Photography Experiments: Aperture, Focal Length, and Sensor Size

Just a quick photography experiment to demonstrate the effects that aperture, focal length, and sensor size can have on depth of field (i.e., how much you can blur the background of a photo.)

It snowed here recently, so I took a photo of a branch with some snow on it, which came out decently enough, but it prompted me to think: what would this look like at different apertures – or even different sensor sizes? So I decided to perform a little photography experiment to find out, and these were the results.

snow on pine tree branch - f5.6First is the original photo – taken at f/5.6, at max zoom (200mm, equivalent to 400mm on a full-frame camera) using my Lumix G2 camera. Even on my smaller micro four-thirds sensor, you can see that the background is completely blurred out – even more so than I could’ve gotten with my f/1.7 lens!

The depth of field in this photo is very shallow – if you look closely at the bottom right of the photo, you can see the bottom part of the branch is slightly out of focus (because it was angled slightly towards me). This gives you an idea of how thin a “slice” of the scene was in focus.

snow on pine tree branch - f22Next, I changed the aperture to f/22, but kept everything else the same. As you can see above, the background is still blurred out, but not as much. It is still blurred somewhat because I was focusing on a branch just a few feet in front of me, while the background is easily another hundred feet beyond that.

Compared to the first photo, you can see that the bottom bit of the branch is in focus – meaning the depth of field was greater, and a thicker “slice” of the scene was in focus.

snow on pine tree branch - f5.9 (compact camera)Finally, for this last picture I switched to a different camera – a compact Canon PowerShot ELPH 320. The aperture here is f/5.9, nearly the same as my very first shot, but as you can see the background is hardly blurred at all! The depth of field here is very deep – a very large portion of the scene is in focus.

Unfortunately, the little compact camera I was using couldn’t zoom to the same focal length – so this photo is at the equivalent of 255mm, instead of 400mm, and that contributes to the greater depth of field as well.

However, the smaller sensor size also has a significant impact – because the sensor is so small, there’s less room for the light to be “smeared out” (as it were), and so less of the background can be blurred.

So, what did we learn from all this? All else being equal:

  • A larger aperture (a smaller f-number) provides less depth of field and allows for a more blurred background.
  • A longer focal length (zoomed in more) provides less depth of field and allows for a more blurred background.
  • A larger sensor allows for less depth of field, which allows for a more blurred background.

This is why compact & cell phone cameras – which usually don’t have large apertures, don’t have long focal lengths, and have small sensors – are at a serious disadvantage when it comes to getting shallow depth of field & that nice blurred-out background look.

Nothing here is terribly ground-breaking in itself, and all of this should be basic “photography 101” stuff, but I still think that actually performing photography experiments like this can be incredibly useful, in the same way that performing physics or chemistry experiments can be useful even if you already know the theory behind it.

As for myself, experiments like this help me develop an intuitive “feel” for how all the different settings and elements work together, so that I can just take the photos I want to take, without having to spend too much time thinking about which setting affects which aspect of the photo.

Perhaps this experiment will help you in the same way, or perhaps it will inspire you to perform your own photography experiments. Either way, I hope it’s been helpful, or at least enjoyable!

Same Picture, Different Lenses

More experiments with digital photography – this time, learning the differences that different lenses (and different focal lengths) produce!

It’s winter around here at the moment, and there’s not much to do outside. So I’ve been spending some time playing around with my new lenses, and learning what kind of effects they have.

And what better way to experiment than to take pictures of… my bookshelf?

my manga shelf 3

This first picture (above) was taken with my kit zoom lens, at its widest setting (14mm). It’s an OK shot, but because the lens I used here is so wide (and the bookshelf itself is so short), it isn’t terribly interesting.

manga shelf - sayonara, zetsubou sensei

This next picture (above) was taken with my 20mm (f/1.7) prime lens. I like this picture a lot more, because the longer focal length (narrower field of view) works better with the size of my shelf, and helps keep the books themselves as the focus (if you’ll pardon the pun) of the picture. Also, the nice shallow depth of field helps bring attention to just the set of books in the middle there, which I like as well.

my manga shelf 2

This picture (above) was again taken with my kit zoom lens, again at 14mm. This one is a little bit better than the first one, but it’s still not terribly interesting, because the books on the left are still too much in focus, even though they are not the ones I was pointing at. Still not bad, but not great either.

manga shelf - lucky star

This final one was taken with my 20mm prime lens. Unlike the first two pictures, I actually took this one from a slightly different position – I backed up a bit – to make up for the narrower field of view. So even though you can actually see a little bit more of the shelf, the books in the middle (my Lucky Star collection) are in sharp focus, but the rest of the books both to the left and right are out of focus. This keeps your attention squarely where I wanted it, and is exactly what I wanted to do.

