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Here's a cool Astronomy Pic of the Day. Its a compilation of 8 other Voorwerps other than Hannys. Until Jimi and I saw Hannys the first time, I had my doubts it would even be visually visible. I wonder if any of these would give up the goods in an eyepiece. Sure would make for a challenge!
Check it out...
http://apod.nasa.gov/apod/ap150404.html
Thanks Dragan,
seems like the Voorwerps of NGC 5972 could be within reach, I will give it a go and let you know :)
I wounder if the clouds will respond to the Sloan G band filter visually like Hanny's Voorwerp did? I will let you know as soon as Luna gets out of the way.
For NGC 5972 with z = 0.03, the OIII 501 main line should be redshifted by about 15nm. That's also the center wavelength used in the study (see here http://www.stsci.edu/hst/phase2-public/12525.pro). Besides a green filter, a comet or Swan band filter (width 25nm) could as well be useful. Which center wavelength and bandwidth does the Sloan G filter have?
Reiner the Sloan G I have is 401 to 500 NM.
The V filter from Johnston-cousins peaks around 525 even though it's center is 545 or so it is a skewed curve and peaks right where you are saying.
To get an extremely narrow band this V filter paired with the Sloan G would be very narrow but a slight disadvantage due to each filter takes a bit off the top. May be interesting and perhaps rewarding.
I attach both sets of curves.