I have been told by a person who owns "Larry Bartletts B&W photography workshop" that Bartlett recommends putting the grain focuser directly on the paper easel without any paper in the easel. Personally I have always had the paper there. Which way is correct, or does it depend on calibration of the grain focuser? Any input appreciated.

-- Peter Olsson (Peter.Olsson@sb.luth.se), November 24, 1998

Answers

Unfortunately Bartlett died before the text was written. The text is by Jon Tarrant.

The closest Tarrant comes to this statement is on p30: "Unfortunately, some writers have confused the focusing issue, suggesting that the image should be focused on a spare piece of printing paper rather than on the baseboard itself..."

He doesn't actually come down and say one way or the other.

Personally, I would suggest that the "correct" answer, as you suggest, depends on the grain focuser. I believe that (a) it should be calibrated to work best sitting on some spare paper, because otherwise the calibration would have to make an assumption about the "usual" paper thickness, and (b) the depth of field of the lens takes care of the very small distances involved.

I have tested this, and can find no difference in prints focused one way or the other. In practice, when I use a black baseboard, I do all the lining-up and focusing with a spare piece of paper.

-- Alan Gibson (Alan.Gibson@technologist.com), November 24, 1998.

A few years ago, one of the rec.photo regulars reported on some careful tests he had done comparing focus on the easel or on a piece of photo paper. He concluded that it made no visible difference. He said he would continue to use a piece of paper for focusing, but would probably stop keeping a sample of each paper type he used.

I don't remember who or when, but it might have been Barry Sherman. Maybe.

-- mike rosenlof (mike_rosenlof@yahoo.com), November 27, 1998.

I think there was a similar discussion recently on photo.net (or perhaps rec.photo.darkroom) where a poster laid out the DOF formulae and showed that at any normal aperture and degree of enlargement the DOF was much more than the thickness of double weight paper. So the conclusion was that you could safely put the focuser on the easel without paper and still be sure of a sharp print.

I've not put paper under my focusers for years, and don't think I lose any sharpness as a result. Of much more concern to me is the risk of focus creep in the lens stage between the time I get an image in focus and the time the enlarger light goes off at the end of the exposure.

-- Kip Babington (cbabing3@swbell.net), November 28, 1998.

To eliminate reflection on the paper during exposure (wich reduces contrast, espescially with thin RC papers), it is best to have a black easel. Therefore, you will need a sheet of paper to see and compose the projected image. I agree with the others that say that the thickness of the paper is non significant considering the DOF. If you still want to use a light colored easel and want to consider paper thickness with your grain focuser, why not cut a piece and glue it under?

-- Jacques Gratton (jgratton@globetrotter.net), December 06, 1998.