No. 3644. Dark ground illuminator for low and moderate powers................. ... £5 0 0

This illuminator is for use with object glasses the numerical aperture of which is not greater than -65 N.A. It is made somewhat on the principle of an ordinary substage condenser but has a specially long working distance. It is provided with an iris diaphragm for transmitted light in the usual manner. When the iris diaphragm is opened to its fullest extent and the tray is swung aside, a special stop can be folded in, which converts the apparatus into a dark ground illuminator. A neutral glass screen is supplied to fit into the tray, in No. 3644. order to reduce the necessarily strong light required for

dark ground illumination to an amount suitable for ordinary transmitted light. With this illuminator, dark ground illumination can be used with all powers up to £ inch (4 m/m) provided the object glass has not an aperture exceeding N.A. -65.

No. 3357. Spot lens for low power dark field illumination, mounted to fit standard substage

No. 3359. Beck aplanatic ring illuminator

for the illumination of opaque objects with powers of ljin., § in. and ^in. The mounts of the object glasses must be specially arranged to take the illuminator. The illuminator consists of a silvered glass ring of such curves that light thrown upwards from the flat mirror is condensed to a very perfect aplanatic focus. The illumination is exceedingly brilliant and is directed upon the object from all sides.

No. 3359A. Beck aplanatic ring illuminator

for ^in. object glass

£10 0

2 10 0

2 10 0

No.3365.—Immersion ring illuminator for oil immersion object glasses with apertures up to 1.3 N.A. For this purpose a special immersion object glass is made in which the whole front mounting is made of glass instead of metal. The glass mounting has an outer surface which is spherical in shape and concentric with the focus of the object glass so that the light from the aplanatic ring illuminator passes through without refraction. The glass front mount has a small aperture in its centre and into this aperture the front lens of the object glass is cemented, so that the portion of the front lens usually employed for mounting it into a metal cell is used for transmitting light to the object. The front surface of the front lens of the object glass is level with the front surface of the glass mount and the whole of this surface is in immersion contact writh the object wdien in use

No. 3365. Immersion ring illuminator with 3 m/m. apochromatic object glass

1.3 N.A......................................................... £20 0 0

No. 3365A. Ditto but with 3 m/m achromatic object glass 1.3 N.A. ............. 12 2 6

No. 3367 Dark well for use with ring illuminators. This is mounted in a ring of the standard substage size and the well has an adjustment up and down and thus provides a suitable stop for obscuring the central beam of light from the mirror ..................... ............ ... 1 10

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La langue de reconnaissance de l'OCR est l'Anglais.

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