Re: calculating focal length of extender?

Richard J Kinch wrote:

See the old Edmund paper on the "Goodwin achromatic barlow" here:

http://www.anchoroptics.com/documents/

Beware ... the knowledge in the other documents there can distract you for months.

Ain't that the truth!
I remember being too strapped to actually order many of Edmund's booklets, but at that time they printed most of the pages in the catalog. Although the pages were only maybe 1/2" tall, we could read the, given a good magnifier...
Wonderful nostalgic resource!

Dave
.

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