I've browsed the web for Gundlach Turner-Reich convertible anastigmats and found what seemed to be two different types of those. Both were 12" in focal length but one was composed of 17" and 25" halves, and the other, of 21" and 28" halves. If the optical systems of both were identical the 21" + 28" combination should be longer in focus then the 17" + 25"....
I did not find any data on this lens modifications. Could anybody please clarify the difference between those?
Thanks.
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