The purpose of auxiliary lens in microscope Can someone explain me the purpose of auxiliary lens in microscope. 
The specification says:
Eyepiece: Extra wide field 10x  Eyepiece w Spectacle Correction 30mm Ocular
Objective 0.7-45x , Auxiliary 2x

And the manufacturer claims that it is having magnification of 90X. Is it true ?
Perhaps they are multiplying the power of Objective, Eyepiece and Auxiliary to get 90X. But is correct to say the magnification is 90 X
BTW this is the microscope I am talking about  and the specification is given at the end.   
 A: This is likely to be a standard Barlow Lens (see http://en.wikipedia.org/wiki/Barlow_lens) which, when attached to one of the normal eyepieces, decreases the focal length by half and thus increases the magnification by 2X.  The previous answer describes a more complicated type of Barlow lens that turns any eyepiece into a zoom lens, which you may or may not have.
A: Auxiliary lens normally serve to cover different zoom ranges.
for example here: http://www.2spi.com/catalog/ltmic/ZTX-3E-Microscope.shtml they say: 

Objective lens:
  Zoom type objective lens that has a range of 1x to 4x comes "standard"
  with the Series 3 "package". We also have available optional auxiliary
  lens that literally "screw on" to the existing standard lens to make
  possible the zoom function covering different zoom ranges. Such
  auxiliary lenses are available as 0.5x, 0.75x, 1.5x, and 2x. The
  installation of a 2x auxiliary lens permits a zoom function of 2x to
  8x. A 0.5x auxiliary lens, reduces the zoom function range to 0.5x to
  2x.

