2" 56mm Planetary EP....

[russ.will]

I was looking through the Northumberland Refractor at the Cambridge University Dept. of Astronomy last night. It was pointed at Jupiter and it was quite a nice view, considering the blustery wind and distinctly average seeing, such as it was between the clouds.

It occured to me that at a 19.5ft focal length it might re-arrange your idea of what EPs might be required for the job in hand. It was too dark to see the writing on the barrel (I could see the star diagonal was a 2" Televue job) so I asked. 56mm, I was told, when looking at the planets. What the hell do they do for widefield?

Russell

[John]

Using a 56mm for planetary is pretty mind blowing but as you say, that sort of focal length sort of re-defines things a bit !.

This might do for a wider field of view but they would need a 4" diagonal

http://www.siebertoptics.com/images/eyepieces/4%20inch%20eyepieces/80%20b%20web.JPG

[russ.will]

Strewth! I presume it comes with an optional (not shown) fold up head cup?

Russell

[kniclander]

how did the view differ from the sort of 4-6" refractor/ 10" dob type view that most of us are used to?

[russ.will]

I think the lesson was that the atmosphere is ALWAYS the limiting factor and thus it is unfair to compare.

I have seen significantly sharper, more detailed views of Jupiter through my 200p and ZS80 on nights of good seeing. Equally, I've also seen low mag views through 'boiling water' that prevented me from reaching deeper into the EP case and Saturday night was one of those nights.

To be fair to the Northumberland and Sutherland scopes, neither had much of a chance. The latter was trained on the Pleiades and that looked murky and dull too. It lacked the jewel like sparkle I have had from my rural Cambridgeshire garden.

It's also worth bearing in mind that both of these wonderful scopes have, over the decades, been encroached upon by the expansion of Cambridge and are thus, basically suburban. So, on all but the clearest nights, they're as much historical artifacts, as useful tools.

The Star Gazing Live event last year, fell on a very crisp -2degC evening and the seeing was far better. The big refractrors gave a much better account of their selves and I remember being fairly impressed with Jupiter through the Northumberland. Now, visual memory is a tricky thing and at that point in time, I basically had nothing to compare the view to, but if push came to shove, I'd say I'm getting at least as good views, on a still night (few and far between though they seem) from my much darker garden.

It's a shame that the IOA can't be uprooted to somewhere more rural, to give the scopes a chance. Then again, it's not like they're the research instruments they once were and we should be thankful that they are still pressed into service, maintained and regularly upgraded.

Russell

[kniclander]

thaks Russ -that's interesting. I found that for planetary viewing the Lp in the suburbs isnt too much of an issue but the seeing is invariably poor compared to a genuine out-of town dark site.