               
              Regards
               
              Ali
               
              ----- Original Message -----
              From: John
              Sent: Sunday, September 28, 2008 9:7 p
              Subject: [Wanna be Astronomers] Re: low magnification astronomy

              Ali,

              Not a problem. I am limited on the pictures that I can take with my
              scope -- it is only on a Dobsonian mount -- however, I have taken some
              good pics of the moon. In my opinion, the 8" Dobsonian is one of the
              best scopes to start doing serious visual observations. I will say,
              however, that even an 8" reflector is limited by sky conditions more
              so than even a 6" reflector. I am a major proponent of the reflector
              telescope. I may be a little bias. When you look at the fact that an
              8" reflector here is states sells for around $300 dollars and will
              give views as good as a 6"-7" refractor that sells for 10X as much,
              and without the problems of chromatic aberration that refractors suffer.

              Yes, Ali, I am blessed with very clear skies here. I am in the high
              desert of Nevada. Where I live is at over 7000' above sea level, my
              main observing site is at over 9600' above sea level. My humidity is
              almost always below 15% and it does not rain here often (less than 10"
              per year). The only problem is that once winter comes, which is very
              soon here, I will not be able to get to my main observing site. That
              is alright though, since my back yard almost always has a limiting
              magnitude of around +6. The only problem is that we see minus 40-50
              below zero Fahrenheit here in the winter, but there is such a
              temperature swing from day to night that we may see 20 degrees above
              zero in the day. I have seen as much as an 80 degree temperature
              difference from day to night here, and as much as a 30 degree
              difference in one hour after sunrise or sunset! Crazy, I know!

              There is one thing that I was going to add, but forgot: When trying to
              figure out what your lowest magnification should be for the telescope
              that you want to use; you simply divide your eyepiece focal length by
              the F ratio of the telescope, this will give you the exit pupil
              diameter. For an adult over about 30 years-old I would go with an exit
              pupil of about 6-6.5, since this is about the maximum diameter that
              your dark-adapted pupil will dilate to anyway.

              John

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