Hi!
Those are photometric filters, often used for scientific observations, they are similar to usual RGB filters but have somewhat different wavelength range that they let through (like in this chart, shown against the usual RGB colour bands: https://www.cloudynights.com/uploads/monthly_06_2024/post-262118-0-84624500-1718728687.jpg). On this scope ,,blue'' is probably a normal blue filter while B, V, R are the photometric versions of blue, green and red. I think these can still be used for photography just fine, but the colours will turn out a bit different than with the usual filters, maybe there is more fine-tuning to be done after combining the channels, I don't have experience with this but you can search astrophotography forums for such results, there should be quite a few people out there who have tried this.
