Need Help 'Calibrating' a Critical Grain Focuser

[Andre Noble]

I have a 'Microsight' grain focuser, inside of which is a thin wire strecthed across the field of view. The eye piece is 'screw focus' adjusted to the wire sharply in order to 'calibrate' the focuser before use.

Well, the little wire has come out, and I'm not positive where in the inner assembly it's proper positioning in order to re-install.

Working without the wire, my intent was to 'calibrate' the grain focuser empirically using a pre-focused negative with from the enlarger onto the baseboard, and then viewing this prefocused image through the grain focuser while 'focusing' the eyepiece of the grain focuser until that image was sharp.

To my suprise, I noticed ithat adjusting the eyepiece 'focus' on the grain focuser did not seem to affect the sharpness of the pre-focused image when viewed through the focuser's eyepiece.

Is this correct?

Is the adjustable eyepiece on the grain focuser, therefore, more like a diopter correction rather than a true focus calibrator?

Thanks in advance for any input.

[Jon Shiu]

I think your eye needs to see the in focus wire and grain at the same time when focusing in order to be accurate. If you take the bottom piece below the eyepiece out, you will see where the "wire", ie a piece of fishing line, was glued across the opening.

[Gem Singer]

Andre,

I always thought that the focusing knob of the enlarger controlled the focus of the negative on the easel. The adjusting ring on the grain focuser functions to control the sharpness of the image of the reticule (cross hairs of the grain focuser). Once the image of the reticule is razor sharp, then the enlarger's focusing knob can be used to focus the image of the grain pattern of the negative. When both images are sharp, the enlarger is in focus. The two focusing adjustments work independently of each other. It seems to me that you would need to replace the reticule mechanically, not optically. If that cannot be done, perhaps it's time for a new grain focuser.

[Andre Noble]

"I always thought that the focusing knob of the enlarger controlled the focus of the negative on the easel."

Well, that's new!

Thanks Jon and Eugene for your input.

[Gem Singer]

Andre,

I was not putting you down or implying that you did not know the function of the focusing knob on the enlarger. If you would have read my entire answer to your question, you would have realized that I was merely attempting to tell you politely that, based on my own experience, attempting to repair a broken Microsight grain focuser is an exercise in futility. The version of the Microsight that I once had was made in France and was called a Thomas Scoponet. I eventually tossed it into the dumpster.

[Andre Noble]

My intuition tells me the adjustable eye piece serves as a diopter correction rather than an internal focus calibration. I found some reference to this idea of the adjustable eyepiece being a diopter corrector to account for various visions elsewhere on the internet.

Even when the little wire was in there, I could crank the eyepiece up and down and not loose focus of the wire easily. Even with wire missing, and much fiddling with the eyepiece up and down, the two sets of prints I made with it are razor sharp.(???)

However, I concede that I don't know if I will need to replace grain focuser or not. those Peak grain focusers sure are pretty!

[Conrad Hoffman]

The eyepiece just allows you to focus on the wires. Your eye can accomodate a fair range, thus the appearance that it doesn't do much. I rebuilt mine with a better quality eyepiece from a microscope or something, then replaced the wire target with a concentric film target that gives me far less trouble keeping my eye focused where it should be. For testing and alignment, I have a procedure on my web site under Darkroom Measurements at http://members.rpa.net/~choffman/index.htm Basically, you set up a 35mm camera with a macro lens, tubes, or whatever, and focus straight down on some contrasty text from about ten inches up. You then slide the focuser in front of the camera and see if the wires come to focus in exactly the same place as the text below. Remember, the "focuser" doesn't really focus anything; that's the job of your enlarging lens. All the focuser does is fold the projected light up to a more convienent location, and provide a magnifier for you to look at it. Just as if you were looking up through clear photo paper from below the enlarger.