Patent ID: 11934032
Assignee: INSTITUT NATIONAL D'OPTIQUE
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 5:
6. A kit for precisely centering an optical element mounted in a barrel having an inner wall and including a cavity having a center axis, the barrel being provided with a set of barrel threads, the kit comprising:
a resilient spacer having an unthreaded cylindrical wall and opposite frontward and rearward rims, the frontward rim being engageable with a spacer-mounting surface at a rearward periphery of the optical element, the rearward rim comprising a rearward rim edge, the resilient spacer being resiliently deformable between a compressed state allowing the insertion thereof within the cavity and a biased state in which the cylindrical wall of the resilient spacer contacts the inner wall of the barrel; and
a retaining ring having a set of ring threads complementary to the barrel threads, the retaining ring having a forward periphery comprising a spacer-abutting surface engageable with the rearward rim edge of the rearward rim of the resilient spacer along a circular edge contact line precisely centered within the cavity when the retaining ring is screwed within the barrel, the spacer-abutting surface having a frustro-spherical profile having a radius of curvature RRing_forward given by the formula:, R
   Ring_forward
  
  =
  
   
    
     
      ⌈
      
       
        
         d
         ring
        
        
         2
         ⁢
         
          tan
          ⁡
          (
          
           
            φ
            threads
           
           /
           2
          
          )
         
        
       
       -
       h
       -
       
        T
        /
        2
       
      
      ⌉
     
     2
    
    +
    
     Y
     r_rim
     2
    
   
  
 

where:
dring is a diameter of the retaining ring along the ring threads;
φthread is a value of a thread angle of the ring threads;
Yr_rim is a half-diameter of the rearward rim edge;
h is a distance, in use, between (i) a first point of contact of the barrel threads with the ring threads proximate to the resilient spacer and (ii) the circular edge contact line; and
T is a distance, in use, between (i) the first point of contact of the barrel threads with the ring threads proximate to the resilient spacer and (ii) a last point of contact of the barrel threads with the ring threads farthest from the resilient spacer diametrically opposite to the first point of contact; and

wherein the spacer-abutting surface has an orientation at the circular edge contact line ensuring that, in use, a resulting force directed towards the inner wall of the barrel is applied to the resilient spacer.