The value of the aperture (iris) of the camera is shown by the F value. (It differs from lower f value.)

The value of the brightest (aperture open) status of the lens is called the open F value.

 

The open F value is used as an indicator of the lens brightness.

(Lens with small open F value is said to be “bright lens”.)

 

The brightness is halved each time, the F value becomes √ 2 times.

When the F value is 2.0 is 1, the brightness is halved F2.8 (2.0 X √ 2 = 2.8).

The distance from the principal point of the lens to the focal position at which the lenses connect the image.

 

In the case of a single lens, the principal point often comes to the center of the lens as described above. However, normally the CCTV lens is made up of multiple lens.

In that case, it becomes the synthesized main point. (The principal point may be outside the lens.)

If it is a C mount len, the distance from the lens to the focal position is fixed. (This is called flange back, becomes 17.526 mm.)

Therefore, the f value (focal length) is an index showing the field of view of the lens.

 

Even with lenses of the same shape, the principal point is closer to the image pickup device if the f value is small.

 

In other words, the field of view gets wider. (Blue line in the figure below)

If the f value is large, the principal point becomes farther from the image sensor. The field of view gets narrower. (Red line in the figure below)

 

Back focus is the distance from final point of lens to the focal plane (camera’s image sensor). If the back focus is out of focus, it will be out of focus too.

The distance (camera flange back) from the C mount of the camera to the image sensor surface may be slightly different depending on the camera. Therefore, when changing the lens or camera, it is necessary to adjust the back focus.

(We combine the camera and the lens. Our company has shipped after adjustment carefully)

In case of lens with back focus adjustment mechanism, you can also adjust by yourself.

At our company we also sell lens with back focus adjustment mechanism as option lens.

 

Lens with back focus mechanism SDS－M19

 

Please contact for more information.

By using a telecentric lens, it is possible to obtain images with less distortion.

I experimented with our telecentric lens RT3, RT5.

 

Attach telecentric lenses RT 3, RT 5 to a USB camera (GR 200 BCM)

shoot with Tlecentric lens　RT3	shoot with Tlecentric lens　RT5
You can see that there are no distortions in the four corners of the screen. This is the feature of a telecentric lens.

 

If you are using a CCTV lens, distortion will be less when using a telephoto lens than a wide angle lens.

I tried with a fixed focus lens of 6 mm and a fixed focus lens of 25 mm.

 

	Attach 8 mm fixed focus lens to a USB camera (GR 200 BCM)
	You can see that the four corners of the paper are distorted.

	25 mm fixed focus lens Attach a fixed focus lens to a USB camera (GR 200 BCM)
	Distortion is not appear in the corners of the paper.

 

There are some with less distortion depending on the performance of the lens.

However, it is quite expensive.

Please contact us if you have any questions.

Parallax means the direction in which the target point can be seen differs depending on the position of the observation point at two points.

Telecentric lenses with less distortion due to parallax.

 

Observe the following sample with different lenses.

　 　 　 　

Observe the sample on the right by changing the lens Field of view 60 X 40 mm Pillar height 60 mm
●Observe by telecentric lens
●Observe with other lens

<2. There is no expansion / contraction of the image within the depth of focus>
　 　

●Observe by telecentric lens
	Observe from the point that the focus is perfectly matched to ± 3 mm (Within depth of focus)

	When the focal length is 105 mm (Focus is perfectly matched)   The left photograph is the one which measured the diameter of the circle of the object. Let’s change the focal length while keeping the diameter size and the circle display (red line).
	Focal length 108 mm (A status in which the lens is raised 3 mm upward from the distance where the focal point is perfect)   You can see that there is no deviation between the circle display (red line) and the circle of the object. There is no expansion and contraction of the image within the depth of focus.
	Focal length 102 mm (A status in which the lens is lowered 3 mm downward from the distance where the focal point is perfect)   You can see that there is no deviation between the circle display (red line) and the circle of the object. There is no expansion and contraction of the image within the depth of focus.
●Observe by other lens
	The left photograph is the one which measured the diameter of the circle of the object. Let’s change the focal length while keeping the diameter size and the circle display (red line).
	Focal length 107 mm (A status in which the lens is raised 3 mm upward from the distance where the focal point is perfect)   You can see that there is a gap between the circle display (red line) and the circle of the object. The image is contracting.
	Focal length 101 mm (A status in which the lens is lowered 3 mm downward from the distance where the focal point is perfect)   You can see that there is a gap between the circle display (red line) and the circle of the object. The image is swelling.

