Posts Made By: Anthony Allsobrook

Hi Nils

Congratulations! And thanks for posting all the photos. That drawtube looks superb. When you post some reports regarding performance, it would also be very interesting if you could note eyepieces used ... as I recall reading in an advertisement somewhere, "The eyepiece is the other half of your telescope".


Anthony
PS Don't forget that you are most welcome to visit your 80/600

Fancy peeping at our southern treasures from so far north ... is nothing sacred anymore?

Well done!

Anthony
Wellington NZ @ 41°S 175°E

Nils,

Did you ever get to compare the 12 mm T4 with the "ancient" 13 mm T1?

Anthony

Hi Inge,

I have used a focusing mask for this purpose. Mine is the very simple type with two diametrically opposite holes in a piece of cardboard, which is placed at the top of the telescope tube. However, I recently found a very interesting variation of the focusing mask which has two circular holes and a triangular hole. The use of the third triangular hole is very cunning ... it gives instant indication on which side of focus you are!!! As you move through focus the triangle flicks to the ofher side of the view. For your 12½" the circular holes should be 5" in diameter and diametrically opposite one another. The equilateral triangle is then cut on a radius at right angles to this diameter, and with one corner pointing towards the centre. It is well described on:

http://cometman.com/Mask.html

Making one is on my "to do" list.

Anthony

Dmitri

Super report on our southern sky, thank you!

On your next trip, do add galactic cluster NGC2516 to your list. Same declination as Alpha Centauri but very different RA. You'll probably need a trip 3 months earlier in the year to see it from a latitude not too far south, since it culminates 7 hours before Alpah Cen. It's a beautiful cluster with several double stars ...

I know Inge has a penchant for open clusters with double stars and would love to see this one.

Anthony
Wellington NZ @ 41°S

Everything North of Dec +35°.

Anthony
Wellington NZ @ 41°S

Inge

Ruling for Moderator - Are SSOs not strictly off topic on the DSO Forum?

Anthony

PS Thanks for the really interesting thread!

Ron

A really enjoyable read ... thank you.

If I may be allowed to correct a absolutely miniscule typographical inexactitude in your article:-

1 Ångstrom = 0.000 000 01 cm and not 0.000 000 1 cm.

Anthony

Jess

An interesting wrinkle is to use a spherical primary mirror (MUCH easier to make than a paraboloid) and correct the spherical aberration using a weak (specially designed) barlow placed before the newtonian secondary. Some thirty years ago the local astronomy club ran such a project. Some twenty such 8" f/6 mirrors were ground and polished to a spherical figure by amateurs. The "barlow" corrector sets (two element achromats) were produced as a special batch by a local optical shop. From memory the corrector slowed the system to f/6.6 ish. Although a very small amount of chromatic aberration was introduced, coma was well contolled. I don't know what happened to the other parameters (like flatness of image plane).

Anthony
Wellington NZ

Inge

Canary Islands trip; here's the view from the NASA Shuttle.

In the middle of the Atlantic Ocean are the Azores; below and to the right Madeira Islands; a bit below them the Canary Islands; well below them Cape Verde Islands.

Anthony