Solar scope 400mm f/137.5

[Chriske]

Busy making a solar'scope'. Optics nearly done, only silvering of the two optical parts needs to be applied.
There are three parts involved, one 400mm diameter flat, tracking the sun, one stationary spherical mirror (400mm f/137.5) and a 500mm square white screen.
All parts are mounted just high enough so the spectators(during open door at our observatory) cannot walk through the light beams.
Both mirrors will be silvered to achieve maximum reflection.

Tracking the sun will be done using an old Vixen mount.

[Mandy D]

@Chriske Very interesting. What would be the optical arrangement of this telescope? A quick sketch might help, if you don't mind. I presume the ultra long focal length is to obtain a decent size image for viewing on your screen. I get 10.93 mm diameter at 1200 mm focal length, so, I guess you will be around 500 mm with that enormous focal length (55 m), which explains the screen size and choice of focal length. I'm sure you have done the number crunching for this and got the correct answer (so, I may wrong), but I think your screen seems a bit on the small size.

I would certainly be interested in knowing more about this project.

[Chriske]

The size of the sun is about 470mm.
Marc who made the primary mirror aimed at 40 to 45m focal length. Measuring was done with a 120mm diameter spherometer. The goal was grinding to 0.022mm on the dial gauge, but I suppose during MOT he ended up with a longer FL. But that's ok the sun will be a little bigger, we don't mind.

For both mirrors there's no tube involved at all. The screen has a nearly 1m tube hanging about 2.5m high. That tube is blackened at the inside and has a oblong hole at the bottom to allow the observers to see the sun from standing position on the pavement.
I'll post some more pictures very soon.

The setup is very simple. This drawing is NOT to scale, in this drawing both mirrors should be farther away from each other. The flat and the screen are very near (at left). The spherical at right is also standing at 2.5m high.

This test setup was only to find its FL.
The mirror stands on a very old Vixen mount.
The tapes will be replaced with strong hooks of course.

[Elp]

Is there a solar filter somewhere or is it screen projection?

[Mandy D]

@Chriske Thank you for the further explanation. Are the plane mirror and screen both tilted at a slight angle to the spherical mirror? I guess focal length is rarely, if ever, critical as long as it can be measured and known where necessary.

I look forward to seeing more about this project as it progresses.

[Chriske]

32 minutes ago, Elp said:

Is there a solar filter somewhere or is it screen projection?

screen projection, no filter

[Chriske]

30 minutes ago, Mandy D said:

@Chriske Thank you for the further explanation. Are the plane mirror and screen both tilted at a slight angle to the spherical mirror? I guess focal length is rarely, if ever, critical as long as it can be measured and known where necessary.

I look forward to seeing more about this project as it progresses.

Only the flat is tilted toward the sun and projects the solar light toward the spherical. The spherical and screen are parallel

[Mandy D]

1 minute ago, Chriske said:

Only the flat is tilted toward the sun and projects the solar light toward the spherical. The spherical and screen are parallel

Ah yes, the angle of the screen will only change the shape of the projected image from circular to elliptical and at that focal length and with the small angle of the flat it will be barely noticeable. Thank you.

[Chriske]

Two mirrors silvered today. We used the 'Spray silvering technique'.
Works fan-tas-tic..!

This is my buddy Fred blowing off the last water drops.
It takes about one hour to finish a 400mm mirror.

[Ratlet]

I was trying to figure out what ASAN was...