World's Simplest Reflecting Telescope

[Stub Mandrel]

I saw this idea on a website ages ago, and have just simplified it and tried it.

Aim a convex shaving mirror at something.

Place a small biconvex lens in front of your eye, rather closer than its focal length.

Look at the mirror through it, with your head to one side of its axis.

Start close and you will see something of the usual mirror view but poorly focused.

Move backwards, things will swim like  Munch's scream, defocus and suddenly the centre of the view will 'pop' into focus.

In my case the view was of a pattern on the net curtain. Only the middle 1/2 of the mirror showed a passable image, but it's enough to see that the principle works.

It would be fun to mock up an astronomical telescope this way by fitting mirror and lens on a stick. I suspect masking the outer part of the mirror would help improve the view. Magnification seemed to be about 2 to 3 times with a 100mm lens.

Could be a fun learning activity with kids either on ground based targets or even the moon, that then leads to a session with a 'proper' newtonian.

[Ags]

Would it be possible to replace the biconvex lens with a plossl or camera lens?

[Charic]

I have a concave shaving mirror that due to its position,  I can see the image  of the ceiling light at its focal ratio when I enter the bathroom (Mrs 'C' must have invisible markers for the placement of items, because even an inch out of place, "she knows!', but I've not attempted  any  practical follow up to this phenomenon.

I was going to use what I see in the bathroom as an apt description to the similarities of someones new scope to that of my bathroom mirror, should the need ever arise!

[Ags]

Well I have tried with a make up mirror and a 15mm plossl and 50mm camera lens. I had no luck with the plossl but got focus on some tree leaves and a corner of a brick wall using camera lens. 

Having used the device, all I can say is... "You think that is a collimation error? THIS is a collimation error!"

[RT65CB-SWL]

I made a 'crude' reflecting telescope for my specialist science project when I was at comprehensive/secondary modern school.

Apparently I did have not enough brain cells to make the grade for the astronomy class, so I ended up in the integrated science class instead. For the final six months we had to choose a science subject and build or do experiments related to it. When my science teacher told the astronomy teacher, they wanted to have a look through my 'crude' reflecting telescope. I think both were quite impressed.

It comprised of a shaving mirror for the primary, a small piece of a flat mirror for the secondary, a small maginifying glass or loupe for the eyepiece, somehow all fixed to a broom handle or dowel with a hole near the centre for a bolt to pass through at the pivot point and attached to short piece of 2" x 2" (50mm x 50mm) timber and a X-legs base for a short pedestal mount. Maginfication was low power, (maybe 15x to 20x max.), false colour was appalling; but I felt pleased that I had made something useless useful for my specialist subject and that I could see some craters on the Moon.

I also made an instrument for measuring the Moon's altitude at a set time, (I think I chose 9pm). Using a protractor glued or screwed to piece of plywood, a lead fishing weight suspended on a piece of piano wire, (the type r/c aero-moddlers use), and two curtain wire screw eyes for the sighting tube. I made notes of the elevation. I also used a compass to record its position and made a note of it too, then included the notes into the final draft for submission.

That's my contribution!   

[Stub Mandrel]

1 hour ago, Ags said:

"You think that is a collimation error? THIS is a collimation error!

Don't chuck away your Tak just yet...

[AKB]

Is this not the classic “Herschelian” telescope design?

https://en.m.wikipedia.org/wiki/Reflecting_telescope#Herschelian

[Stub Mandrel]

59 minutes ago, AKB said:

Is this not the classic “Herschelian” telescope design?

https://en.m.wikipedia.org/wiki/Reflecting_telescope#Herschelian

Almost, but in the Herschelian the eyepiece and primary are joined together ?

[Chriske]

23 hours ago, AKB said:

Is this not the classic “Herschelian” telescope design?

https://en.m.wikipedia.org/wiki/Reflecting_telescope#Herschelian

Made a few of these Hershel telescopes in the past . Was a fun project.
It was a very small mirror (80mm - 3"+). To have this scopes producing good images, focal length was 1500mm, so f/18.7.
This 'long' focal length gave me this result :

Although the primary mirror was tilted 1.1°  all well within the Airydisk..!(just)
For more convenient observing I added a secondary mirror.