As promised Pat,
Here is two subs. Both are taken within 10 mins of each other ( allowing time to fit the filter, refocus and restart guiding ). Both are taken with my astromodified Canon 350d, 180sec long at ISO400 with my 8" f/4 imaging newtonian. My backyard is Bortle 8. Im pretty sure I don't have to say which is which but I think its pretty clear from this what they are capable of. To be fair this image is taken with 78% moon fairly close to the target but both images are under the same conditions.
In answer to your question, yes your subs need to be longer or higher iso with the filter. They are also not recommended for small apertures ie: under 5" for a reflector and its hard work on my 5"SCT ( but not impossible ).
Cheers
Ryan
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