JML Optical

Introduction to Multi-Element Lens Systems

The use of an additional element or two for achromatic cemented doublets and triplets significantly improves performance over a singlet. In fact, each additional spherical lens element added into a design gives the lens designer six more degrees of freedom (two radii, thickness, air-space, glass index and dispersion) to help in achieving the desired system performance. It is therefore not surprising that extremely sophisticated lens systems (e.g., imaging lenses used in creating integrated circuit patterns) can have as many as twenty individual lens elements.

Consider the many parameters which must be controlled: distortion, lateral and longitudinal color, spherical aberration, astigmatism, spot size field curvature (or MTF-based performance), large field angles, telephoto, telecentric and zoom requirements, specific locational tolerances for entrance and exit pupils, back focus, precise magnification, vignetting, and overall space constraints and specialty requirements such as periscopes and endoscopes, to name just a few.

CCD/CCTV Lenses require very sophisticated design and construction in order to provide exceptionally high-resolution, color imaging at very large lens apertures. JML offers several types of CCD/CCTV lenses.  These include manual iris, focus and manual zoom lenses as well as auto iris and motorized zoom lenses, wide field lenses for detector array imaging (e.g., CCD cameras), laser diode lenses, F-Theta scan lenses, relay lenses, board lenses

enlarging lenses and telecentric lenses.

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For a complete list of JML’s lens assemblies, please see our Multi-Element Lens List.

If there is a particular application not shown and you would like assistance, please call us at 585-248-8900 or email us.  If we cannot meet your requirements with one of our thousands of off-the-shelf lenses, we can custom design a lens to meet your specifications.  There is no cost and no obligation.

CCD/CCTV Video Camera Formats

35mm Movie Format

Roll Microfilm Formats, 16mm Film Size

Microfiche Formats

35mm Film Size

Roll Film Picture Formats

Useful Terms and Formulae

EFL. The effective focal length is measured with an object at infinity. The tolerance is +/- 2%.

f/#. This number defines the light gathering ability of a lens and is determined by dividing the EFL by the diameter of the entrance pupil.

Magnification. This is the designed magnification at which the performance is specified. The performance remains the same when the lens is used at the reciprocal of its magnification. The lens can also be used at other magnifications, however performance may change.

Half Angle. The designed half angle is one-half of the total field angle of the lens yielding the edge resolution/contrast as specified in the lens listing.

Resolution/MTF. The first number is line pairs (or cycles) per millimeter (l/mm). The second number is the percent contrast at the given l/mm. Resolution is measured on the short conjugate side.

Limiting Resolution. Maximum resolution at a contrast level of 6%.

CCD/CCTV Lenses

Most CCD/CCTV lenses are made with the standard C-mount (17.52mm FFD), while some are available with a modified CS-mount (12.5mm FFD).  The type of mount you select is determined by the camera you are using; however, C-mount lenses can be used on CS-mount cameras with a 5mm adapter ring (P/N MFX 20165/000). All of our CCD/CCTV lens elements are anti-reflection coated to enhance the light transmission through the system.

Figure 1

Auto Iris Lenses

It is extremely important to control the amount of light transmitted through the CCD/CCTV lens that is imaged onto the camera detector. JML’s auto-iris iris controlled lenses maximize the efficiency of CCD/CCTV cameras. This type of lens allows for continuously variable adjustment of light level whether the iris servo-amplifier is located in the lens or in the camera.

A built-in neutral density filter makes it possible to operate some lenses at an effective aperture of f/500 without negatively affecting image quality.

CS-Mount, Galvanometer Type Auto Iris Lenses (Mechanical Construction and Technical Specifications)

The lenses of the galvanometer series contain a galvanometer drive, i.e., a moving-coil instrument principle whereby the iris blades are moved instead of a pointer.  The galvanometer is driven either directly (variable DC voltage control) or by means of a printed circuit amplifier (auto iris control) in the lens.

The galvanometer auto iris models are controlled by a video signal and outside accessible potentiometers are used for “level” and ALC adjustments. If the DC control types are to be used, then the required control printed circuit has to be integrated into the camera.  Once the lens has been screwed into the camera, the slipping mechanism on the CS-mount connection allows radial turning of up to 340° to locate the cable connection at the desired point.

Figure 2

Adjustment of the Galvanometer Auto Iris Lenses Signal Level

The camera signal level can be adjusted from 0.4 to 1.0 Vpp using potentiometer ➂. Please refer to Figures 3and 5. An oscillograph and sufficiently lighted test picture (min. 3000 Lux) are used for this purpose. If these test aids are not available, an approximate adjustment will have to be attempted according to the subjective picture impression: turn control ➂ to the left if the picture is too bright and to the right if t he contrast is too low.

