Travel plan for Indonesia (Sumatra and Java) in october - question about the weather

I'm planning a trip to Sumatra and Java at the beginning of october for 3 weeks, but I'm worried about the weather. Not so much about rain, but about the overcast sky, since I'll bring my camera gear and I'd like to get as much sun as possible for nice pictures.

I know there are going to be a lot of clouds anyways, but is there a significant difference between september and october?