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?
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.
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.
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.
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!
As a refresher, this is the result of my first experiment with trying to control depth of field:
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.
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:
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.)
This is one of the new Micro Four-Thirds System cameras – also known as “mirrorless interchangeable lens system” cameras, or sometimes “EVIL (electronic viewfinder interchangeable lens)” cameras. (And isn’t that an awesome acronym for a camera system?)
This camera has many of the same features I loved about my old Canon PowerShot S3 IS:
Electronic viewfinder that shows a full view of what the sensor sees
Good zoom range (based on what lens you use, of course)
Decent lens speed (again, based on what lens you use)
Almost the same size & weight (without the lens)
And while it misses out on a few other features I really like (side-mounted memory card slot, standard AA batteries), I think I’m willing to give up on those for the ability to switch lenses and get more depth-of-field and better low-light performance. (The battery thing in particular is something I realized I’m just never going to see – so few cameras these days still use standard AA batteries anymore; and especially not any sort of DSLR or interchangeable lens camera.)
On top of all that, this camera is not too terribly expensive – which is something that always bothered me, since there really was a big gap in price between super-zoom cameras (which is what my old PowerShot S3 IS was categorized as) and any sort of entry-level DSLR or EVIL camera. For example, B&H Photo (which is an awesome store, BTW) has this camera (just the body only, no lens) for just $299 at the moment – and that’s not bad!
On the other hand, lenses for micro-four-thirds cameras are still a bit rare and a bit more expensive than their DSLR equivalents, but hopefully that will change with time. (And if not, well, there’s always adapters!)
So, I think I’m going to upgrade to this camera, because I feel like I’ve gotten to the point where I can’t get any more out of my old camera in terms of creative options. It’ll be interesting to see how I get along with having to switch lenses – something I’ve (obviously) never had to do before. It’ll also be fun to have a camera with a bigger sensor, and thus a larger possible depth of field.
Needless to say, I’m pretty excited! I’ll be sure to post some photos once I get the camera, and maybe even re-do some of my experiments with depth of field for comparison. Should be fun!
But recently I realized something that, in retrospect, I should have known all along – that not all f-stops are created equal. Or, to put it another way, f/2.8 on my camera might not be the same as f/2.8 on your camera.
The key fact was that the f-stop is not an absolute size – it’s a ratio.
This realization came about as I was trying to learn to do some creative depth of field related stuff with my Canon PowerShot S3 IS (as a follow-up to my previous experiments with depth of field) and I just couldn’t quite get that nice shallow depth of field I wanted. Then I was reading a new photography book I picked up recently called Understanding Exposure and I suddenly realized what I had been missing.
The basic principle is this – with point & shoot cameras (or any camera with a small sensor), the image being focused by the lens is being projected onto a very small square. In order to get the light to focus on this small square, your aperture (the size of the opening in the lens, which is what the f-number represents) has to be pretty small, otherwise the whole thing would be out of focus.
Throw in some other limitations (like the smaller size of lenses overall in point & shoot cameras, and the smaller distances between the lens elements and the image sensor) and basically in these sorts of cameras you are always going to have a physically small aperture – even if the f-number suggests otherwise. This is because the f-number is the ratio between the physical size of the lens opening and the focal length of the lens itself.
Because of this ratio nonsense, it means that you can have two cameras set to the same f-stop even though they have radically different physical sizes. The only thing that matters is the relative ratio between the lens opening and the focal length. Size is irrelevant.
However, size most definitely IS relevant when it comes to determining depth of field (or more technically, determining the circle of confusion). Because of their overall smaller sizes, point & shoot cameras come closer to being theoretically perfect pinhole cameras (which have theoretically infinite depth of field – or put another way, they have no blur because they focus everything perfectly). Larger cameras with larger sensors (and having both of these things is very important) can generate a smaller depth of field, which is why photos from such cameras (e.g., DSLRs) can achieve that amazing background blur that is often used to make interesting photos.
To put this in concrete terms, when my camera is set to f/2.8, it is focusing the image on a very small sensor (see the picture comparison of a point & shoot sized sensor to a DSLR sized sensor on the right). So even though the ratio of my camera’s aperture gives us f/2.8, the actual light rays coming in are focused very sharply in that very small space.
Conversely, with a DSLR using a lens set to f/2.8, the image is focused on a much larger sensor. Because of the larger size of the lens and the sensor, the light rays can be “blurred” out a bit more – the circle of confusion is bigger – and thus you get that nice shallow depth of field effect.
It’s this critical fact which explains why it’s so hard to achieve this shallow depth of field effect on smaller sensor cameras (like point & shoot cameras – and that includes both compact cameras and even the physically larger “super-zoom” cameras like mine).
The next time you have your camera out, turn it around and look into the lens and see if you can see the aperture – the actual opening. If you can fiddle with the aperture controls while you’re looking you can see it move, if that helps you identify it. If you have any sort of point & shoot camera, you’ll see that it is actually very, very small – even if you’ve set it to a “large” aperture (small f-number).
Of course, the other side of this coin is that point & shoot cameras have an amazingly deep depth of field – one that most DSLRs can only dream of. Still, in my experience at least it’s better to err on the shallower side, at least for the types of photos I like to take.
People who are more knowledgeable about photography might be saying “well, duh” at this point – but it really took me a long time before I understood all of this, and I have to imagine that there are lots of other casual, amateur photographers like me out there who maybe have been wondering the same thing. But now, hopefully, we all have a better understanding of how lens & sensor size affect depth of field, even though the f-stop number itself is the same.