Where should the secondary mirror be placed in a concave mirror telescope?

[Abd Errahmane]

hello,

I found a concave mirror telescope in my town
I think that it is very good for making Newton telescope
Estimated length of 20 cm
I will make a telescope , but I have a problem , I do not know the place of the focus
and the place of secondery mirror; after focus or before

can you help me please!

 

[Abd Errahmane]

Any replay

 

[Abd Errahmane]

any replay

 

[russ_watters]

Point a flashlight at it and use a piece of paper to find the focal point, then do the math to find the focal point for infinity.

 

[Abd Errahmane]

thank you russ watters

 

[Bob S]

I have a chunk of glass I bought at a garage sale for $3.00. It is 22" diameter and 2" thick, and is concave on one side (I didn't know this until I took it home and cleaned it off). It has a focal length of 2 meters, and is unsilvered. I have been using it as a small coffee table since about 1970. What was the mirror for?

 

[mgb_phys]

Probably a telescope mirror, 60cm f3.5 would make a reasonable Dobsonian cheaply.

 

[Abd Errahmane]

can you help me in the tube of telescope , can it be by plastique or keybord or fe

 

[HallsofIvy]

Whatever will keep out extraneous light and is not heavy. Probably a thin plastic tube would be best. Use whatever you like to reinforce it and support it from the outside.