View Full Version : Rodenstock 4x magnifier/focusing a loupe

Michael R
9-Aug-2016, 07:02
Yes, I searched old threads first, but found no definitive conclusions.

A friend exiting LF gave me his Rodenstock 4x Magnifier. It seems to be brighter than my old cheapo loupe so I'd like to use it. Some questions:

1) The instructions for "focusing" read as follows: "To focus, keep the magnifier steady in front of the eye and turn the focusing ring until optimal sharpness is achieved. This process will also correct sight defects up to -2.5 dptr."

I'm confused. Is it focusing or adjusting the diopter correction? Isn't it one or the other? Since I wear glasses, I wouldn't use diopter correction. I would have thought a "focusable" loupe would need a separate ring for focusing.

2) Is the whole "focus" thing a red herring when it comes to loupes and ground glass viewing? You frequently read people saying to make sure the loupe is focused on the ground side of the ground glass to avoid focus error, but isn't the image we see through the loupe formed on the ground side anyway? Even if the loupe is "focused" on the near side of the ground glass, we're still seeing the image formed on the ground side, right? Maybe it won't be quite as crisp, but when focusing the camera "best" would still be "best" (for lack of a better phrase). It's not like an out-of-focus loupe would cause you to focus on some "alternate" image leading to out of focus negatives.

Bob Salomon
9-Aug-2016, 07:14
Let's start over again, and forget what you just read and posted.
The first thing to do is to adjust the eyepiece of the loupe so that it is focused on the grain side of your ground glass. I have posted this many times in this forum but, apparently you have not searched thourghly.

1 take the lens off of your camera.
2 while the camera is on a tripod point the front of the camera at a light source.
3 put the loupe, with its skirt down, on the gg and focus the eyepiece of the loupe until you sharply see the grain of your gg.

Put your lens on your camera and start taking pictures. Put a piece of tape over the focus ring of the loupe to prevent inadvertent changing of the set position or use a permanent marker to make index marks for the proper setting for your eyes.

Michael Graves
9-Aug-2016, 07:15
Technically speaking, it is solely a diopter correction. Place the loupe against a ground glass with composition markings and turn the barrel until they are in sharp focus. Now when you focus your camera, you will see a nice crisp focus on the ground glass. Of course the diopter won't always stay where you put it, so you might have to do this again periodically. But for us people poor eyes, diopter correction is essential.

9-Aug-2016, 08:15
The concept of your No. 2 point is correct. Best is best and if your optical aid is out, Best is still best.

Bob Salomon
9-Aug-2016, 08:35
2 the image is formed on the ground side of the gg. If your loupe is in focus on the top side of the gg and not the grain side then you are out of focus by the thickness of the gg. And, if a fresnel is over the gg then you are out of focus by the thickness of the fresnel plus the thickness of the gg. Always focus on the grain of the gg.