AstroTasmania
January 14th, 2007, 08:45 AM
I often see posts and emails where people have referred to their cassesgrain, newton, dobsonian or barlow lens. I have to assume that many newcomers pick up on these names and use them as standard and are blissfully aware that they are using a person's name!
OK, so who are these people?
Issac Newton, he invented the reflecting telescope, being the inventor, the telescope type was named after him and referred to as a "Newtonian". There are also combination scopes such as the Cassegrain-Newtonian.
John Dobson, who we have all heard about, took a standard Newtonian telescope and mounted it on a simple easy to use alt azimuth mount, which did a lot to popularise the Newtonian telescope, so the mount was named after him - a "Dobsonian" mount, all too often abbreviated to a dob. It is only the simple mount which is the Dobsonian component, the optical tube is still a Newtonian.
Peter Barlow, mathematician and astronomer invented th 2-element negative lens, which when used with positive lenses increase the magnification of the positive lens. In modern terms, the positive lens is the main telescope objective and its primary image can be enlarged by a factor of two or more when used in conjunction with an eyepiece, or create a real image at the film plane of a camera. More exotic versions are now available in higher magnification factors, they can have 3 or more lenses in combination and are often called tele-negative lenses. TeleVue Powermates are a fine example.
Cassegrain, of which there are many variations. First developed in 1672 by Laurent Cassegrain the Cassegrain reflector is a combination of two mirrors used in some telescopes, which are then known as Cassegrain telescopes. Schmidt-Cassegrain, Argunov-Cassegrain, Maksutov-Cassegrain, Dall-Kirkham, Schiefspiegler, Ritchey-Chrétien, which in its true form does not use a front corrector plate. These and others are variations on the basic design.
And so it goes, every telescope design bears someones name, and as such always starts with a capital letter. Thanks to these guys, we can explore and enjoy the heavens better than they ever could.
Clear skies...
OK, so who are these people?
Issac Newton, he invented the reflecting telescope, being the inventor, the telescope type was named after him and referred to as a "Newtonian". There are also combination scopes such as the Cassegrain-Newtonian.
John Dobson, who we have all heard about, took a standard Newtonian telescope and mounted it on a simple easy to use alt azimuth mount, which did a lot to popularise the Newtonian telescope, so the mount was named after him - a "Dobsonian" mount, all too often abbreviated to a dob. It is only the simple mount which is the Dobsonian component, the optical tube is still a Newtonian.
Peter Barlow, mathematician and astronomer invented th 2-element negative lens, which when used with positive lenses increase the magnification of the positive lens. In modern terms, the positive lens is the main telescope objective and its primary image can be enlarged by a factor of two or more when used in conjunction with an eyepiece, or create a real image at the film plane of a camera. More exotic versions are now available in higher magnification factors, they can have 3 or more lenses in combination and are often called tele-negative lenses. TeleVue Powermates are a fine example.
Cassegrain, of which there are many variations. First developed in 1672 by Laurent Cassegrain the Cassegrain reflector is a combination of two mirrors used in some telescopes, which are then known as Cassegrain telescopes. Schmidt-Cassegrain, Argunov-Cassegrain, Maksutov-Cassegrain, Dall-Kirkham, Schiefspiegler, Ritchey-Chrétien, which in its true form does not use a front corrector plate. These and others are variations on the basic design.
And so it goes, every telescope design bears someones name, and as such always starts with a capital letter. Thanks to these guys, we can explore and enjoy the heavens better than they ever could.
Clear skies...