Average and Peak Value Control

Figure 3

If the picture is still not satisfactory, despite correct level adjustment, it may be due to large differences in brightness levels in the picture (possibly highlights) which falsify control. This can be corrected with the Pk/Av potentiometer.  When leaving the factory, the lenses are set at an average control level. Continuous adjustment up to 100% peak control value is possible by turning the control to the right to provide better recognition of picture areas that are too bright.

Adjustment of the DC Control Lens

The switch should be set to DC if a convertible camera is being used.

Figure 4

Figure 5

CONNECTION ASSIGNMENT

A) Galvanometer type lenses

Red: DC supply voltage

White: video signal

Shield: ground (–)

B) DC Control Lenses:

Red (+):

Black: } Drive Coil

White:

B) Green (+): } Damping Coil

B) Shield: NC

➀ Focusing Ring (manual)

➁ CS-Mount (with 340° slipping

mechanism)

➂ Level Control

➃ Sensor Control (100% average

value – 100% peak value)

➄ Cable Length Approx. 50 cm

(1.65 ft.)

➅ Cover

TECHNICAL DATA

Power Supply:* + 7–18 V/DC

Current Consumption: Max. 30 mA

Input Signal:* 0.4 – 1.0 Vpp CVS

Input Impedance:* High impedance

Iris Range: 1:14 – 1:500

Iris Response Time: Min. 1.5 sec.

Iris Accuracy:* +/- 10% at +20°C (+ 68°F)

Sensitivity:* < 10% video signal

Temperature Range: -20°C to +50°C (-4° to +122°F)

Automatic Iris Closing: Yes

(*Applies only to galvanometer type models)

Ring Type Auto Iris Lenses (Mechanical Construction and Technical Specifications)

All auto iris lenses of the ring type series work according to the simplified principle of a rotating magnet measuring instrument. In this construction, instead of a pointer, the iris vanes are moved

Adjustment of the Signal Level

The video signal of the camera can be adjusted with potentiometer ➂ between 0.3V and 1.5Vpp. Please refer to Figures 6 and 7. An oscillograph and test picture are used for this purpose (light condition more than 3.000 Lux). If these test aids are not available, an approximate adjustment must be carried out according to a subjective picture impression, in which the control ➂ should be turned to the left for a picture that is too bright or to the right if the contrast is too low.

Average and Peak Value Control

If the picture’s image is not satisfactory after the correct adjustment level has been made, perhaps it is due to a sizeable difference in brightness within the picture (highlights). This large range of brightness, which tends to falsify the control’s signal, can be corrected by adjusting the pk/av potentiometer ➃.  When leaving the factory, the lenses are set at an average control level. By turning the control to the left a continuous adjustment of up to 100% of the peak value control is possible. This gives better differentiation of the picture areas that are too bright.

Figure 6

CONNECTION ASSIGNMENT

① Focusing Ring (manual)

➁ CS-Mount (with 340° slipping

mechanism)

➂ Level Control

➃ Sensor Control (100% average

value – 100% peak value)

➄ Cable Length Approx. 50 cm Red: DC Supply Voltage

(1.65 ft.) White: Video Signal

➅Cover Black: Ground (–)

➆ Gain Control Potentiometer Shield: Ground (housing)

TECHNICAL DATA

Power Supply: + 7–18 V/DC

Current Consumption: Max. 30 mA

Input Signal: 0.3 – 1.5 Vpp BAS

Input Impedance: High impedance

Iris Range: 1:1.2 – 1:500

Iris Response Time: Min. 1 – 1.5 sec.

Iris Accuracy: +/- 10% at +20°C (+ 68°F)

Sensitivity: < 10% video signal

Temperature Range: -20°C to +50°C (-4° to +122°F)

Automatic Iris Closing: Yes

Figure 7.

Gain Control

If the reaction of the iris control is too slow or too fast, you can adjust the gain control by using a third potentiometer ➆, located under the cover

Telecentric Lenses

Parallax (perspective error) allows us to process the world in its true three dimensional state, e.g. closer objects appear relatively larger than those placed farther away. This phenomenon of changing magnification as a function of working distance is found in most conventional imaging systems. However, it is unacceptable in some metrology applications where the part under inspection is of finite depth that is greater than the depth of focus of the lens system. Telecentric lenses optically correct for this occurrence so that objects remain the same size independent of their distance over a range defined by the lens. A telecentric lens system typically incorporates an afocal design with the aperture stops located at the common focus of the front and back lenses resulting in the chief rays being parallel to the optical axis in both the object and image spaces. A constant viewing angle and a constant magnification can therefore be achieved in the case when:

• The object and image surfaces are tilted with respect to the optical axis;

• The lens is defocused on either object surface or image surface.

