Camera Sensors and the Megapixel Myth

A topical subject -- I've just had my sensor professionally cleaned, which led me to research the difference between dust on the sensor, dust in the viewing optics and dust on the lens... which in turn led me to research the specifics of what a sensor is, the different types of sensor you get, and the difference in quality from one to the next.

DUST OMG

If you peer through the camera viewfinder and see dust, then the dust is NOT on your sensor. It will, 99% of the time, be on the reflex mirror, focusing screen or inside the viewfinder itself.

If you consider the diagram above, you can see that any dust on the illustrated path of light will show on the viewfinder. Generally speaking, while this is annoying, it's not the end of the world and won't show up on your images.

If you are seeing little dust spots on your image, it is probably dust on your sensor. Technically speaking it could be on your lens, but it would take a sizeable bit of dust on the lens to show in the final image, due to the way the focusing works. With every lens there's a minimum distance that it will focus at and anything closer gets blurrier and blurrier - well imagine how blurry a tiny dust spec would be right on the front lens element, and you get why it's unlikely to be a dusty lens if you can see it on the final image.

So, dust on the sensor. If you can see it on the viewfinder it won't show on the image - similarly if it's on the sensor you won't see it on the viewfinder. To check for dust on your sensor, mount a lens which can be set to 50mm or longer, close the aperture right up (f/22 or thereabouts), and shoot either a uniform blue sky, or a neutral white/grey surface like a wall. You might be able to see the spots on the LCD screen, or just pull the image off and look at it on your computer. It should be easy enough to spot -- if not, then you clearly have nothing to worry about. :)

Your camera's sensor is the equivalent to the film in film photography. It's the bit that is exposed to the light to generate the image (to continue the analogy further, if the sensor is akin to the film, a RAW image is akin to the negative, and the final JPEG is akin to the print). As such the sensor is incredibly sensitive and really if anything permanent happens to it, your camera is FUBAR.

Cleaning the sensor is a delicate matter. I googled and googled the phrase "sensor cleaning" to hell when my camera had dust, and most more experienced photographers will say it's something you can do yourself as long as you're careful and purchase the right tools. DISCLAIMER: You MUST get specialist tools to clean your sensor and you MUST follow the right procedures to avoid permanent damage. The general procedure involves first using a rocket blower to blast any loose bits of dust off the sensor -- once this is done, you can use a wet-clean technique to remove any bits which are stuck on. It's really important that you use the right tools for this - the right cleaning solution, the right swab -- if you mess up you could cause permanent damage to your sensor.

I could go into all the details but let's face it -- I am a klutz at the best of times. The other night, for example, I dropped a totally NOT hot casserole lid onto the worktop (didn't break thank god), then less than five seconds later, dropped my iPod on the kitchen floor. So when I realised I had dust on my sensor, I sent my camera off to be cleaned by a professional. It wasn't that expensive, and even though I was without my camera for three days, as someone who would have almost definitely ruined the sensor had I cleaned it myself, it was well worth it.

Sensor Size, Crop -vs- Full Frame, and Mega-Pixels

This fantastic post on the Photography Forum explains it much better than I can, PLEASE read it through, but I'll attempt to give my own summary perspective on it a little too.

Basically put, the larger your sensor is, the more light will fall on it. If there is not enough light, the sensor signal must work harder to detect what little light is there, which results in a "noisy" or "grainy" shot. You can manually boost the amount of light that hits your sensor by opening the aperture (a faster lens will help with this), slowing the shutter speed, or upping the ISO, which will make the sensor more sensitive to light -- but will still result in digital noise.

A full-frame camera will contain a sensor which is the equivalent size to a 35mm camera. As a brief aside I'll explain what that means to your field of view. If you're ever looking at lenses and see a phrase like "50mm on a crop sensor, which equates to 80mm in 35mm format", what they're referring to is the effective field of view; a shot taken at 50mm focal length on a crop sensor camera will produce the same result as a shot taken at 80mm on a full-frame camera. So you can extrapolate that to mean that 50mm on a full-frame camera will give a wider field of view.

