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Hi All,
Yes the Cone Nebula is an extremely difficult target. Somewhat to much worse than the Horsehead (IC434 & B33). On one occasion only, in virtually perfect conditions up at Mudgee in the 46cm, I'm pretty certain I saw one "edge" of the cone nr the star at the tip of the cone and possibly the other edge too. There is no "nebulosity" really to be seen. It is an edge between complete darkness and almost complete darkness. Not for the faint of heart.
I cannot understate the difficulty of this object. I spent the best part of 20 minutes at the ep before I could feel "pretty definite" about one of those edges. By comparison, the observation the other night of the Z CMa jet, once I was certain I had the correct field and correct star and worked out the field orientation, it took at most 5-10 seconds at x247 before I blurted out excitedly "I can see it !!!!!).
A H-Beta filter may help, but I seem to remember that nearly all the emission is H-Alpha, which explains why it images relatively easily even with short exposures (CCDs are much more sensitive to red than the eye) and that the OIII emission is pretty low too. Don't quote me on that one, I'm going on recollection -- I seem to remember reading a paper on it about 5 years ago that made a comment on the strength of various emission lines in the Cone Nebula and that stuck -- but I can't find the reference now.
Keep an open mind and have a go by all means (don't let me discourage anyone) but don't be disappointed if you end up with a negative. In perfect conditions, I'd say the minimum aperture is 46cm or thereabouts.
Best,
Les D
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