JML now offers a line of telecentric lenses with focal lengths ranging from 13mm to 216mm designed specifically for your size CCD camera. For ease of mounting, we also offer C or T mount adapters for coupling.

Telecentric Video Microscope with High NA

A telecentric microscope has a larger usable range of depth of focus compared to a standard system. The depth of focus is a function of numerical aperture.  Although it may be the same for telecentric and standard lenses, the usable depth of focus of a telecentric lens in practice seems to be greater for a visual system.  The reason is that the telecentric lens has a constant magnification in every focus position.  When out of focus, the image is soft, but the positions of details and edges are correctly shown.

Beam Expanders

These large-aperture, fixed-magnification beam expanders are designed and assembled for specific wavelengths thus allowing for precise control of the optical aberrations. Uses for these beam expanders include interferometry and Gaussian beam diameter control over large distances, as well as general applications where expanded beam sizes are desired.

Laser Diode Lenses

Mounted and Unmounted Type

JML’s laser diode lenses can be used to either collimate or focus laser light. These lenses were designed to be used at specific wavelengths, but with minimal refocusing, they can be used throughout various wavelength ranges.

Aspheres

JML supplies both unmounted and mounted aspheric glass lenses as well as JML designed spherical multi-element mounted lens assemblies. Any of the aspheric glass lenses listed can be custom mounted in metal barrels to meet your specific mechanical requirements. The transmission graphs for the various glass types used for our aspheres are shown in the glass transmission graphs.

Multi-Element Lenses

JML’s three element laser diode lens assemblies are available for applications in which enhanced-beam characteristics are important. The designs are optimized to reduce spherical aberration, astigmatism and coma. Each element is anti-reflection coated to achieve an overall system transmission which exceeds 95%. The lenses are mounted in small diameter aluminum barrels.

Applications

JML’s multi-element laser diode lenses and aspheric glass singlets are designed with two criteria in mind. First, the lenses are optimized to compensate for the aberrations introduced by the diode’s cover glass. Second, because working distance is important, our designs allow the diode lens to be positioned and/or adjusted without disturbing the laser itself. JML also supplies lenses for optical communication use in the 1.3-1.5 micron wavelength region. Other typical applications for these lenses include:

• Bar Code Scanning

• Gun Sights

• Magneto Optical Disk Drives

• Fiber Optic Coupling

• Laser Printers

• Cable TV

• Line Levelers

Please refer to the product listing chart on pages 30-31 for technical specifications.

A variety of focal lengths and numerical apertures serve to produce varying spot sizes at predictable distances from the lenses. Please contact us for any of your requirements so we may assist you with an off-the-shelf lens selection or custom design.

Flat Field Laser Scan Lenses

JML is a world renowned designer and manufacturer of flat field laser scan lenses. Our products are commonly found in high-energy laser marking devices, graphic arts printers, image scanners and other information processing equipment used in the laser scanning industry.  Scan lens design involves balancing and co-optimizing six optical parameters with mechanical considerations such as weight and space envelope. Our engineering and design staff has years of experience customizing scan lens designs to satisfy variable requirements.  We balance the following key parameters to ensure that the scan lens design is optimized for your particular application:

Telecentric Scan Lens.  Telecentric scanning lenses are designed to focus the beam such that the chief ray is always perpendicular to the flat field. This type of lens configuration has the system “stop” located at the front focal point of the lens system or where the beam is deflected from the axis. In a single-axis scanning system, the stop is located at the scanning mirror, whereas for two-axis scanning the stop is mid-way between the mirrors.

Scan Length.  The scan length (SL) can be thought of as the image height of the scan lens. Mathematically, scan length is defined as the product of the calibrated focal length and twice the field angle (radians) in object space:

SL = 2*(field coverage) = f*2Ø

Scan Linearity.  Scan linearity is the degree to which the performance of a particular scan lens design follows the equation SL = 2*(field coverage) = f*2Ø. The scan linearity of a system can be defined using either the percent position error or percent velocity error.  Scan linearity is defined as a percentage of the expected (design) scan height using the percent position error technique. The difference between the expected (design) and observed scan heights at any scan angle divided by the expected design height yields this measure of linearity once converted to a percentage.