 

We have various of telecentric lenses available.

Please check this out for details. → Telecentric lens

1. What is distortion?

Distortion (distortion aberration) means the position in which the image projected through the lens is distorted.

Generally, lenses of wide-angle type are likely to cause barrel type aberration and telephoto lenses are very easy break to pinch winding aberration

 

<Barrel aberration>	<Pinch Winding Aberration>

 

2. Method for Calculating Distortion

 

Optical distortion can be determined through the following formula, where the ideal image height is denoted as Y and the actual image height is denoted as y’:

 

 

3. Example of shooting using a fixed-focus lens

 

	Using 8 mm fixed focus lens
	Using 12 mm fixed focus lens
	Using 25 mm fixed focus lens

Fixed focus lens

 

A lens with an extremely low amount of distortion is known as a telecentric lens.

Telecentric lenses exhibit low distortion characteristics, making them well-suited for precise measurements.

 

 

Telecentric Lens

⇒ For more information about telecentric lenses, please refer to “Types and Features of Telecentric Lenses.”

 

 

4. Difference in distortion due to camera sensor size

Even when using the same lens, distortion can vary depending on the camera’s sensor size.

 

 

 

The distortion varies based on the size of the camera sensor, as illustrated below:

Smaller sensor sizes yield lesser distortion,
Larger sensor sizes result in greater distortion.

 

 

 

Regarding the variations in distortion due to sensor size, lens manufacturers may present information in two manners:

1. Noting values for each sensor size,
2. Indicating only the maximum value at the corresponding sensor size.

When presenting values categorized by sensor size,
(As exemplified by our f=25mm lens, compatible with 6 million pixels)  

 

 

When indicating the maximum size accommodated (maximum distortion value),
(As illustrated by our f=25mm lens, compatible with 12 million pixels)  

 

 

 

5. Summary:

– Distortion (geometric distortion) refers to the warped state of the imagery projected through the lens.

– For precise measurements or situations where minimizing distortion is crucial, it is recommended to use lenses with extremely low distortion, such as “telecentric lenses.”

– The distortion level varies depending on the camera’s sensor size.

We are also available to assist you in selecting fixed-focus lenses and telecentric lenses. Please feel free to contact our technical support for further assistance.

 

Aberration is the deviation from the ideal image formation in the optical system.

It is divided into two include: single chromatic aberration and monochromatic aberration.

You can further break down from here.

• Monochromatic aberration (axial chromatic aberration, magnification chromatic aberration)
• Single chromatic aberration (spherical aberration, coma aberration, astigmatism, field curvature, curvature aberration)

1. Monochromatic aberration

Chromatic aberration occurs due to the difference in refractive index depending on wavelength (color).

 

 

<About monochromatic aberration>

 

The focal point is connected at one point. However, the refractive index varies with the wavelength, the focal position will be shifted. This will occur as color drift and color blur on the screen.

 

It is a photograph of 10 yen coin at 1000 times.

The above picture was taken with the ultrahigh magnification microscope (SH350PC-2R) with low price.

The picture below is taken with a super high magnification microscope （USH130CS-H1） using a high performance lens

 

●Taking by the ultra-high magnification microscope （SH350OC-2R） with low price
●Taking by a ultrahigh magnification microscope （USH130CS-H1） using a high performance len

 

You can see that color misalignment occurs when enlarging a part of the above picture (taken with the ultrahigh magnification microscope （SH350PC-2R）

 

2. Monochromatic Aberration

 

Monochromatic aberration, excluding curvature aberration, arises from variations in the angle of incident light passing through the lens and differences in the position of passage (inside and outside the lens), resulting in disparate refractive indices.

Symptoms such as contour blur and smudging manifest on the screen as a consequence.

 

2. Actual footage of monochromatic aberration

 

This image was captured at 1000x magnification of the surface of a silicon wafer. The photograph on the left was taken using a high-magnification microscope, specifically the discontinued model SH350PC-2R. On the right, the image was captured using an ultra-high-magnification microscope equipped with a high-performance lens, the USH130CS-H1.

