I am in possession of a damaged example of the above.

The objective is rattling in its seating and there seems to be a 2.4mm thick component missing from the lens. By this I mean that, with the lens retainer fully home, there is a 2.4mm gap. The surviving front(?) lens element is chipped also.

I am in a position to make a new lens and I understand that the original might have been an achromatic doublet, probably cemented.

Can anyone tell me what the focal length should be?

I have read the admirable Peter Laidlericon's archive without achieving enlightenment on this topic.
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