Do you know what a lens group actually does? Like, why is it necessary? There are tons of articles and videos out there about cameras and the introduction to them, but there isn’t a lot about lenses. Photographers probably don’t understand why specific lenses have a set number of aperture blades. Did you also know that more aperture blades don’t necessarily mean a better quality lens? And you probably won’t get better bokeh too? We asked experts at Canon, Sony, and Tamron to share their knowledge with us.
The Very Basics of a Lens
- Prime: A fixed focal length. It can’t zoom. The zoom on your phone is done digitally.
- Zoom: The opposite of a fixed focal length.
- Aperture: Also known as an F Stop. It controls the amount of light that hits the sensor. F stops also give photographers control over how much of the scene in front of you is in focus.
- Weather Sealing: How well it can resist the elements and dust.
- Groups: Glass elements within a lens assembled together to accomplish a function.
- Elements: The individual pieces of glass within a lens.
- Coatings: These go onto the glass elements.
- Bokeh: Colloquially, it refers to the quality of the out of focus area that a lens renders.
Groups and Elements
The lens of a camera is made up of different elements. Think of these elements as the pieces of glass in a pair of eyeglasses. They’re cut and shaped in various ways to accomplish different goals. When you put these elements together, they form a group. Think of that as stacking eyeglasses. Of course, stacking glasses is a pretty silly idea, but it needs to be done in the world of photography to accomplish specific functions. Groups are essential, but more groups don’t necessarily mean a lens is better.
All That Glass
“If you’re speaking about how the elements are arranged in lenses, lenses are typically described in their optical construction as a number of elements and number of groups,” explains Mark Weir, Senior Manager of Technology at Sony. “There’s nothing that says that individual elements need to be arranged in groups. But typically individual elements can be assembled in a group or can be operating together in a group to perform a certain function.” He continues to state that individual elements will be bonded together in a group to form an optical property that would not be possible with a single element. And it only gets more complicated from there based on the design–which we’re going to get to later on.
In fact, Drew MacCallum, Senior Technical Specialist over at Canon USA, says that this is overall a very complex discussion. “When a series of lens elements are combined they form a group,” states Drew. “We count that series of lenses as a group. Also, a single lens by itself can be considered a group.” The confusion doesn’t end there as he adds that there are several types of lens groups; Single, Double, Triplet, and Symmetrical.
“Each of these groups uses different shapes of lenses to construct a focal length. Various shaped glass (concave, convex) and different materials such as Fluorite and lens coatings like Canon’s Air Sphere Coating and Super Spectra Coating is used to direct rays of light in the most direct way as possible reducing aberration such as color or distortion. Engineers use complex computer systems to model various lens designs.”
Of course, this all is dependent on the design of the lens and what the lens is supposed to do in the first place. “Every lens design requires a different optical formula,” explains Pat Simonetti, Director of Operations over at Tamron USA. “Depending on what the lens needs to achieve (fast aperture, minimum object distance, focal length such as super tele, ultrawide, all-in-one, etc.), the designer will select the elements and layout required to meet the demands.” This means that a 50mm macro lens will have a different design than a 50mm f1.2. Pat continued to state that a lens designed with fewer elements and fewer groups means that less correction was needed to achieve the lens specifications for that particular lens.
More importantly, Drew says that element design is crucial. Typical spherical lens elements do not direct light rays and do not converge parallel rays of light at the same point. Think of it sort of like a magnifying glass and how it focuses light to a point in which it may burn something. So instead, aspherical lens elements were designed to do this. Element design also enhances sharpness. Drew states that these lenses need to be super precise when being created. Where Aspherical lenses take the cake though is with Sony.
In fact, Mark tells us that Sony takes a lot of pride in their technology with Extreme Aspherical elements. These lens elements were introduced with the G Master series of lenses. So what do these do? They’ve got a lot to do with the quality of the bokeh. To make them, Sony has to work with the flatness and surface precision of the element.
Further, Mark states that the light transmissivity of a lens is very important. In fact, this has to do with the forming of the elements themselves. “Complex optical formulas with lenses that have 20 or so elements are doing a very good job of ensuring that light transmission is high,” explains Mark. “The movement to wider and wider aperture lenses have very complex optical formulas.”
