Adapters vs Speed Boosters

When I first bought the Canon M50, I only had the kit lens. I went to Khulna University (my go to place for photography) and took some photos of my wife. This was the first time I was shooting with this camera so it took a moment for me to figure things out. The kit lens gave me decent photos but there were no bokeh or background separation the way I expected. 

Where was the promised bokeh? I used to take photos on smart phones. One of my primary reasons to switch to a digital camera was the promise of good background blurs.  I started researching what was wrong. Soon enough, I realized that I need better lens than the kit lens. 

It was clear to me that I needed a fast lens if I want to blur the background. But what lens should I buy? Back then, I wish I knew what to look for in a new lens, specially the factors I described in Lens Buying Guide blog post. But unfortunately I didn’t. 

Beyond EF-M

As my search for suitable lens went on, I came across the concepts of speed boosters and adapters. As I started to understand the different Canon Cameras and Lens Mount options, I realized that there weren’t as many lens options for Canon’s EF-M mount as there were for EF mounts. 

So I acted on the advice that a speed booster would be a good choice for Canon M50 to adapt those EF lenses. Most people glorified Speed boosters above normal lens adapters for various reasons. And I didn’t have a clear understanding of what was going on. 

It was after some period of time, I started understanding more about speed boosters, how they worked and what are their drawbacks. I also got to understand the Flange Distance and how it affected the adaptation of lenses. At some point it all made sense to me and I could clearly understand what was what. In this blog post, I would try to explain these two concepts from my understanding. This is going to be a post I wish I read when I was just starting. 

How to adapt lenses?

Lets start with adapters first because speed boosters are also adapters themselves. They just have some extra added on benefits and some compromises. But let is be clear – all speed boosters are adapters. 

Lenses attach to what we call a lens mount on a camera. Different camera systems use different types of camera mounts. Canon has 4 major different camera mounts themselves – EF, EF-S, EF-M, RF. You can read about these in details in our blog post – Canon Cameras and Lens Mounts. 

 Lenses can be mounted on their respective mounts natively – that is, you don’t need anything else. But there’s also ways in which we can use lens from one mount to another. For example, we can use Canon EF lenses on Canon’s EF-M mount or Sony’s FE mount with additional accessories. These are called adapters. Adapters let us use one type of lens on a different type of lens mount. 

When a lens sits on the lens mount, it needs to be placed in a required distance from the sensor. This is called the flange distance. Each lens mount has a defined flange distance and lens makers make sure that they construct the lens with that distance in mind. When you set a lens maintaining this flange distance from the sensor, the lens can properly focus from the nearest focus distance to infinity. But if you set it closer to the sensor or far away from the sensor, the focusing is affected. You can read more about this issue on our blog post on Flange Distance. 

Canon EF lenses need to be 40mm far away from the sensor. And EF-M lenses need to 18mm. So the lens mount on the Canon EOS M50 is situated approx 18mm from the sensor. If we put a EF lens just 18mm from the sensor on the M50, it would not work. Adapters play a role here. They sit on the EF-M mount and provide an EF mount at 22mm distance. So now we can mount the EF lens on this adapter which sits 40mm from the sensor and works as expected. 

This is basically how we adapt lenses. We take a lens that has a longer flange distance and create an adapter that makes up for that longer distance. For this reason, we can only adapt lenses with longer flange distance to systems with shorter flange distance. But we can’t do vice versa. The blog post on Flange Distance elaborates more on this. So please do check it out if you want to understand more. 

Full Frame vs Crop Sensor Lens

There are lens which are made for full frame sensors. For example the EF series. And then there are lenses made for crop sensor cameras like the EF-S series. As you can read more in the Crop Factor blog post – the lenses made for full frame sensors produce a larger Image Circle that covers a full frame sensor. On the other hand, crop sensor lenses have smaller image circle that only cover crop sensors. 

So what happens when we mount a full frame sensor compatible lens on a crop sensor? The image circle is bigger and it has light that falls outside the smaller sensor. We “waste” some light that a full frame sensor could have utilized. And we also get a “cropped” view. 

This is where speed boosters come into play. They shrink the image circle in a way that the entire image circle now falls on the smaller sensor. We no longer waste the light. And we also get a wider field of view. 

Speed boosting

A speed booster catches the otherwise wasted light from a full frame compatible lens and projects this onto a smaller sensor. This gets in relatively more light than before. When we discussed Fast Lens, we mentioned, a lens is faster if it gets more light. So if the same lens could somehow magically bring in more light, wouldn’t it be “faster” in that sense? 

Speed boosting is no magic. It just focuses the light that would have spilled outside the sensor on to the sensor and thus brings in more light. Making the same lens “faster” as we can now reliably increase the shutter speed and shoot faster. 

Since we’re making the same lens faster, this is called “speed boosting” and the special type of adapters which do this are called “speed boosters”. As you can see, speed boosters are special type of adapters which allow us to mount full frame compatible lens on a crop sensor while using the extra light, making the lens faster to shoot with. 

Speed boosters project a larger image circle on a smaller sensor. This is why they only work with lenses designed for full frame sensors. We can speed boost EF lenses but we can’t speed boost EF-S lenses. 

Speed boosters gain us more light, larger field of view but they use a glass element to do this. Since light has to pass through additional glass, the image quality can be affected slightly. That’s one of the downsides. You may notice some chromatic aberrations and vignetting while using a speed booster. Auto focus is also slightly slower on a speed booster. 

Adapters vs Speed Boosters

Simple adapters can adapt both full frame and crop sensor compatible lenses. This means you can use both EF and EF-S lenses using an adapter. But it will have the crop factor. There are no glass elements in between, so there are no significant compromises in image quality. Auto focus works quite fast too.  

Speed boosters can make the lens fast, get a larger field of view but the glass element can affect image quality. And a speed booster can not mount a lens built for a crop sensor. They can only mount EF lenses. Auto focus works a bit slower. 

I have both speed boosters and adapters. I like to use speed boosters with EF lenses when I want a larger field of view and more light. I use the adapters to mount some of the wonderful crop sensor lenses like Canon EF-S 55-250mm lens which is kind of my favorite lately. 

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