 

Taking by the ultra-high magnification microscope （SH350PC-2R）with low price	Taking by a ultrahigh magnification microscope （USH130CS-H1） using a high performance lens

The picture on the left shows a blurred outline.

 

(3) Spherical Aberration

* Spherical aberration does not cause blur.

It results in the symptom of curved lines around the edges of the screen. This symptom is divided into two types: pincushion and barrel distortion.

 

(For more information on spherical aberration, please refer to “What is Distortion?”)

The range of the scene in the photo taken by camera is shown in degrees. It is also called view angle.

 

It is important to determine the view angle of the lens when taking photos. This field angle is determined by the focal length of the lens and the field angle of the camera.

 

In the specifications of the lens, the range appears when the camera is set in the horizontal position is indicated by view angle of horizontal, vertical and diagonal. If only one thing is marked, it is called view angle of the diagonal.

 

Lens with a wide view angle is called a wide angle lens and lens with a narrow view angle is called a telephoto lens.

If you can sacrifice the magnification, 0.5 times of auxiliary lens will extend the WD

 

0.5 × auxiliary lens for standard lens TG-0.5 <Example> When 0.5 times auxiliary lens is attached to TG 500PC2, the standard magnification from 23 to 140 times will be changed 11 to 70 times, The standard focal length was 90 mm will be changed to 160 mm.

 

In that case, the position of LED ring light attached to the tip of the lens also departs from the object, the illumination becomes dark. Thus, changing more intense illumination or removing the diffuser plate will be very necessary.

	High brightness 80 lights LED ring light GR-80N2
	With removable diffusion plate

It is possible to change the position of the ligh using LED angle. However, it will disturb the extended WD. Therefore, it is necessary to use twin arm light (SPF – D 2) or LED spot light (GR – FL 21)

	I used a 0.5 times auxiliary lens to extend W.D. If you use the LED angle to lower the lighting position, the extended W. D will be lower.
Therefore, we recommend using twin arm lighting (SPF – D 2) or LED spot lighting (GR – FL 21)
	Twin arm LED light SPF-D 2   Stationary type dimmable LED twin arm light.

 

Please contact for more information

W.D is the distance from the observation object to the object side lens. It is also called working distance. W.D. becomes narrow if the lighting projects more than the lens.

 

Let’s measure the depth of focus of our high magnification microscope.

A glass scale of 0.2 mm pitch I shot it at an angle of 45 °. In order to get depth if it is inclined by 45 °, multiply 1 / √ 2.
Lens at scale 2 without auxiliary len
0.5 mm x (1 / √ 2) = 0.35 mm if it is judged that the focal point is at 0.5 mm
Lens at scale 4 without auxiliary lens
0.3mm x X（1/√2）＝0.21mm if it is judged that the focal point is at 0.3 mm

 

The magnification and depth of focus will be the same even if an auxiliary lens is attached.

If you use 2x auxiliary lens, the depth of focus is 0.21 mm” at “scale 2” as above.

Let’s try to measure the depth of focus of our medium magnification lens (SDS – M).

＜1＞　 Lens medium magnification lens （SDS-M） Magnification 20x Object　 0.5mm pitch glass scale GS-0.5

If it is judged that the focus indicated by the red frame is in focus … 0.5 x 7 x 0.71 = 2.5 mm

＜2＞　 Lens medium magnification lens （SDS-M） Magnification 60x Object　 0.2mm pitch glass scale GS-0.2

If it is judged that the focus indicated by the red frame is in focus … 0.2×3 x 0.71 = 0.42 mm

 

＜3＞　 Lens medium magnification lens （SDS-M） Magnification 120x Object　 0.2mm pitch glass scale GS-0.2

If it is judged that the focus indicated by the red frame is in focus … 0.2 x 2 x 0.71 = 0.3 mm

I measured the depth of focus of our low magnification microscope.

Case 01   Model used Lens: Low magnification lens SDS-LRS Camera: 5 MP USB camera   Taking an object at an angle of 60 °

 

I took a picture by tilting the gold scale to 60 °.

The aperture of the lens is open.

The depth of focus is not an objective number but it is a subjective value.

 

90 mm X sin 60 ° = 78 mm.

In the vertical direction, the focal depth is 78 mm.

