Since the rising of Canon 40mm f/2.8 STM, there are so many DSLR Canon camera users who get slightly confused to choose fix lens in small size and affordable price. For the size, Canon 40mm f/2.8 STM is the smallest lens of canon today. The length is just about 2.28 cm and its filter diameter is 52 mm. it is very thin which can save space and at a glance it looks like a camera without a lens. And for the 50mm f/1.8 one, the length is 4.1 cm. regarding the weight, these two lenses are the same. It is about 130 g.
The question is, with similar price and specification, which lens will be better for purchase and which one gets the better quality?
Let’s discuss it one by one:
1. They are both EF lenses
Both Canon 50mm f/1.8 and Canon 40mm f/2.8STM are EF lenses which means they can be used on body camera with APS-C sensor (for example, Canon EOS 7D, 60D, 650D, 600D and etc.). Apart from that, they are compatible for cameras with full frame sensor (like Canon EOS 5D MK III, 6D, 1D MK IV and etc.)
2. They both are the same weight
The weight of these two lenses is exactly the same. Both weigh 130 gram.
Both these two lenses are simple seen from the aspects of its specification and design. Both got no distance focus window. They do not have image stabilizer feature and both have small barrel focus.
1. Canon 50mm f/1.8 lens has a longer body which is around 41mm, while Canon 40mm f/2.8STM is shorter 22.8mm. Because of its shorter body, it will be more practical and easy to carry everywhere without taking much space.
2. The size of diaphragm is different. It is pretty obvious that Canon 50mm f/1.8 got wider aperture compared to Canon 40mm f/2.8STM. It means Canon 50mm lens can absorb more light using maximum aperture lens of 2.6 X extra to the camera. Apart from that, the bigger the aperture the thinner the Depth of Field (the background will be more blurred).
3. The Mounting of both lenses is different. Seen from the quality of their materials, Canon 40mm f/2.8STM has better plastic quality. Moreover, mounting lens of 40mm f/2.8STM is made of metal while 50mm f/1.8 one is made of plastic.
4. The aperture blade of both lenses is also not same. Canon 50mm f/1.8 got 5 blade apertures so it can produce pentagon shaped bokeh. For the Canon 40mm f/2.8STM, the number of aperture is seven which can make the bokeh shape of this lens become rounder. Which one is better? It depends on each photographer’s personal taste and preference. From the aspect of the optic quality and sharpness, both lenses are identical. They are both sharp especially on f/4 to f/8.
5. For you who record videos using DSLR, Canon 40mm f/2.8STM would be the better choice because it got faster focus and smoother than the 50mm f/1.8 lens.
6. From the aspect of price, canon 50mm f/1.8 ($125) is cheaper than Canon 40mm f/2.8STM ($199)
So, which one is better, Canon 50mm f/1.8 or Canon 40mm f/2.8STM?
Actually, both got their own strengths and weaknesses. The most obvious excellence of 50mm f/1.8 lens is on its diaphragm opening which is bigger so it will be better to use in a low-light condition or to get narrower DOF. From the aspect of price, 50mm f/1.8 is slightly cheaper so it will suit beginners who want a lens in affordable price with good optic quality. But from the aspect of quality, the material of this lens is still under the 40mm f/2.8STM one.
For DSLR videographer, Canon 40mm f/2.8STM can be a better choice because it has focus ability which is faster and smoother. Apart from that, the material quality is also much better especially the quality of lens mouthing which is made of metal. For the size, this lens is smaller and more practical to carry anywhere. However, this lens only has maximum diaphragm opening of f/2.8 so the ability to shoot of this low-light lens is defeated by the 50mm f/1.8 lens.
So, the presence of Canon 40mm f/2.8 is not to replace Canon 50mm f/1.8, but it is more about completing canon EOS lens collection. Though there are some similarities each lens got their own strengths and weaknesses.