Decoding Photographic Lenses

Transcription

1 Decoding Photographic Lenses Wouldn t it be nice if photographic equipment and supply manufacturers made purchasing their equipment more consumer friendly? Sometimes their terminology and abbreviations can be confusing for even the most experienced photographer. A prime example is all the terms and abbreviations used by lens manufacturers. The same feature will be called by different names depending on which manufacturer you are looking at. A prime example is Image Stabilization which is the same as Vibration Reduction which is the same as Vibration Compensation which is the same as Optical Stabilizer. These are terms used by Canon, Nikkor (Nikon), Tamron, and Sigma for the same feature. To help simplify things for everyone, I have researched the terminology and abbreviations used by many of the major lens manufacturers. In this article you will find plain English explanations of those terms and abbreviations. So no one claims I am playing favorites, I will address the companies in alphabetical order. For the sake of full disclosure, I shoot Nikon and I am a big fan of Tamron and Sigma. Before we get into the brand specific definitions, it is probably best if I cover some information common among all lens manufacturers. First, modern photographic lenses are not made up of a single piece of glass but rather a series of multiple lens elements or pieces of lens. The characteristics of a lens is defined by combining several lens elements of varying sizes, shapes, and individual characteristics within a single lens barrel. Some of the terms found in use by the lens manufacturers are actually terms used to describe the characteristics of the various lens elements found in their lenses. Secondly, you will frequently see reference to the term aspherical lens or aspherical lens element. This refers to a specially shaped lens element which helps correct for problems created by light passing through the edge of a normal shaped (spherical) lens element. The difference can be seen in Example 1. Spherical Lens Focus plane Critical edge rays Aspherical Lens Example 1 As seen in the example, the edges of an aspherical lens element are flattened when compared to a normal (spherical) lens element.

2 Thirdly, you will frequently see the term chromatic aberration thrown around when talking about lens characteristics. Tokina s website does the best job of explaining this term in plain English, Chromatic aberration is the inherent tendency for glass to disperse (separate) a ray of light into the colors of the rainbow. The rainbow effect created by a glass prism is the most dramatic demonstration of chromatic aberration. In lenses, it is much less pronounced, but still creates slightly out of focus colors, akin to an optical noise that has a negative impact on the quality of the picture. Last but not least, most lens manufacturers will designate focal length and aperture (f-stop) information the same way. Somewhere on the lens you will find information similar to the following: mm 1: mm 1: mm 1:2.8 (These are not the only combinations you will see, but merely examples of possible combinations.) This information helps you identify the focal length and aperture (f-stop) limitations of the lens. The first part (18-55 mm, 135 mm, mm) identifies the focal length ranges attainable by the lens. The mm or the mm lets you know this is a zoom lens covering the range from 18 mm to 55 mm or 70 mm to 200 mm. When a single number is shown such as the 135 mm in the example above, it means the lens does not zoom but in fact has only a single or fixed focal length. Today the term Prime is often used to identify a fixed focal length lens. The second part (1: , 1:1.4, 1:2.8) identifies the aperture (f-stop) limitations of the lens (how much light can get into the lens). When you see something like 1: on a zoom lens, it lets you know when you are zoomed to the widest angle (shortest focal length) for the lens you can obtain a minimum f-stop number of 3.5 and if you are zoomed to the tightest shot (longest focal length) you will only be able to obtain a minimum f-stop of 5.6. This means the amount of available light decreases as you zoom in on your subject. Lenses which come with cameras as a package will often have this feature and are often referred to as Kit Lenses. On prime lenses or on some more expensive zoom lenses you at times find only one number listed such as 1:1.4 or 1:2.8. This lets you know the lens can be set to a minimum f-stop of 1.4 for the first example or 2.8 for the second example at any time regardless of the focal length currently being used. Prime lenses will always have only one number because the lens only has one focal length. Some zoom lenses are designed to work at lower f-stop numbers regardless of which focal length is selected. Lenses with the smaller single f-stop numbers are known as Fast Lenses because faster shutter speeds are attainable when using the smaller f-stop numbers. Fast lenses are usually higher end lenses and will quite a bit more expensive than kit or lower grade lenses. For more information on kit lenses, fast lenses, or prime lenses, check out the articles I have written in the past on these topics. They can be located in the archives of my blog at