This low magnification lens has an aperture function.

If you close this aperture, the depth of focus will deepen.

Since the focus is on the whole screen, this method can not calculate accurately. But it will be over 100 mm.

---

Case 02   Model used Lens: Low magnification lens SDS-LRS Camera: 5 MP USB camera   Taking an object at an angle of 45 °
1．Set 20.0 mm x 15.0 mm as the field of view (about 20 times)
Open	Close
In same 20 times level, shoot a board carrying a capacitor with a height of 20 mm
Open	Close
2．Set to 10.0 mm x 7.5 mm field of view (about 40 times)
Open	Close
In the same 40 times, shoot a board carrying a capacitor with a height of 8 mm
Open	Close

 

The depth of focus decreases since the magnification increases.

You can adjust by using the aperture.

However, increasing the amount of narrowing will cause the image to become dark, so it is necessary to significantly increase the amount of light.

 

You can cover it to some extent by adjusting items such as “Brightness” “Gain” “Exposure” on the camera side.

Popular focused on a general lens is one point.

(Except for special lenses for precision measurement like telecentric lenses.)

There is a region with less focus blur before and after the point where perfect focus is on.

This is called depth of focus.

When it deviates from a point where it is completely in focus, it gradually blurs. Where is the practical range will be the subjectivity of the individual. By narrowing down the optical path, you can gradually reduce this degree of blurring. However, by narrowing, the image becomes dark, so you can not use it with a lens with a high magnification.

 

	The left picture is our company’s USB microscope USB microscope with aris MS200PC3（20x～110x）

 

Compare the images when opened and narrowed with this irised microscope.

(When you narrow down the aperture, the depth of focus becomes deeper.)

＜at 50x＞
●Glass scale
Tilt the 0.5 mm pitch glass scale to 45 degrees and observe straight from the top

＜Open the aperture＞	＜Close maximum aperture＞

Since it is tilted to 45 degrees, it will be the depth of focus if multiplied by 1 / 1.41.

The focus on individuals depends on individual opinions.

If it is judged that 4 pitches (= 2 mm) are matched, 2 mm × (1 / 1.41) = 1.42 mm can be said as the depth of focus.

●For board

Tilt the substrate at 45 degrees and observe it 50 times.

(1.6 mm × 0.8 mm electronic components are lined at 1 mm pitch.)

 

＜Open the aperture＞	＜Close maximum aperture＞

＜at 100x＞
●Glass scale

I also checked the times at 100 times for your reference.

Since the magnification is high, the glass scale has been changed to 0.2 mm pitch

＜Open the aperture＞	＜Close maximum aperture＞

 

if this range is judged as a practical range, focus range is 1.2 mm × (1 / 1.41) = 0.85 mm

Please note that narrowing the aperture will make the lens darker and the resolution will also decrease.

(For details, please refer to “NA (Numerical Aperture)”.)

 

 

3．Depth of focus/techniques to increase depth of field

 

◆Explanation: About lens depth of focus/depth of field

 

Before introducing the trick, I would like to explain the depth of focus of the lens.

 

Depth of focus is also expressed as DOF ​​(Depth of Focuse).

 

In air (N=1) DOF＝(0.55/(2×NA²))+(1/M×K/NA)

(Explanation of formula)

The first item is “Item determined by resolution.”
The second item “K” is a “constant determined by the resolution of the observer’s eyes” and varies from person to person.
“M” is the “total magnification of the lens.”

 

What can be said from this is that in order to deepen the depth of focus,

The only way to do this is to lower the magnification or lower the NA.

At the same magnification, the only option is to lower the NA.

 

The specifications below are from the same manufacturer and series.

The one on the left is a megapixel compatible lens, and the one on the right is a general-purpose lens with low resolution.

When comparing lenses with the same magnification and focal length, general-purpose lenses have a deeper depth of focus.

The only way to lower the NA with the same lens is to narrow down the aperture.

 

When using different lenses, if the magnification is the same, the longer focal length is better.

The NA decreases and the depth of focus increases.

 

 

◆Introducing tricks: “Aperture” and “Digital zoom”

 

If it is up to about 50x, you can use “aperture” and “digital zoom” together.

Even a simple microscope made with a fixed focus lens

Achieves deep depth of focus/depth of field.

