Another Use for Yellow Gloves

I recently noticed that the rear glass element of my Variable Neutral Density Filter was loose, making it difficult to adjust the amount of light passing through. As these filters are fairly expensive I wanted to see if it could be repaired, before I considered a replacement.  

I contacted the vendor and they confirmed repair was possible and offered two options: send the filter in for repair or do the job myself.  Although the lens is still covered under its 10-year warranty, I opted for the latter after reading the instructions provided and reckoning the steps were well within my abilities.

A Variable ND Filter consists of two pieces of glass, each of which has a retaining ring designed to hold the glass in place.  The two pieces of glass are housed together in a single filter ring.  The outer piece of glass can be rotated to adjust the amount of light blocked (hence the variable nature of the filter).  The filter ring is marked with a scale ranging from MIN to MAX to indicate the amount of light being blocked.  The retention rings thread inside the filter ring and can sometimes become loose. This is what happened to my filter.  

The instructions provided:

Overall approach: 

• First remove the outer glass, then tighten the inner glass, then align the outer glass and tighten.  

Detailed steps:

• Note: On each retention ring are two notches opposite of each other, i.e., 6 and 12 o’clock.  
• Insert a two point compass, or something similar, into the notches of the outer ring and turn counter-clockwise to loosen.  
• Remove the glass
• Insert the compass into the notches of the retention ring holding the inner glass 
• Turn the ring clockwise to tighten the inner glass.
• When ready to reinstall the outer glass set the filter ring to MAX.
• Turn the top glass until it reaches its darkest point, then back off slightly and tighten the top ring.
• Note: This is done to assure the two pieces of glass are correctly aligned to each other.  
• Tighten the outer retention ring and the fix is completed. 
• Note: Be careful not to introduce any dust inside of the filter (between the two pieces of glass) and make sure the glass stays free of fingerprints.  After tightening the inner glass, I cleaned each piece of glass to remove fingerprints etc.  Then I blew compressed air into the filter ring to remove any lingering dust. Finally I installed the outer piece of glass. Through these steps I wore rubber gloves to avoid leaving fingerprints.