10X WideField fn20mm Focussing Eyepiece with Reticle Horizontal Scale with crosshair. Fits a 23.2mm (inner diameter) Eyepiece Tube.
This eyepiece is a focussing eyepiece which means it has a knurled ring at the top which, when rotated, extends the length of the eyepiece. This ensures that the scale can be made to remain in focus at the same time as the subject under examination. It is a high quality composite lens eyepiece that gives a wider field of view compared with a standard fn18mm eyepiece. (fn = Field Number). Suitable for use with many biological and materials upright microscopes. Not suitable for stereo microscopes which have a eyepiece tube. The reticle scale is held in place with a narrow threaded retaining ring inside the underside of the eyepiece. Alternative reticle patterns can be supplied such as counting grids and object sizes.
An eyepiece with this reticle is used in two ways:
a) To Make Measurements
Using Microscope Eyepiece Reticles to Make Measurements
To make a measurement it is necessary to convert the distance between one interval on your reticle scale into calibrated units on the observed subject on the microscope for each magnification that you wish to use. (The fact that a reticle scale may be 10mm long is entirely irrelevant and should be disregarded – we cannot understand why the manufacturers even mention it.). To calibrate the reticle you require a subject of known size under observation, then you simple observe how many intervals on the reticle scale are covered by this known dimension and calculate the interval width accordingly. For example if you are looking at an object on your microscope which is known to be 50 microns wide and 70 of the intervals on the scale are covering this object then the calibrated value if each division at that magnification is 50/70 = 0.714 microns per interval.
Obviously, for each calibration you should calibrate the scale and we recommend keeping a table of calibrations next to the microscope.
The most common tool used to calibrate the eyepiece reticle is a ‘stage graticule’, (also known as stage micrometer or stage reticle or graticule slide or calibration slide). This is essentially a standard microscope slide made of glass or metal with a scale or series of blobs of known size etched onto it. If your measurements need to be traceable to a known standard with a certificate this can be provided. To obtain the most accurate calibration of your eyepiece reticle you need to use all, or as much as possible of the reticle scale’s width in your observation.
These are typically 76mm x 25mm slides with a scale marked on the centre of them. Often this scale is placed within a circle to aid location. The size and resolution of the scale is variable and it is possible to obtain multiple length scales on a single graticule slide. Indeed this is essential if you are calibrating a wide range of magnifications on your microscope. It is essential that, for every magnification the greatest extent of the eyepiece reticle scxlae covers the scale on your stage graticule. For transmitted light microscopes a glass stage graticule is used. For a metallurgical/reflected light microscope a mirrored scale is required (often this scale can be used for both transmitted and reflected light microscopy)
Calibrating lower magnification microscopes such as stereo zoom microscopes and monozoom systems
In this case a stage graticule which is large enough probably does not exist. So it is more common to use a set of Vernier calipers to make your calibration. REMEMBER to calibrate for each magnification used. If the zoom knob is continuous you will need to make marks on the knob for each calibrated magnification point.
Calibrating your camera system
The calibration values you may have made using the eyepiece reticle are wholly irrelevant and cannot be used for your camera images. To calibrate your camera you should have a calibration procedure within the software requiring, typically, a stage graticule. Each magnification should have its own calibration value and must be correctly selected for measurements and ‘on-image’ scale bar annotations. Certain top end microscopes and camera/software combinations that we supply can eliminate any possible errors in calibration selection by automatic feeding of the current magnification selected from the microscope to the software.
b) Collaborative Work
The reticle usually has a vertical line, where this line bisects the horizontal scale it effectively forms a crosshair which can be positioned onto an object of interest so that another observer can immediately find it.