However, both “aperture” and “digital zoom” tend to reduce resolution.

Use a 4K (8 million pixel) camera and a corresponding high-resolution lens.

It is recommended.

 

A 4K camera (8 million pixels) with a 50mm lens compatible with 10 million pixels,

I added a close-up ring so that I could take macro shots at 50x magnification and took some comparison shots.

 

 

 

Photographed the same board as above under the same conditions.

 

 

（１）At 50x, depth of focus/depth of field can be adjusted just by changing the lens aperture

<When opening the aperture>	<When fully opened>

 

 

（２）After adjusting to achieve 50x magnification with a digital 2x zoom, fine-tuning the aperture of the lens to adjust the depth of field.

<When opening the aperture>	<When fully opened>

 

 

（３）The benefits of using this trick:

 

– Since fixed-focus lenses are used, zooming is not possible.
– However, unlike macro zoom lenses, the working distance is not fixed.
– This flexibility allows for longer working distances (W.D.), system miniaturization, and adjustment of depth of field.
– Depending on the lens selection, you can achieve any fixed magnification ranging from 5x to 50x.”

 

 

 

 

 

4．Summary

 

The depth of field, also known as the zone of acceptable focus, refers to the area with minimal focus blur around a perfectly focused point.

The practical range of depth of field is subjective and varies from person to person.

However, by combining “aperture adjustment” and “digital zoom,” you can achieve a deep depth of field with a simple microscope made using fixed-focus lenses, up to around several times magnification.”

If the wide range is 1 to 1000 times, it means that a lens with a zoom ratio of 1: 1000 is necessary. Currently, only the high zoom level of 1: 12 is available around the world.

To achieve such a wide range, three methods are available:

 

The zoom ratio is 1: 6.5 with our variable magnification lens standard type (SDS – M).

In other words, a wide range of 1 to 1000 times physically is impossible.

zoom lens　SDS-M

model number	mount	Supported camera	W.D.	magnification ※１
SDS-M	C mount	1/2、1/2.5、1/3inch	90mm	20～120x

High Magnification Zoom Lens: SDS-FZR

 

Mount: C-Mount

Compatible Cameras: 1/2, 1/2.5, 1/3 Inch

Working Distance: 95mm

Magnification: 40x to 240x *2

*2 When mounted on our 1/2-inch camera and observed on a 17-inch monitor

However, changing the lens necessitates a review of the illumination setup.

Especially for observations at ultra-high magnifications like 1000x, substantial brightness in illumination becomes essential.

We have lenses and illumination available that exceed 1000x magnification, as follows:

 

Ultra-High Magnification USB Microscope: NSH130CS-R

 

Total Magnification: 200x to 1450x

2. **Objective Lens Exchange System:**
Since the consideration of implementation, it has been possible to choose a zoom lens with an interchangeable objective.

Originally, the microscope comes with a standard 10x objective lens,
resulting in a comprehensive magnification range of 200x to 1450x.

We have prepared the following optional objective lenses, allowing you to replace the standard 10x objective lens and achieve a wide magnification range.

 

 

Option: 2x Objective Lens QM Plan Apo L2 (2X)

Magnification: 40x to 240x

 

 

Option: 5x Objective Lens QM Plan Apo HL (5X)

Magnification: 100x to 600x 

 

 

3. Simultaneous Use of Optional Lenses

The standard lens provided by our company is:
Standard Lens: SDS-M

 

 

 

Mount: C-Mount

Compatible Cameras: 1/2, 1/2.5, 1/3 Inch

Working Distance: 90mm

Magnification: 20x to 120x *1

*1 When mounted on our 1/2-inch camera and observed on a 17-inch monitor

By using the following optional 0.5x lens in conjunction with this front lens,
the magnification range can be extended to 15x to 90x.

 

0.5x Auxiliary Lens: TG-0.5 

 

 

 

*To be inserted at the current lens’s leading edge.*

In this case, along with a reduction in magnification, the focal length will change from 90mm to approximately 170mm.

If the height of the pole is insufficient, we also offer extension poles.

By using the following optional 2x lens in conjunction,
the magnification range can be expanded to 60x to 360x.

 

Extender (x2): RCS-20

 

 

 

 

*To be placed between the camera and the current lens.*

In this case, the magnification will decrease, but the focal length will remain at 90mm.

