Genesis of a Lens Hood...

[sandeha]

Yup, that'll be the lens design then.  The why of their inventing centre spot filters for WA lenses, though I wasn't aware of them being necessary for a 90mm.

Just checked - there's no darkening on the corners of my 90mm Angulon negatives, though I've always shot at f16 or f22. 

[sandeha]

Lens coverage means different things to different people so concrete data will be hard to find.  However, if the image circle of the 90mm Angulon is just over 125mm the Optar may be slightly less.

http://www.largeformatphotography.info/forum/showthread.php?t=14915

That may be where the vignette is coming from.

[Madrigal]

Awesome. Nice work on the lens hood. I should make one of these.

[Scott]

Lens coverage means different things to different people so concrete data will be hard to find.  However, if the image circle of the 90mm Angulon is just over 125mm the Optar may be slightly less.

http://www.largeformatphotography.info/forum/showthread.php?t=14915

That may be where the vignette is coming from.

Well, that stinks.