Anyway, back to the point. The benefit of a full-frame camera is a wider field of view and better low-light performance. The flipside of that is how crazy-expensive they are. Nikon's biggest full-frame model, the D3X, retails at around £5000, whereas even the most expensive crop sensor cameras will usually come in less than £1000.

Now, on to what's known as the MEGAPIXEL MYTH. This is one that I was extremely gratified to read about, as it is kind of annoying hearing people bleat on about how many megapixels their camera has as if that makes it better - something I felt even before I was interested in photography.

A few weeks ago a friend of ours was considering switching away from iPhone to another phone model, and gave the reason that the camera that came with it had 14 megapixels. I still pride myself to this day that I was able to dissuade him from this before I even read up about the megapixel myth, purely by following the logic through in my own mind.

Enough boasting from me. The megapixel myth basically states a fallacy that more MP = better image quality. This is not necessarily true! My DSLR has a modest 10.2MP. Heck, Nikon have a full-frame camera model, the D3S, which has just 12.1MP. The truth is, a smaller sensor has a "sweet spot" when it comes to MP resolution, and if you try and cram more MP into a smaller sensor, you're going to end up compromising the image quality by creating sometimes-unacceptable levels of digital noise. So to Dan I said, it doesn't matter if your phone has a 14MP camera, the sensor is way too small to produce a decent-quality image.

Megapixels do matter to an extent, and especially in two particular areas: cropping and large-scale printing. If you're going to crop a huge amount out of a shot, more MP will allow you to do so and maintain image quality when the shot is scaled up to a bigger size. Similarly, if you're going to take a shot that's meant for, say, a huge wall poster or a billboard, I would imagine the MP count would be important there too.

There's a great article from the New York Times which explains the Megapixel Myth and also some genuine tests that were done to disprove it.

I hope this post has helped you to understand your camera's sensor a little better. Needless to say, the bigger sensor you can afford, the better the image quality will be, and megapixel size is NOT the effective comparison tool you think it is when considering which camera to buy next.

Bridge Cameras

This post is almost entirely inspired by my bestest friend Imogen, who yesterday emailed me saying her future father-in-law offered to buy her a camera. I love that my geekery is rubbing off on her. The Fuji Finepix range came up as a possible choice, prompting me to research the concept a little for my own education and nosiness.

The term "bridge camera" (aka "megazoom", "superzoom") is kind of an unofficial term used in the photography community to describe cameras which "bridge" the gap between compacts and DSLRs. Key differences between a bridge camera and a DSLR:

- No internal reflex mirror (this one is key! DSLR stands for Digital Single-Lens Reflex)
- No optical viewfinder (due to no reflex mirror) - what you do get instead is an electronic viewfinder
- No interchangeable lenses
- Typically smaller image sensor (not to be confused with megapixel size)

It seems that not all bridge cameras lack the above features though - for example the Samsung NX10 has interchangeable lenses and an APS-C (crop) sized sensor (same as my Sony A230) but is still considered a bridge camera due to no reflex mirror.

Bridge cameras nowadays will appeal to people who want more quality than a compact camera without all the expense and jiggery-pokery of a DSLR. Today's bridge cameras often come with INSANELY long optical zoom lenses - take the Fuji Finepix HS10 which comes with a 24-720mm optical zoom. To put it in perspective, a Nikon 500mm VR lens will set you back at least £5000. That's FIVE THOUSAND POUNDS, folks. As I mentioned in a previous post, optical zoom is much better quality than digital zoom so immediately the HS10 stands out as offering something pretty outstanding for the price.

Now, I can't get into the specific calculations and stuff because, well, it's way beyond my capability, but one of the perceived downsides of a bridge camera is that, even though they do tend to have wide apertures at the wider angles of the lens, the depth-of-field available is not great due to the smaller sensor. This means that unless you specifically position your subject close to the camera and far away from the background, you won't be able to get the blur or bokeh that a DSLR would give you. A shot like the below would not be possible with a bridge camera; the foreground and background flowers would be much more in focus, which means the main subject wouldn't be as well defined:



Some of the reviews I have read of a few bridge cameras also have it that the overall image quality is not as good as with a DSLR, as well as there being a little time lag with the scene on the LCD or electronic viewfinder updating with what's actually happening in front of you - this can make a major difference in sports or any shooting where your subject is moving fast.