3 Now that we have covered some global lens basics, it is time to dive into the manufacturer specific information. Canon Canon loves their terminology and abbreviations. They seem to have the most of the companies I researched. AF Stop Feature (AF-S)-This feature is present on many EF-IS telephoto lenses. When you are using a focusing mode that enables continuous focusing, you can press the AF-S button to momentarily stop focusing so an object passing between you and your desired focusing point will not reset the focus. It seems there are four buttons located around the barrel of the lens for easy access of the AF-S feature. Aspherical Elements (AL)-This has been discussed above. Canon uses the abbreviation AL to identify lenses with aspherical elements. Circular Aperture (CA)-The aperture diaphragm is constructed with curved blades. Canon claims the curved shape of the blades creates more natural looking affects in the out of focus areas of the image. The photographic term bokeh is used to describe the aesthetic quality of the out of focus area of an image. Canon s circular aperture is designed to create a more pleasing bokeh in images. Diffractive Optics (DO)-Special multi-layer elements created by bonding diffractive coatings to the surfaces of two or more lens elements. Those elements are then combined to create a single multi-layer element referred to as a DO element. Lenses with DO elements are smaller and lighter than comparable lenses which use more traditional lens element construction. Dust and Water Resistant Construction (DW-R)-Designates lenses (appears to be specific to L-Series lenses) which are specifically designed to be resistant to dust and water by the use of additional rubber seals and specially designed connections. EF Mount-A fully electronic lens mounting system developed by Canon. Canon claims this fully electronic mount system has none of the shock, operational noise, abrasion, play, lubrication requirements, slow response, lever operation limitations, or other design restrictions related to mechanical linkage mechanisms. EF-S Lenses-These lenses are for use with Canon cameras which have been designed with the smaller APS-C sized sensors such as those found on the 40D, 50D, and EOS Digital Rebel Series cameras. Floating System (Float)-Lenses featuring this system are designed so that the gap between lens elements changes as the focusing distance changes, hopefully reducing optical aberrations which may be found in lenses with utilize lens elements mounted with fixed gap distances. Flourite Elements (CaF2)-Used in high-end supertelephoto L-Series lenses. One fluorite element has the same corrective ability as two Ultra-low Dispersion elements. This allows for a more compact design in longer focal length lenses.

4 Focus Preset (FP)-With this feature you can program a set focusing distance in the memory of the camera. This preset distance will not interfere with normal focusing and photo taking. An example of a way to use FP is to set up an FP on the goal at a soccer game. Use the camera as normal during the game, but when the ball is kicked towards the goal, you can access the FP and instantly be on focus for the ball going through the goal. Full-Time Manual Focusing (FT-M)- Is it just me or shouldn t the abbreviation be F-TM to match the name. Lenses with this feature can be manually focused at any time without having to disable the autofocus on the lens. This allows the photographer to tweak or fine tune the focus on the fly. Inner and Rear Focusing (I/R)-Inner focusing lenses use lens element groups in front of the diaphragm to focus while a rear focusing lens uses lens element groups behind the diaphragm to focus. Both of these systems allow for faster focusing times on autofocus lenses and also allow for more compact lens construction. An added benefit is the front of the lens does not rotate while focusing, so the orientation of filters which have a specific top and bottom are not affected as the lens focuses. L-Series Lenses-These lenses are the flagship lenses of Canon. L-Series lenses are easily identified by the red band around the outer barrel. These will be the highest quality and most expensive lenses created by Canon. Optical Image Stabilizer (IS)-Also referred to as Image Stabilization. This technology allows you to shoot at much slower shutter speeds than possible without Image Stabilization. The technology in the lens corrects for shake or vibration which would normally result in a blurry image. Canon claims you can shoot in up to four stops less light (which equals eight times less light) than you could without Image Stabilization. Sub Wavelength Coating (SWC)-Found on wide-angle lenses, Canon claims this proprietary lens coating is supposed to reduce ghosting and flare better than other traditional coatings, especially lenses with large curvature lens elements. UD (Ultra-low Dispersion) Elements (UD or S-UD)-Lens elements specially designed to reduce color fringing or chromatic aberration. UD elements seem to be specific to L-Series lenses. Ultrasonic Motor (USM)-The autofocus mechanism is driven by a motor system built directly into the lens rather than by a motor built in the camera body. Canon claims their USM is much faster and quieter than conventional motor drive systems. The Canon website states they have two variations of their USM lenses. Some large aperture and supertelephoto lenses are Ring-type USM lenses which allow for manual focusing of the lens without the need to switch out of auto mode first. Many EF lenses incorporate a Micro USM design. Nikkor (Nikon) Nikkor is the lens division of Nikon. Nikon seems to like lots of abbreviations and terminology also (but still not as much as Canon).

