Like new 2" IDAS narrow band (nebula) filter. I bought this new a few months ago and only used it twice. I'm now moving to a scope that can only take 1.25 inch eyepieces and can no longer use this. I will be replacing this with the 1.25" version. This filter is unique as the following excerpt says better than I can:
"The IDAS Narrow Band Nebula Photo-Visual (NBN-PV) filter is a new filter design using the IDAS-unique Multi-Bandpass Technology (MBT). This allows the creation of a filter with very narrow passbands around both the H-Beta / O III emission lines, and the H-alpha / N II / S II emission line groups. This combines the high contrast views of narrowband filters with the convenience (and economy) of covering all of the important nebula emission lines in a single filter. The resulting filter is great for visual use or monochrome imaging of emission nebulae." See Hutech web-page for plot of transmision curve.
$145 including shipping to con-US.