OPTICAL TERMINOLOGY
1. Field Number (F.N.) and Practical Field of View
The field number (F.N.) is referred to as the diaphragm size of eyepiece in mm unit which defines the image area of specimen. The diaphragm diameter actually seen through eyepiece is known as the practical field of view (F.O.V.) which is determined by the formula:
Eyepiece F.N.
F.O.V. = Objective lens magnification (mm)
2. Working Distance (W.D.)
The distance between the front edge of the objective lens and the specimen surface (with the surface of the cover glass in case of the cover glass objective lens) when the specimen is focused.
3. Parfocal Distance
It is the distance between the objective lens mounting plane and the specimen. In UIS2/UIS objective lenses, the parfocal distance is designed at 45mm.
Working distance and parfocal distance | Objective lens | |||
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Parfocal distance
Working Distance (W.D.)
Focal plane
For parfocal distance of the
4.Relationship between the objective lens's focal length and magnifications
Indicated magnifications of UIS2/UIS objective lenses are the values when the focal length of the tube lens is 180 mm.
Focal length of tube lens
M(ob)=
f
M(ob): Objective lens magnification
f: Objective lens's focal length
5. Total Magnification
5.1 Observation through eyepiece (binocular observation)
M(bino)=M(ob)⋅ M(oc)
M(bino): Total magnification for binocular observation
M(ob): Objective lens magnification
M(oc): Eyepiece magnification
5.2 Video monitor observation
●Total magnification for video monitor
M(video monitor)=M(ob)⋅ M(video camera adapter)⋅ Monitor magnification*
M(video monitor): Total magnification on the video monitor
M(ob): Objective lens magnification
M(video camera adapter): Projected magnification for video camera adapter including photo eyepiece
(refer to Figure 1)
* Refer to Figure 3 for "Monitor magnification"
●Practical field of view for video monitor observation
Practical field of view for | = | Image device size * |
video monitor observation | M(ob)⋅ M(video camera adapter) |
M(ob): Objective lens magnification
M(video camera adapter): Projected magnification for video camera adapter including photo eyepiece
(refer to Figure 1 for projected magnifications) * Refer to Figure 2 for image device size
Figure 1 Video camera adapter and projection magnifications
Video camera adapter (Projection lens) | Projection magnifications | ||||||||
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video camera mount adapters |
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| 0.63x |
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| 0.5x |
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| 0.35x |
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| 0.25x |
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Figure 2 Imaging device size |
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Camera format | Diagonal |
| Horizontal |
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| Vertical | |||
1/3" | 6.0mm |
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| 4.8mm |
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| 3.6mm | ||
1/2" | 8.0mm |
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| 6.4mm |
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| 4.8mm | ||
2/3" | 11.0mm |
| 8.8mm |
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| 6.6mm | |||
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The above table is for standard image device sizes. |
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Check your device size for precise calculation. |
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Figure 3 Imaging device size and monitor magnifications | |||||||||
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Camera format |
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| Monitor size (diagonal) |
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9" |
| 12" |
| 14" | 21" |
| 27" | ||
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1/3" | 38.1x |
| 50.8x | 59.2x | 84.6x |
| 114.1x | ||
1/2" | 28.6x |
| 38.1x | 44.5x | 63.5x |
| 85.7x | ||
2/3" | 20.8x |
| 27.7x | 32.3x | 46.2x |
| 62.3x | ||
Example
What is total magnifications for video monitor when objective lens is 50x, video camera adapter
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