At the time of writing this post, I am using my first camera, the Canon EOS M50. So this post is going to explain certain decisions in respect to this camera. But in general, if you understand the concepts and why I made a choice, you should be able to apply that reasoning to your current camera and make your own choice.
In this blog post, I am going to discuss some key factors we should be aware of while making a lens purchase decision. I am going to elaborate on each choice I make. But at the same time, if you’re on a hurry, you can take a look at the “quick recommendation” I make at the end of each section.
Lens Mount
The lens mount is where we place our lens. Each camera manufacturer has one or more lens mount designs. As a result, different cameras have different mounts. To buy a lens for a particular camera, we need to know what lens mount that camera uses and buy a lens that supports that mount.
Canon has four popular lens mounts. You can read about them in our post about Canon Cameras and Lens Mounts. Canon M50 and other Canon M series cameras – they all use the EF-M mount. So any lens that has an EF-M mount would work natively on the Canon M50. You can find EF-M mount supported lens from both Canon and third party lens makers.
Canon has some official lenses for the EF-M mount. But to be honest their collection is not amazing. However, there are third-party vendors who have some excellent lenses for EF-M mount. Tamron and Sigma are two such lens makers. I also recently started using a lens from 7artisans, a Chinese company that makes really affordable professional-grade lenses for crop sensor cameras.
Adapting Lenses
As we can see the lens choices for EF-M mount is kind of limited. But canon has a good amount of lenses for it’s EF and EF-S mounts which we can adapt to our M50 using different adapters. This is true for other camera systems too. The camera you’re using might also have different adapters to let you use lenses made for another mount. So look out for those if the natively supported lens collection for your camera is not great.
For the time being, remember, your Canon M50 or any M series camera natively supports EF-M lenses and it can also use any EF and EF-S mount lenses with the help of adapters. But RF mount lenses can not be used directly or with an adapter anyway till now.
If you’re using a different camera model, do a quick search on what lenses can be adapted to your system. Interestingly, Canon’s EF series has a very large Flange Distance making the EF lenses very adaptable to a lot of camera systems. Chances are there’s an adapter to mount Canon EF lenses on your camera too.
Adapters and Speed Boosters
If we want to use EF or EF-S lenses on a Canon M series camera, we need some sort of adapters. There are two kinds of common adapters available – Adapters & Speed boosters. Lets start with the second one first – The blog post on Crop Factor explains how the Canon M50 has a cropped / smaller field of view and can gather only a part of the light transmitted by the lens.
A speed booster tries to fit the full image circle generated by a lens onto a smaller sensor. Thus getting almost a full frame equivalent field of view and more light in the process. But this light goes through additional pieces of glass so the image quality can very slightly degrade. Although you may not notice the degradation until your pixel peeping.
Don’t worry if you don’t understand the technicality behind speed boosters right away. Just remember – they help reduce the effect of crop factor and as a side effect, it can bring in more light. This also means you can have the same effect of a wider aperture – your camera would let you choose faster shutter speed and smaller f-stop numbers for the same lens.
For example, The Canon EF 50mm F/1.8 lens gives me up to F/1.2 when mounted on a Viltrox Speed booster. Amazing, isn’t it? Speed boosters are more expensive and doesn’t support EF-S lenses. It’s because speed boosting is only possible for full frame lenses when adapted to a crop sensor camera. If the image circle is not bigger than the sensor, there’s simply no extra light available to “boost” the shooting speed.
The other type is just normal adapters. They don’t have any optical or glass elements. They just put the lens in the required flange distance by adding some empty space. As a result, they can’t manipulate the image circle anyway and have the crop factor on the field of view. But no additional glass means you get a very slightly better image quality. Normal adapters are usually cheaper. Adapters usually support both EF and EF-S mounts.
Common Adapters
Speed boosters: I have personally used the Viltrox Speedbooster and loved it. There are some other speed boosters available in the market too.
Remember, if you’re using speed boosters, your lens choices are limited just to EF lenses. You can’t use EF-S lenses on a speed booster.
Adapters: Canon has their own adapter for adapting EF and EF-S lenses to EF-M mount cameras. Viltrox also has a normal (non speed booster) adapter. There are some third party vendors too – Andoer, Comlite etc. I would recommend the official Canon one or Viltrox one as they are more popular.
One thing to notice here – some very cheap adapters would come without the connectivity pins. It would be better to avoid them. Because there will be no electronic connection between the camera and the lens. This would mean there would be no auto focusn and no exif data. Some lens which have stepping motors (STM) might not work without the connectivity either. It’s always safer to buy adapters that have these pins and retains the electronic connection unless, of course, you know for sure what you’re doing.
