Re: (IAAC) prism doubt

>Hi yan,
>You have used Prism to detect PN in a star field. What kind of Prism is
>that? What will you see if you use one? I have never used a prism till now
>to see a PN. Can you pls tell me how to go about it and what are its

Hi Vishnu,

At the beggining, I used a prism device taken from a microscope assembly
(if I remember well) lent by a friend. It had 3 triangular prisms (60
angle I guess) aligned such as this:

/\  \/  /\

This mounting allows the line of sight to be kept straight. This device
(prisms cemented in a tube) was attached at the eye-end of a choosen
eyepiece over the lens (with gluing paper, something I am ashamed to be the
tinker that made it:-)

But now, I have a more luxuous solution provided by a Rainbow Optics
spectroscope (visual) : one can see the adds at the end of Sky & Telescope
about it. This is a blazed grating that spread the light: it can be screwed
at the field lens of the eyepiece as one do with Lumicon filters or colored

The result on PNs is obtained thanks to their emission line spectrum. Stars
shows continuous streaks of light when focused properly (continous
spectrum) and the PN remains stellar thanks to the OIII emission lines
(well, with some training, one can separate Hbeta images and even HeII or
Hgamma on bright samples).
This is very useful when you are looking for very small PNs, those that
look stellar at any power and that you have to check carefully a good
finding chart in order to really find it. With the prism, you just have to
look to a stellar point amidst the continous star spectra.

I have to put something about it on my web site, but if you know how to put
48 or 72 hours in a day, I am interested :-))

Anyway, if you have further questions, do not hesitate to get in touch.

clear skies, yann.

Yann Pothier
11 impasse Canart, 75012 PARIS, FRANCE

To UNSUBSCRIBE from the 'netastrocatalog' lists, use the Web form at: