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Increasing Image Magnification*
919
NOTES, CASES, INSTRUMENTS INCREASING IMAGE MAGNIFICATION*
but the focusing adjustment has sufficient latitude to compensate for the difference.
I N RETINAL PHOTOGRAPHY JACK H. PRINCE, F.R.M.S. ( E N G . )
Columbus, Ohio
A TIMING UNIT FOR TONOGRAPHY*
By increasing the camera tube length of S. I. A S K O V I T Z , M.D. the Zeiss-Nordensen retinal camera and us Philadelphia, Pennsylvania ing the auxiliary lenses incorporated in the W i t h the increasing interest in aqueous instrument, a much larger picture of a small outflow determinations 1 during the past few lesion can be obtained. In fact the optic nerve years, efforts have been made to simplify can be made to cover most of a 35-mm. frame clinical tonography so that the procedure without noticeable reduction in resolution. may be readily applied by any ophthalmolo T h e tube immediately in front of the gist. T h e present paper describes a small camera body and behind the light deflection timing unit designed toward this end. prism is detachable. If this is replaced with F o r all practical purposes, it suffices in a tube six inches longer and the —0.75D.general for an assistant to write down the auxiliary lens is turned into position, an in tonometric readings every 15 seconds 2 crease in magnification of X 2 is obtained. throughout the four- or five-minute total in If the tube length is increased to eight inches terval, thus eliminating the need for any and the — 1.5D lens is used, then the magnifi expensive auxiliary recording equipment. 3 cation is even greater. T h e entrance pupil However, to note the tonometer values at is changed by this procedure but it does not regular intervals soon becomes monotonous affect the picture unduly. T h e field stop is for both tonographer and assistant, and it is provided by the camera frame. easy to miss one or more readings, even with T h e mathematically ideal lengths of tube are probably a little longer than quoted here, * From the Ophthalmology Research Laboratory (Dr. I. H. Leopold, director), Albert Einstein * From the Department of Ophthalmology, The Medical Center, Northern Division. This work was Ohio State University. supported by a grant from the Weinstock Fund. ■
*
<
-
EXTRA
TUBE
LENGTH
FILM ,
Fig. 1 (Prince). Diagram showing the simple alteration in the effective focal length of the camera objective to produce a larger image.
NOTES, CASES, INSTRUMENTS INCREASING IMAGE MAGNIFICATION*
but the focusing adjustment has sufficient latitude to compensate for the difference.
I N RETINAL PHOTOGRAPHY JACK H. PRINCE, F.R.M.S. ( E N G . )
Columbus, Ohio
A TIMING UNIT FOR TONOGRAPHY*
By increasing the camera tube length of S. I. A S K O V I T Z , M.D. the Zeiss-Nordensen retinal camera and us Philadelphia, Pennsylvania ing the auxiliary lenses incorporated in the W i t h the increasing interest in aqueous instrument, a much larger picture of a small outflow determinations 1 during the past few lesion can be obtained. In fact the optic nerve years, efforts have been made to simplify can be made to cover most of a 35-mm. frame clinical tonography so that the procedure without noticeable reduction in resolution. may be readily applied by any ophthalmolo T h e tube immediately in front of the gist. T h e present paper describes a small camera body and behind the light deflection timing unit designed toward this end. prism is detachable. If this is replaced with F o r all practical purposes, it suffices in a tube six inches longer and the —0.75D.general for an assistant to write down the auxiliary lens is turned into position, an in tonometric readings every 15 seconds 2 crease in magnification of X 2 is obtained. throughout the four- or five-minute total in If the tube length is increased to eight inches terval, thus eliminating the need for any and the — 1.5D lens is used, then the magnifi expensive auxiliary recording equipment. 3 cation is even greater. T h e entrance pupil However, to note the tonometer values at is changed by this procedure but it does not regular intervals soon becomes monotonous affect the picture unduly. T h e field stop is for both tonographer and assistant, and it is provided by the camera frame. easy to miss one or more readings, even with T h e mathematically ideal lengths of tube are probably a little longer than quoted here, * From the Ophthalmology Research Laboratory (Dr. I. H. Leopold, director), Albert Einstein * From the Department of Ophthalmology, The Medical Center, Northern Division. This work was Ohio State University. supported by a grant from the Weinstock Fund. ■
*
<
-
EXTRA
TUBE
LENGTH
FILM ,
Fig. 1 (Prince). Diagram showing the simple alteration in the effective focal length of the camera objective to produce a larger image.