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Project News

My astronomy project:
Design a 24" f/2.75 Newton telescope



  1. Ray trace around the focuser

1: Ray trace around the focuser

Is there any chance that a 2" focuser and coma corrector could be used without vignetting or narrow the field that's needed to the 17 mm 100 degree eyepiece?

Here I did a new attempt. I have reduced the inside diameter of the telescope tube to 640 mm. I also has lower the focus plane to have a distance of 10 mm above the focuser's top.

There is not so wise to have a very narrow tube, the baffles will not be effective and it can cause reflections and then stray lights that interfere.

Design a Newton telescope with the Newt-Web tool, 24 inch f/2.75

The focuser dimension is now reduced from 75 mm to 50 mm inside. I have also lower the demand on the field at the focus, now it shall only cover 30 mm diameter.

As you can see the 100% illuminated light ray (red lines) area can be reach without hitting any obstacles in the 2" focuser. But a lens in a coma corrector must be smaller to fit inside the focuser, maybe at maximum 44 mm and that will not be good enough, it will cause vignettting.

The secondary mirror has been downsized to 162 mm and its size is now 27% of the primary mirror. What I have been told it's impossible to use the mirror all the way out to the edge, maybe in this case the last 2 mm have to be masked out. That's something we don't want, we could use a bigger mirror but then it obscure the light path more then necessary.

The main mirror is no problem, you could have a 625 mm mirror and only use the central 600 mm, it will just be a bit heavier.

Here is the new design file if you want to do some test by your self:

Newt-Web design page:

It looks as if we have to go back to the 3" focuser and then a 3" coma corrector. Next time I will optimize the telescope to take that parts, the 3" coma corrector has a long building length and it will not be easy to fit in here.

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