SRTLM Instruction Manual

When it comes to lens meters, auto lens meters are the mainstream these days, and there may be people who have never used manual lens meters before. I think that the lens meter itself is still an essential item for those who work with eyeglasses.

I created a simulation tool with the hope that you would learn the properties of eyeglass lenses through a manual lens meter. Hereafter abbreviated as SRTLM.

If you would like to know about lens meters and eyeglass lens roughly, please read about Lens Mater .

Features

  1. Measurement of single vision lenses (spherical and toric) can be simulated.

    • Focusing of lens

    • The movement of the corona image (*) accompanying the movement of the lens (vertical movement, horizontal movement and rotation), the rotation of the focusing glass, the occurrence of astigmatism due to the tilt of the lens, etc.

      *The coronal image consists of a small disk called a target that moves back and forth along the optical axis, and has 36 concentric pinholes. A bundle of rays passing through a pinhole is visualized as an image with a focusing glass. There are also types of targets that combine corona target and a cross target (cross slit). This tool assumes only corona targets.

  2. You can check the shape of the test lens.

    • The test lens is rendered in 3D, including sections along the strong/weak principal meridians.

  3. Ray tracing is reproduced in 3D

    • How rays emitted from the target form an image on the focusing glass is simulated.

    • Movement, rotation, and tilt of the test lens are reproduced in real time.

    • * Ray tracing cannot be seen with the actual lens meter. Since SRTM is a simulation tool, it draws ray traces.

  4. You can create, save, and recall the lens you want to simulate.

    • It can be specify the spherical power, cylindrical power, axis direction of the cylindrical lens, refractive index, center thickness, and front curve.

    • The created lense can be saved and loaded.

Features omitted in SRTM compared to a real lens meter (assuming a manual telescopic lensmeter)

  1. Diopter adjustment

    In the original lens meter, there is an eyepiece system after the focus glass, It is necessary to adjust the dioptric power to see the focusing glass clearly, but this is omitted in SRTM (see the imaging diagram in Fig. 1).

  2. Prism compensator

    SRTM does not assume the measurement of prism lenses and cannot create prism lenses.
    Therefore, the lens system for the prism compensator has also been omitted (see the imaging diagram in Fig. 1).

Prerequisite

  • It is assumed that you have some knowledge of eyeglass lens when using SRTM. about Lens Meter If you refer to this, I think that you can operate without any problems.

Startup screen

Figure 1 shows the screen when SRTLM is started.
Default lens data appears in the Lens Data section. For a lens that include astigmatic correction, there is two points of focus.
SRTLM draws the state when the focus is on the (-) side at startup. This is by design.

Each section is color coded to explain each feature.

* I will explain first, about the text boxes displayed in the blue frame (Lens Settings section), the red frame (General section), and the green frame (Lens Data section). Please observe the following rules.

blue frame background gray do not enter the number directly change with slider or spin button
red frame background gray do not enter the number directly change with slider or spin button
green frame background sky blue can enter numbers directly can also use the arrow keys to change

* Hereafter, the lens meter is abbreviated as LM, and the focusing glass as FG.


Fig. 1 Screen configuration

Below is a list of features, color-coded by section in Fig. 1.
Click on the underlined feature name to go to feature details.

[Ⅰ] Upper side of screen
(1) General Operate as functions of LM
#1 Target Position Function to move the target back and forth on the optical axis
(equivalent to the LM's power measurement dial)
#2 Crosshair Rotation Ability to rotate FG's crosshair
(2) Lens Settings Manual operation
#1 Lens Rotation Operations required to measure astigmatic lens
#2 Lens Position Vertical and horizontal movement of the lens
to position the corona image at the center of the FG
#3 Lens Tilt LM does not have the function to display the tilt of the lens.
In SRTLM, It is intentionally provided because it can be expected to have a large effect as a simulation.
CheckBox Utility Functions
#4 Tilt Following Link the lens movement with the curve on the back of the lens.
Since the back surface of the lens is in contact with the lens holder of the LM, the tilt of the lens changes according to the curve of the back surface of the lens when the lens moves up, down, left, or right. Normally, when the lens is fixed after being moved, it tilts, so it is checked by default.
#5 Crosshair Following If checked, the movement of the lens will follow the crosshair at any angle (this is not possible with the actual LM).
This is a feature for future use and is not checked by default.
#6 Reversal Reverce the orientation of the lens.
It is possible to simulate the meniscus shape of spectacle lenses and how the center thickness of the lens affectted the orientation of the lens.
(2) Lens Data Various data of the lens
#1 spherical power Enterable: See details
#2 cylinder power ditto
#3 Cylindrical lens axis ditto
#4 refractive index ditto
#5 center thickness ditto
#6 curve in front of lens ditto
#7 Radius of the front surface of the lens Cannot be entered:
Calculation results based on lens data are displayed
#8 Radius of the minor meridional direction
on the rear surface of the lens		 ditto
#9 Radius of the mojor meridional direction
on the rear surface of the lens		 ditto
DATA IN Loading saved lenses data
DATA OUT Saving created lenses data
(4) Others: Buttons
RESET CURRENT DATA Returns to the initial state of the lens set in [Lens Data]
RESET Return when loaded with [Data In]
EXIT Program exit
1x 1x: Magnification of corona image (default)
2x 2x: Magnification of corona image
10x 10x: Magnification of corona image
AF(Check Box) Simulation of lens settings when making glasses.
When unchecked, the lens position, target position, and lens rotation change randomly.
[Ⅱ] Lower side of screen
(1) Left Window Ray Tracing
(2) Right Window Drawing of focusing glass(FG) and corona image

