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  • Spotting Scope Size

    My spotting scope only goes up to 45x with 50mm lens. Do any of you know what is the highest magnification and diameter I need to see .30 holes at around 500 meters or approximately 500 yards.

    Tom
    T.Bruner

  • #2
    Thomas,
    Wow that is gonna be a hefty optic I think. Seeing a single hole from a 308, at 500 yards, sounds more like a telescope then a spotting scope. If he doesn't comment here, you might PM Rebhawk who works with optics of that nature.
    CelticRaven

    -- Poor is the country with no heroes and worse yet, is the country that forgets its heroes.

    Plan for what CAN happen, not what HAS happened.
    --CelticRaven

    The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
    --Thomas Jefferson

    Comment


    • #3
      Hey Guys,
      For a purely range scope, with just about zero tactical application, there was some discussion a while back on the web, about using some of the larger Meade ETX Telescopes for this purpose, as well as working as an extended range spotter for larger calibers. I've never done it, so the information is speculative at best, though it was reported to be very effective and relatively cost effective by the users, at the time.
      Respectfully,
      Harry
      "It's better to live one day as a lion, than one hundred years as a sheep", Old Roman Proverb.
      "For those who have fought for it, freedom has a flavor the protected will never know", Author Unknown.
      "Cry havoc and let slip the dogs of war!", Shakespeare, Julius Ceaser, Act III, Scene I.

      Comment


      • #4
        Thomas:
        The max useful magnification, under ideal conditions, is something like 60x per inch of aperture. If you have mirage, you can't go that high.

        The other consideration is the resolving power of the scope. Your naked eye can resolve objects as small as about 60 arc seconds (taking into account the eye's imperfections from theoretical), which is an arc minute, which in turn is about 0.016667 degrees. We can use 1/2 that angle, or 0.008333) degrees as one angle of a right angle to figure out the distance. Thus, a 308 diameter hole is 60 arc seconds wide at a range of:

        Tan(0.008333) = 0.154 / Range

        Where 0.154 is 1/2 the diameter of a 0.308 bullet, since we are also using 1/2 the angle.

        Solving for range, we get:

        Range = 0.154 / Tan(0.008333)

        Range = 1059 inches, approximately.

        In yards, that is:

        Range in Yards = 1059 / 36

        Range in Yards = 29.5 yards, approximately, with the naked eye, assuming a 5mm pupil.

        The important thing here is not the magnification so much, however, it is the size of the scope. The resolving power of a scope theoretically is:

        Resolution in arc-seconds = 0.02 x (wavelength / D)

        where D is the diameter of the objective in centimeters and wavelength is in nanometers. For our purposes, we can use 500 for wavelength.

        Thus, your 50mm scope, if perfect, should resolve objects:

        0.02 x (500 / 5) = 2 arc seconds. Let's use a "safety factor" of 3 times this number, just like the safety factor of 3 that is commonly accepted for the eye. and say 6 arc seconds. Thus, your scope should be able to resolve a 0.308 bullet hole out to:

        Tan(0.00083333) = 0.154 / Range

        Solving for Range like we did in the eye example, this gives us:

        10588 inches, which is equal to 295 yards. No coincidence. Your 50mm scope has an objective 10 times the diameter of your 5mm pupil, so it can resolve the same size object out 10 times as far. Doesn't matter how much magnification you add to the scope, it ain't gonna see 308 holes much past that distance, and that's probably in perfect conditions.

        Now, if you want a scope that can see out to 500 yards, you can just set up a ratio to find the diameter necessary, since all these are linear equations:

        50 / 295 = D / 500

        If we solve for D, we get an aperture of:

        D = (50 x 500) / 295 = 84.7, call it 85 mm. That's a pretty big piece of glass.

        As for magnification, you're going to need 500 / 29.5, or at least 17x, but again, the important factor here is the diameter of the objective lens.

        Now, all these numbers are theory. I suggest you borrow something like a Kowa 80mm spotter, and see what you can see.