My personal opinion is that a bridge camera has a very specific niche market -- someone who wants more versatility than your standard compact camera but isn't interested in or ready to get into the real detail and perfectionism of DSLR shooting. If this is you then a bridge camera is a great and affordable choice, but if you do end up really getting into photography and wanting something that delivers a little more, you'll inevitably make the leap into the full DSLR market.

Jargon: Key Words

I was just reading over the last couple of posts I made and realised I'm jabbering away about RAW and post-processing terms like "Unsharp Mask", all terms which will pass a new starter by completely. I will cover the whole RAW vs JPEG debate in a later post, as well as some of the basic post-processing techniques, but let me just fill you in on the basics of what some other terms mean.

Shooting in RAW

In basic terms, if someone says they are shooting in RAW they are referring to the file format of the shot in the camera. A RAW file is the digital equivalent of the negative in 35mm cameras; it captures the raw data of the shot without applying any processing whatsoever. This means that every possible pixel of data within the parameters of the settings you have chosen, will be captured and made available to process with.

On the flipside, shooting in JPEG, your camera will apply a certain amount of processing to a shot as soon as it is taken; most notably it is a "lossy" file format, and the automatic compression applied to the file within the camera makes much of the detail unchangeable in post-processing. For example, if I underexpose a shot slightly, with the JPEG file I will be limited as to what detail I can recover in the darker areas; with RAW there is a lot more that can be recovered, which is handy for me as my camera tends to shoot a little dark anyway.

RAW files themselves are not viewable as a preview or thumbnail and you have to install special software to view and edit the images. RAW files also tend to be anywhere from two to six times the size of a JPEG file.

I shoot RAW+JPEG -- it uses a huge amount of space on my memory card and hard drive, but it enables me to pick and choose via the JPEG preview which shot I want to edit and publish.

I really need to clear some of those old shots out, actually.

Post-Processing Terms

For starters, in future posts you may see me mentioning "PP" -- that refers to post-processing, which is adjusting the shot in software such as Photoshop or, in my case, GIMP.

Unsharp Mask -- confusingly-named tool for sharpening an image. This method is preferred to any generic "Sharpen" tool you may have as it offers more control.

Levels -- the Levels tool is for adjusting colour and contrast using the image's histogram as a guide. I'm not totally au fait with the science behind it, but it involves moving sliders around to get the desired contrast and level for the overall image or for each colour channel.

 

Curves -- similar to the Levels tool, the Curves tool shows you the image histogram with an initially straight diagonal line running through it, which can be adjusted as needed to increase or decrease the various tones of the image. For example if you pull down the lower end of the line, and pull up the higher end, you are darkening the dark tones and brightening the bright tones, thus adjusting your contrast.  Again, you can choose each colour channel for more specific results.

Both Levels and Curves are tools I use instead of the standard Brightness/Contrast tool, as they both offer a lot more control over how bright and dark you make the different tones.

Focal Length

Focal length is a term used to describe the length of a lens. It is always shown in millimetres and describes what level of zoom it offers. Exactly what the distance is measuring is something a little too sciency for me but you can find a very wordy explanation at Wikipedia.

The human eye sees roughly at a focal length of 45-50mm. The longer the lens, the further in it will zoom. Anything shorter than 50mm is described as "wide-angle", it offers (obviously) a wider angle of vision than the longer lenses.

Incidentally I am on the verge of dropping £150 on a 70-300mm zoom lens. Purchasing everything on my Amazon Wish List will require me to win a small fortune on the lottery at some point.

That covers most of the basic stuff I prattle on about.

I think?

Jargon: The Exposure Triangle Part III -- ISO.

Ugh, totally lazy late update from me. Believe it or not I've been so caught up in actual photography I've had no time to blog about it. :)

So far I've described how aperture and shutter speed can control the amount of light that falls onto your camera's sensor. ISO is more about light sensitivity. In the old film days you would have to buy different types of film for indoor or outdoor shooting; the indoor film would have a higher sensitivity to light, meaning it was able to detect it better.

