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

yes this idea was posted by Ed Barker in the WSDSOH Vol 2 some 20 years
ago. It is not easy but can be done. The other method is to get a
transmission grating and use that. Bausch and Lomb many years ago made an
SDE eyepiece which was preceisly that

At 17:40 15/06/98 +0100, you wrote:
>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

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