Re: (IAAC) Markarian 205 - 8inch F/10

At 12:30 PM 6/14/98 +0100, you wrote:
>I have followed this discussion with some interest and I am surprised that
>Jeff has not jumped in yet.
>Anyway when observing planetaries you have to have some knowledge of the
>type of object that you are looking at before using the OIII filter. Jack
>Marling and Steve Gottleib always recommended using both the OIII and
>H-beta filter and comparing the brightness at both wavelengths as some
>objects have low OIII emission due either to the temperature of the central
>NGC2392 appears to have a normal emission spectrun form the numbers in the
>ESO-Strasbourg catalogue so its colour should be green/blue from the
>emission lines 
>I like your project idea to try and map the reflection vs emission
>component of diffuse nebulae using the UHC filter. Perhaps if you get any
>results you could write it up for the Webb magazine. You might also try and
>use the H-beta filter to map out the extended low excitation nebulosity.
What I didn't think about with my last contribution to this discussion was
the use of a prism. Prisms are readily and cheaply available and if you
don't have one lying around you can get them cheaply from places selling
government surplus equipment. They don't need to be spectroscope 60 degree
prisms, though these are nice. 45 degree prisms used in the correct
orientation give quite adequate dispersion to give some idea of the spectrum
of a planetary, especially if you use a low telescopic magnification. 
The only awkward bit is finding the correct viewing angle but this is just a
matter of wiggling your head and prism around until you see something.
Those gifted with a manual dexterity greater than mine could contrive an
ingenious arrangement to support the prism between the eye and the scope.
This will give a good idea of the distribution of emmission features around
the nebula at different wavelengths and also a good idea of why a nebula
does or does not respond to a particular filter.
P.S. Does anyone know where you can obtain optical cement as I sat my
eyepiece box on my direct vision prism and disconected the components. I
could probably lay my hands on some canada balsam but was wondering if there
was anyting more up to date. The glass superglues such as Loctite Glasbond
seem prone to form bubbles as they set so are not so good.
Nick Martin, Bonnyton house, By Ayr, Ayrshire KA6 7EW ,Scotland, UK.
 Longitude 55 24'56" Latitude 4 26' 00".
"Thou star of evening's purple dome
 That lead'st the nightingale abroad,
 And guid'st the pilgrim to his home." 
   To the Evening Star by T.Campbell