These days with the nifty DSLRs we have, we have more control over what ISO setting we use, as well as being able to ramp it up to much, much higher than was available in the past.

The lowest ISO setting available on most DSLRs is ISO100. This setting pretty much allows us to control the exposure of the shot purely using aperture and shutter speed. If you're in a position to shoot in darker conditions and allow for increased shutter speed (i.e. through use of a tripod) then the lower ISO is still the way to go, to maintain the integrity of the shot. However if you find yourself in a dark condition with nothing but your hands to stabilise the image, bumping up the ISO can allow you to keep your shutter speed relatively fast - noise is always preferable to blur, and some editing software even comes with a noise reduction feature which can help.

In the below pic I was in a fairly crowded bar with no choice but to ramp up the ISO to keep the shutter speed fast enough to reduce blur. In this instance it actually works really well, giving the shot a gritty, "rock star" edge to it:



Of all the settings I use, this is the one I always, without fail, forget to set back if I then shoot in brighter conditions. If you look closer at the sky you can see what I mean:



Blech, I hate looking at shots from when I first started.

So there you go. Higher ISO can enable shorter shutter speeds but compromises the quality of the shot with digital noise.

Thus concludes my crappy explanations of the exposure triangle!

Jargon: The Exposure Triangle Part II -- Shutter Speed

So we've talked about Aperture and its role in the Exposure Triangle, and how to create bokeh using shallow depth of field. The next part of the triangle is the shutter speed.

Where aperture is the size of the opening which allows light into the lens, the shutter speed is the length of time your camera's sensor is exposed to the light. Use faster shutter speeds to capture instant moments and sharp images where the subject (or you yourself) is moving.



In this shot the wind was blowing a little, but where the exposure is set to 1/250th of a second, there is no movement blur.

If the light is low, the shutter speed will need to be increased in order for enough light to fall on the sensor and your shot to be correctly exposed. You can balance this somewhat by opening up the aperture wider (and increasing your ISO... more on this in a later post).



This shot was taken in the evening in my living room -- we only have two 60-watt uplighters lighting the room, and as I had the camera in Aperture Priority mode, the camera automatically chose an exposure of 0.5 seconds. This may not seem a lot but if you're shooting a moving subject or hand-holding the camera it can be an age. I had my elbows propped on the table to reduce hand-shake.

So for moving subjects or bright-light situations, a faster shutter speed is required. You can set your camera to Shutter Priority mode to control the shutter speed and let the camera work out the other particulars.

There will also be instances where you are actually aiming for a longer exposure; because you want to illustrate movement, or during night-time shooting, shooting fireworks or similar.



Here I was actually deliberately trying to capture the movement of the carousel so I switched to shutter priority mode and stopped down to 1/8th of a second. I wanted to go for longer but the shots were coming out way over-exposed even with the smallest aperture. Normally in long-exposure situations you absolutely MUST use a tripod (to avoid movement blur due to hand-shake) but miraculously I managed to stay still enough for this.

So, to capture crisp blur-free shots, a faster shutter speed is required (and wider aperture to compensate the light). To illustrate movement or shoot outdoors, a longer shutter speed is needed.

Next jargon post will be on ISO.

Jargon: The Exposure Triangle Part I - Aperture (and Bokeh)

There are a million blogs and a million articles on the web that will explain these terms in more eloquent or technical ways than I can, but I will give it my best shot.

When taking any photograph, the first consideration has to be the exposure. The exposure is exactly that: how well the camera's sensor was exposed to the light at the moment the shot was taken. There are three main things to consider when aiming for the right exposure: Aperture, Shutter Speed, and ISO; known collectively as The Exposure Triangle.

Aperture

Aperture was, for me, the more confusing term when I first started out. The aperture setting controls the size of the lens opening to allow more or less light into the camera. If you consider your camera lens to be like the human eye, the aperture would be the size of the pupil. Bigger = more light, smaller = less light.

As well as controlling the amount of light let in, the aperture also controls something called Depth of Field; that is, the area or amount of the shot that is in focus. A narrow depth of field means that only a small area of the shot is sharply in focus:



See how just a small part of the fence is sharp, but the foreground and background are all out of focus? That's what a wide aperture will do to a shot, especially one where your focus is very close.