5 AF DC-Nikkor lenses (DC)-DC lenses feature Nikon s exclusive Defocus-image Control technology. This allows the photographer to control the spherical aberration in the out-of-focus foreground and background areas. This is done by rotating the DC ring located on the lens. The resulting rounded out-offocus blur is specially designed for portrait photography. Nikon claims they have the only lenses in the world which offers such a feature. Aspherical Lens Elements (ASP)-Here is that term again, only Nikon uses ASP to designate lenses containing aspherical lens elements. Close-Range Correction System (CRC)-Nikon considers CRC as one of its most important focusing innovations. CRC is supposed to help achieve superior image quality at close focusing distances. It is also supposed to help improve focusing range. This is similar to the Floating System used by Canon in that the lens elements move independently of each other in a floating element design. Distance Information (D)-When D-type or G-type lenses are combined with compatible Nikon camera bodies, subject to distance information is relayed from the lens to the camera. This results in features such as 3D Matrix Metering and 3D Multi-Sensor Balanced Fill Flash. DX Nikkor (DX)-DX lenses are specially constructed for camera bodies utilizing the smaller DX sized sensors. These lenses are not recommended for Nikon camera with the full size or FX sensor as the image coming from the lens will not fill the entire FX sensor. Cameras currently using the FX sensor are the D3 series cameras and the D700. Extra-low Dispersion glass (ED)-Lenses with ED glass are supposed to be sharper and have better color correction by minimizing chromatic aberration. Nikon claims their ED glass is superior to Flourite glass used by other lens manufacturers because they say Flourite glass easily cracks and is sensitive to temperature change which will negatively affect focusing. Internal Focusing (IF)-Nikon states IF lenses are lighter, more compact, and faster focusing that conventional lenses. The internal optical movement also means the lens barrel length does not change as you focus. M/A Mode (M/A)-A feature found on Nikkor AF-S lenses which allows switching from auto to manual focusing with virtually no lag time (according to Nikon) regardless of the AF mode in use. Nikon claims this is a feature exclusive to Nikon. Nano Crystal Coat (N)-This is a special anti-reflective coating. Nikon claims this coating will virtually eliminate lens element reflections across a wide range of wavelengths and is particularly effective in reducing ghost and flare peculiar to ultra-wideangle lenses. It is gets its name from the fact it utilizes multiple layers of Nikon s extra-low refractive index coating which is made of nano sized particles. One nanometer is equal to one millionth of a millimeter. Rear Focusing (RF)-Although these lenses contain multiple lens element groups, only the rear group moves to adjust focus. Nikon claims this results in smoother and faster auto-focusing when compared to non-rf lenses.

6 Silent Wave Motor (SWM)-Found in Nikkor AF-S lenses, this silent wave motor design converts travelling waves into rotational energy which operates the focusing system within the lens. Nikon claims this results in lenses which focus smoother, more accurately, and more quietly. Super Integrated Coating (SIC)-This is Nikon s exclusive multilayer lens coating. Nikon claims it greatly reduces lens flare and ghosting. Nikon says the SIC is tailored to each specific lens element. Nikons says this results in lenses that meet much higher standards than the rest of the industry. Vibration Reduction (VR)-Nikon s equivalent to the Canon Image Stabilization. Nikon claims you can hand hold your camera while shooting in light three to four stops lower light (six to eight times lower light) than with non-vr lenses. Olympus Zuiko Digital is the name brand used for Olympus brand lenses. These lenses are specially designed for the Olympus E System cameras. ED- The Olympus website states ED refers to lens elements which are used extensively to correct the color blurring that can occur when telescopic lenses are extended to their maximum focal length, while the digital-dedicated design ensures high-definition performance with clear, crisp images from edge to edge. On the Zuiko Digital lens website you will find diagrams of the various lenses showing combinations of ED lens elements, Super ED lens elements, and ED Glass Aspherical Lens elements. Super High Grade (SHG)-The term used to designate the higher end Zuiko Digital lenses. Supersonic Wave Drive (SWD)-This identifies lenses with the advanced lens focusing drive system. Pentax In researching Pentax I was able to find detailed information on their various classes of lenses, but only limited information on the various characteristics of lenses and lens elements. Aspherical Lenses (AL)-This is the Pentax term and abbreviation for aspherical lens elements. DA Series Lenses (DA)-The Pentax website states The PENTAX DA series of lenses is designed specifically for PENTAX digital SLR cameras. DA lenses are matched with the digital sensor in a compact, efficient design, to offer the best combination of price and performance. D FA Series Lenses (D FA)-The Pentax website states The PENTAX D FA series, compatible with PENTAX 35mm film cameras, but built specifically for digital SLRs, utilizes lens coatings, curvature and positioning of optical elements to virtually eliminate flare and ghosting for clear, high-quality images with digital SLR cameras. DA Limited Series Lenses (DA Limited)-DA Limited lenses are Prime lenses. The Pentax website states The unique DA Limited series of prime lenses offers incredible sharpness and image quality made

