I'm pretty new to this system and just recently bought the 5600HS. I noticed that the flash only goes to 85mm, what does that mean when I use a lense at a longer focal length than 85? will the photo not be properly exposed?
Exposure will not be affected.
85mm is the limit the most any brand flashes can reach, by moving the flash tube (=the l&) behind-ahead only, inside the head.
To go to longer ones, i.e.: 135mm or 200mm, it would need very heavier fresnel-lenses on its front, like big theatre-projectors do.
Settings likewise 85mm, compress the sent lightning, (it beeing like a cone shaped) from its border toward its center; so, lightening less space/area but as more strongly.
This way, allows the sent light to go to longer distances according with Lens' Focal-length, then avoiding to lighten what stays outside(around) the Lens' sight.
It means increasing the Flash's useful-power onto the long distances getting tele-photos; where, otherwise the most light would go as dispersed around.
If You get a 135mm Lens, just some light will go as "wasted" around, on things outside the picture; but the whole scene will be lightened at all, however.
And CAMERA PROPERLY EVALUES THOSE LIGHT WHICH COME BACK TO IT FROM THE SCENE's area only; as "Through The Lens" (TTL).
If the situation does not overtake Flash's power-limit, picture gets no reason to work out as under-exposed.
Instead, problems may start whether You use a widest Wide-Lens, more wide than Flash do.
I.e.: Flash sets up to 24mm, with a 15mm Lens.