Alternately, the percent velocity error technique involves calculating the percentage difference between the velocity of an image spot at a specific field angle and the velocity at the optical axis of the lens.

Input Scan Angle (Ø). Input scan angle, or half the total angular field of the scan lens, should always be maximized no matter what beam deflection technique is used.

Power Loss and Spot Size. Most scan lens designs are diffraction limited so the spot diameter is defined as the product of a constant (which depends on the truncation ratio and pupil illumination), wavelength and f-number.  Since power loss also depends on the truncation ratio, power loss and spot size must be balanced in a scan lens design and weighted depending on the relative importance of spot diameter, peak spot intensity and total spot power.

Depth of Focus. The depth of focus of a scan lens is defined as the axial distance over which the image spot diameter is relatively constant. Depth of focus is directly proportional to the f-number and consequently varies with truncation ratio.

Wavelength. A scan lens designed to operate at a single wavelength is simplest and most cost-effective. Multi-wavelength designs become increasingly more complex because additional optical elements are required for color correction.

Mechanical Constraints. Allowable space envelope, mounting interfaces and maximum scan lens weight are just some of the parameters that need to be considered simultaneously with optical performance. 

These design parameters are no different from those of any multi-element focusing objective. What makes a laser scan lens system unique (and different from an astronomical telescope, for example), is the balancing of wide angular field, flat image plane and linear relationship between input scan angle and image height. The figure below is a schematic of a representative scan lens system.  Our high performance scan lens elements are produced through hours of precision polishing by expert craftsmen using in-process metrology. The metal housings are manufactured to exacting tolerances and inspected prior to integration. Prior to shipment, all assembled units are tested in the JML Quality Assurance laboratory for output laser beam spot size, uniformity and energy level. The lenses are electro-optically measured for spot size using 5 Photon BeamScan® modules mounted on custom built laser collimator equipped optical benches.

Wide Field Imaging Lenses

JML offers an A series (medium resolution) and a B series (high resolution) of wide field imaging lenses. All of the lenses in both series are housed in black anodized aluminum barrels and all elements are antireflection coated for maximum transmission. Lenses designed for detector array imaging require the following performance attributes:

1.Wide field imaging–Allows the use of short focal length and short barrel length lenses in applications where space is limited such as document scanners.

2. Flat field imaging–Minimizes tilt and image curvature because the pixel at the outside edge of the array is just as important as the one in the center. The lens must be corrected to perform well over the flat surface of the array.

3. Precision focus–The lens must be very well corrected because the resolution must be equal to or better than the required pixel size.

4. Optically “fast”–The f-numbers typically must be f/4.0 or faster to allow sufficient light to be imaged onto the array.  Typical applications for our wide field lenses include:

• Data recording

• CCD imaging

• Document scanning

• Non-contact measurement

• Image digitizing

• X-ray imaging

• High-speed photography

• Pattern recognition

• Guidance systems

If one of our standard lenses does not meet your requirements, please contact us and one of our sales engineers will be happy to discuss a custom design or modification of the lenses listed to meet your exact specifications.

Relay Lenses

JML offers a number of relay lens assemblies from stock. These are specialty lenses optimized usually for 1:1 magnification; however, they are often used at .5X to 2X magnification. A relay system implies that the object is relayed to an image plane, which is at a finite distance and does not require significant magnification or reduction. At 1:1 the object to image distance will be approximately 4 times the EFL of the lens. For a 50mm relay lens of 1:1 magnification the object to image distance will be approximately 200mm. Lens construction is typically symmetrical, although we have asymmetrical designs optimized for specific conjugates or magnifications. Typical applications include film to CCD transfer or fiber optics image relay and night-vision systems.  All air to glass surfaces are AR coated and many of them are coated with high efficiency coatings.

Enlarging Lenses

JML offers a series of enlarging lenses which can be used for standard photographic enlargement purposes. These lenses can also be used for CCD imaging applications much like our wide field imaging lenses. These enlarging lenses include the standard M39 x 1p threaded mount, which is the universal mounting thread for most photographic enlarging equipment.

JML’s lenses exhibit excellent contrast imagery across the entire field of coverage. The lenses are designed and corrected for spherical aberration, coma, field curvature, distortion and color aberrations. The recommended magnification range for most of these is between 2X 15X. Typical applications for our enlarging lenses include:

• Enlargement or reduction of original films onto paper

• CCD imaging

• Scanning

• Inspection of circuit boards

• Automatic positioning

If one of our standard lenses does not meet your requirements, please Contact Us and we will be happy to discuss a custom design to meet your exact specifications.

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