7 specifically for PENTAX DSLR cameras. PENTAX DA Limited lenses are ideal for even the most discerning photographer who demands top performance in an ultra-compact package. The high-grade aluminum construction of the DA Limited series provides the utmost durability and elegant design. DA Star Series Lenses (DA*)-The Pentax website states The PENTAX DA* series of high grade lenses, designed exclusively for PENTAX digital SLR cameras, features the quiet SDM (see SDM below) focus system and tightly sealed, weather-resistant and dust-resistant construction to enhance durability for use in rainy or dusty conditions. Extra-Low Dispersion Glass (ED)-Lens elements designed to correct chromatic aberration. FA Series Lenses (FA)-The Pentax website states The PENTAX FA series is designed for film SLR cameras, but is also compatible with digital SLR cameras. The FA series features full-frame image coverage with full automatic and manual aperture control. FA J Series Lenses (FA J)-Pentax used to show a series of lenses designated as FA J lenses. These lenses were budget lenses made for 35mm sized sensors/film. These lenses have no aperture rings. These lenses no longer appear on the Pentax website. FA Star Series Lenses (FA*)-Top series lenses for Pentax film slr cameras. This series is no longer listed on the Pentax website. Internal Focus (IF)-No additional information was found for this abbreviation. Super Direct Drive Motor (SDM)-This is an ultrasonic autofocus drive system. No additional information was found for this abbreviation. Super Multi Coating (SMC)-No additional information was found for this abbreviation. Super Protect Coating (SP)-No additional information was found for this abbreviation. Weather Resistant (WR)-No additional information was found for this abbreviation. Sigma Sigma is a major player in the third party lens market. They manufacture lenses for all major camera brands. APO Lenses (APO)-Lenses specially designed to correct for chromatic aberration through the use of Special Low Dispersion glass (SLD) and Extraordinary Low Dispersion glass (ELD). Aspherical Lens (ASP)-This is Sigma s version of the aspherical lens. They state the use of aspherical glass allows for exceptional performance while maintaining a compact size. DC Lenses (DC)-This is Sigma s high performance lens series designed for use on cameras with the APS-C sensor.

8 DG Lenses (DG)-This is Sigma s high performance lens series designed for use on 35mm film cameras and digital cameras with full size sensors. Dual Focus System (DF)-The linkage between the inner focusing mechanisms and outer focusing ring are disengaged when the focusing ring is moved to the AF (auto focus) position. EX Lenses (EX)-Sigma describes these as The exterior of this lens is EX-finished to denote the superior build and optical quality, and to enhance its appearance. Floating System-Sigma also utilizes a floating element system to increase image quality and decrease lens length. This is similar to the Canon Floating System or the Nikkor (Nikon) CRC. Hyper-Sonic Motor (HSM)-This denotes lenses which contain a motor driven by ultrasonic waves which Sigma claims allows for faster and quieter focusing. Inner Focus (IF)-IF lenses change focus through movement of the inner lens groups allowing for focusing without changing the physical length of the lens. Optical Stabilizer (OS)-Sigma s version of Image Stabilization or Vibration Reduction. Sigma claims a photographer can pick up an additional 4 stops of hand holding ability with OS. Rear Focus (RF)-Focusing is achieved through the movement of the rear lens elements which Sigma claims allows for high speed, silent focusing. Teleconverter Compatible Lens (CONV)-Sigma states This lens can be used with the APO Teleconverter EX. It can increase the focal length and will interface with the camera's AE (automatic exposure) function. Sony The information below is based on the current Sony α (Alpha) lens system. Some Sony cameras can also accept some Dynax/Minolta/Konica Minolta lenses as well. Minolta was founded in 1923 in Japan. In 2003 Konica and Minolta merged to become Konica Minolta. In 2006 Konica Minolta decided to exit the camera/photographic market selling this division to Sony. It was after this acquisition of Konica Minolta that Sony seems to have stepped up their dslr offerings. Advanced Distance Integration Flash Metering (ADI)-Sony claims this flash system allows for more accurate flash exposures than conventional TTL flash systems. Aluminum Alloy Lens Barrel-Aluminum alloy is used in the construction of G Series and other high end lenses resulting in light, more durable lenses. Aspherical Lens-Sony was nice enough to not use any strange terminology or abbreviations for aspherical lenses. They just simply call them aspherical lens elements.

