There are many ways to make a DIY telescope found everywhere on the internet. I think that I have made it in the most easiest way, from things that are already available in your home.
The telescope is a Keplerian model which shows inverted images but has a wide field of view. You can use this as a finder scope on a bigger telescope too (if you can somehow fix it to the bigger scope).
Two double convex lenses: the most important part of the telescope are the lenses , they have to be clean and of good quality. I made the telescope with some parts I had at hand you can try and improvise. Objective lens : Double convex Diameter=50mm and focal length=500mm=50cm. You can easily find it on amazon and Ebay for less than 3$.
Eyepeice lens : Double convex lens of Diameter= 25 mm and focal length=4cm. If you wonder where you can find that,go to amazon and search for google cardboard VR lenses
If you use the same lenses the telescope is going to be about 60 cm long when complete.
Step 1: Making the Telescope Tube
Here we have a black chart and a thick white paper chart(card paper). The white chart was thick and strong.
cut 17cm*40cm pieces from both charts.
glue one side of the black paper to the white (glue the one of the longer edges of both sheets together).
now keep the lens at the end of the sheet and roll it along the circumference of the lens.
it is shown in one of the images how the lens fits into the tube.
secure the lens end with the masking tape.
*IMPORTANT* : Don't finish the tube right away with the same diameter follow the next step .
Step 2: Extending the Tube
Once you've secured the lens end with tape, keep the toilet paper roll to the other end and fold the char along its circumference.
this is to reduce the diameter of the tube from 50mm to 40 mm gradually. (the toilet paper roll is about 40 mm in diameter)
you can see that the tube now looks like a long truncated cone.
after securing the other end with masking tape "remove the toilet paper roll" (don't secure it yet).
go ahead and close all the edges of the tube as shown in the image.
Cut a 10 cm long toilet paper roll and on the inside put a black chart piece of the same dimensions.
once you've done that secure the roll on the end of the tube.
The tube is now 50 cm long and it must look completely black from inside.
Step 3: The EYEPEICE : Its the Hard Part
the lens is about 2.5 cm in diameter the same as the neck of the bottle. Thus , it will fit perfectly.
Cut the bottle neck off and secure the lens. the lens is secured from the other end of the neck and not the mouth of the bottle the threaded mouth of the bottle must remain outwards and the neck must hold the lens.
Just like in the previous steps cut a 10 cm long piece of white and black sheets and roll it along the circumference of the bottle neck. make it a larger in diameter by using cardboard rings cut from the toilet paper roll .
just make the diameter enough for the chart to be able to slide in and out of the telescope tube .
I know its is not clear how it is done , just put the lens in the bottle neck and you will figure out the rest.
secure the length of the eyepiece tube with masking tape.
THIS SHOULD NOT LOOK LIKE A TRUNCATED CONE. IT SHOULD BE A STRAIGHT CYLINDER .
Step 4: Completing the Telescope
The eyepiece must slide into the tube as in the image
And the whole telescope must be completely covered by black chart inside.
now make another truncated cone 10 cm long and having a little less than 5cm as the smaller diameter.
wondering why ?
to make a dew shield and stray light shield , also it helps to keep the objective lens secured in place.
NO GLUE ON THE LENSES . NEVER DO THAT . NOT EVEN TO THE EDGE OF THE LENS. MAMA FRICTION WILL HOLD THE LENSES IN PLACE.
once you've finished the last piece just slide it from behind the telescope all the way up to the front it must be tight and must not come off the front end of the telescope.
MATHEMATICS OF THE TELESCOPE IS IMPORTANT .
go to the next step .
Step 5: The Important Numbers
the completed thing is about 60cm long.
Magnification=focal length of objective / focal length of eyepiece= 50cm/4cm = 12.5x
resolving power = 120 / Do(diameter of objective in mm) = 120 / 50mm = 2.4
diameter of exit pupil = Do / M = 50mm / 12.5 = 4mm
focal ratio fr = fe / Dep = focallength of eyepiece/dia of exit pupil = 40mm/4mm = f/10
also focal ratio = fo/Do = 500mm/50mm = f/10
my scope has a good field of view and enough magnification to call it a spy glass .
you can see the bumpy lunar surface and three Galilean moons of Jupiter . but the planets throw up all over the place due to chromatic aberration. if any one has a solution to that please comment.
this thing can collect light from faint stars too . Andromeda can be seen as a faint smudge through this.
look at the images through the scope, (I took them with a phone camera) and find the buildings in the original image so you can understand its magnification better.