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

>The only caveat to this would be a case where any object had a
>significantly bright emission feature which was excluded by a particular
>filter's bandpass. Are there any common examples of this folks know of -
>maybe certain types of emission features being darkened relative to the
>background by an H-beta, or by some of the "custom bandpass" filters? Just

As a planetary nebula fan, I have been searching (not enough at present)
for a filter that would exclude typical planetary lines (Hbeta and OIII
lines) in order to show more apparently the central stars that are imbedded
in too bright nebulosity (like NGC 6543, 7009, 6210, 6572, etc.). I have
tried two blue filters (thinking that central stars were rather "blue")
with no evident enhancement of the central stars: these are a light blue
one and the Kodak Wratten 38A. This last one seems too large for that
purpose and future experiments will be done with something like the 47B.

By the way, I have found a cheap UHC/OIII filter (with only 46%
transmission at 500nm). It actually works on planetaries in a good site
(small but real contrast enhancement) and should be useful under light
polluted skies: it is the wratten 65A.

I think that visual observing of the deep sky should be useful with
filters, not only interferometric ones (OIII, Hbeta) but colour ones too.

clear kies, Yann.

Yann Pothier	tel: 01 43 41 43 29
11 impasse Canart, 75012 PARIS, FRANCE
Email: ypothier@abi.snv.jussieu.fr
Site : http://pegase.unice.fr/~skylink/publi/cielextreme

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