Through the looking glass – my attempt at understanding lenses

The common eye sees only the outside of things, and judges by that, but the seeing eye pierces through and reads the heart and the soul, finding there capacities which the outside didn’t indicate or promise, and which the other kind couldn’t detect.

-Mark Twain

I have three ‘cheap’ lenses (in photography, cheap is relative).  I know, I know.  Anyone who knows anything about photography says,  “Spend the money on the lenses, not the body.”  However, I consider this an entry-level camera and it’s a HOBBY, not a profession.

My first lens was the kit lens (i.e., the lens that came with the camera). It is a EF-S 18-55mm f/3.5-5.6 IS.

Two out of three ain’t bad. My Canon EF-S kit and telephoto lenses

It’s a what-now?  It’s amazing how many different sites have different info on this.  I’ve checked several sources, and using the theory that the majority must be right, here’s what I found out. Please correct me if I’m wrong!

EF and EF-S refer to the mount on the body of the camera – that is, where the lens and the camera meet up.

EF stands for electro focus.  In other words, a fine motor within the lens controls the focus.

The S stands for small image circle or short back focus, depending who you believe.  All it really means is that the rear part of the lens is closer to the image sensor that on a regular 35 mm SLR camera.  Because it’s closer to the sensor, it means that it takes less glass to make, which therefore makes it less expensive.

I’ve read conflicting things about this, but it appears the consensus is that an EF lenses can be put on EF-S cameras without the world coming to a crashing end.  However, it is going to crop the image.

This brings us to crop frame and full sensor cameras – another topic for another day.  Suffice it to say that full sensor equals very expensive.  The Canon T3i is a crop frame camera.

An EF-S lens cannot go on an EF body. This means that if I every upgrade to a full sensor camera, I won’t be able to use my EF-S lenses on that body.  Should that day ever arrive, I’m pretty sure that I won’t want to be using the lowly EF-S lenses.  Why use crayons when you have oil paint?

On an EF-S lens, there is a white square and a red dot.  It’s important to use these dots and squares to line things up when mounting the lens to the body.  I’m embarrassed to admit that it took me a while to figure this out.  Reading the manual is for sissys.

I also have a Canon EF-S 55-250mm f/4.0-5.6 IS Telephoto Zoom Lens.  In Canada, I shopped around (on the internet, so does that count?) and the cheapest I could find it was on Amazon.  I just checked and it’s gone up $29 since August, but it’s still a decent price as the next best price I could find was north of $300.  It was ordered through Sun Electronics and arrived within a few days by courier. I have no affiliation with this company and don’t get anything from them to say nice things.

Now about those numbers.  If two numbers appear on the lens preceeding the ‘mm’, it can be zoomed in and out.  On the zoom lens, I can go as wide as 55 mm and as close as 250 mm.  I can also go anywhere in between.

Based on my scribbled notes from my class, I will attempt to explain what it really means because, to me, it isn’t totally clear.  Focal length (55 mm or 250 mm, or whatever) is the distance from the sensor to a predetermined spot on the lens.

This might not be the best analogy, but no one ever said coming up with original content for the internet would be easy.  If I’m looking out a window and I want to have a wide view, I need to be fairly close, say 18 cm (or about 6” for my imperial system friends). If I step away from the window so that I’m 55 cm away (about 2 feet), I now have a narrower view – I see less of the scene outside.  I’m the sensor, the window is the lens, and the distance between is the focal length.  This of course isn’t a perfect analogy because the lens magnifies what you are seeing to fill the sensor.  If I were 55 cm away, I’d see the walls and anything else in the room in my sightline.  The camera doesn’t.  It fills the sensor with the content found in the window, so even though you see less stuff, you see it in more detail.

This brings us to the f/stop numbers.  On the telephoto lens, Canon EF-S 55-250mm f/4.0-5.6, the widest my aperture will open is f/4.0 when I’m at a 55 mm focal length and f/5.6 when I’m at a 250mm focal length.  A low f/stop number equals a very open aperture which equals lots of light coming in.

My third lens is what they call a ‘nifty fifty.’  It’s a Canon EF 50mm f1.8 II Lens.  I bought it on sale from Future Shop for $107 (taxes included).  It’s now $119 plus tax, but they go on sale quite regularly.  It only has one focal length – 50 mm.  That means that I can’t zoom in or out. 50 mm is considered a ‘normal lens’.  That is, it approximates what the human eye sees.  The f/1.8 gives a really wide aperture.  What does this mean in real life?  I can use this lens to take pictures without a flash in lower light conditions.  It’s also known as a portrait lens and gives the nice blurry background.  A wide aperture lets you use a fast shutter speed (hence why they are called ‘fast’ lenses). I love this lens.  There are more expensive versions that have an f/1.4, but this one is working well for me.

Back to the lens, “IS” is for Image Stabilization” It minimizes camera shake, especially when zoomed in (longer focal length). It’s a good idea to turn it off when you are on a tripod because it tries to steady the image, and if it can’t, it doesn’t like it very much.

Next time, I will attempt to figure out some of the camera controls.


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