Whenever I try to find information online about the difference, say, between 135mm and 85mm lens, the responses confuse the heck out of me, so much that it makes me feel dumber than I did before I started. I also can never really understand the aperture thing, or the thing that says f1.8 or f1.2.
Let me start off by saying, that anything with aperture 1.8 and above cannot be zoomed, so you have to either stand far or close to get the shot you want.
The difference between the lenses is this:
Canon EF 135mm f/2L USM Lens
You will need to be at a pretty big distance to your subject to get a portrait. So, if you need to shoot in cramped spaces, this is not the lens for you. However, if you are going to be quite far from your subject, this is the one to go. Think about it. When you’re taking the photo, do you want to be standing like 5 meters away from your subject? Of course, if you are trying to photograph people on stage or something, or doing sport, this is really nice.
The highest aperture for this lens if 2, which means you will get a pretty decent background blur.
Canon EF 85mm f/1.2L II USM Lens
This is the grand lens that all the professionals want to get their hands on, and I totally understand why!
The reason being, that with an aperture of 1.2, you can get a really amazing background blur. The higher the number (1.2 is the highest), the bigger the blur, the lower the number (like 4), you will see that the blur isn’t all that great.
85mm is when you can stand at like about a meter or two away from the subject and get a pretty decent shot of the person’s upper body. For a whole body shot, you probably want a lens that’s less than 85mm. This is great for newborn babies, as well as portrait from the waist up.
Difference between f/1.2 and 1.8: You can clearly see the quality difference if you take a photo with 1.8 vs the 1.2. The 1.2 has better lighting, the image looks simply astonishing.
Canon EF 35mm f/1.4L USM Lens
This one is great if you want to take a portrait of someone’s entire body, without stepping too far away. Remember that the smaller the mm is, the less distance you have to be for you to take the person’s photo, so you would be able to take a photo of my entire body if you were just two meters away, whereas for an 85mm, you’d need to step further than that.
Also, remember that this lens cannot zoom.
So hopefully this can somehow unravel a little mystery for exactly what difference are the lens. Of course, there are other lenses available which I didn’t really have time to test, but I wanted to write an easy to understand version where I’m comparing the few, without making it so confusing for people to understand. Hope this made it somewhat easier for you, because I know I never understood by reading the articles cos I felt they were aimed for professionals who really knew their terms.