        Regards,
        --Hawk
        There are few problems a well-placed 308 cannot cure. --- Hawk

        Gentlemen! You can't fight in here! This is the War Room! --- President Merkin Muffley in Dr. Strangelove

        Rocket Science is much more fun when you actually have rockets! --- USN Recruiting Commercial

        A little revolution now and then is a good thing --- Thomas Jefferson

        Only the dead have seen an end to war --- Plato

        "In Ireland, in Lebanon, in Palestine & Berkeley, Patty Hurst, heard the burst, of Roland's Thompson gun & bought it!!!" --- The Late Warren Zevon, Roland The Headless Thompson Gunner

        In the 1500's, the Roman Catholic Church sold indulgences to forgive sin. In the 21st century, we call these carbon offsets. ---Hawk

        �Fight like a man, so you will not have to die like a dog� --- Calico Jack Rackham's Mistress

        Comment


        • #5
          Hey Lee,
          Yeah...that's just great ...now I have a nose bleed ...Okay, where are the tissues ...Thanks, Bro ...
          Respectfully,
          Harry
          "It's better to live one day as a lion, than one hundred years as a sheep", Old Roman Proverb.
          "For those who have fought for it, freedom has a flavor the protected will never know", Author Unknown.
          "Cry havoc and let slip the dogs of war!", Shakespeare, Julius Ceaser, Act III, Scene I.

          Comment


          • #6
            [quote]
            Hey Lee,
            Yeah...that's just great ...now I have a nose bleed ...Okay, where are the tissues ...Thanks, Bro ...
            Respectfully,
            Harry[/b]
            Luckily, I changed the last part from Arctangents to a ratio calculation...

            If it got lost in all the math, all anyone now has to do to figure out what size spotter they need to see 308 holes at a given range is use the ratio:

            50 / 295 = D / Range

            If you know either the Range or D (diameter of spotter) you can figure out the other one.

            Got another caliber you need to spot? Then do the above calculation for a 308, then just multiply by the ratio of the calibers. For example, if I wanted to see 50 cal bullet holes at 1000, I'd first do the calculation for 308:

            50 / 295 = D / 1000

            D = 169 mm

            Now, multiply by the ratio of the calibers:

            D = (0.308 / 0.500) x 169

            D = 105mm roughly.

            Again, all these numbers are theoretical. However, they do match pretty well Harry's comment about using a Meade ETX for long-range spotting. Meade ETX's currently come in 90 and 125 mm sizes.

            Cheers,
            --Hawk
            There are few problems a well-placed 308 cannot cure. --- Hawk

            Gentlemen! You can't fight in here! This is the War Room! --- President Merkin Muffley in Dr. Strangelove

            Rocket Science is much more fun when you actually have rockets! --- USN Recruiting Commercial

            A little revolution now and then is a good thing --- Thomas Jefferson

            Only the dead have seen an end to war --- Plato

            "In Ireland, in Lebanon, in Palestine & Berkeley, Patty Hurst, heard the burst, of Roland's Thompson gun & bought it!!!" --- The Late Warren Zevon, Roland The Headless Thompson Gunner

            In the 1500's, the Roman Catholic Church sold indulgences to forgive sin. In the 21st century, we call these carbon offsets. ---Hawk

            �Fight like a man, so you will not have to die like a dog� --- Calico Jack Rackham's Mistress

            Comment


            • #7
              [quote]
              <div class='quotemain'>Hey Lee,
              Yeah...that's just great ...now I have a nose bleed ...Okay, where are the tissues ...Thanks, Bro ...
              Respectfully,
              Harry[/b]
              Luckily, I changed the last part from Arctangents to a ratio calculation...

              If it got lost in all the math, all anyone now has to do to figure out what size spotter they need to see 308 holes at a given range is use the ratio:

              50 / 295 = D / Range

              If you know either the Range or D (diameter of spotter) you can figure out the other one.

              Got another caliber you need to spot? Then do the above calculation for a 308, then just multiply by the ratio of the calibers. For example, if I wanted to see 50 cal bullet holes at 1000, I'd first do the calculation for 308:

              50 / 295 = D / 1000

              D = 169 mm

              Now, multiply by the ratio of the calibers:

              D = (0.308 / 0.500) x 169

              D = 105mm roughly.

              Again, all these numbers are theoretical. However, they do match pretty well Harry's comment about using a Meade ETX for long-range spotting. Meade ETX's currently come in 90 and 125 mm sizes.

              Cheers,
              --Hawk
              [/b]
              T.Bruner

              Comment


              • #8
                Thanks guys for the info. I usually use a 12 inch shoot-n-see target as 500 meters and 500 yards. I can see where the bullet hits using this kind of target.

                Tom
                T.Bruner

                Comment


                • #9
                  Check out the big brain on RebHawk!!!