*However, it is not highly recommended to adopt this method.*

Using auxiliary lenses to stack lenses may lead to various issues. While reducing magnification may have minimal impact, increasing magnification presents optical challenges such as:

– Darkening, requiring an increase in illumination.
– Pronounced color aberrations and reduced lens resolution at higher magnifications.

Therefore, it is advisable to consider the methods outlined in options ① or ②.

For inquiries regarding illumination and lenses, or to request a demonstration unit, please contact our Technical Support

We will introduce our “High-magnification lens “.

Our FZ series zoom len is a high magnification zoom lens.

The field of view at the minimum magnification is 9 × 6.7 mm (if 1/2 inch camera is used).

 

There are 0.5 times auxiliary lens (option) with our other lens (DS series).

I will divert this auxiliary lens.

A field of view of 18 x 13 mm can be secured. (If using 1/2 inch camera)   The left photo shows a circle with a diameter of 10 mm   With a 1 / 2.5 inch camera, you can see the whole 10 mm circle.

 

By installing it between the camera and the main lens, you can change the magnification without changing the WD (working distance).

However, there is a disadvantage that the brightness declines (the F value increases), the resolution and the contrast are lowered and the focus is not sharp.

 

x2 rear converter	Install it between the camera and the main lens.

You can change the magnification by attaching it to the front (object side) of the main lens. It is also possible to change WD (working distance).

 

0.5x auxiliary lens for sds-m lens　TG-0.5

 

<0.5 times change in magnification and focal length when using auxiliary lens>

	magnification	working distance
TG500PC2	25x～135x	90mm
TG500PC2 +0.5x auxiliary lens	13x～65x	150mm～160mm

 

<Difference in appearance when 0.5 x auxiliary lens is attached to TG500PC2>

TG500PC2 (without 0.5 auxiliary lens at the lowest magnification)	TG500PC2 (with 0.5 auxiliary lens at the lowest magnification)

You can see that the field of view has expanded by attaching 0.5 times the auxiliary lens.

* When using a 0.5 times auxiliary lens, the working distance changes and the distance from the lighting to the object increases. Thus, it is necessary to change the position of the lighting using the LED angle.

LED angle　LED-A2	LED ring light at LED angle

 

From the size of the object you want to shoot, you can calculate the necessary lenses.

The needed thing at this time is the size of the image pickup device of the camera and the distance to the object (WD).

 

For example, if you want to secure a vertical field of view of 300 mm with 1 m WD, how many millimeters should the f value be? (I will use a 1/2 inch camera.)

 

The image sensor size of 1/2 inch camera as follows.

f = (distance to object (mm) X vertical size of imaging device (mm) / vertical field of view

= (1000 mm X 4.8 mm) / 300 mm = 16 mm

Choosing a lens with f = 16 mm will ensure the desired vertical field of view.

You can calculate the horizontal field of view as well.

 

By the way, you can easily calculate the horizontal field of view.

If it is a square type imaging device, the aspect ratio is 4: 3 . Therefore, the horizontal field of view will be 400 mm without calculation.

 

We have various CCTV lenses available. Please check this for details.

 

A lens designed for photographing a close distance is called a macro lens.

In the macro lens, the magnification can be changed continuously, and the focal length is constant (unchanged) is called macro zoom lens.

Though the magnification can be changed continuously, the one whose focal length changes will not be strictly a zoom lens.

Sometimes it is called a variable magnification lens distinguished from a zoom lens.

 

If you do not change the magnification frequently and want to reduce the price, you should you variable magnification lens. If you change the magnification frequently, a macro zoom lens is recommended.

Zoom lens is a lens in which the image size can be varied continuously while the image remains in focus.

The zoom ratio of 12 (1:!2) is the physical limit of zoom macro lens.

In addition, the lens in which the magnification can be varied continuously while the image does not remains in focus is not a zoom lens but a lens with variable magnification.
In other words, focal distance changes but magnification also changes is cheaper than the zoom lens is the characteristics of the lens with variable magnification.
Our company has various types of lenses. Please see the products here.

You can choose the lens according to the characteristics such as magnification, focal length, price, etc.

Besides, please consult us to select appropriate lenses. Please contact the technical support.