By performing these experiments, I’ve really gotten an intuitive feel for what sort of results I’ll get with each lens, and with the different focal lengths (and, of course, f-stops). Sure, I knew intellectually what should happen, but until I see it in action, I don’t really get a feel for it – and I’m one of those sorts of people who learns best by seeing & doing.

There’s still more for me to learn about photography, but these experiments are a neat (and fun!) way to learn (and understand) techniques and give meaning to all the often confusing terminology used in the world of photography. I highly recommend trying some experiments of your own – you might be surprised at what you can learn!

(If you’re interested, you can see all the pictures I took (along with others in my office) here.)

Depth of Field Experiments – Parts 2 and 3

More experiments into understanding and controlling depth of field (or the lack thereof) – this time, with my new camera and new lenses!

You might remember my previous experiments with depth of field – well, with my new camera (and new lenses), I decided to re-run those experiments.

As a refresher, this is the result of my first experiment with trying to control depth of field:

depth of field experiment 2 (wine)

This was taken with my old Canon PowerShot S3 IS camera, with an aperture of f/3.5, an exposure of 1/8th of a second, and a focal length of 25.2mm (equivalent to 159mm in traditional 35mm terms).

In other words, to get this effect, I had to zoom in a bit and set the focus as close as I could to the front bottle of wine. Even so, the bottles in the back, although blurred, were still identifiable. My old camera (like most point & shoot or non-interchangeable lens cameras) was just not capable of creating very shallow depth of field (at least, outside of super-macro mode when focusing on something only an inch away from the lens).

When I got my new camera, one of the first things I did was re-run this experiment.

dof experiment - final result

This was the best I could do with the stock (kit) lens that came with my new camera. This was taken with my Panasonic Lumix DMC-G2 camera, using a 14-42mm (28-84mm in 35mm terms) f/3.5-5.6 zoom lens. The aperture was f/3.5 (as in my previous experiment) and the exposure was 1/13th of a second, with a focal length of 42mm (84mm equivalent).

As you can see, the results were pretty much the same as in my original experiment, with perhaps a little bit more background blur, due largely to the fact that my new camera has a larger sensor (and thus, as I’ve mentioned before, the same f-stop number actually means a slightly larger physical aperture).

More recently, however, I got a new, faster lens (that is, one with a larger aperture – meaning, a smaller maximum f-stop number). Specifically, I got a 20mm (40mm equiv.) f/1.7 lens.

Naturally, almost as soon as I got it, I tried re-running my experiment again. (I was in a bit of a hurry though, so I didn’t pull out all my wine bottles; instead I opted for just one.) This was the result:

depth-of-field experiment - take 3

The larger aperture (smaller f-number) of this new lens gives a very, very shallow depth of field, allowing me to completely blur out the background.

This picture was taken at the same place as all the others, but now the background (in particular, the orange & red wall hanging) is much, much more blurred out – almost to the point where you can’t make out what it is.

This last picture’s technical details are: 20mm (40mm equiv.), f/1.7, and 1/50th of a second exposure.

As you can see, with the much larger aperture, I was finally able to achieve that shallow depth of field I’d always wanted.

Even though this new lens has a fixed focal length (a.k.a. it’s a “prime” lens, meaning it can’t zoom at all), it is now my go-to lens, especially for indoors photos. That’s because, in addition to the nice shallow depth of field, the larger aperture also means it lets in more light, which lets me take photos in low light (e.g., indoors) at a faster shutter speed (and also, lower ISO setting) than my other lens or my old camera could.

In the end, all these experiments with depth of field and different lenses (and cameras!) have taught me a lot, and helped me get a “gut feeling” understanding of depth of field and focus and how they relate to one another. (Time will tell whether this actually leads to taking better photos.)

Depth of Field Experiments

Some experiments into understanding (and controlling) depth of field (or the lack thereof).

I’m a sucker for certain “classic” photography effects. You’ve probably already seen the results of my obsession with the silky-waterfall effect and my experiments with macro mode, but there was another effect I have been trying to master – getting the “out-of-focus background” effect by controlling the depth of field.

