A few months ago I bought a new 135mm Doctor-Optic enlarging lens. First usage f ollowed by deliberate tests showed that lens gave what I consider to be a very ' curved field' effect projected onto the base board. To put it simply, a 'wok' wo uld have to be used as an enlarging easel with this lens.
I tested with normal 5x4 neg's but mainly by scratching lines on an over exposed neg which was then h eld in a glass neg carrier. The neg was projected on to a sheet of paper on the base board to give about a 16x12 image and the centre of the image focused. The scratched lines went out of focus as they extended to the edges of the paper (al l 4 edges). By raising each paper edge by about 8 to 9mm I could get the lines i n focus along their full length. When an edge was lowered it was possible to see the image of the line return to an out of focus condition. If I set the lens to get the lines in focus around the perimeter of the paper then of course the cen tre was out of focus. The base, enlarger (a wall mounted De Vere 54) and lens ar e all in line/square etc to each other.
I reported this to the company that sol d me the lens and they very quickly sent a new Doctor-Optic 135mm lens. I've tes ted this and it gives just the same results i.e. to get the image in focus acros s the paper all four edges have to be raised by 8mm or so (right and left hand e dges more so if the image is landscape format).
In the past when using a friend s enlarger with an old Taylor-Hobson lens I never remember seeing the same effec t, well I'm sure my friend would not have put up with it!
Am I being too critic al here? Do you consider this lens is o.k. to use?I don't and I intend to send it back. Stopping down helps but 'soft' detail can still be seen around the edge s of prints that are anywhere near 'full frame'.
I would welcome any comments.