mental4astro
24-11-2009, 11:43 AM
Hi all,
This is not an original idea, but one adapted from the 'Telrad finder chart' idea.
Finding objects sometimes can be very difficult, like galaxies and planetary nebulae. Doing this from a light polluted area, like Sydney, the challenge is even more so.
You can use DSC's. I don't have such a unit, nor am I looking at getting them. So I'm stuck with charts.
To this end I've made myself a set of "finder rings" scaled to the charts I use. These are circles drawn onto a sheet of acetate film (overhead projector film) which are then placed over the section of the chart I'm following. These circles serve to surround the field of view seen through the finder scope (or scopes) being used.
To get the scale correct, you will need to sit down with your finder (doesn't need to be mounted onto your scope) along with your atlas, another sheet of acetate film & a fine marker pen. Aim your finder at a bright star rich area of the sky, like the tail section of Canis Major or Scorpius. Using the crosshairs for reference, rotate and move your finder until you have two 'brightish' stars which span the whole of the field of view of the finder without moving the finder. Locate these stars in your chart and mark them on the acetate film (with the film over these stars!)
Next task is to measure this distance with a ruler, half it, and you then have the radius of the circle you need to scribe.
I use two charts during my sessions: The Cambridge Star Atlas, and the Asahi charts I found in the 'Beginners' forum. The Cambridge is a good all-round atlas, while the Asahi charts are highly detailed. I also use two finders on my big dob. To this end I've made two sets of "finder rings" to use with each finder.
I've also uploaded a section of sky pertaining to that surrounding the bright galaxy NGC 253 visible at this time of year, to show the surrounding stars through my 7X50 finder, which I would then use to track down this sucker. A mate of mine had been having trouble locating it. This tool may help a little, hopefully, :rolleyes:.
This is not an original idea, but one adapted from the 'Telrad finder chart' idea.
Finding objects sometimes can be very difficult, like galaxies and planetary nebulae. Doing this from a light polluted area, like Sydney, the challenge is even more so.
You can use DSC's. I don't have such a unit, nor am I looking at getting them. So I'm stuck with charts.
To this end I've made myself a set of "finder rings" scaled to the charts I use. These are circles drawn onto a sheet of acetate film (overhead projector film) which are then placed over the section of the chart I'm following. These circles serve to surround the field of view seen through the finder scope (or scopes) being used.
To get the scale correct, you will need to sit down with your finder (doesn't need to be mounted onto your scope) along with your atlas, another sheet of acetate film & a fine marker pen. Aim your finder at a bright star rich area of the sky, like the tail section of Canis Major or Scorpius. Using the crosshairs for reference, rotate and move your finder until you have two 'brightish' stars which span the whole of the field of view of the finder without moving the finder. Locate these stars in your chart and mark them on the acetate film (with the film over these stars!)
Next task is to measure this distance with a ruler, half it, and you then have the radius of the circle you need to scribe.
I use two charts during my sessions: The Cambridge Star Atlas, and the Asahi charts I found in the 'Beginners' forum. The Cambridge is a good all-round atlas, while the Asahi charts are highly detailed. I also use two finders on my big dob. To this end I've made two sets of "finder rings" to use with each finder.
I've also uploaded a section of sky pertaining to that surrounding the bright galaxy NGC 253 visible at this time of year, to show the surrounding stars through my 7X50 finder, which I would then use to track down this sucker. A mate of mine had been having trouble locating it. This tool may help a little, hopefully, :rolleyes:.