A set of three usual achromatic bright field objectives (Leitz 10/0,25, 45/0,65, oil 100/1,30) were modified for luminance contrast as follows: The 45x and 100x magnifying objectives were equipped with transparent plane-parallel plates, mounted in the back focal plane of these objectives. In the middle of each plate, a circular beam stop was mounted. The beam stops were in black color, their surfaces matt and non reflecting. By preparing absorbing elements with different diameters, suitable sizes of absorbers could be tested out for each objective. Fig. 9 demonstrates the rebuilding process for the 45x objctive.

Fig. 9: Rebuilding of the objective 45/0.65 for luminance contrast
a: unscrewing of the objective
b: plane-parallel plates with beam stops in different diameters
c: shaft with absorbing element

The 10x magnifying objective was equipped with a different beam stop, consisting of a black centric area and three radial arms, being free from any transparent reflecting components (construction plan in fig. 10 ). This element was mounted in an uncentered position so that luminance interference contrast was achievable independent from additional light absorbing slides inside the condenser.

Fig. 10:
Light absorber with three radial arms

Moreover, two Cassegrain-Schwarzschild mirror objectives were tested out, made by Zeiss Jena (fig. 11): 125/0.90 (katadioptric water immersion, suitable for cover slip preparations) and 40/0.65 (katoptric system, only suitable for preparations without cover slips). The technical data of these mirror objectives are presented in table1 (5, 6).

Fig. 11: Mirror objectives Zeiss Jena
a:   W 120/0.90  160/0.17
b-d:   40/0.65 160/0.65

Table 1: Technical data of the Zeiss Jena mirror objectives

construction feature	water immersion, katadioptric	no immersion, katoptric
magnification	125 x	40 x
focal length	1,5 mm	4,5 mm
maximum aperture (peripheral mirror)	0,90	0,65
minimum aperture (central mirror)	0,31	0,31
missing disc	12 %	22 %
working distance	0,45 mm	2,5 mm
color correction	UV-IR-apochromatic	UV-IR-apochromatic
planarity	like plano objectives	like plano objectives
lens putty	no	no
semitransparent mirrors	no	no
thread	RMS standard	RMS standard
balance conditions	like usual lenses	like usual lenses
scheduled tubus length	160 mm	160 mm
scheduled thickness of cover slips	0,17 mm	no cover slip
length	45 mm	45 mm
diameter	35 mm	35 mm
weight	240 g	210 g

All alignments of the beam stops in the objectives and their corresponding illuminating components in the condensor were controlled and documented by an phase telescope. Basic alignments for commom objectives with lenses are shown in fig. 12, equivalent alignments for mirror objectives in fig. 13.

Fig. 12: Typical alignments in luminance contrast objectives (modified lenses), controlled by a phase telescope
a: ojective 45/0.65, Bright field                                  d: objective 10/0.25, bright field
b: objective 45/0.65, luminance phase contrast         e: objective 10/0.25, luminance interference contrast
c: objective 45/0.65, luminance dark field                 f: objective 10/0.25, luminance dark field    
 

Fig. 13: Typical alignments in mirror objectives, controlled by a phase telescope
a: bright field            b: luminance dark field           c: luminance phase contrast
d: luminance interference contrast (uncentered perforated screen in the condenser)
e: luminance phase contrast with two-colors double-contrast
f: luminance interference contrast with tow-colors double-contrast

The microscopic images presented here were taken in bulb or flash light, using an Olympus camedia C 7070 camera, adapted with a Leica vario photo ocular (range of magnification: 5x – 12.5x)..
 

Copyright: Joerg Piper, Bad Bertrich, Germany, 2007

[Introduction]
[Resolution and focal depth]
[Principles of luminance contrast]
[Modification of lenses]
[Mirror objectives]
[Illuminating apparatus]
[Material and methods]
[Results]
[Further technical developements]
[Discussion]
[Summary]
[Links]
[Contact]
[References]
[Image gallery]