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Photography Exposure - 10 Common Questions Answered

After getting the basics of photography exposure nailed, most people still have a few little lingering questions that can be tricky to find answers to. That's the purpose of this article, to put to bed some of those uncertainties. I can remember being unsure about several of these areas long after learning about aperture, shutter speed and ISO. So let's take a look...


Q: What's The Point Of Exposure Compensation?

A: I used to swing between Manual and Automatic/Program mode, without stopping to think about the (now obvious) benefits of Aperture Priority (AV for Canon) and Shutter Priority (TV for Canon) modes.

So the idea of shooting in Program, but then going to the trouble of manually changing the exposure, using exposure compensation controls seemed silly. Of course, it's not silly, because it actually saves precious time when shooting.

Say you're in AP mode, and there's a significant amount of white (e.g. snow) in your scene. The camera's metering gets things slightly wrong, mistaking white for blown out highlights, and you take an under-exposed photo. Dialling in +1 or +2 stops of exposure compensation allows you to stay in AP mode, and just override the camera's reading.

Exposure compensation can be '+', to increase brightness, or '-', to decrease brightness, and is adjustable by around 1/3 of a stop at a time. It's a kind of semi-manual way of shooting, and is really useful. Try it!


Q: Does My Lens Have A Sharpest Aperture?

A: Yes. It's generally about 2 f.stops down from wide open. For example, if your maximum aperture is f2.8, you might find that f.5.6 yields the sharpest results. Similarly, f.2.8 would be the optimal aperture for a f.1.4 lens, etc. You have to experiment and check the results to see how your lens performs though. No set-in-stone rules here.

Image by: Bui Linh Ngan

I remember being confused when I first heard this, because I'd just learnt about how the smallest aperture (highest f number) produces the largest depth of field (i.e. the largest area of your photo in sharp focus). But this is a different thing entirely. Your sharpest aperture is not a matter of depth of field, but sharpness and crispness within the in-focus area, however large/small that may be.


Q: I Just Want Keep Things Simple When Shooting Events, Street Scenes and People. Is There A Recommended Aperture Setting?

A: To keep it brief, yes, f.8. You may have heard the photographers' expression, "f.8 and be there". In other words, select f.8 and put yourself in the interesting places you need to be to get great photos. I like that 'keep it simple' attitude.

Obviously, f.8 will sometimes push the shutter speed too low to create sharp photos, in which case you'll have to stop down. But it's a decent base point to work from a lot of the time.


Q: Sometimes I Think A Photo Looks Fine On The 3" LCD, Then Later On My Computer I See Blown Highlights and Black Shadows. Is There A Solution?

A: Yes, use the histogram, that's what it's there for. Don't worry if you've taken one look at that complicated graph thingy and thought, Nope, that ain't why I like taking pictures! I did the same to begin with. Big mistake.

The histogram is a very simple graphic that displays all the information in your photo, from shadows on the left, through the midtones and into the highlights on the right hand side. It provides an instant overview of your exposure.

photo histograms

Histograms are also a useful tool in post-processing (top right)

If the graph is bunched up in peaks to the left, you know you've probably underexposed. Conversely, when there are peaks up against the far right wall of the histogram, your images features clipped (blown out) highlights. It's an easy, instant check. (Tutorial on using a photo histogram)

As a rule of thumb, it's worth 'exposing to the right'. In other words, erring on the side of overexposing, rather than underexposing, so the histogram shows more info on the right hand side of the graph. The reason is that noise creeps into dark shadows more readily than bright areas. You can easily rescue contrast later in post-processing.


Q: How Much Physically Larger/Smaller Is Each Successive F.stop?

A: Double the size/half the size of the previous one/next one. So f.4 is half the size of f.5.6 and twice the size of f.2.8. Apparently if the level of increase/decrease in brighness were any less, the human eye would barely be able to detect it. There is an explanation for the incredibly unhelpful number sequence of f.stops, but it's probably incredible unhelpful to delve into it!


Q: What's The So Called Reciprocal Shutter Speed/Focal Length Rule?

A: In order to avoid camera shake and keep your pictures nice and sharp, always use a shutter speed of at least the equivalent number to the focal length. So a focal length of 100mm would require a 1/100th second shutter speed.

BUT - that only applies when shooting on a full frame camera, which, if you're reading this guide, you almost certainly aren't. I don't either. So for most of us, who use a 4/3rds sensor (and whose cars are more expensive than our cameras!), a shutter speed of 1.5x the focal length is needed. For example, shooting at 100mm would demand a shutter speed of 1/150 of a second for sharp results. Here is a full tutorial on taking sharp photos.

The reciprocal rule is especially important when using a telephoto lens


Q: In Low Light, When It's Not Possible To Shoot At A Shutter Speed 1.5x Focal Length, Should I Just Slow Down The Shutter Speed To Get The Shot Anway?

A: Well, clearly, it's pointless to make technical perfection your one and only goal. Photos are interesting because of the subject, so yes, it can sometimes be worth incurring a bit of camera shake for the sake of capturing a moment that won't come again.

But that shouldn't be your first option. Never be afraid to increase ISO. Remember the exposure triangle? The ISO is an important part of it, and a little bit of noise for the sake of a faster ISO speed is no big deal really. So increase ISO first, and drop shutter speed later if you absolutely have to.


Q: Is There An Exposure Mode That Photographers Seem To Use The Most?

A: Yes, Aperture Priority (AV for Canon users). Obviously, the caveat is that all modes exist for good reasons, and they are each suited to different situations. But on the whole, and certainly for me, AP mode has the broadest range of applications.

Depth of field is the key thing that I want to be able to control in most pictures, and modern DSLR's are so good at judging the exposure that I'm happy to leave mine to it. That way, I can set the aperture, allow the camera to select an appropriate shutter speed for creating a good exposure, and shoot away.


Q: If Aperture Priority Is A Good Default Setting, Program/Automatic Is Good For Speed/Ease And Manual Gives You Total Control, What's The Point Of Shutter Priority Mode?

A: Well, it is probably the mode that I use least, but there are some situations when nothing else will do! At sports games I tend to shoot in Shutter Priority the whole time (sports photography tips). It's the perfect mode for this situation, because you need to freeze fast moving subjects and get the exposure right before the moment has gone.

Image by: John Togasaki

So I choose a really quick shutter speed, and try to leave enough depth of field to account for the movement of players on the pitch (i.e. there's the chance that the subject can stray out of focus if the aperture is too wide). If necessary I step up the ISO a touch. The same principles apply to wildlife photography too.


Q: Is Shooting In Raw Mode Complicated?

A: No. I'm not sure where this idea gets propagated. Perhaps it's partly because of the other technical jargon that is sometimes used in connection with Raw files. But the reality is that shooting Raw is an incredibly simple and powerful way to improve your photography.

A Raw file contains literally the 'raw' data recorded by your camera's sensor, with none of the many adjustments that are instantaneously applied to JPEG's. All these adjustments are done in 'conversion' software, like Photoshop Elements or Lightroom. (Introduction to the Raw file format)

Amongst the many adjustments, like contrast and colour temperature, that can be made when processing Raw files, is exposure. I tend to find that I can increase/decrease the exposure by up to about 2 stops without the image quality being affected. The ability to fine tune (not radically alter) exposure retrospectively is a big asset. (A guide to converting Raw files in Photoshop Elements)


Any follow-up questions or feedback to these 10 photography exposure q's? Feel free to use the comments below...

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