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How to Minimize an Optical System for a Compact Imaging Device

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OEM components for a compact microscope-based imaging device

While microscopes and other imaging devices have traditionally been large, modern design techniques are leading to more compact systems. However, the miniaturization of these systems raises an important question: how do you lay out an optical system in a compact device?

As a leading provider of optical components for the life science, medicine, and industrial fields, this question often comes up in our discussions with manufacturers of microscope-based imaging devices. Here, we provide a few ideas on how to minimize an optical system for a compact device.

Key Considerations for Designing a Compact Optical System

An optical system that extends from a microscope objective to a camera’s imaging surface (imaging optical system) consists of three units:

  • An objective, which is placed close to the specimen
  • A tube lens, which focuses the flux of light from the objective
  • A camera adaptor, which projects images onto a camera at an appropriate magnification

It’s important to select and combine the appropriate units from the various options according to the device's purpose. Here are some factors to consider for each component:

1. Objectives

We provide more than 100 types of UIS2 objectives, including the X Line series, which offers high performance levels for three important elements of an objective: numerical aperture, chromatic aberration correction, and image flatness. These objectives also have a parfocal distance of 45 mm, are compensation free, and have a small physical footprint. Our X Line objectives, along with some of our other objectives, support wavefront aberration control.

Use our Objective Finder to filter the objectives according to your most important parameters (e.g., numerical aperture, magnification, use of a cover glass, oil immersion, and color aberration). This handy online tool helps you compare their performance to select the best option.

2. Tube lens

Either the SWTLU-C or the U-TLU can be selected as the tube lens unit. Both units are compensation free. The SWTLU-C produces a 26.5 mm image circle to cover a super wide field of view, so we recommend that it is combined with an X Line objective.

Product name Image circle Total length Max. outer diameter Weight Mounting thread
SWTLU-C 26.5 mm 33.6 mm 45 mm 94 g Engagement (φ 39) and screw-in (M41 × 0.5 mm)
U-TLU 22 mm 63.6 mm 60 mm 350 g Circular dovetail (proprietary Olympus method)

Table 1: Differences in specifications between the SWTLU-C and the U-TLU tube lenses

3. Camera adaptor

We provide four types of camera adaptors with different projection magnifications: the U-TV1XC, the U-TV0.63XC, the U-TV0.5XC-3, and the U-TV0.35XC-2. Please select the field of view that you need based on the sensor size of the image pickup device for your camera.

Producing Compact Imaging Devices for Large Fields of View at Low Magnification

In the life science field, there has been an increased demand to produce compact imaging devices that enable wide fields of view with observations at low magnification.

In light of this, let’s consider how the length of an imaging optical system can be minimized by using the UPLXAPO4X, a typical low-magnification objective in the X Line series. This process can be done in four steps:

Design of an imaging optical system

Figure 1: Basic layout of an optical system

1. Determine the field of view

The value obtained by dividing the objective’s field number (OFN) by its magnification is the maximum range that can be viewed on the specimen surface. Because the OFN of the UPLXAPO4X is 26.5, the range that can be viewed on the specimen surface can be calculated as: 26.5 / 4 = φ6.625 mm. Our UIS2 objectives are designed to have a parfocal distance of 45 mm (distance A).

2. Select a tube lens

Our UPLXAPO4X objective has an OFN of 26.5, and it can be combined with a tube lens that produces a 26.5 mm image circle to take full advantage of its performance. Accordingly, we recommend you combine the SWTLU-C tube lens with an X Line objective. This combination enables you to obtain images that are clear and homogeneous, even at the center of or around the image pickup device.

3. Select a camera adaptor

Next, select a camera adaptor. As shown in Table 2, the distance to the imaging surface (distance C) can be shortened by using the different reduction ratios of various camera adaptors. The length of an optical system can be minimized by combining the tube lens with a camera adaptor that has a 0.35x magnification.

U-TV1XC
1x
U-TV0.63XC
0.63x
U-TV0.5XC-3
0.5x
U-TV0.35X-2
0.35x
SWTLU-C 181 mm 160 mm 129 mm 109 mm
U-TLU 166 mm 145 mm 114 mm 94 mm

Table 2: Distance C for tube lenses combined with different camera adaptors

It is important to select an adaptor magnification so that the value obtained by dividing the camera sensor’s diagonal width by the adaptor’s magnification won’t exceed the image circle of the tube lens.

For example, let’s say you select a camera adaptor with a 0.35x magnification due to the restricted total length of the imaging optical system and combine it with a 1/1.8-inch camera (with a diagonal width of 9 mm). In this case, you need to divide 9 by 0.35 to find the value for comparison (25.7):

22 < 9 / 0.35 = 25.7 < 26.5

So, the SWTLU-C (rather than the U-TLU) should be selected as the tube lens.

Microscope camera sensor and tube lens

Figure 2: Camera sensor size and image circle for the tube lens

4. Determine distance B

In steps 1 to 3, we selected the units required for the imaging optical system. After that, all you need to do is determine distance B as the final parameter.

Since all UIS2 objectives are infinity-corrected optical systems that are compensation free, you can change distance B to suit your needs.

We recommend that the length ofBis between 50 mm and 165 mm. In this example, we selected 50 mm as the length of B to build a compact device. But you can select another length depending on your desired layout. For example, you can extend the distance to insert an optical system for reflected illumination.

Final Thoughts about Designing Compact Optical Systems

Following steps 1 to 4, you can build an imaging optical system with a total length of 204 mm (Figure 3). Properly combining our UIS2 objectives, tube lenses, and camera adaptors enables you to also design short optical systems for compact devices.

Compact optical system for a microscope-based imaging device

Figure 3: Illustration of a compact imaging optical system with a total length of 204 mm

One factor that’s often overlooked is the camera size (distance D in Figure 1). High-sensitivity cameras generally have a cooling device, so they tend to be large. Make sure to consider the camera size when you set the optical system’s total length (L).

Related Content

The Importance of Compensation-Free Optics in Microscope Design

Why Objectives with Wavefront Aberration Control Are Essential for Good Microscope Design

Good Optics—Improving Single-Molecule Sensitivity in Confocal Microscopy

OEM经理

Bunryu Arashi在欧洲奥林巴斯科学解决方案担任OEM经理。Bunryu拥有12年的显微镜产品开发经验,曾经为奥林巴斯BX和CKX系列显微镜设计过物镜,相机适配器,以及照明光学系统。他拥有日本大阪大学的工程学硕士学位。

2021年3月25日
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