Future Upgrade & Long Term Compatibility
If you have plans to upgrade your camera body and reuse your existing lenses, it might be a good idea to keep compatibility / adaptability in mind. For example, if I want to upgrade from my Canon EOS M50 to Canon EOS R5, I should consider buy EF and EF-S lenses more as they will be supported on R5 with an adapter.
Quick Recommendation
Buy lenses that work natively with your lens mount. Look out for adapters that allow you to use other lenses too.
For Canon M50, try to prioritize EF-M mount lenses. Buy EF / EF-S mount lenses if you have a compatible adapter. Do not buy RF or any other mounts. Adapters support both EF and EF-S. Speedboosters only support EF lenses.
However, If you would some day like to upgrade to a different camera and use the same lenses, keep compatibility in mind.
Manual Focus vs Auto Focus
Auto focus is a huge time saver and an extremely useful feature. It’s usually better to buy lenses which have autofocus support. And the faster the autofocus is, the better it is. I would not buy a manual focus lens unless there’s a very specific feature that offsets the need of auto focus.
When you’re recording a video, autofocus would be immensely beneficial. I would even go and say that without autofocus, it would be extremely difficult to shoot a good footage. Pulling focus manually is a difficult chore, even so when your subject and you – both are moving. And not just in video, when shooting fast paced scenes, like a bird in flight or an action event like motor sports, you really need to keep your focus on your subject while you press and hold the shutter to take shots after shots in burst mode. Manual focus would be a terrible choice in such scenarios.
But with all these praises to auto focus, manual focus has it’s own use cases too. Auto focus is machine driven – the camera uses some techniques to lock on focus. One such technique is to depend on contrast of the scene to determine focus. In low light and or low contrast scenes, auto focus will struggle a lot. You would often see the lens repeatedly hunting focus and failing to lock on – this where you want to switch to manual focus to nail it.
Some lenses would let you further tune your focus by moving the focus ring slightly. This is also very handy and one of the things to look out for. Once you have autofocus locked on, you can further move the ring to nail critical focus. Learning to use the focus magnification tool would save you from a lot of focus related issues in the long run.
Quick Recommendation
Buy lens with autofocus support.
Focal Length
The next thing we would need to think about is the focal length. You can safely assume focal length is equivalent to how long you can zoom into. Focal length is measured in millimeter and the longer the focal length is, the longer you can zoom.
Anything below 35mm is considered wide angle. These are good for landscape, architecture, interior, group photos. In general, when you want to cover a very wide area without stepping back with your camera, you would want a wide angle lens.
50-60mm is usually considered standard lenses. They produce a field of view which more or less match with our human eyes. These lenses are good for nature shots, taking portraits or day to day general photography. 50mm has so far been my go to focal length for taking portrait shots.
70-200mm range is considered the telephoto range. You can zoom quite a bit into your subject. The 80-90mm range is often used in taking portrait shots. The higher range is useful in sports, product and wildlife photography.
Anything above 300mm is considered super telephoto lenses. If you want to take a photo of the moon, or a bird so far away, you want a lens with long focal length. These lenses are very useful when you can’t get close to the subject for various reasons. May be you’re sitting in a stadium and want to shoot a football game? You need a super telephoto lens.
Depending on what you want to photograph and how close you can get, you should buy lenses of certain focal length. Each focal length affects the field of view – how much of the scenery you can fit into your photo.
Also lenses with long focal lengths need high quality optics for sharp photos. You may see some quality issues on cheaper telephoto lenses on longer focal lengths. Checkout some shots at different focal lengths. That should help you decide what lens and what focal length you want.
Remember, there’s no set rules to use a certain focal length for certain type of photography. While it’s unusual, you can take a portrait shot with a wide angle lens if you want to bring in the surrounding areas into the frame. Similarly, you can also shoot street photos with a 80mm. Don’t hesitate to experiment and bring out your inner creativity.
Since the Canon M50 is a crop sensor camera, the equivalent focal length on a full frame would be 1.6 times the focal length on the lens. A 50mm lens would become a 80mm (unless speed boosted or manipulated by anyway) on the M50. So unless you’re using a speed booster, multiply the focal length of a lens by 1.6 to assume the field of view on your Canon M50. You can better understand this phenomenon in this blog post – Crop Factor.
Prime Lens vs Zoom Lens
There are lenses which can have a variable focal length. For example, the kit lens that comes with Canon M50 has a focal length of 15-45mm. You can rotate the ring on the lens to change its focal length. A lens that has an adjustable variable focal length is a zoom lens. Zoom lenses need more optical elements and are usually heavier. Cheaper zoom lenses have narrow aperture and zoom lenses with wider aperture usually costs more.
