Really slow f-ratio mirrors

Hi Michael,

You can purchase a 6 inch achro at f/30 from D&G Optical.

A flat at 45 degrees (uncoated) works very well.
Many years ago I built an 8 inch newtonian telescope with no aluminium coatings on either the primary or secondary flat for solar work.

Incidently, I have recently designed and partly built now a solar telescope based on f/12 achromat and a heliostat.

Eamonn A
MPC J62
www.kingslandobservatory.com

Michael,
When I saw the long focal lengths been mentioned I had visions of you using it you to set your neighbours curtains on fire :lol:
I wasn't too far off, at least it involved the Sun, an interesting idea and one that I saw on the web elsewhere, I cant remember where.

BTW, you should think of getting some sort of eyesight insurance :lol:

Many years ago I built an 8 inch newtonian telescope with no aluminium coatings on either the primary or secondary flat for solar work.

Incidently, I have recently designed and partly built now a solar telescope based on f/12 achromat and a heliostat.

Now I'm interested. I thought about doing this some years ago myself, simply using the notion that the Sun is bright enough to have its image seen without the need for optical coatings anyway. Have you any pictures Eamonn?

Seanie.

Hi Seanie,

Unfortunately I don't have any pictures. Apparently, I had just completed the telescope at the time and let another astronomer see Sun spots. He was impressed what he saw and asked would I sell the solar telescope. I agreed a price and he took it with him. It was basically a fork mounted open frame telescope.

Only recently I designed a much bigger arrangement to obtain high res images. This is a partly built tubeless solar telescope based on f/12 achromat and a heliostat. I decided to have the objective stationery and the mirror tracking. The image would then project through a whole in a shed.

The heliostat tracking is important. Some preliminary results in design show that the accuracy and repeatability of the system is about 3 milliradians over a long period of time. This is about 10 arc minutes or a sixth of a degree. The Sun itself is a disk subtending an angle of about 10 milliradians so it wasn't considered necessary to do much better than that when using a much larger heliostat. At 12 feet the pointing accuracy will be 12 feet x 0.003 = 0.036 feet = 0.43 inches = 1 cm

Eamonn A
MPC J62
www.kingslandobservatory.com

Michael,
When I saw the long focal lengths been mentioned I had visions of you using it you to set your neighbours curtains on fire :lol:

I might bring it to Greece with me

"Stand back everyone, the telescopes are mine! Stand back or I'll burn tham all down!!
Ha..Ha Ha...HaHaHaHaHa :evil laugh: "
:twisted:

Hi Michael,

You can purchase a 6 inch achro at f/30 from D&G Optical.

A flat at 45 degrees (uncoated) works very well.
Many years ago I built an 8 inch newtonian telescope with no aluminium coatings on either the primary or secondary flat for solar work.

Incidently, I have recently designed and partly built now a solar telescope based on f/12 achromat and a heliostat.

Eamonn A
MPC J62
www.kingslandobservatory.com

Thanks Eamonn.
I'll check them out.