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5 Why so many low quality Reduction Lenses in the microscope eyepiece camera market

5.1  Wrong stop position and size

            However, most of the Reduction Lenses did not obey the above rules. Most of the design did not consider objective lenses’ stop position and size.  Here we show an example of the same lens, but with different MTF in coupled or miscoupled conditions.

ToupTek Photonics | ToupCam

ToupTek Photonics | ToupCam

The wrong coupled condition: the real image ray fans from the objective lenses are the same
at different field. The MTFs are strayed always from the diffraction limited MTF value.

           The correct coupled condition: the real image ray fan structure from the objective lenses is not the same at different field. The MTF is reach to the diffraction limited value.

5.2  Different magnification Reduction Lenses have different sizes

            In the Reduction Lenses market, different magnifications often have different sizes. This is often caused by the design problem. The designer does not consideration the whole structure of the microscope and the Reduction Lenses.

            Further, the different Reduction Lenses should have the same conjugate distance between the real image of the objective lenses and the sensor. TouTek engineers designed and optimized all of these lenses at a time to ensure this basic requirement. This often increase the fabrication cost but make the microscope eyepiece camera more coordinated.

ToupTek Photonics | ToupCam

The different Reduction Lenses have the same conjugate distances

5.3  Long conjugate distance

              Another issue is that the conjugate distance should have a moderate distance. Some of the Reduction Lenses in the internet often have long distance (for example 120mm), which will make the whole digital microscope system look ugly and will not match with your beautiful microscope itself.

5.4  Ghost image problem

           The fourth issue is the ghost image often appeared in the center of the image. The possible reasons may be

1. The lens did not coated with multiple layer thin films
2. The tube is not blackened or blackened with bad quality
3. The IR-CUT is cheap which cannot cut off the infrared light thoroughly
4. Ghost image formed on the sensor plane.

5.5  Black spots

           The fifth issue is the black spots appeared on the captured image. This is because of the following drawbacks

1. There are dusts scattered on the sensor. This often caused in the installation process because of the badly polluted workshop and is often appeared for those cheap camera companies.
2. There are scratches or dusts on the IR-CUT. IR-CUT is a focal plane component in the camera and a strict production environment is needed for this part. ToupTek  purchase the IR-CUT from our mother company who is a public company and makes the IR-CUT, OLPF used in commercial digital cameras of SONY, NIKON, CANON and OLYMPUS et al. They have 80 sets of high-end coating machine which is the best factory in the field of IR-CUT and OLPF production.
3. There are dusts and scratches on the field lenses. Field lens is also an intermediate image plane component. It has strict requirement for its surface quality.

ToupTek Photonics | ToupCam

Field lenses with large NA=0.2(left) and small NA=0.025(right) which is often the case for the microscope

              From the above analysis, one can find if there is a small dust on the field lenses with lower NA, most of the light will be blocked by the dust and thus there will be a few or no light impinge on the image sensor, thus a blurred black spot will appeared on the image. ToupTek  gives strict requirement for the field lenses and sources the best factory to polish this field lens to ensure the product quality. Even with this strict requirement, they are still 20% substandard lenses that did not pass the examination in our clean room. One can find the strictness of this part.

5.6  Reduction Lens NA and its image quality

The microscope objective’s NAs are listed in the table shown below.







Object Lenses NA






Reduction Lenses NA






             From the above table, one can find the largest Reduction Lenses NA is 0.025 for the 10X objective lenses. ToupTek chooses 0.025 as the NA of the Reduction Lens to ensure the light from the objective lens can be totally transfer to the sensor plane. Most of the lens in the internet only set the NA to 0.01 or even lower to reduce the pieces so as to reduce the fabrication cost. This will cut most of the light and increase the noise for you camera.

5.7  Reduction Lens with low MTF value

              The MTF is an expression describing the reduction in contrast of a sinusoidal signal (60% contrast sine waves) as a function of spatial frequency. The limiting resolution of an electronic detector is the smallest target size that is detectable above the noise threshold, a concept that is often referred to as the frequency of limiting resolution, which is the spatial frequency for which the MTF falls to a value of 3 percent, corresponding to the limit of visible detection.

                The MTF of the Reduction Lenses should not be lower than that of the Object lenses MTF/magnification.







Resolution Distance






MTF(pairs/mm) of the Object lenses






MTF of the Reduction Lenses






              The low quality Reduction Lenses try to use few lenses (for example doublet). This will cause the lower MTF value and thus cannot discriminate the distance which can be resolved by the objective lenses. This will be cause the waste of the objective lens discrimination power.

              As show below, all of the ToupTek’s Reduction Lenses MTFs reaches to the diffraction limited resolution.

Another interesting phenomenon is that the maximum MTF value is 120, not 40. This is because we select 0.025 as all the Reduction Lens’s NA.

ToupTek Photonics | ToupCamToupTek Photonics | ToupCam

ToupTek Photonics | ToupCamToupTek Photonics | ToupCam
 MTFs of 0.37X, 0.50X, 0.60X and 0.75X Reduction Lens

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