Mechanical Engineering / Apps / Aperture Creator

To create an aperture, first select the aperture type you would like to create among the different propositions:

Then, fill-in the required parameters:

The rest of this article will detail the meaning of each parameter depending on the aperture type you have selected. The machining options are detailed in our article General Machining Options.

Regular apertures are classical pinholes-like apertures commonly used in optical systems. These apertures are relatively easy to set up and only require 3 values to be entered:

• Outer diameter is the aperture total mechanical diameter. The system is tolerance-ignorant such that you will have to take tolerance into account as you input a diameter value. Check our article on Mechanical Engineering for some recommendations;
• Inner diameter is the aperture clear area which will let the optical rays pass through. The inner diameter must be smaller than the outer diameter to be valid. We recommend that you keep a gap between the two, at least 1 or 2 mm larger than the mechanism you will use to hold the aperture in place (e.g. retainer ring);
• Thickness is the depth of the cut in the machine code. It is important to keep this value slightly larger than the actual thickness of the raw material you will use to cut your aperture to be sure that the tool will cut completely through the sheet. Read our recommendations on Mechanical Engineering.

Darkfield apertures are often used to shape illumination to generate out-of-field rays. They must be coupled with a regular aperture that will cut the rays generated by the darkfield aperture. Darkfield imaging is typically used to highlight very small details like scratches on transparent materials or mirrors, or to visualize scattering samples like in biology.

Darkfield apertures require more parameters to be set:

• Outer diameter and thickness are identical to regular apertures and you can therefore consult our section on regular apertures for their meaning;
• Inner diameter, at contrario to regular apertures, is the diameter of the ray blocking area of the aperture. In a 1:1 imaging system, you will want to keep this inner diameter slightly larger than the one of the matched regular aperture to ensure no rays are generated that will pass through the regular aperture. A 10% margin is a good place to start with if you do not know where to start from;
• Darkfield diameter is the diameter of the clear area that will generate the out-of-field rays. Along with the focal length of the projection lens, the darkfield diameter defines the steepest rays generated by the system. We recommend keeping it below the mechanical mounting by 1 or 2 mm like inner diameters in regular apertures;
• Num branches is the number of branches in your aperture. Because it is not possible to have a metal disk floating in the center of the aperture, at least two branches are required to hold the inner disk to the outer one. To avoid artefacts due to directional effects, it is usually recommended to use an odd number of branches;
• Branches spacing is the thickness of the branches. It is recommended to keep this value larger than the thickness of the plate used for the aperture for rigidity purposes by at least a two-fold.

L-Shaped apertures are less often met in optics but can be used to generate interference patterns when used in conjunction with a grating. It is called like this because the aperture has the shape of a “L” letter.

The l-shaped apertures require the following parameters:

• Outer diameter and thickness are identical to regular apertures and you can therefore consult our section on regular apertures for their meaning;
• Aperture width is the clear area width. This value must be larger than the endmill used to generate the pattern;
• Aperture length is the length of the side arm of the “L” shape without taking into account the width of the aperture. The aperture length and width are constrained by the outer diameter of the aperture;
• Corner radius is the radius of the cut for the aperture. This value must be larger than, or equal to, the radius of the endmill used in the machining process. The corner radius must also be smaller or equal to half of the width of the aperture to be physically possible.