Complex sentence: In the case of the GE Synchro-Press with M sync for instance, shutter speeds as long as of a second still diminished its guide number, though it was still an impressive 140 (ft) at a second exposure.
Split into simpler sentences: In the case of the GE Synchro-Press with M sync for instance, shutter speeds as long as of a second still diminished its guide number. Its minimum guide number was still an impressive 140 (ft) with a second exposure.