9 Circular Aperture-This seems to be a lot like Canon s Circular Aperture feature. The diaphragm in the aperture is specially constructed to result in a more natural and less blocky appearance in the out of focus areas of the image sometimes referred to as a nicer bokah. Distance Encoder-Sony says this is a lens component that directly detects the position of the focusing mechanism, and sends a signal to the CPU in order to measure distance to the subject. During flash photography, this data is very useful in calculating how much flash output is appropriate to the scene. The distance encoder plays an integral part in ADI flash metering, which delivers high-precision flash metering that is unaffected by the reflectance of subjects or backgrounds. Double Telephoto Zoom-I am going to let Sony explain this one. Through the use of a telephototype lens structure, the length of a fixed focal length lens can be made shorter than its actual focal length. A double telephoto zoom lens takes this principle of design one step further, by combining two such telephoto-type structures to produce a telephoto zoom lens that is extremely compact. DT Lenses-These lenses are designed for use specifically with Sony dslr cameras which utilize the APS-C size sensors. Extra low Dispersion Glass (ED)-Much like everyone else s ED glass, Sony claims It dramatically improves chromatic aberration at telephoto ranges, and provides superior contrast across the entire image, even at large aperture settings. Floating Mechanism-The spacing between the lens elements changes as the focusing distances change such as found in the Canon Floating System and the Nikkor (Nikon) CRC. Focus Hold Button (FHB)-Once the desired focus has been achieved, this button can be depressed while recomposing the shot to keep the focus from changing. This button can also be set as a depth of field preview button. Focus Range Limiter (FRL)- This function allows you to set the autofocus to work only within a specified distance range. G Series Lenses-These lenses are a step above the average Sony α lens. The G Series lenses are large aperture lenses allowing for use in lower light situations. (IE-These are Sony s fast lenses.) Internal Focusing (IF)-Only the center lens elements move so the lens barrel length does not change. Another plus is the lens front does not rotate so positional filters are not affected. Multi-layered Coating-Just like everyone else, Sony uses multi-layered coatings to reduce flare and ghosting in their lenses. Rear Focusing-Only the rear lens elements move allowing for quicker focusing and shorter minimum focusing distances. The lens front does not rotate so positional filters are not affected. Super Sonic Wave Motor (SSM)-This is Sony s version of the quick and quiet focusing motor system.

10 Super SteadyShot-Sony s version of image stabilization. What makes this version different is that Sony chose to incorporate the image stabilization into the camera body rather than into the lens. T* Coating (T-star)-According to Sony this is an exclusive coating found on ZA Series lenses which results in higher light transmission and minimal flare and ghosting. ZA Series Lenses-These are Sony s top of the line lenses developed in a joint relationship with Carl Zeiss. Sony touts these lenses as the cream of the crop. Tamron Tamron is another major player in the third party lens market. Tamron also makes lenses for use with all the major camera manufacturers. Tamron had some of the lengthiest and most detailed explanations I found. Anomalous Dispersion Glass (AD)-Tamron states this is a special type of optical glass which achieves even more precise control of chromatic aberration. There is a more technical explanation in the Tamron catalog. Auto-focus/Manual-focus Switching Mechanism (AF/MF)-A selector on the focus ring allows for quick and easy switching between auto-focus and manual-focus. Broad Band, Anti-Reflective Coating (BBAR)-Tamron s multi-layered coating designed to reduce flare and ghosting. DI Lenses-DI stands for Digitally Integrated. Lenses designed for use especially with digital cameras. These lenses are compatible with cameras featuring full size digital sensors. DI II Lenses-These are the lenses designed especially for use with digital cameras featuring the smaller APS-C sensor. You might want to check out a Tamron catalog for the full explanation they give for the DI II lenses. It is fairly lengthy. Extra Refractive Index Glass (XR)-Tamron claims XR glass bends light at steeper angles allowing for lighter, smaller lenses while maintaining superior lens quality. Again you might want to check out a Tamron catalog for their lengthy description. High Index, High Dispersion Glass (HID)-Lenses designed for better color correction while remaining compact and lightweight. Hybrid Aspherical Elements (ASL)-Tamron s version of aspherical glass. Tamron claims their Hybrid Aspherical Technology allows the use of a single element rather than multiple lens elements while maintaining image quality. Inner Focusing System (IF)-A focusing system which provides for a non-rotating lens front and a closer minimum focusing distance.

