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The optolong l-pro and the other reputable manufacturers of light pollution filters are more versatile than the duo and tri-band filters that seem to try and replicate narrow band with an OSC, so it depends what you want to image.
Look at the transmission data for each and see if they match your intended targets.
For an OSC go 2 inch, you aren't going to change it often. Filter size only seems to be important when you have to put a bunch in a filter wheel
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