Typically speaking, more groups and more elements in a lens doesn’t necessarily mean that the lens is better. This is because of coatings, and you’d be shocked at how important they are. “Without coatings, due to refraction, the light amount transmitted through the lens is reduced by roughly 4% for each element that is not coated,” states Drew. “If you remove the coatings on all the elements/groups in the RF 50mm F1.2L USM, the light reduction would be reduced by half or more.” That’s astonishing, and it’s why Canon emphasizes coatings so much. But Canon isn’t alone in this. Tamron, and the rest of the industry all confirm just how essential lens coatings are.
Across the industry, camera and lens companies develop similar coatings that do more or less the same things. These coatings also help each lens establish its own unique look. Tamron’s coatings help not only control light but also reflections, color rendition, and even protect against debris.
Here’s what Pat says their coatings do:
A new revolutionary AX (Anti-reflection eXpand) Coating is accomplished through Tamron’s proprietary deposition technology that addresses the difficulty of applying uniformed coating using existing technology. Now the coating can be applied uniformly edge to edge, even if the convex surface has a strong curvature. As a result, the reflectance and color rendition at the peripheral part of the element is the same as the center. The new AX Coating, which is especially effective for wide-angle lenses that tend to let in harmful light from peripheral areas, effectively minimizes ghosting and provides outstanding uniform image clarity.
New Fluorine Coating for improved durability – The durability of the front element coating is greatly improved with the development of new Fluorine Coating. With the new fluorine compound that has excellent water- and oil-repellent properties, the lens surface is much easier to wipe clean and less vulnerable to damaging effects of dirt, dust, moisture, and fingerprints, and enabling your important lenses to be continually protected on a long-time basis.
Reduce flare and ghosting with eBAND and BBAR
Two highly developed lens coating technologies, eBAND (Extended Bandwidth & Angular-Dependency), which uses nanotechnology, and BBAR (Broad-Band Anti-Reflection) combine to increase light transmission and to reduce flare and ghosting to imperceptible levels. The lens delivers high contrast, sharp and clear images and significantly reduces ghosting and flare that might otherwise occur under backlight conditions, where portraits are often shot. The result provides the advanced levels of sharpness and contrast that today’s high resolution 50+ megapixel DSLRs require.
Get That Bokeh
The notion on the web is that a photographer can get better bokeh from a lens if there are more aperture blades. That’s one of the reasons why companies can charge more. I mean, just think about Sony’s G Master lenses and the 11 aperture blades they sport. The same applies to Panasonic’s Lumix Pro lenses. Obviously then, you’re going to get creamier bokeh if you have more aperture blades, right? Well actually, that’s not totally correct.
“They are not always in odd numbers,” states Drew. “The EF 24-105 F4 L IS USM is a 10 blade aperture while the same focal length EF 24-105 F3.5-5.6 IS STM is a 7 bladed aperture. The EF 24-70 F2.8L USM is a 9 bladed aperture, all of which use circular blades to give a circular bokeh in the background.” He continues to state that the number of aperture blades only really has to do with the starburst effect.
The only real visual that could be considered is with an aperture with even number of blades, you get an equal amount of “starburst” (8 blades, 8 points), with an odd number of blades, you get a 2x that number of points on the starburst (9 blades, 18 points). – Drew
Adding to this, Mark explained that different aperture blades are for different optical designs. He conveyed to us that optical designers typically aim to get as round of an aperture as possible. “It all depends on how you’re looking at the photograph and the rendering of the defocused elements,” Mark states. He added that the optical design could also just be purely stellar.
When we think about the dimensions of lenses, some options that come to mind are some of Sony’s latest lenses and just how small they are. What’s more, we’ve wondered why some lenses are so much bigger than others. For example, Sony’s 50mm f1.4 lens options for A mount grew massive over the years. The industry followed suit with longer and broader 50mm lenses than we’ve seen in the past. So we were curious as to why these lenses have become so much more substantial. “There are several factors that govern the size of the lens,” explains Mark. “One is the focal length. Focal length, together with flange distance tends to be a defining factor.” He continued stating that this is why rangefinder lenses are smaller than SLR lenses. Part of the reason why this occurs is due to the lens itself being moved further and further away from the imaging sensor. The closer a lens is, the smaller the lens can be. Optical designs also tend to change to ensure that light transmission is at its maximum.