11 Low Dispersion Glass (LD)-Lenses designed for greater sharpness through the reduction of chromatic aberration. SP Series-SP stands for Super Performance. This is the more advanced or professional line of Tamron lenses. Vibration Compensation (VC)-This is the Tamron version of Image Stabilization/Vibration Reduction. Tamron claims their system gives a photographer a 4 stop advantage. Tamron claims their system is more advanced than any other system because their system can correct for shake in any direction, not just along a vertical or horizontal plane. Zoom Lock (ZL)-A feature I really like on Tamron lenses is the zoom lock. When you rotate your zoom ring to the smallest focal length, you can lock the barrel so it will not zoom out. It prevents the lens barrel from extending (creeping) while packing the camera around. Tokina Tokina has been around for a very long time, but for some reason it is not a lens brand I see much in the area where I live. Aspherical Optics (AS)-This is Tokina s version of aspherical lens elements. AT-X Series Lenses (AT-X)-This stands for Advanced Technology Extra. Tokina claims they use only the most current and advanced technology available in their lenses. AT-X Pro Series Lenses (AT-X Pro)-These lenses are fast lenses featuring single minimum f-stops of either 2.8 or 4. Focus Clutch Mechanism (FC)-This is a unique system found on AT-X Pro lenses for switching between auto and manual focus. The best way explain this feature is to let Tokina do it for me. Tokina AT-X PRO series lenses all feature the patented Focus Clutch Mechanism for switching the lens between auto focus and manual focus modes. The manual focusing ring can move (be snapped) back and forth between an AF and MF position. When the focusing ring is forward in the AF position, it is not engaged to any of the internal focus gearing and will turn freely. Without the added weight of the metal ring the camera can auto focus the lens more quickly and smoothly. For manual focus, simply rotate the focus ring all the way to one side or the other on the focus travel, either infinity or it s closest focusing distance, then pull back (towards the mount plate) on the manual focus ring. While pulling back, rotate the ring from one side of the focus travel to the other. When the gears align, the focus ring will snap back into the MF position and the lens can be focused manually. To return the manual focus ring to auto focus mode, simply snap the ring forward from any point.

12 Floating Element System (FE)-Tokina also offers lenses with floating lens elements to help correct for some optical aberrations. This appears to be similar to Canon s Float or Nikon s Close-Range Correction (CRC). F&R Aspherical (F&R)-This lenses claim to be fame appears to be the use of a large 50mm front aspherical element (Tokina claims it is one of the largest in use today) and a 20mm rear element. Tokina claims this results in even illumination even in the corners and correction of spherical aberration across the entire image. High-refraction, Low Dispersion Glass (HLD)-Higher quality optical glass found on Tokina s wide angle and standard zoom lenses. This glass has a higher refractive index and lower dispersion properties which Tokina claims helps prevent lateral chromatic aberration. Internal Focus System (IF)-Lens elements are moved within the lens housing so the lens neither changes length nor rotates. Internal Rear Focus System (IRF)-Similar to the Internal Focus System, but only the rear lens elements move. Multi-Coating (MC)-Tokina s approach to using a multi-coated surface to prevent surface reflections. Tokina claims Tokina has developed and perfected a unique coating technique for all of its optics so that they will maintain faithful color reproduction and render clean, sharp images. One Touch Focus Clutch Mechanism (One Touch FC)-Similar to the Focus Clutch Mechanism above only the lens can be switched back to manual focus from any position. You don t have to rotate the focus ring to either end to return to manual focus with the One Touch feature. Super Low Dispersion (SD)-Tokina s approach to combating chromatic aberrations in optical glass through the use of specially designed lens elements.