From: rlombardo3@gmail.com   
      
   In engineering, the exact focal length and position are not required as one   
   simply adjusts the axial position of the lens relative to the focal plane to   
   obtain the smallest spot (circle of least confusion).  Exact focal length is   
   not needed, nor measured typically.   
      
   As you are interested in monochromatic light focusing, the problem is less   
   challenging, but manufacturing tolerances must also be considered in   
   attempting to determine the exact value.  Zemax optical design software can   
   be used to input tolerances and Monte Carlo simulations be run to estimate   
   the range of focal variations.   
      
   As you are also no-doubt aware, the focal lengths given include the back,   
   front, and effective.  All rather nebulous in any attempted measurement.   
      
   Can you describe why you need to know the focal length so accurately.  For   
   theoretical studies, you can simply use the provided focal length and for   
   empirical work, you can measure the focal length by iteratively measuring   
   the focused spot and moving the lens until the smallest focused spot is   
   obtained.  Most automated MTF stations have this ability, typically in the   
   visible or far-IR band only.  Using a blackbody source with a   
   narrow-bandwidth filter at 1553 nm along with a detector sensitive in that   
   band would provide an accurate measurement.  The MTF stations I've used use   
   a calibrated stage that reads in 0.001", which is accurate to a higher level   
   than you need.  There are companies that can provide this service, but at a   
   non-standard wavelength cost might be prohibitive.   
      
   I suggest having the focal length measured at nominal wavelength that   
   transmits 1553 nm light and then correct the focal length from visible (for   
   example) to your wavelength using refractive indices of the lens materials   
   to obtain the adjusted focal length.   
      
   Please contact me directly at ltec@cox.net if you need more specifics.   
      
   Ciao,   
      
   - Russ in Santa Barbara   
      
      
   "laser"  wrote in message   
   news:74359794-c7a7-422c-9c96-2bb548b4aac1@googlegroups.com...   
      
   http://search.newport.com/?q=KPX115AR.18   
      
   To whom it may concern,   
   I am trying to get focal length of this lens at 1553nm. In specifications,   
   tolerance of the focal length of this lens is +/-1% and it is not enough for   
   my application. I would like to get the focal length of this lens within   
   <+/-0.1-0.2% error.   
      
   Would you please let me know what is a best way to know the answer?   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)