What is Focusing And Barlow Lens?

What is Focusing in Microscope?

Two Main Focusing Adjustments

1.Coarse Adjustment

• Moves the lens or stage rapidly over a large distance.
• Used first to quickly find the general image of the specimen under low magnification.
• Fast but rough; only for initial focusing.

2.Fine Adjustment

Type

Independent-Axis Coarse and Fine Adjustment

Coaxial Focus: A focusing system that has both the coarse and fine focusing knobs mounted on the same axis.

Electric Focus Adjustment

Computer-controlled focusing

Electric Control Focusing

Focusing controlled by the manual control box

Parameter

Rough adjustment of travel

Rotate the coarse adjustment button to determine the maximum distance the worktable can move up and down

Fine tuning accuracy/grid value

Rotate the fine-tuning button once to adjust the distance the workbench moves up and down

Fine tune the itinerary

Rotate the fine-tuning button to achieve the maximum distance for the worktable to move up and down

Upper Limit Position

The upper limit of coarse adjustment (referred to as the "upper limit") is a safety locking device in the microscope focusing mechanism, used to limit the highest position of the coarse adjustment handwheel to move the stage (upright mirror) or objective lens (inverted mirror) upward, to prevent damage to the lens or slide.

• Position: Usually located on the inside (left/right) of the coarse adjustment handwheel, it is a small rotatable knob/dial.

Adjustable Tightness

Coarse and fine adjustment of elasticity, also known as focusing damping adjustment, means that the damping force of the focusing handwheel can be adjusted:

Tighten → When the handwheel rotates, it feels heavy and does not shake;

Loosen → The handwheel rotates lightly and smoothly.

Barlow Lens

For Biological

 

For Stereo

Barlow Lens Explained

A Barlow lens is a diverging lens that alters the focal length of a microscope and, therefore, the field of view. They also alter the working distance between the objective lens and the specimen, which is a critical variable for many applications such as PCB soldering and inspection.

A Barlow attaches to the bottom of the objective lens on a stereo (low power) microscope when there is a need for either more or less of one of the following variables:

• Working Distance
• Field of View
• Magnification

The most common type of Barlow lens is the Reducing Barlow. A Reducing Barlow reduces the magnification power of the microscope, but has the advantage of increasing the field of view and the working distance between the objective and the specimen. Reducing Barlows are typically 0.3x, 0.5x and 0.75x although other powers are available.

As an example, a 0.5x Barlow lens will halve the magnification power of the microscope, but it will double the size of the field of view. It will also increase the working distance between the objective and the specimen.

By the same token, a 2.0x Barlow will double the magnification and halve the field of view of a microscope. In other words, each different power Barlow has a proportionate effect on magnification and a direct inverse proportional effect on the field of view and working distance, as shown below.

BARLOW MAGNIFICATION CHART (values approx.)
BARLOW (X)	WD (in)	EYEPIECE (X)
		10		15		20
0.5	7.9	3.5	22.5	5.2	34	7	45
0.75	5.2	5	34	8	50	10	68
1	3.9	7X	45X	10.5X	67.5X	14X	90X
1.5	2.6	10	68	16	101	21	135
2	1.9	14	90	21	135	28	180
		min	max	min	max	min	max