I'm mounting a serise of bookshelves (for books!) on an interesting wall.
It seems that several horizontal 2x4's have been mounted on the face of the vertical studs, which are there, 16" apart, but deep behind the drywall. I can use the horizontal lines for 2 of the 4 shelves, but what do I do about the other two? For those, I basically have Drywall, followed by over an inch of "air" before I hit the stud.
The only thing I can think of is to use some sort of a seroius plug that you would use when there are no studs and drive completly thru it and hitting the deep stud as well. I'm not sure though, if hanging a heavy shelf on even thick long screws is gonig to break, or bend and destroy the drywall directly under the screw.
I was planning on using standard brackes, with 2 screws each into the wall about 7" appart.
Drywall anchors will hold a fair amount of weight. You could check the approximate weight of the items that will be on the shelf and then go by the weight rating on the anchors to determine if that is a suitable solution. One concern with using anchors with brackets (it sounds like your using simple metal L brackets, yes?) Often the brackets have two holes at the top that are pretty close to each other. If you install drywall anchors too close to each other they will not live up to their weight rating. So this could be a problem. Specially since its the screws at the top that will hold the most weight.
The next step if you determine that drywall anchors are not adequate would be to install some 1X material that the brackets would sit on. if you ran these the full vertical distance you could anchor into the horizontal studs. A little construction adhesive wouldn't be a bad idea ether if you install some 1x's.
There are also systems available that come with a metal track that installs vertically that you can instal brackets on.