For those that aren’t familiar with the term, “depth of field” refers to the amount of a picture that’s in focus. As usual, Wikipedia has an excellent article on the topic if you’re after more detail. The trick with cameras is that depth of field is controlled largely by the aperture you’re using when you take a picture. A larger aperture (smaller f-number) gives a shallower depth of field, and a smaller aperture (larger f-number) gives a greater depth of field. (Confusing, I know.) The theoretical “perfect” pinhole camera has an infinite depth of field, meaning everything is in focus no matter how far away, but in reality there is no such thing as a “perfect” camera, so every picture-taking device – including your own eyes – has some sort of depth of field, even if it’s very large.

Anyway, although you’d think that with photos you always want everything to be in focus, the fact is that you can use blurring to sort of “focus” on one thing – blurring out the background, for example, is often used with portraits to keep the focus on the person.

Now, knowing the relationship between aperture and f-numbers should let me create this effect whenever I want – in theory. In practice, I’ve had some trouble getting it “right.” Oh, I got some nice blurring when I used macro mode – which basically gives my camera a very, very, very small (shallow) depth of field, but it also meant that I could only focus on things very, very, very close to the camera. Useful for closeups of flowers – not so useful for anything else.

So the other day I sat down and decided to try some experiments. To gauge the results, I needed something that stretched away from the camera for some distance, so I could gauge what was in focus and what was out of focus.

Taking a tip from some photography sites which used a similar example, I set up my dining room table with a bunch of bottles of wine from my wine rack. This is what it looked like to start with:

wine line up

This was taken in manual mode on my camera, but I got the settings by using “Program” mode and just depressing the shutter button half-way so the camera gave me it’s “recommended” exposure settings. They are (for the curious): Exposure of 1/8 second, and aperture of f/2.7 (the largest aperture my camera has).

At first, I was a little disappointed – after all, the background is out of focus, but not by very much. The effect I wanted wasn’t very pronounced, and I knew it had to be possible – but what was I doing wrong?

Somewhere along the way (probably in The Digital Photography Book by Scott Kelby) I had read about portrait photographers using a “short zoom lens” (85-100mm focal range) because it produced such nice results for portraits – which, as I said earlier, often utilize a shallow depth of field to produce a blurred background that helps draw attention to the person in the picture.

“Well hey,” (I said to myself), “I’ve got a zoom lens on my camera that I think can do at least some of that focal range.”  So I tried zooming in a little. The results? Have a look:

wine in focus

Well now – that’s much more like it! The bottles at the back are very much out of focus – more so than in the first picture. I might be onto something here!

Now, although the above picture turned out quite nice, I did make the mistake of letting the camera auto-focus for me – that’s why the “Fools Bay” botle is in focus instead of the first (closest) bottle. (My camera at the time was set to auto-focus on whatever was bracketed in the middle of the picture.) So, time to switch to manual focus!

depth of field experiment (wine)

Ahhh, much better.

Now, it’s worth noting a few things about these last 2 photos:

  • They were shot at f/3.5 – a smaller aperture than the original picture. Yet, there is (or appears to be, at least) more blur – this is counter-intuitive to what I thought I knew about aperture and depth of field.
  • According to the EXIF data in the photos, the focal length was 23.8mm – nowhere near the 85-100mm I mentioned reading about for portraits (although this may simply be because the bottles were closer to me – and my camera –  than a person would normally be when having their portrait taken).

Still, despite the somewhat counter-intuitive results, at least I know now what to do to produce this effect on-demand. (And now you do, too!)

So with all that, I lined up one last shot – the one I’m most proud of:

depth of field experiment 2 (wine)

That was just what I had in mind when I set up the bottles on my table – and being able to actually produce it on my own was very satisfying. It’s little successes like this that make photography such an interesting and fun hobby!

So, now I know the tips to getting that nice blurred background effect:

  • Set up your camera a bit further away from your subject
  • Zoom in a little bit
  • Use the largest aperture (smallest f-number) that you can at that level of zoom
  • Don’t forget to make sure you’ve got the focus where you want it (i.e., watch out for auto-focus)

Yay! Another successful photography experiment.

I expect to be adding some filters (ND-grad and circular polarizing) to my collection soon – so we may have some experiments using those tools soon as well. Stay tuned!