Contrary to zoom lenses, a prime lens has one fixed focal length. You can not change it. A prime lens needs less glass elements, usually lighter and can have wider aperture. Prime lenses can also have better image quality compared to equivalent zoom lenses. Having a wider aperture means you can usually have more light and background blur on prime lenses.
Zoom lenses offer more versatility. For example, with a 18-200mm lens, you can cover many use cases with just one lens. There are of course expensive zoom lenses which offer both variable focal length and wide apertures. But they are heavy and expensive.
In my case, I use the Kit lens for taking wide angle photos. I have a Canon EF 50mm f/1.8 prime lens on a Viltrox speedbooster for taking portraits and stuff. I also use the 7artisans 35mm f/0.95 for similar use cases (as the crop factor makes them similar focal lenghts). For taking photos of birds, I prefer the EF-S 55-250mm F/4-5.6 IS STM lens. I also have a EF 70-300mm F/4-5.6 which I am not very fond of because of image quality.
Quick Recommendation
Buy zoom lens for versatility, prime lens for quality. Choose a focal length based on what you want to shoot.
Aperture
The f-number denotes how wide the aperture is. It’s calculated with respect to the focal length, that’s why see numbers like – “f/2” meaning the diameter of the entrance pupil of the lens is half of the focal length. On a lens with 50mm focal length, f/2 would mean the diameter of the pupil is 25mm across.
Since the focal length at a given time is fixed, the smaller the f number, the wider the aperture can open. On a 50mm focal length, 50/2 is actually smaller than 50/1.4. This is why the smaller the f number (f/1.4 > f/2), the wider the aperture is.
While choosing a lens, you should try to get a lower f number aka wider aperture. Wide open aperture would let in more light. So in low light situations, the wider aperture will be beneficial. It would also let you use fast shutter speed, so you can freeze objects in motion without making the scene darker.
This is why wide aperture lenses are often called “fast lenses“. The wider the aperture, the more light it gets in, the faster the shutter speed can be, thus the faster the lens is. An wider aperture also blurs the background more and causes the depth of field to be shallow / narrow.
So if you would like blurry backgrounds or subject separation from background, it would be better to get lenses with lower f-number. f/1.4 is a better choice than f/1.8.
But also remember, as the focal length grows, getting the f-number lower means your entrance pupil needs to have bigger diameter. This is why we see those tanky telephoto lens because on a 400mm, f/2.8 needs the lens to be really fat and heavy. And that also means it’s going to be more expensive. On the other hand, something like f/4 or f/5.6 would be of more reasonable size.
For this same mathematical reason, you would see that some zoom lenses (variable focal length) also has a variable maximum aperture. It can have f/4 when you’re on a shorter focal length but when your focal length grows, the same entrance pupil is now actually f/5.6.
Quick Recommendation
Lower f-numbers are better. f/2.8 or better (lower number, ie: f/1.4) should give you nice background blur and better low light performance. It would also help with faster shutter speed.
Image Stabilization
Lenses with image stabilization helps in many cases. If you’re using a slow shutter speed (may be in low light?) or have a shaky hands or for some other reasons, if there are chances of small vibrations, a lens with image stabilization helps.
One very common scenario I faced – when I was taking photos from distance on a telephoto lens, when I pressed the shutter, it used to have a micro shake / vibration but it was way more amplified because I was on a telephoto lens making my photo blurry. Image stabilization helps a lot in such cases.
Quick Recommendation
Prefer IS, specially in long focal lenghts.
Motor Type
In the Canon eco system they have the very popular STM and USM motors. But other lens makers can use different technology and terms. Check out what STM and USM does and find equivalent technology for your preferred lenses.
STM (stepping motor) types are usually very quiet and silent with very fast auto focus. USMs are even better. They are usually quieter, faster and very good for professional videography.
You would want STM or even better, USM lenses if you record videos and wouldn’t want the noise of a lens motor hunting for focus and the mic picking it up along with your own voice. But for photography it wouldn’t matter much unless you need to be quiet for a specific reason or you really want very fast auto focus for your line of work.
Quick Recommendation
For Canon lenses, Prefer STM and USM. USM is better than STM. For other lens makers, find lenses with fast auto focus and silent motors.
Understanding Lens Specifications
When you want to buy a lens, you would often encounter descriptions / specifications like this – EF-S 55-250mm F/4-5.6 IS STM – what does it mean? First, the lens mount type: EF-S.
Then we have the focal length range, 55-250mm which means it’s a zoom lens and judging by that focal length it falls largely in the telephoto category. The f-number tells us that it can open as wide from f/4 to f/5.6 based on focal length.
On shorter focal lengths, it can have f/4 and on longer ones, it can open up to f/5.6. Yes, sometimes, lens have variable maximum aperture based on the focal length as explained in the Aperture section above. The IS part means it has image stabilization. And STM means it has STM type motor.