If that previous statement and paragraph confused you, it can be explained as thus:
- Light enters a lens.
- To hit the sensor, it needs to go through layers of glass. Some of this glass has coatings.
- The light is focused into this tube that is a lens.
- The more glass this light has to hit, the weaker the light becomes.
- Consider the aperture of the lens and how it opens and closes to focus the light beam.
- Then the sensor soaks up the light.
A more straightforward way that I think of this is thinking of a hose. Imagine you’re above a pipe laying flat out at you and that you’ve got a hose. Your job is to ensure that the water from the hose goes through the pipe as evenly as possible. Think of the jet stream of water as light. The pipe is your lens. Now imagine hitting the opening of the pipe with water from the hose at an angle. That’s pretty difficult to get the light to transmit through the pipe then, right? So adjusting and aligning the hose in its relation to the pipe gets the water through the pipe evenly. Indeed, light transmission is a complicated part of physics that lens manufacturers have figured out while not necessarily making a larger lens.
This is the case with Sony’s 24mm f1.4 G Master lens option. It’s a relatively small lens, but the best part is that it’s very lightweight. This is because they kept the optical formula in such a way that it isn’t heavy. According to Mark, this is a challenge due to needing to keep aberrations and distortions in the lens to a minimum. Combine this with wanting to create lenses with a specific aperture, and you’ve got some difficulty.
“Aperture had a profound effect on lens design. The engineers need to control the light as it comes through the lens and they need to take extra steps to control them. Sometimes to do this, they’ll make the lens larger. What Sony has done with the 24mm lens is utilized our ability to shape lenses in a different way. Such as with super flat glass molding. This is a lot in our G Master lenses.” – Mark
Issues with Lens Design and Software
In general, look at many lenses over the years and you’ll see they have become bigger when compared to similar lenses of the same camera system. Specifically, this statement applies to prime lenses. And as Drew points out, zooms haven’t really increased in size. “Lenses have not necessarily become ‘bigger’ over the years, for example, the RF 24-105 F4L IS USM is smaller than the EF version,” explains Drew. “While the RF 50mm F1.2L USM is larger than its EF equivalent, the level of sharpness and detail has also increased. The goal in that design was to have a very high specification lens, meaning fast aperture, with low distortion, and low aberrations.” He continued to state that if you take the RF 35mm f1.8 Macro lens into consideration, it was able to have a faster aperture and a .5x Macro ability while remaining the same size as the EF 35mm F2 IS USM.”
“Mirrorless does not necessarily mean everything is smaller. You still have some physics to deal with, especially when dealing with a large full-frame sensor. If you take into account, the upcoming RF 15-35 F2.8L IS USM, and RF 24-70 F2.8L IS USM lenses, both of those are relatively the same size as their equivalent EF lenses and are the first F2.8 lenses for full-frame to have Image Stabilization- which generally makes lenses larger.”
Smartphones and Fixed Lens Cameras
If you were to look at what Apple, Samsung, Google, and others did with their phones and portrait mode, you’d wonder how they create bokeh. Well, it’s all done with software. With actual, dedicated camera lenses, it’s done organically. Typically, the more compact a lens is, the more software correction it needs for bokeh. Mark states that a lot of software correction is required when working with fixed lens cameras. It’s evident in the RAW files, but it’s also one of the ways camera manufacturers can put a super-telephoto lens on a point and shoot. “It’s less like in ILC cameras,” states Mark. He continued to explain that software correction is not really there with full-frame lenses.
Software is typically applied to handle distortion, fringing, etc. “There’s a lot of it in smartphones,” explains Mark.
To add to this, cameras with low pass filters sometimes add diffraction effects according to Drew. “Things like Digital Lens Optimizer that take corrections for lens aberrations into account, but also diffraction effect and changes made by the low pass filter.” This is one of the reasons why cameras without a low pass filter exhibit sharper results at the micro-level. But low pass filters help with things light high ISO noise suppression.
Overall, lenses are very complex optical devices that help photographers create images that weren’t possible before. Of course, this also doesn’t mean that the image quality delivered is what the photographer wants. Lots of photographers love opting for vintage lenses and adapting them to their cameras for a specific look. Many modern lenses these days deliver a very clean, and almost clinical look to them, but getting that balance is really important.