digital camera

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.

First 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.

Next, 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.

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!

New Year, New Camera

Keith gets a new camera, and proceeds to totally geek out over it, as expected.

OK, so it’s not quite the new year yet… but it’s close enough. I finally decided to pick up that camera I’d been looking at – a Panasonic Lumix DMC-G2 – and it arrived yesterday. So even before the battery is finished charging, I’d already started taking comparison pictures. (Why yes, I am a huge geek, why do you ask?)

As you can see, the new Lumix DMC-G2 is almost exactly the same size (and weight) as my venerable old PowerShot S3 IS. This is great for me because I don’t need to buy a new camera bag or anything – it fits just fine in the bag I already have. Also, I don’t have to worry about straining my neck while carrying this thing, since it’s almost exactly the same weight as well. A big fancy camera is nice and all, until you have to lug it around all day on your neck.

Like my old Canon, the Lumix has an electronic viewfinder built-in along with a swivel screen, both of which are features I really like. The Lumix does have a few more buttons on it, but it’s not really that many more.

Here’s a front view of the two cameras side-by-side – old vs. new. I keep the extension tube on the Canon all the time, which is why it looks almost the same size. If it wasn’t attached, the Canon would be much shorter – although when the camera is on, the zoom lens does extend a bit.

I opted to buy the “kit” lens to start with – it’s a 14mm-42mm f3.5-5.6 lens (with the 2x crop factor in Micro Four Thirds cameras, this means it’s equivalent to a 28mm-84mm lens on a more traditional SLR camera).

Some people look down at kit lenses, and I can understand why. Since the kit lens is often the first lens you own, you want to use it for everything (it’s often the ONLY lens you own, at least at first), so it needs to be reasonably good at many things… which of course tends to mean that it’s not particularly great at any one thing.

However, I wouldn’t knock this lens – I may not have much experience with interchangeable lenses, but this one seems quite solid, it’s not too heavy, and (so far anyway) the pictures it produces are quite nice and free of noticeable aberrations.

Eventually I’ll want to pick up a so-called “pancake” lens (a fast one – that is, one with a very low maximum f-stop number, meaning a very large maximum aperture) with a fixed focal length, but for now, this lens will do.

As I may have mentioned before, the screen on the DMC-G2 is not just a swivel screen, it’s also a touch screen, which is very clever. You can just touch the screen to set the auto-focus point, which is really, really, really easy compared to using the 4-way controller and the menus to move it around.

I doubt I’ll use the touch screen for more than the focusing, though. Most of the other menus are just as easy to get to using the 4-way controller, and that way I don’t have to get the screen dirty.

One nice thing about this camera compared to my old one is that the eyepiece for the viewfinder sticks out a bit more – this makes it more comfortable to look through, since your nose is not squished up against the back of the camera. Very nice.

For now, I’m leaving the lens hood on, but very soon I’ll pick up some UV filters for the end, and I think I’ll keep them on – I’ve never been a fan of keeping the lens hood on your camera all the time.

Fortunately, some of my old filters can still be used on this camera. My ND-Grad filters, for example, came with 2 mounts and 2 adapter rings, one for a 58mm mount (which is what the extension tube on my old Canon is) and one for a 52mm mount (which is what my new lens uses). I’ll need to get a new UV and polarizing filter though – but fortunately those are not at all expensive. (Which is a good thing, since the “pancake” lens I hope to get uses yet another different mounting size (46mm and 37mm, depending on whether I get a Panasonic or Olympus lens).

One of the things I’ll be doing right away is re-trying my depth of field experiments – I’ll be sure to post pictures from that as soon as I’m done.

Unfortunately it’s winter right now, which means the scenery is somewhat boring, and it hasn’t snowed since that one weird snowfall in October, so there’s no pretty snow to take pictures of either, so for the moment, I must content myself with taking pictures of things indoors. (My rabbits are going to get lots of screen time, I’m sure.)

Anyway, that’s my new camera – I’m quite pleased with it, and I’ll be sure to post more pictures and updates as time goes on!

Finally Time for a New Camera

IT IS TIME... for me to finally upgrade to a better camera.

After nearly 5 years of using my venerable old Canon PowerShot S3 IS, I think it’s finally time I took a step up and got a new camera. After much research and thought, I finally decided that the right next step up cameras for me is the Panasonic Lumix DMC-G2.

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:

Swivel screen
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!

(Camera picture by Flickr user senza senso.)

Not all F-Stops are Created Equal

Explaining why that blurry background effect is harder to get on your point & shoot camera, even though you might have it set to the same f-stop as a DSLR.

When I first started dabbling in photography, I did my usual reading-up on the technical aspects of things – shutter speeds, f-stops, circles of confusion, depth of field, etc. And for a long time, I thought I knew what I was doing.

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.

Why I Still Use My Canon PowerShot S3 IS Camera

Why I still use my 2006 vintage Canon PowerShot S3 IS Camera, despite being a bit old.

Considering how fast the digital camera world moves forward (in terms of technology), you might find it surprising that I – a huge technology geek – am still using my 2006-vintage Canon PowerShot S3 IS camera, even though it has been replaced by more than a few new models from Canon (at least 5 new models, by my count – and quite possibly more).

Now you might be wondering why I’m sticking with an older camera like this – but I assure you, there is a very good reason. And that reason is, basically, that Canon has not come out with a newer, “better” camera that is comparable to the venerable S3 in terms of features, price, performance, and accessories.

For example, the direct successor to the S3 is the S5, which is basically the same camera, but with 8 megapixels instead of 6, a newer image processor, and a hot shoe for attaching an auxiliary flash.

Sounds great, right? Well, yes and no. While at first glance the S5 seems like it is “better,” there is one other change that’s really annoying – the memory card slot on the S5 is on the bottom of the camera, inside the battery compartment, instead of on the side like in the S3. This means that you can’t switch memory cards easily while on a tripod, since the battery compartment is usually blocked by your tripod mount. And while this seems like a minor nit-pick, you also have to consider that the other new features of the S5 just aren’t quite compelling enough to justify buying an entirely new camera. (Remember: these cameras aren’t cheap, and they don’t have the same resale value that a full DSLR would have.)

There are more examples as well. Moving up the Canon “S” series of cameras we come to the SX10 and Sx20. Now, these are both very nice cameras, but again, they have some downsides that make it just not-quite-good-enough to justify spending a whole bunch of money on a new camera.

One aspect of the new cameras in the “S” series is that the lens speed (i.e.,largest aperture setting) has been slowly going down. My S3 has a max aperture of f/2.7 at the wide end, and f/3.5 at full zoom – but the SX10 and SX20 have max apertures of f/2.8 at the wide end and f/5.7 at full zoom.

And things don’t get any better if you jump up to the next range of Canon cameras – the PowerShot G series. Oh, sure, the early G series cameras had decently fast lenses (f/2.0 at the wide end, which is impressive for what is technically still a “point and shoot” camera), but the later G series all got bumped up to f/2.8 at the wide end, which is… not as impressive.

(For those who are a little confused as to what I’m talking about with these crazy f-numbers and references to “fast” lenses, this article from Wikipedia offers a good explanation. Generally speaking, a smaller f-number means a larger aperture, which means more light can come into the camera in a given amount of time.)

And let’s not forget that I’ve invested a fair bit of change into accessories for my camera. I’ve got filters and wide-angle lens adapters, which I would prefer not to have to re-buy with a new camera. Now, while the S5 would take the same accessories, but the SX10 and SX20 would not. And as for the G series, well, some of them support my accessories (mostly the earlier models) but some do not.

And I’m still not done – because some of the models above have the nice swivel-screen that is so handy to have, but others don’t. And some have the same electronic viewfinder, but others have a rather simple see-through preview hole, which does not actually show you what your picture will look like (instead, you have to use the full-sized screen).

I also am rather particular in my camera using regular AA-size batteries, so that I can find replacements easily in the field if I need to. Also, I can carry extra spares easily and charge them all using standard battery chargers, instead of needing special manufacturer-specific chargers.

So, as you can see, while there are many newer cameras to choose from, none offers the same excellent mix of features and accessories as my venerable old S3:

Swivel screen
Side-accessible memory card slot (not in the battery compartment)
Uses standard AA batteries
Accessories via a 58 mm mount on an adapter tube
Viewfinder that shows a full view of what the sensor sees (it’s electronic, not optical, but it’s still handy)
Good optical zoom range (12x)
Decent lens speed (f/2.7 – f/3.5)

For sure, newer cameras offer some of the same features (along with other benefits from being newer & using better technology), but none of them offers the same blend of features. And none of the benefits of the new cameras is, as of yet, compelling enough to make me spend several hundred dollars on a new camera, when my old one does just fine, thank you, and has all these features that I like, and won’t require me to re-purchase all new accessories.

Maybe someday Canon will come out with a new camera that offers the same features as the PowerShot S3, but with upgraded technology (hint hint, Canon!), then maybe I’ll consider upgrading. But until that day comes, I’m sticking with my trusty little S3.

Photos licensed under a Creative Commons Attribution-Share Alike 2.5 license. Photo credits: HendrixEesti, Yug and Rama. (Click on the photos themselves for further details.)