Might as well throw this into the anamorphic forum explosion!   I came across this focusing solution earlier this year by taking my 20% understanding of comments made on varied forums about optics and vaguely knowledgeably combining elements from the large amount of random glass I've amassed over the years. I don't claim to know much about optics, and I'm certainly no engineer, but this technique has worked when I didn't have the budget to rent a set of Kowas or the like.   This is definitel