A QUICK QUESTION...

APM Germany sell a 10" refractor (apo). A mere snip at 44,990euro. Tube weighs 45kg.

That refractor must be a very fast focal ratio (f/6 or less)? The 12" South refractor manufactured by Grubb of Dublin for the Dunsink observatory is an f/18 with a huge immovable British Equatorial mount ( the foundations go right down into the bedrock) and a sizeable dome. Using that and modern 6" refractors for comparison even a 10" f/6 would be impractical except as an observatory telescope.

A 10" f/6 Dob would be manageable and the least expensive but a 10" Newt would have to be f/4 for use on a German Equatorial mount (GEM) and the mount would add cost. A 10" SCT would be the most compact and a really good match for a GEM but is more expensive and a 10" SCT on a GoTo fork mount may be the most expensive option.

The 12" South refractor manufactured by Grubb of Dublin for the Dunsink observatory is an f/18 with a huge immovable British Equatorial mount...

I'm curious - I thought the Dunsink 12" refractor was on a German Equatorial Mount, but like John, the guide at Dunsink described it (I think) as a British Equatorial Mount.

My understanding of the British contribution to telescope mounts was what is called the English (or Yoke) mount - similar to a Fork mount but with the telescope mounted between two parallel beams. Can anyone shed any light on this?

Phil.

PS - see en.wikipedia.org/wiki/Equatorial_mount for a discussion on mounts.

I was puzzled by that myself. When I inquired on Cloudy Nights I was informed I was informed that it's more commonly known as an 'English Mount' or 'English Cross Axis'. On viewing this link: home.earthlink.net/~indig/DesignMusings/...esign_Mountings.html , however, I have come to the conclusion that it's a different variation of the German mount. But it's neither an English Yoke nor an English Cross Axis, I last saw it just a couple of weeks ago.

Maygray,

To cut through all the confusion:

Just buy a reflector with diameter approx 3-4 inches wider than an equivalent refractor (10 inch apo refractor = Approx 13-14 inch high quality reflector.) and you have a roughly equivalent telescope for planetary detail,and superior for everything else.

Not an equivalent price though!

Peter.

jhoare wrote:

APM Germany sell a 10" refractor (apo). A mere snip at 44,990euro. Tube weighs 45kg.

That refractor must be a very fast focal ratio (f/6 or less)? The 12" South refractor manufactured by Grubb of Dublin for the Dunsink observatory is an f/18 with a huge immovable British Equatorial mount

I was lucky to see the longest refractor in the world in Berlin last year ( a former colleague of mine used to work at the observatory but still has a key to the observatory:wink: It looks like a huge cannon . It still has bullet holes in it from WW2 (Allies probably though it was an artillery piece :roll: )

The 12" South refractor manufactured by Grubb of Dublin for the Dunsink observatory is an f/18 with a huge immovable British Equatorial mount

I wouldn't say immovable (unless you mean fixed, its certainly not portable ) - its a nicely balanced piece of kit, easy to move around and the mechanism still works a treat - though you do have to wind the weight back up every so often and then realign. The optics are still pretty sharp though.

Here's a photo I took at our last months talk and observing session afterwards: