Today I thought I would do a review of a common prime lens, the Canon EF 50mm f/1.8 mk ii.
I bought a Canon EF 50mm f/1.8 on amazon.com for $70. Full lens details can be found on canon's lens page, but I'll give you my thoughts on the lens after having used it for a while.
Why did I get this lens? Why I needed a lower f-stop? Well here's the thing, after going to the georgia aquarium, I was dissapointed that most of my shots were either too dark or the fish were too blury. Even with full control over camera settings, I couldn't get settings to match the low lighting of the aquarium. The only solution was to get a lens that would let in more light. That's where the low f-stop comes in.
The f-stop indicates the area of the opening in the lens that allows light through, [f-stop detalis can be found here]. By adjusting from a 3.5 (or even 5.6) f-stop to a 1.8 f-stop, that would allow 6.3 times more light into my camera letting me bump up the shutter speed and get the shots I wanted.
Due to lens optics, zoom lenses are less able to have low f-stops and it is most common to find low f-stops in prime lenses with fixed focal lengths. The 50mm f/1.8 is the cheapest lens in the sub-f/2 range. When you get to the f/1.4 and f/1.2 range, lens prices can get into the hundreds and even thousands of dollars.
The shots above show how the EF-S 18-55mm f/3.5-5.6 lens compares to the EF 50mm f/1.8. They both were shot in the same room with the same light. The ISO was the same and the focal length was the same. The difference in f-stop can be seen in the blur on the left. The shutter speed was so low that my body movements blurred the shot. The image on the right doesn't have that blur because the shutter was only open ~1/10th the time thereby eliminating any natural blur from me.
A lower f-stop has a shorter depth of field (DOF) than a higher f-stop. A smaller DOF means more blur in the foreground and background which can be a great way to isolate a subject in a shot. Because of the short DOF, the 50mm f/1.8 is a good lens for portrait shots; it helps isolate the person being shot and results in an overall soft effect.
Example of DOF at f/1.8
example portrait shot
So above you can see the advantages of a wide aperture. The 50mm f/1.8 does a great job for the price, but there are a few downsides to this entry-level prime lens.
This lens has a plastic body and a small filter size resulting in a very cheap feel when you hold it. The difference is quite noticeable when swapping lenses with a higher quality lens. There is also a little looseness in this lens and the lens rattles if you shake it any. My concern is that this lens ultimately won't have the lifespan of my other lenses. I will just have to throw it around a little less than my other lenses, guess I'll have to change my juggling act a little.
Cheap-feeling construction on a cheap lens isn't a huge problem for me, however, the lens' ability to focus, or, rather, lack of ability to focus is my problem. Perhaps I have just become spoiled by canon's USM technology, but this lens has trouble finding the subjects often having to hunt even in good light and it is slow. One of the benefits to a lower f-stop lens is supposed to be better low-light focusing, that isn't the case with this lens. Again, my expectations can only be so high when paying $70 for a lens.
This lens is a great addition to any kit, especially if you're on a budget. You can get more flexibility in low light as well as having a soft lens for portrait shots. You'll have to get used to moving around to correctly crop your shots, much easier with zoom.
Overall, this lens is a great purchase for the price, but know that if you buy this lens, and like it, it's only a matter of time before you upgrade to a more expensive lens.
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