Optical assembly for medical imaging devices
Optical assemblies for use in medical or other devices so as to image an object under examination onto an image sensor include a plurality of lens elements that can be retained in lens barrel. The lens elements and the lens barrel can be sealed with a compressible gasket. In one example, at least one lens element is made of an injection-moldable plastic and at least one lens element is made of a relatively dispersive optical glass. A lens barrel diameter or lens diameter can be selected to permit access to the object under examination with surgical or other tools. Aperture plates can be situated so as to reduce flare in the object image.
1. A multi-element lens, comprising a plurality of lens elements situated so that an effective focal length is about 1.8 mm, an f-number is less than about 8, and distortion is within about 15% off-theta at full field of view of 140 degrees, wherein the plurality of lens elements includes, from object-wise to image-wise along an optical axis, a first lens element, a second lens element, and a third lens element of a common optical material, and a fourth lens element of a different lens material.
2. The multi-element lens of claim 1 , wherein the first, second, and third lens elements are made of a common optical plastic, and the fourth lens element is made of a flint glass, and the first through fourth lens elements have optical surfaces defined by, from a most object-wise surface to a most image-wise surface:
Surface
Radius of Curvature
1
+60.000
2
+0.973
3
−8.125
4
−1.491
5
+2.831
6
−1.193
7
−2.674
8
inf.
3. The multi-element lens of claim 1 , wherein the first, second, and third lens elements are made of a common optical plastic, and the fourth lens element is made of a flint glass, the optical plastic has an Abbe number of about 24 and the flint glass has an Abbe number of about 56.
4. The multi-element lens of claim 1 , wherein most image-wise surfaces of the first lens element, the second lens element, and the third lens element are aspheric surfaces.
5. The multi-element lens of claim 1 , wherein most image-wise surfaces of the first lens element, the second lens element, and the third lens element are aspheric surfaces, the aspheric surfaces of the first lens element, the second lens element, and the third lens element are defined by
K
a 2
a 3
a 4
+0.5073543
0.0
0.0
0.0
+0.0
−0.018796213
−0.036606083
−0.068263035
+0.0
+0.11189657
+0.014471055
+0.044036317
wherein K is a conic constant, and a 2 , a 3 , and a 4 are aspheric power series coefficients.
6. The multi-element lens of claim 1 , further comprising a first aperture plate defining a flare reducing aperture situated between the first lens element and the second lens element and a second aperture plate situated between the third lens element and the fourth lens element.
7. The multi-element lens of claim 1 , further comprising a lens barrel configured to receive the first, second, third, and fourth lens elements, wherein the first lens element includes a circumferential channel and a rim adjacent the channel so that a compliant gasket retained in the circumferential channel is situated to be compressed between the rim and a lip of the lens barrel.