A few months ago I bought a new 135mm Doctor-Optic enlarging lens. First usage followed 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' would 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 held 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 (all 4 edges). By raising each paper edge by about 8 to 9mm I could get the lines in 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 centre was out of focus. The base, enlarger (a wall mounted De Vere 54) and lens are all in line/square etc to each other. I reported this to the company that sold me the lens and they very quickly sent a new Doctor-Optic 135mm lens. I've tested this and it gives just the same results i.e. to get the image in focus across the paper all four edges have to be raised by 8mm or so (right and left hand edges more so if the image is landscape format). In the past when using a friends enlarger with an old Taylor-Hobson lens I never remember seeing the same effect, well I'm sure my friend would not have put up with it! Am I being too critical 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 edges of prints that are anywhere near 'full frame'. I would welcome any comments. Regards Russell

-- Russell Fox (rsfox@armour.softnet.co.uk), November 07, 1999

Answers

I have never heard of that brand before. I would back out of that deal as quick as you can. Enlarging and copying (process) lenses are supposed to be corrected for a flat field. this one sounds like a cheap knock-off.

-- Tony Brent (ajbrent@mich.com), November 07, 1999.

Russell, does your enlarger have the correct condensers to use with a 135mm lens? They have to be matched. Doctor is or/was once a respected German optical house. They took over the factory when another well known manufacturer bit the dust. Goertz? Kilar? I can't remember. I believe they made mostly commercial Video lenses. Maybe Zoomar? You could put this lens in another enlarger, or another lens in your enlarger to see wherein the fault lies. Good luck.

-- Bill Mitchell (bmitch@home.com), November 07, 1999.

Doctor Optic was a very large manufacturer of optics, binoculars and even the reflectors for BMW headlamps. They also made projector lenses.

Did is operative as when the owner died a few years ago the banks put the company into receivership. The lens divisions were purchased by Rodenstock and Zeiss. The binocular division had been reformed under the Doctor Optic name.

The last Doctor Optic distributor in the U.S. was Bogen.

-- Bob Salomon (bob@hpmarketingcorp.com), November 07, 1999.

Yes Bill, the correct condensers are in place. The enlarger is fine, De Vere enlargers are very well built.

-- Russell Fox (rsfox@armour.softnet.co.uk), November 07, 1999.

Try the same test with another lens of another brand; if you get the same result then your enlarger is out of alignment. Of course if you get sharp corners and center with another lens, then there's something wrong with the Docter lens.

The Docter lens could simply be that bad.

-- John Hicks (jbh@magicnet.net), November 07, 1999.

Russell, I didn't mean to critisize your enlarger. My first enlarger was a 4x5 DeVere. I was 16 years old and very proud of it, and remember it fondly to this day. It was built like a tank as I recall. I could never afford a good lens for it, and used the 15cm uncoated Heliar off my camera. I also remember that I nearly lost my job clerking at the camera store over it, but, as old age creeps up, I can't remember the details. Some things are better left forgotten. Mitch

-- Bill Mitchell (bmitch@home.com), November 07, 1999.

I would consider this lens to have unacceptable performance. If the performance was poor wide open, but good at two or more stops closed down, it might be acceptable. If all four corners focus above the focus point of the image center, then the reason can't be a misaligned enlarger. As other posters have suggested, getting good results from another 135 mm lens would demonstrate that the problem is with the Doctor Optic lens. Perhaps this lens just doesn't cover 4x5.

-- Michael Briggs (MichaelBriggs@earthlink.net), November 08, 1999.

Exactly what lens do you have? 135mm is not very descriptive. Could this be a 135mm f9.0?

-- Bob Salomon (bob@hpmarketingcorp.com), November 08, 1999.