I paid my way through college re-writing and vectorizing Atomic Structure codes that had already gone through 20+ years of migrations, starting from the IBM 704.Every trick in the book to squeeze those codes into available memory and make them run. Like pass Real array into a Sort routine as an Integer Array to save clock cycles in the routine. The programmer had to know the exact representation of a Real value to know it would sort correctly as an Integer. That took some time to figure out- especially as I needed to convert Real on the 60-bit machine that it ran on to Double Precision on a 32-bit machine. Rebuilding lenses from the 40s and 50s is about the same. After a while you know which elements between lenses can be exchanged, which can't. How far to change spacing, shimming, etc. I've had photographers from around the world send me lenses to rebuild. I like to see what they do with them. I consider myself a Tinkerer of lenses- not a real repairman. Real Photographer- I suspect one will know when they are a real photographer all on their own. Declaration of REAL means something on a computer, not so much elsewhere.