There is two type optical system in old or low price microscope based on a finite optical system, recent and high-performance model based on an infinite optical system.
The image quality of a finite optical system is enough in bright field, dark field, and phase contrast microscopy. In an infinite optical system tube length could design flexible therefore filters, mirrors, and prisms could easily build in the optical pass. This feature is suitable for design reflected illumination system and differential interference contrast microscopy.
The objective lens of a finite optical system works like a magnifying glass, the light through the objective lens form images. On the other hand objective lens of an infinite optical system does not form an image, the light through the objective lens is the parallel beam, the parallel beam form image behind the tube lens.
These two optical systems are not used in the same system, therefore we must pay attention whether the optic equipment is a finite optical system or an infinite optical system when you bought optical equipment.
An objective lens of the finite optical system has a mechanical tube length the distance that from the mounting position of the objective lens to the mounting position of the eyepiece (see figure), the mechanical tube length was determined by each manufacturer and each model. Every manufacturer adopts a 160 mm mechanical tube length in almost all models, and it is written as 160 on the barrel of the objective lens. Many old lenses do not show mechanical tube length on the barrel of the lens, probably because all were finite correction systems and mechanical tube length was 160 mm. Some metal microscopes with finite correction system have different mechanical tube length such as 210 mm, objective lenses with different mechanical tube length could not use on the same microscope, please check mechanical tube length when you purchase an objective lens. The objective lens of the finite optical system with same mechanical tube length can use in the same system even if manufacturers are different.
The objective lens of the infinite optical system has indicated ∞ on the barrel, and even if the manufacturers are different, it can be used together.
The distance from the mounting position of the objective lens to the focusing point is called as the parfocal distance (see figure), the parfocal distance of almost all recent objective lens is 45 mm, even if manufacturers are different the objective lens with same parfocal distance could use on the same microscope. Some special lenses have different parfocal distance and the old objective lenses have a short parfocal distance. The old objective lens of Olympus has a parfocal distance of 36.65 mm and the old Nikon objective lens has a parfocal distance of about 33 mm. The objective lenses with different parfocal distance cannot use on the same microscope.
In my environment, the objective lens of finite optical system of Olympus and Nikon are used on the same microscope, the objective lens of infinite optical system of Olympus, Zeiss, Leitz and unknown Chinese manufacture are used on the same microscope.
Finally about the objective lens mounting thread. Almost all objective lens is attached to RMS thread. The RMS standard prescribed by Royal Microscopical Society. The RMS thread is a screw with a diameter of 20.32 mm. From the old to the current model, most objective lenses are fixed with RMS thread. The recent expensive model adopts more large screw such as 26 mm in diameter. Please check the diameter of the mounting screw before purchasing the objective lens.
All the objective lenses of infinite optical system with RMS lens mounting thread listed here can use together on the same microscope.
The image quality of a finite optical system is enough in bright field, dark field, and phase contrast microscopy. In an infinite optical system tube length could design flexible therefore filters, mirrors, and prisms could easily build in the optical pass. This feature is suitable for design reflected illumination system and differential interference contrast microscopy.
The objective lens of a finite optical system works like a magnifying glass, the light through the objective lens form images. On the other hand objective lens of an infinite optical system does not form an image, the light through the objective lens is the parallel beam, the parallel beam form image behind the tube lens.
These two optical systems are not used in the same system, therefore we must pay attention whether the optic equipment is a finite optical system or an infinite optical system when you bought optical equipment.
An objective lens of the finite optical system has a mechanical tube length the distance that from the mounting position of the objective lens to the mounting position of the eyepiece (see figure), the mechanical tube length was determined by each manufacturer and each model. Every manufacturer adopts a 160 mm mechanical tube length in almost all models, and it is written as 160 on the barrel of the objective lens. Many old lenses do not show mechanical tube length on the barrel of the lens, probably because all were finite correction systems and mechanical tube length was 160 mm. Some metal microscopes with finite correction system have different mechanical tube length such as 210 mm, objective lenses with different mechanical tube length could not use on the same microscope, please check mechanical tube length when you purchase an objective lens. The objective lens of the finite optical system with same mechanical tube length can use in the same system even if manufacturers are different.
The objective lens of the infinite optical system has indicated ∞ on the barrel, and even if the manufacturers are different, it can be used together.
The distance from the mounting position of the objective lens to the focusing point is called as the parfocal distance (see figure), the parfocal distance of almost all recent objective lens is 45 mm, even if manufacturers are different the objective lens with same parfocal distance could use on the same microscope. Some special lenses have different parfocal distance and the old objective lenses have a short parfocal distance. The old objective lens of Olympus has a parfocal distance of 36.65 mm and the old Nikon objective lens has a parfocal distance of about 33 mm. The objective lenses with different parfocal distance cannot use on the same microscope.
In my environment, the objective lens of finite optical system of Olympus and Nikon are used on the same microscope, the objective lens of infinite optical system of Olympus, Zeiss, Leitz and unknown Chinese manufacture are used on the same microscope.
Finally about the objective lens mounting thread. Almost all objective lens is attached to RMS thread. The RMS standard prescribed by Royal Microscopical Society. The RMS thread is a screw with a diameter of 20.32 mm. From the old to the current model, most objective lenses are fixed with RMS thread. The recent expensive model adopts more large screw such as 26 mm in diameter. Please check the diameter of the mounting screw before purchasing the objective lens.
Olympus finite optical system objective lens
Olympus SPlan
These are an objective lens of the finite optical system.
Mechanical tube length: 160 mm
Parfocal distance: 45 mm
Achromat
Lens mounting thread: RMS
The achromat is a lens that corrected the chromatic aberration of two colors, blue and red.
