How to Adapt a Door Viewer "Fish-eye Lens" on to a Full-size Camera

Step 3 Further Modifying Your Reducer/Adapter...

Now that the narrow end of the reducer has been shortened, the next step is to shorten the wide end of the reducer. Start by measuring 5/8ths of a inch from the top threading ring on the reducer and mark it with the indelible marker. Using the threading ring as a guide for the edge of the ruler, mark off 5/8ths of an inch around the reducer. (Pictures 1 and 2) If you prefer metric, use 16mm as your guide. Make sure at least three of the marked points are close together in a row.

Tip: If your ruler is a bit faded or it's hard to read where 5/8ths of an inch is, mark a reference point to it on the ruler before marking off the reducer.

Once the points have been marked, give the ink a couple minutes to dry, and then take your rubber band over the top of the reducer and line its edge up just below your reference points. Since the band has a tendency to want to be crooked, use the three dots in row as a guide to line up at least one section of the band as straight as possible. That will be the side where you will start sawing. Make sure all other reference points are just above the rubber band, and the band is fairly even. Draw a line connecting all the points around the reducer using the band as the guide now. (Picture 3)