Quite some time ago I reported on some testing of Computar lenses for ULF work. If interested the thread is at http://largeformatphotography.info/lfforum/topic/498719.html
At that time I did not have a 270mm Computar to test but I speculated that if its coverage were equal to that of the 210mm, 240mm and 305mm Computars it should cover, or come very close to covering, 12X20. A few months ago I acquired a 270mm Computar, but for various reasons I was unable to actually test the lens until just a few days ago. I am pleased to report that the circle of illumination of this lens does indeed cover 12X20", with just a bit of movement. Of course, in order to get decent performance on the corners you will need to stop down to f/45 or f/64, but that is not such a big deal since we generally do this anyway with 12X20 format.
Many people want to know if the Kowa Graphic is the same lens as the Computar. There does not appear to be a definitive answer to this question. I have tested a couple of Kowa Graphics, both 240mm, that had the same coverage as the 240mm Computar. However, so far I have not seen a Kowa Graphic in 210mm, 270mm and 305mm with as much coverage as the Computars of this focal length.
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