This is a vintage Foth Anastigmat 50mm f3.5 lens, which I believed to have come from a Foth Darby 3 folding 127-film camera (manufactured from 1935-39). It's designed for 3x4cm negatives on 127 film. It has the highest serial number currently known to exist for these lenses - 86967, with sources for these cameras saying that approximately 87000 were numbered, although more were made without serial numbers.

Condition is mechanically good but worn, with internal dust and fungus. It needs a good clean but care should be taken since the whole inner lens body rotates to operate the iris, and excessive force opening it may damage the iris. The iris (13 blades?) currently works well. I'm supplying it with a cloth storage bag.

I tested it by using cardboard shims to mount it in an M42 converter on a Sony A3500 mirrorless camera - an SLR cannot  be used since the rear part of the lens tube will obstruct the mirror. All pictures were taken at f8, ISO 800, weather was cloudy:
Church (230 yards away) 1/1000th f8
Tree (30 yards) 1/1000th f8
Garden (Bird bath 17 yards) 1/160th f8
Brick bit (about 7ft) 1/500th f8
Plants on end of roof (11ft) 1/500th f8

For more information about these cameras and lenses see
http://camera-wiki.org/wiki/Derby
http://camera-wiki.org/wiki/Derby#Lenses
https://vintage-photo.nl/the-flattering-foth-derby/
http://quirkyguywithacamera.blogspot.com/2016/07/may-foth-be-with-you-derby-camera.html

As always I'm starting low and with no reserve. I'm separately selling some other photographic items. If you buy multiple items from me please request a combined postage invoice, I'll do my best to get it down to the lowest possible price. I do not make any profit on postage, prices have recently risen.

International buyers: The postage price shown is based on an estimate of packed weight, around 200g; if it turns out to be cheaper than expected I will refund the balance. Because of frequent problems with overseas post I have switched to tracked postal services for some items. If combined postage is used for multiple items the tracking fee is charged on the package as a whole, not individual items, and postage works out much cheaper per item. Please note that eBay will add VAT or sales tax to the final price including postage in some countries.