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Yes, the simple red filter just doesn't have a high enough transmission to let the fainter features show up.

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Which is the Brand and model of your filter?

I have not been able to find transmission data for the Wratten 23A (light red) but I found these for the 25 (red) and 29 (deep red). At 656 nm they have transmisson of 88% and 90% respectively. The 29 is very interesting: it could be a very cheap substitute for a Ha filter for testing Ha visibility on nebulae.

Edited by Mauro Da Lio (12/16/07 06:10 PM)

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