Green things on canon 1300d penta mirror, what should I do?

It's very difficult to tell exactly where they are or even what they are from the pictures. If you can locate them precisely then  I would suggest you dampen a cotton bud with isopropyl and wipe very gently to try to remove them. If that doesn't work then it will be a case of finding a camera repair shop.

They won't affect your pictures but if it is something organic then you never know what it might grow into so early removal is advisable.

Ray UK wrote:

It's very difficult to tell exactly where they are or even what they are from the pictures. If you can locate them precisely then I would suggest you dampen a cotton bud with isopropyl and wipe very gently to try to remove them. If that doesn't work then it will be a case of finding a camera repair shop.

They won't affect your pictures but if it is something organic then you never know what it might grow into so early removal is advisable.

I tried to do what you suggested and it didn't quite work, it made the green things go black and the pentamirror got some water mark on it. However, I don't plan on using this camera in the future anyway so there was nothing to lose. Thanks for the help regardless.

The viewfinder after attempting to clean the pentamirror with cotton bud and isopropyl

Ryan997 wrote:

I tried to do what you suggested and it didn't quite work, it made the green things go black and the pentamirror got some water mark on it.

As it had that reaction I would guess the marks were some sort of corrosion of the surface silvering, you have removed the corrosion and exposed the damaged surface below. Not much you can do apart from replace the pentamirror which obviously wouldn't be economically viable. It was worth a try anyway.

Incidentally the watermark that isopropyl sometimes leaves behind can be removed with lens cleaning fluid.