Does anyone have any recommendations for a backpack style bag in which I want to carry my Pentax K10D with three or four lenses including a Sigma 50-500 ('Bigma') with handle? Or can anyone tell me what won't work from their experience, please? I suspect that the bags with side access will be too small.
Same problem here! And yes you're right side access will not do the job. I have a Lowerpro (look at their web site);sorry don't remember which model, but I think the super or pro treker AW. Lots of space for filters batteries etc and I use the note book compartment for wallet, maps, books and other bits and pieces when travelling. Only drawback is shuffling everything round when you change lenses; but I suggest for carrying you always keep the 500mm lens back on and keep the same layout. I would highly reccomend you go to a shop and look at them before buying.We all have different lenses and storage needs!
Depends what the other lenses you want are. I had a Nikon D80, Sigma 50-500, two shorter zooms (18-50 and 12-24) and two Nikon flashes in a LowePro MicroTrekker last week. With a bit of playing I've fitted two bodies, that lens and a small 70-300, two standards and a flash in there before too.