The Use of Finder Slides

For the preparation of most of the images in the "Display Demonstration Materials" set, it is necessary to have a method for relocating the specific microscopic field that was photographed. This is accomplished by the use of "Finder Slides", special glass slides that have grids of reference marks imprinted on them. After the sample slide has been satisfactorily positioned and a photomicrograph has been taken, the sample slide is removed from the stage (very carefully, so as to avoid moving the stage position) and is replaced by the finder slide (suitably oriented - see below). The position of the finder slide is then "read" by recording the reference grid markings that appear in the center of the microscope field of view: it is usually necessary to switch to a lower magnification lens - at least briefly - so as to see enough of the finder slide markings to be able to "read" the position, because, at higher magnification, only a small part of the reference markings can be seen. The lens magnification used when the sample slide was photographed is then recorded, along with the finder slide position that was noted. To relocate the photographed field in the sample slide at a later date, the process is reversed: the finder slide is placed on the stage and the recorded reference markings are found. Then the finder slide is replaced by the sample slide (again being careful not to move the stage); with practice and care it is possible to relocate specific fields of sample slides (even those photographed at very high magnification) using this process. Finder slides are produced by a number of suppliers and are - as might be expected - rather expensive (the ones in our set cost between $150 and $200 each). As of this date (3/27/2003), we have several finder slides, made by two different suppliers. They have arbitrarily been designated Finder Slides A (3 copies) and Finder Slides B,B' (2 copies of each). Finder slides A were obtained from Gurley Precision Instruments (Troy, NY, catalogue #7100). When placed on the microscope stage with the label to the left, and photographed using the 6.3X lens (full field width = 1000 um), they reveal an image such as shown below:


It is obvious that the labels are "upside down" but, in practice this turns out to be a very minor inconvenience. By convention, we "read" this field as "N-17, slightly to the right and "up" from the very center of the grid square. All three Finder slides A show the exact same reference point when placed on the stage, so long as care is taken not to move the stage when the slides are exchanged. One can describe the finder slide location to almost any desired degree of precision: for example, "N17/P17" (there is no O row) means that the horizontal bar separating squares N17 and P17 was in the center of the field, while "M17 - lower left" means that the lower left quadrant (upper right in "real space") of square M17 was in the center of the field of view.

Finder slides B, also called "The England Finder" were produced by Graticules Limited of Tonbridge, Kent, England and purchased from Ace Scientific. They are now available (Finder Slides B') from Electron Microscopy Sciences (the USA distributor for Pyser - SGI, in Edenbridge, Kent, England). When placed on the microscope stage with the label to the left, and photographed using the 6.3X lens (full field width = 1000 um), they reveal an image such as shown below:


It is obvious that here the labels are "right-side up" and that the field would be read as O30, slightly shifted towards quadrant 1. Both copies of Finder Slide B give identical reference information, which can be "read" to a very high degree of precision. Unfortunately, Finder Slides B' are slightly different from B: while the "column" placement of the two batches is the same, the "rows" differ by about one unit; thus reference square P-23 on finder slides B corresponds to reference square O-23 on finder slides B'.

While it is not advisable to "switch" types of finder slides, the following crude "triangulation" could be used to get a rough conversion from A-type to B-type finder slide readings: Finder A - N1; N31; W16 are equivalent to Finder B - O4, quadrant 1; O16, quadrant 1; E31.

NOTE to staff (ISFa, SFOS): One copy of finder slide A and one of slide B have been placed in the wooden storage cabinets (B2004), along with hard copy of this explanation. One copy of slide A and one of slide B' have been placed in the metal storage cabinet in the MS-I MDL common area, also along with hard copy of this explanation. The remaining finder slides (one each of A, B, and B') are in the small file cabinet in my office (B2032 - MRA).