RELATED APPLICATIONS

This application claims priority to Taiwan Application 108139653, filed on Nov. 1, 2019, which is incorporated by reference herein in its entirety.

BACKGROUND

Technical Field

The present disclosure relates to an imaging optical system, an image capturing unit and an electronic device, more particularly to an imaging optical system and an image capturing unit applicable to an electronic device.

Description of Related Art

With the development of semiconductor manufacturing technology, the performance of image sensors has improved, and the pixel size thereof has been scaled down. Therefore, featuring high image quality becomes one of the indispensable features of an optical system nowadays.

Furthermore, due to the rapid changes in technology, electronic devices equipped with optical systems are trending towards multi-functionality for various applications, and therefore the functionality requirements for the optical systems have been increasing. However, it is difficult for a conventional optical system to obtain a balance among the requirements such as high image quality, low sensitivity, a proper aperture size, miniaturization and a desirable field of view.

SUMMARY

According to one aspect of the present disclosure, an imaging optical system includes six lens elements. The six lens elements are, in order from an object side to an image side, a first lens element, a second lens element, a third lens element, a fourth lens element, a fifth lens element and a sixth lens element. Each of the six lens elements has an object-side surface facing toward the object side and an image-side surface facing toward the image side.

The fourth lens element has positive refractive power. At least one of the six lens elements is a freeform lens element, and at least one of the object-side surface and the image-side surface of the at least one freeform lens element is a freeform surface.

When an axial distance between the object-side surface of the first lens element and an image surface is TL, a maximum image height of the imaging optical system is ImgH, half of a maximum field of view of the imaging optical system is HFOV, a central thickness of the fifth lens element is CT5, and a sum of axial distances between each of all adjacent lens elements of the imaging optical system is ΣAT, the following conditions are satisfied:
0.80<TL/ImgH<6.0;
50.0[deg.]<HFOV; and
0<CT5/ΣAT<1.1.

According to another aspect of the present disclosure, an imaging optical system includes six lens elements. The six lens elements are, in order from an object side to an image side, a first lens element, a second lens element, a third lens element, a fourth lens element, a fifth lens element and a sixth lens element. Each of the six lens elements has an object-side surface facing toward the object side and an image-side surface facing toward the image side.

At least one of the six lens elements is a freeform lens element, and at least one of the object-side surface and the image-side surface of the at least one freeform lens element is a freeform surface. Each of at least three of the six lens elements has an Abbe number smaller than 50.0.

When an axial distance between the object-side surface of the first lens element and an image surface is TL, a maximum image height of the imaging optical system is ImgH, and half of a maximum field of view of the imaging optical system is HFOV, the following conditions are satisfied:
0.80<TL/ImgH<6.0; and
50.0[deg.]<HFOV.

According to another aspect of the present disclosure, an imaging optical system includes six lens elements. The six lens elements are, in order from an object side to an image side, a first lens element, a second lens element, a third lens element, a fourth lens element, a fifth lens element and a sixth lens element. Each of the six lens elements has an object-side surface facing toward the object side and an image-side surface facing toward the image side.

At least one of the six lens elements is a freeform lens element, and at least one of the object-side surface and the image-side surface of the at least one freeform lens element is a freeform surface.

When an axial distance between the object-side surface of the first lens element and an image surface is TL, a maximum image height of the imaging optical system is ImgH, half of a maximum field of view of the imaging optical system is HFOV, a central thickness of the first lens element is CT1, a central thickness of the second lens element is CT2, a central thickness of the fourth lens element is CT4, and a central thickness of the sixth lens element is CT6, the following conditions are satisfied:
0.80<TL/ImgH<6.0;
50.0[deg.]<HFOV;
0<CT2/CT4<1.5;
0<CT6/CT4<2.0; and
0<CT1/CT4<1.5.

According to another aspect of the present disclosure, an image capturing unit includes one of the aforementioned imaging optical systems and an image sensor, wherein the image sensor is disposed on the image surface of the imaging optical system.

According to another aspect of the present disclosure, an electronic device includes the aforementioned image capturing unit.

