This article was first posted on my older photography blog. Since I am going to reuse the domain for something else, I will slowly move the most useful articles over here.
So you are at the store, you have the money in hand, you know what you want and even the spouse agreed that you need a new lens. Yet, you cannot make up your choice between the three lenses the guy has put on the counter. They all have the same aperture, same zoom range and about the same price. Which one should you pick?
Some times, the devil is in the details. In this article, we are going to look at all the small features that might swing your vote from one lens to the other.
Circular aperture means that when you are shooting at very small aperture (ex: f/22), the aperture remains circular instead of going hex/octa/decagonal. This is mostly visible on bright circular subjects like the sun or street lights when shooting at night. It is a very important feature for night and landscape photographers because it gives the light sources an unnatural shape.
Non rotating front element
This feature is only available on zoom lenses and it allows the front element to keep its orientation while zooming. This means that if you put a filter on your lens, it will stay in the same position no matter how much you zoom in or out. This is mandatory when using gradient filters so the dark part remains in the upper part of the frame.
Constant length / internal focusing
When zooming or focusing, the front element of some lenses moves back and forth. This might seem like a small thing but it can get down right annoying when you want to take macro shots and the bug fly away each time the front element gets too close. Also, as time passes by, the lens gets looser and the front element might start to slide in or out without you doing anything. Some people also see this as a way for dust to get inside the lens. Constant length lenses keep their size what ever is happening.
You camera might not be weather sealed but it is still reassuring to know that your lens has some protection when it is accidentally splashed or when you really want to take a shot and there is a small rain. There are two levels of weather sealing for Canon lenses. Click here for a full list of all Canon weather sealed lenses.
Big fat zoom / focus ring
No mater the size of your fingers, having big rings means that you can make small adjustments without your eye having to leave the view finder or fearing that your finger will hit the front lens element.
Focus distance switch
The goal of these switches is to constrain the minimal focusing distance to a certain range. This can be useful to prevent the lens from focusing on objects close by, but it is mostly useful to speed up focusing when shooting at objects in the longer range.
Tripod collar ring
I always thought that all lenses that could be mounted on a tripod came with a tripod so I was quite surprised when I saw that my macro lens (100mm f/2.8 Macro) could have a tripod ring but did not come with one. Of course Canon sees this as a way to sell me another over priced accessory, but thanks to Chinese copy cats, there are now cheap alternatives on eBay.
Now that my rant is over, I find it very convenient that my lens could be mounted directly on the tripod instead of having to mount the camera. First it allows a better weight balance then it makes it easier to move from landscape to portrait mode.
None of the features above should be seen as a deal breaker, but if you are torn between two equivalent lenses from two manufacturers, it is a good idea to look at these features and see which lens has the ones you might need.