[Ⅰ] - (1) - #1 Target Position (unit : [D] diopter)

to Startup Screen

[Ⅰ] - (1) - #2 Crosshair Rotation (unit: [°] degree)

to Startup Screen

[Ⅰ] - (2) - #1 Lens rotation (unit:[°] degree) Operation to manually rotate the set lens.

to Startup Screen

[Ⅰ] - (2) - #2 Lens position (unit: mm) Operation to move the lens up, down, left, and right by placing the hand on the set lens.

to Startup Screen

The relationship between lens movement and corona image position change is omitted here. If you want to learn about the ophthalmic lens, please set several [Lens Data] and check the positional relationship between the lens and the corona image. The deviation of the corona image from the center of FG means the amount of prism (symbol Δ: unit: [Diopter]). One scale of the crosshair corresponds to 1Δ[D].

[Ⅰ] - (2) - #3 Lens tilt (unit:[°] degree)

to Startup Screen

Originally, the function is linked to lens movement, so the spin button is not necessary, but it is purposely provided for SRTM simulation purposes.

The astigmatism produced by tilting the lens was about 0.4D. Actually, it is slightly different from the corona image of the SC(-) lens for correcting astigmatism. The corona image itself is slightly below the center of the FG crosshair If you set the magnification of the corona image to [x10], you can clearly see the deviation from the center. The imaging state is also not clearly linear, and other aberrations are included. SRTLM can also simulate the properties of such lenses.

[Ⅰ] - (3) Setting the lens data

You can directly enter a number in each text box, but you can also use the arrow keys to increase or decrease the number. The following describes how to use the arrow keys. It's a very useful feature once you get used to it.

#1, #2 S [spherical power], C [cylindrical power] : Take S as an example (C has the same specification).

to Startup Screen

Each can be set from +10.00D to -15.00D. Each time the refractive power is changed, the refractive power shown at the target position in the General section and the position of the slider will change. The ray tracing window also changes in real time.

#3 Ax [axial direction of the lens]

to Startup Screen/

It can be set from 180.0(0.0)° to 179.5°. The ray tracing window changes in real time as the angle is changed. Also, the position of the lens rotation slider in the Lens Settings section changes.

#4 n [refractive index]

to Startup Screen

It can be set from 1.000 to 2.500. The ray tracing window changes in real time as the refractive index changed.

It seems that lenses for eyeglasses are used as 1.5 to 1.9 (1.523 to 1.892 for glass materials, 1.498 to 1.76 for plastic materials). Currently, I recognize that plastic with a refractive index of 1.60 is the mainstream material.
If you specify less than 1.3, the drawing of the ray tracing window may be disturbed or an error message may be displayed.

#5 t [center thickness]

to Startup Screen

It can be set from 00.00 to 15.00mm. The ray tracing window changes in real time every time as the center thickness changed. As is clear from the cross-sectional shape of the lens, (+) lenses tend to be thicker in the center, while (-) lenses tend to be thinner. It is a little less than 1.0 to 2.0mm for the (-) lens. For (+) lenses, it varies greatly depending on the lens diameter.
Please simulate with SRTL how to reduce the thickness of the (+) lens when making eyeglasses.

#6 curve [Curve of the front surface of the lens (refractive power of the front surface)]

to Startup Screen

It can be set from -15.0 to +15.0. The cross-sectional shape of the lens is determined by specifying the curve of the front surface of the lens. If the curve is positive, it is convex to the right; if it is negative, it is convex to the left. Lenses for spectacles are not convex to the left, but SRTLM is a simulation tool, so even if they are convex to the left, they can be set. In the case of spectacle lenses, I think that 5 curves were common in the past, but I think that 3 to 4 curves are more common these days. It seems that the frame that incorporates the lens is also designed according to these curves.

* I wrote "curve (refracting power of the front surface of the lens)" in the title. Then the unit should be D (Diopter). I don't know why it is called a curve, but the refractive power of the lens (the refractive power of the lens front and rear surfaces, the lens thickness, and the refractive index determine the refractive power of the lens) and It may have come to be called a curve to distinguish it. Certainly, considering the cross-sectional shape, the expression "curve" seems intuitive and easy to understand.

[DATA IN] Loading saved lens data

to Startup Screen

[DATA OUT] Save set data

to Startup Screen

When saving, if you add "#" to the beginning of the file name and save it, This data will be displayed by default the next time you start SRTLM.

[Ⅰ] - (4) Others

Checkbox 1x: magnification of corona image (default)

to Startup Screen

Checkbox 2x: magnification of corona image

to Startup Screen

Checkbox 10x: magnification of corona image

to Startup Screen

Checkbox AF

to Startup Screen

Simulation of lens settings when making glasses.

When unchecked, the lens position, target position, and lens rotation change randomly.