                  Lee, Thanks for the post,

                  James
                  "Ever since I was a kid I've had snakes as pets. They're clean and quiet. You give them rodents and they give you pure, unconditional indifference." Carl Hiaasen

                  "The Constitution is NOT and instrument for the government to restrain the people, it IS an instrument for the people to restrain the government - lest it come to dominate our lives and interests." - Patrick Henry

                  "War was always here. Before man was, war waited for him. The ultimate trade awaiting its ultimate practitioner." ? Cormac McCarthy

                  Comment


                  • #10
                    Hi, I am new here.

                    So, is here anyone, who knows Meade or Bresser optics closer? I would like to buy Bresser Redtail 25-75x90 and I still do not know, anything about this Manufacturer. I mean nothing from the first hand .. just from the users.

                    Comment


                    • #11
                      Hey Ares,
                      Welcome to Paradise, Bro.
                      I'm not familiar with either optic, so I'll defer to those with greater experience in that area.
                      Pinned for posterity...
                      Respectfully,
                      Harry
                      "It's better to live one day as a lion, than one hundred years as a sheep", Old Roman Proverb.
                      "For those who have fought for it, freedom has a flavor the protected will never know", Author Unknown.
                      "Cry havoc and let slip the dogs of war!", Shakespeare, Julius Ceaser, Act III, Scene I.

                      Comment


                      • #12
                        Hey Rebhawk,

                        So, were you the lead alien in the Jack Nicholson movie "Mars Attacks" or what? Big brain indeed..... .
                        But seriously, this was an excellent post and will help me pick out a real spotting scope for what I want to accomplish although I guess the one's at Harvard and Mt. Palomar are in use right now.

                        Jet
                        Isshin Ryu Student

                        Comment


                        • #13
                          [quote]
                          Hey Rebhawk,
                          So, were you the lead alien in the Jack Nicholson movie "Mars Attacks" or what? Big brain indeed..... .[/b]
                          GAK GAK, GAK GAK GAK...

                          Ooops, I'm sorry, what was that? LOL.


                          But seriously, this was an excellent post and will help me pick out a real spotting scope for what I want to accomplish although I guess the one's at Harvard and Mt. Palomar are in use right now.

                          Jet[/b]
                          Everybody needs to remember that all these calculations are theory only. There is nothing better than getting your hands on a scope like the one you plan to buy, and having a look to see what you can see, and how far you can see it

                          Cheers,
                          --Hawk
                          There are few problems a well-placed 308 cannot cure. --- Hawk

                          Gentlemen! You can't fight in here! This is the War Room! --- President Merkin Muffley in Dr. Strangelove

                          Rocket Science is much more fun when you actually have rockets! --- USN Recruiting Commercial

                          A little revolution now and then is a good thing --- Thomas Jefferson

                          Only the dead have seen an end to war --- Plato

                          "In Ireland, in Lebanon, in Palestine & Berkeley, Patty Hurst, heard the burst, of Roland's Thompson gun & bought it!!!" --- The Late Warren Zevon, Roland The Headless Thompson Gunner

                          In the 1500's, the Roman Catholic Church sold indulgences to forgive sin. In the 21st century, we call these carbon offsets. ---Hawk

                          �Fight like a man, so you will not have to die like a dog� --- Calico Jack Rackham's Mistress

                          Comment


                          • #14
                            I made a mistake on my first post. My spotting scope goes up to 45x, 60mm lens, not 50 mm lens.

                            Tom
                            T.Bruner

                            Comment


                            • #15
                              [quote]
                              I made a mistake on my first post. My spotting scope goes up to 45x, 60mm lens, not 50 mm lens.

                              Tom[/b]

                              The ratios should still work:

                              50 / 295 = 60 / Range

                              Solving for Range, we get:

                              Range = 354 yards for 308 holes.

                              Cheers,
                              --Hawk
                              There are few problems a well-placed 308 cannot cure. --- Hawk

                              Gentlemen! You can't fight in here! This is the War Room! --- President Merkin Muffley in Dr. Strangelove

                              Rocket Science is much more fun when you actually have rockets! --- USN Recruiting Commercial

                              A little revolution now and then is a good thing --- Thomas Jefferson

                              Only the dead have seen an end to war --- Plato

                              "In Ireland, in Lebanon, in Palestine & Berkeley, Patty Hurst, heard the burst, of Roland's Thompson gun & bought it!!!" --- The Late Warren Zevon, Roland The Headless Thompson Gunner

                              In the 1500's, the Roman Catholic Church sold indulgences to forgive sin. In the 21st century, we call these carbon offsets. ---Hawk

                              �Fight like a man, so you will not have to die like a dog� --- Calico Jack Rackham's Mistress

                              Comment

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