The examination of the objectives can only be attempted when the different faults of the objective are known.
It doesn't fit with their alleged party objectives or any tactics they've ever employed.
Two objectives were assigned, the first running E.
Five objectives were laid down, and exploitation was to be carried out beyond the final one to Welsh Ridge (N.
Up to this line four successive objectives were assigned; from there onwards the second phase of the advance was to carry the assailants to the line of the Scheldt canal and the Sensee.
The subsequent history of the development of the art of manufacturing glass disks for telescopic objectives will be found in the article Glass: § Optical.
This road system bears plain marks of having been made at different times, and with different objectives, but we have no evidence that any one part was abandoned when any other was built.
Between these extreme examples stands the ordinary photographic objective: the portrait objective is corrected more with regard to aperture; objectives for groups more with regard to the field of view.
(3) Telescope objectives have usually not very large apertures, and small fields of view; they should, however, possess zones as small as possible, and be built in the simplest manner.
This artifice is specially adopted in objectives for astronomical photography ("pure actinic achromatism").
On this account the lines D and G' are united for ordinary photographic objectives; the optical as well as the actinic image is chromatically inferior, but both lie in the same place; and consequently the best correction lies in F (this is known as the " actinic correction " or " freedom from chemical focus ").
Abbe succeeded in computing microscope objectives free from error of the axis point and satisfying the sine condition for several colours, which therefore, according to his definition, were " aplanatic for several colours "; such systems he termed " apochromatic."
This Is Produced In The Same Amount, But In The Opposite Sense, By The Oculars, Which Are Used With These Objectives (" Compensating Oculars "), So That It Is Eliminated In The Image Of The Whole Microscope.
The Best Telescope Objectives, And Photographic Objectives Intended For Three Colour Work, Are Also Apochromatic, Even If They Do Not Possess Quite The Same Quality Of Correction As Microscope Objectives Do.
The Bulgarian scheme of operations, necessarily offensive, suffered from the weakness of having two objectives - the Ovche Polye and Salonika - and being based on two main lines of communication diverging towards the rear - Kyustendil and Seres - Drama.
For strong objectives there is, however, only one optical tube length in which it is possible to obtain a good image by means of wide pencils, any alteration of the tube length involving a considerable spoiling of the image.
A series of objectives with short focal lengths are available, which permit the placing of a liquid between the cover-slip and the front lens of the objective; such lenses are known as " immersion systems "; objectives bounded on both sides by air are called " dry systems."
- Weak and medium microscope objectives work like photographic objectives in episcopic or diascopic projection; in the microscope, however, the projected image is not intercepted on a screen, but p?
Soc., 1882, p. 463) we have the following table for the limits of the magnification numbers, for various microscope objectives, µ = o ooi mm.: A=nsinu.
For this reason the objectives have been called monochromats, as they have only been corrected for light of one wave-length.
Very large apertures occur in strong microscope objectives, and hence the two conditions are not compatible.
By experiment Abbe proved that old, good microscope objectives, which by mere testing had become so corrected that they produced usable images, were not only free from spherical aberrations, but also fulfilled the sine-condition, and were therefore really aplanatic systems.
By using these glasses and employing minerals with special optical properties, it is possible to correct objectives so that three colours can be combined, leaving only a quite slight tertiary spectrum, and removing the spherical aberration for two colours.
And C. Chevalier, at first after the designs of Selligue, produced objectives, consisting of several achromatic systems arranged one above the other.
Selligue had no particular comprehension of the problem, for his achromatic single systems were simply telescope objectives corrected for an infinitely distant point, and were placed so that the same surface was turned towards the object in the microscope objective as in the telescope objective; although contrary to the telescope, the distance of the object in the microscope objective is small in proportion to the distance of the image.
It would have been more correct to have employed these objectives in a reverse position.
This system will always be aplanatic. These objectives permitted a much larger aperture than a simple achromatic system.
Although such systems have been made recently for special purposes, this construction was abandoned, and a more complex one adopted, which also made the production of better objectives possible; this is the principle of the compensation of the aberrations produced in the different parts of the objective.
33),and constructed objectives with an aperture of 135°.
Objectives with definite undercorrection can however only produce really good images with glass covers of a specified thickness.
For this reason Amici constructed objectives of a similar aperture and focus for different thicknesses of glass covers.
Weak and strong microscope objectives act differently.
Since, however, the difference of chromatic magnification cannot be overcome in powerful objectives, this error is still further increased by the eyepiece.
As powerful achromatic objectives show differences of chromatic magnification in the same way as apochromats, compensation eyepieces can be used in combination with these objectives.
With very powerful objectives these methods are insufficient; and a condenser is fitted below the stage plate.
Hence a condenser, for lighting with very oblique cones, must have about the same aperture as the objective, and therefore be of very wide aperture; they therefore closely resemble microscope objectives in construction.
Especially powerful achromatic condensers are really only magnified microscope objectives, with the difference that they are not corrected for the thickness of the cover slip, but for the thickness of the glass on which the object is placed.
For exceptionally accurate work microscope objectives are sometimes used as condenser systems. When using immersion objectives, an immersion condenser must also be used if rays of extreme obliquity are wanted, for, in consequence of the total reflections, rays can only come from the upper plane surface of the condenser, which have not a larger inclination to the axis than about 41°, varying according to the refractive index of the glass.
Beck, which can be conveniently fitted in and used for objectives with different focal lengths.
To examine objects with objectives of high power and low free object distance, the apparatus for side-illumination is not sufficient, and a so-called vertical illuminator is used.
With these microscopes, which are not stereoscopic, objectives of any power can be used.
For slight magnifications rough adjustment is sufficient, but with objectives of a focus below 4 in., a fine adjustment is wanted.