Reducing / Expanding Adapters

GPCs are solely designed to compensate for the spherical error that is induced into the beam when a large chunk of glass (in this case all the combined prisms built into a binoviewer) would otherwise create a huge color error. So unfortunately, no, a GPC can never replace a barlow lens.

Since we sell neither Bresser telescopes nor Hexafoc focusers, unfortunately we can't answer this question with confidence. Please inquire the exact thread dimensions from Bresser to see if it will fit.

No, you simply have to loosen the six M2.5 headless setscrews with the included 1.3mm Allen wrench key and then simply slide it out (and replace if needed with our BDS Direct Thread adapters). They are marked with (5) on page six of the instruction manual: https://www.baader-planetarium.com/en/downloads/dl/file/id/175/product/2856/instruction_manual_for_all_baader_diamond_steeltrack_bds.pdf

Since we don't sell neither Explore Scientific telescopes, unfortunately we can't answer this question with confidence. Please inquire the exact thread dimensions from Bresser to see if it will fit. Please note that we have various RT-Adapters available, if the focuser should not fit natively: https://www.baader-planetarium.com/en/catalogsearch/result/?q=RT-adapter

In fact, we do not recommend removing the mirror from the housing because, as you said, it can cause alignment problems when you reassemble it. If at all possible, you should try to clean it inside the housing. Please refer to our general cleaning instructions, which apply to all types of optics, even if not specifically mentioned: https://www.baader-planetarium.com/en/downloads/dl/file/id/110/product/0/cleaning_and_maintenance_of_optics_a_short_instruction_guide.pdf

As you describe, this is exactly the procedure we recommend. Coarse impurities are removed with a blower, then the mirror can be gently cleaned with our Optical Wonder Liquid and the enclosed microfiber cloth. Alternatively, you can use original Kleenex tissues in combination with our Optical Wonder Liquid. However, make sure that you are using the original Kleenex cloths without any additives.