A smaller aperture limits the amount of light coming into the camera, but also ensure more of the shot is in focus:



Here you can see the sundial in the foreground is just as in-focus as the trees and sky in the background.

Ok so here's where it gets confusing, and why it is this way, I couldn't tell you. To select a larger aperture on your camera, you have to choose a smaller number, and to select a smaller aperture, you choose a higher number.

Narrow depth of field = smaller number = wider aperture.
Wide depth of field = larger number = narrower aperture.

In order for your shot to be correctly exposed, if you limit your aperture you must then slow your shutter speed to allow enough light in to the camera. I'll go over shutter speed in more detail in a later post.

If you select your camera's Auto mode, you will have no control over any of the settings; however all DSLR cameras and even some Point and Shoot models have an Aperture Priority mode. This will allow you to select the aperture size you want, and the camera will then work out the optimum shutter speed to correctly expose the shot. I currently shoot almost exclusively in Aperture Priority mode.

Bokeh

Ahh, bokeh. I've come to realise from my reading that bokeh is a notion that is more pleasing to amateurs, and the more experienced photographers out there don't really consider it that much.

The word "bokeh" (pronounced "bock-eh", not "bow-kay") is a Japanese word and it refers to the part of a photograph that is out of focus. A lot of people, myself included, will compose a shot not just to capture a subject, but also to capture some attractive bokeh in the background. I find it pleasing to the eye; in the professional world I don't know how much weight it carries. To achieve bokeh, one must open up their aperture really wide when photographing a foreground subject; the subject will be in focus, the background out of focus, and this blurry background is the bokeh.



See how the cute little flower is sharp and then there's loads of out-of-focus jazz in the background? That background jazz is bokeh. The best bokeh, in my opinion, is created with a really narrow depth-of-field (the capability for which, my current lens just doesn't have) and contrasting colours or lights in the background. Bokeh itself can be an artistic device, or can be used to highlight the subject of the shot even more.



My next Jargon post will be about shutter speed.

Happy snapping.
xxx

The First Camera

So I admit, I didn't spend a huge amount of time researching which should be my first camera. I asked around a little, got a couple of suggestions, and read a few reviews online before settling on a Sony Alpha A230. It was cheap and the general online consensus was, it's a great beginner's model.

If you're looking to get into photography for the first time, when considering your camera choice I urge you to do the following:

1) Consider the cost. I know a cheaper camera generally means less quality, but if you spend four digits on your first camera and then decide photography isn't for you, you'll kick yourself. Think about the upper limit of your budget, and start looking at cameras a bit cheaper so you have some leeway.
2) If you can afford it, get a twin lens kit. What I mean by that is: most "high street" single-lens cameras come with a standard zoom lens, which is around 18-55mm with a maximum aperture of between f3.5 - 5.6 (I'll explain what that means in a bit). I bought a single-lens kit and already (two days after receiving the camera) am wishing I had the longer lens too. A twin lens kit will come with a second zoom lens, around 55-200mm. If you're serious about your photography, you'll need that second lens.
3) Buy a memory card at the same time. When considering your memory card, think about what kind of photos you want to take. If you think you'll take a lot of action shots and want to do that cool thing where you keep your finger down and it takes tons of shots in succession, you'll want to be sure that your memory card is fast enough to write a picture before accepting the next one. You'll need to think about what format you want to shoot in too, when deciding what size to get, but I firmly believe 8GB is big enough for any starter, and 4GB might even suffice if you want to shoot exclusively in JPG.
4) When shopping around, for the love of god use a price comparison site like Camera Price Buster (a UK site, I'm sure there are sites just like it for other countries). Not only does it query all the major (and minor) online retailers, but also provides totally legitimate voucher codes to enable you to pay the cheapest possible for your item. I was able to get my Sony for £300 by using this site -- much cheaper than had I just gone to the first high-street retailer I could think of.


In my next post I'll give a brief rundown on the terminologies and what that means when considering what sort of photographer you want to be.

Happy hunting!