The objective lens written as Plan in the objective lens stands for a plane indicates that the lens is corrected to flat in the entire field of view.
SPlan the notation used only by Olympus, they might have insisted that flatness is above the Plan objective lens.
The magnification of the objective lens is shown using a color code.
Black: 1x
Red: 4x
Yellow: 10x
Light blue: 40x
White: 100x
The color ring near the lens tip represents the immersion media.
Black: oil.
Olympus A
Mechanical tube length: 160 mm
Parfocal distance: 45 mm
Achromat
Lens mounting thread: RMS
These are attached to CH-2 etc.
Olympus phase contrast objective lens
A series and SPlan series are also available combined with same phase contrast condenser.
Mechanical tube length: 160 mm
Parfocal distance 45 mm
Achromat
Lens mounting thread: RMS
Red color ring on the front side of the lens indicates that the phase contrast is supported.
Olympus DPlan Apo 60
Mechanical tube length: 160 mm
Parfocal distance: 45 mm
Apochromat
Lens mounting thread: RMS
The color code of magnification is blue.
Apochromat is a lens which corrected the chromatic aberration of three colors.
Old Olympus 4x objective lens
Mechanical tube length: 160 mm
Parfocal distance: 36.65 mm
Achromat
Lens mounting thread: RMS
Old Olympus 10x objective lens
Mechanical tube length: 160 mm
Parfocal distance: 36.65 mm
Achromat
Lens mounting thread: RMS
The color code of the lens magnification is different from the current regulation.
There are color rings corresponding to the phase contrast near the tip of the two lenses on the right side. The red ring indicates positive phase contrast, white ring indicates negative phase contrast.
PLL: positive low low, NM: negative medium.
Old Olympus 40x objective lens
Mechanical tube length: 160 mm
Parfocal distance: 36.65 mm
Achromat
Lens mounting thread: RMS
The color code of the lens magnification is different from the current regulation.
Old Olympus 100x objective lens
Mechanical tube length: 160 mm
Parfocal distance: 36.65 mm
Achromat
Lens mounting thread: RMS
The color code of the lens magnification is different from the current regulation.
The color ring of the lens tip represents the medium during liquid immersion.
In the current rule, black is oil, white is water, red is other.
The second lens from the right and the left of this picture has red and white double coloring. These two are phase contrast lenses, the color code indicate phase contrast negative (white) and phase contrast positive (red). I do not know the meaning of double ring.
From the numerical aperture, it is oil immersion, but there seems to be no color code indicate immersion media on these two lenses.
Old Olympus 1.3 x and 2x objective lens
Mechanical tube length: 160 mm
Parfocal distance: longer than 45 mm
Achromat
Lens mounting thread: RMS
The color code of the lens magnification is different from the current regulation.
Since the difference of parfocal distance, it can not be used with the objective lens with the parfocal distance of 36.65 mm.
The barrel is short and parfocal distance is longer than 45 mm, therefore it is possible to use with an objective lens with the parfocal distance of 45 mm, after adjusting the focus.
Left: Olympus 48x objective lens
Mechanical tube length: 200 mm
Parfocal distance: unknown
Achromat
Lens mounting thread: RMS
Right: Olympus 100x objective lens
Mechanical tube length: 210 mm
Parfocal distance: unknown
Achromat
Lens mounting thread: RMS
Both are considered to be lenses for metallurgical microscopes.
It can not be used with a microscope with different mechanical tube length.
It will be difficult to obtain a microscope that these lenses can use.
Nikon finite Optical system objective lens
Old Nikon objective lens
Mechanical tube length: 160 mm
Parfocal distance: about 33 mm
Achromat
Lens mounting thread: RMS
The color code of lens magnification is the same as the current regulation.
It is an objective lens attached to Nikon S type microscope etc.
Because it has different parfocal distance as Olympus old objective lens, it can not be used together.
Nikon objective lens
Mechanical tube length: 160 mm
Parfocal distance: 45 mm
Achromat
Lens mounting thread: RMS
The color code of lens magnification is the same as the current regulation.
20x is a bright green label.
Because the parfocal distance is same with Olympus objective lenses, it can use together.
Infinite optical system objective lens
Olympus objective lens for a metallurgical microscope
Olympus Neo SPlan NIC
NIC indicates correspond to differential interference contrast.
Those not attached with the NIC are not compatible with differential interference.
Parfocal distance: 45 mm
Achromat
Lens mounting thread: 26 mm
The lens mounting thread is not RMS.
Olympus objective lens for Fluorescence microscopy
UPlan Apo
Parfocal distance: 45 mm
Apochromat
Lens mounting thread: RMS
Olympus objective lens for Fluorescence microscopy
UPlan Fl
Parfocal distance: 45 mm
Semi apochromat
Lens mounting thread: RMS
Leica objective lens
Semi apochromat
Parfocal distance: 45 mm
Lens mounting thread: RMS
Chinese made objective lens
Parfocal distance: 45 mm
Achromat
Lens mounting thread: RMS
I bought this objective lens about $30 on eBay.
Although it is not compatible with fluorescence microscopy, it can be used with a fluorescence microscope.
The field of view is flat there is no quality problem.
Zeiss objective lens corresponds to Differential Interference Contrast microscopy
Plan NeoFluar
Parfocal distance: 45 mm
Achromat
Lens mounting thread: RMS
These objective lenses correspond to fluorescence and differential interference contrast microscopy.
There is variation in parfocal distance among these lenses, therefore, when changing objective lens focus will be out of focus.
Zeiss objective lens
AchroPlan
Parfocal distance: 45 mm
Achromat
Lens mounting thread: RMS
These are Plan lens, but the field of view is not flat enough.
All the objective lenses of infinite optical system with RMS lens mounting thread listed here can use together on the same microscope.
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