Previously, I had tried to figure out the focus and got relatively close to perfect focus through trial and error. However, I thought that since I had arranged to go to Specsavers to order new lenses for my final product it would be worth asking if they knew of a formula that could help me achieve the exact focus of the image. At first we had to find out the strength of each lens. Both convex lenses had a +15 magnification but it was just getting the distances between them that would allow a focus image that was the hard part. I was lucky enough to be given a formula for exactly this.
Specsavers were a huge help as I was able to get lenses custom made and a complex formula that I would have struggled to figure out myself.