Tag: exposure

The Exposure Triangle – A Primer

JasonLeave a comment

When we look at the elements of composition, the three that everyone constantly considers are shutter speed, aperture settings and ISO (or ASA in the old days of film). These three factors make up something called the Exposure Triangle.

Exposure Triangle

Readers of the blog have seen this before, in my post about The Future of Photography. The rules of the exposure triangle (such that there are rules in photography…) state that if you want to keep the lighting the same in your shot, as you increase one factor, another must decrease proportionally, while the third is kept the same. What does that mean? Simple – let’s take scenario I encountered when on a photo shoot with some friends touring the waterfalls of South Carolina. While shooting, I saw a perfect scene to demonstrate how this would be manifested.

For our first example, let’s set set up our camera and take a picture of a waterfall. In order to hand hold, and easily compose things, we have the following settings.

  • A shutter speed of f 1/250
  • An aperture of f 4.5
  • And an ISO of 100

Fabulous – but in looking at the photo, we’re not crazy with how the photo looks. Something is off, and we want to change one of our settings to make for a better composition. I’d like to see the same photo but with some blurred water. Now in your own photography it could be something else, like a flower to be sharper throughout the entire depth of the frame, or the background of a portrait to be completely blurred. So, how do we accomplish that? This is where understanding what each factor does to the composition:

Shutter speed

Shutter speed controls how quickly the shutter opens and closes. The higher the setting, the faster the “action” is – so you can freeze something like a speeding bullet, a blade of a moving helicopter, or the wing of a hummingbird.

Aperture

The aperture is the size of the opening on your lens. Think of it like a hose that controls flow rate. You could use a really skinny hose that only lets a teensy bit of water through, or a fire hose that just gushes gallons and gallons. Now, as you open the aperture wider, and let more light in, you also do something called creating a shallow depth of field. And the more shallow your aperture is, the less focused things will be in the foreground and behind your subject.

ISO

The ISO is the noise or sensitivity setting for your camera sensor. This changes how sensitive the sensor is to light hitting it. Lower ISO settings make it more sensitive to light, higher settings make it less sensitive. Back in the days of film, this was done by using films of a certain ASA value (which ironically was referred to as film speed, but I digress…) But the fun thing to consider is that once you inserted film in a camera, you were stuck with that film setting until you finished every frame, so ISO adjustability in digital cameras was a HUGE advancement.

Okay, so now, back to our example photo. Now in our example, we want to make the water more blurred, so we have to slow the shutter down, not speed it up. Okay, so let’s do that:

New shutter speed = 0.5″ (one half second)

So, what’s going to happen? Well, because we are now letting the shutter stay open a LOT longer (0.5 seconds is HUGE, but we need that to really blur water)! As a result, more light is going to hit the sensor, and make it way too over-exposed, so we need to compensate for that by adjusting the other two controlling elements – aperture and ISO. Now in this example, our ISO is already as low as it can go, so our only option is to make our aperture opening much smaller:

  • A shutter speed of f 0.5″
  • An aperture of f 29.0
  • And an ISO of 100

See how we did that? Now, this shot is going to have much more blurred water, and our exposure stays consistent. But, we’ve effectively made the same shot with a different composition!

See how the shutter speed and aperture will change the entire composition? Yes, I blurred the water, which was my primary goal, but look at the log in the foreground. Now it’s a little out of focus due to the shorter depth of field. Pretty fun stuff, eh? I should also mention now that since I slowed the shutter speed to half a second, there was no way I could hand hold that, so I mounted it to a tripod in order to prevent camera shake.

As a reminder, for a strict metadata comparison, that’s what happens when you account for the exposure triangle:

Shot 1

  • Shutter speed = 1/125th
  • Aperture = f 4.5
  • ISO = 100

Shot 2

  • Shutter speed = .5 seconds
  • Aperture = 29
  • ISO = 100

Happy shooting!

Author note: I was going to post this article in response to a question that came to me from Quora. Imagine my surprise when I realized I had never written a post in 10 years on something as fundamental as the Exposure Triangle!  It may have been written and lost in the server crash from a few years ago, but thanks to Quora for giving me the reason to re-create it now!

Setting bracketing exposures – aperture priority

Jason12 Comments

Over the past few years, I’ve had several people ask me how to set bracketing exposures on camera bodies for multiple exposures.  When I say multiple exposures here, I am talking in excess of 3 shots.  The reason for this is because by default, most Canon cameras (at least all the ones I’ve put my hands on) only have a single over and underexposure allotment on each side of the initial exposure settings.

Let’s take a look at the numbers…say we meter a scene and it says that according to the center point, we should be at f8, with an ISO of 100 and a shutter speed of 250.  So, if we want to expose this multiple times over and under that initial group of settings, since Canon only allows 1 over and 1 under, we will need to make additional adjustments if we want more than the 3 exposure set.

Here’s the entire f-stop range (well, not all of it, but enough for our purposes):

fstop

So, in order to get the full range of exposure, our aperture would need to manually be set to f2.8, f8.0, and then f22 and then let the camera capture the over/under.

For ease of manipulation I always start at the lowest end and work my way up, so in this scenario, I’d start with f2.8, press the shutter 3x, then move up to f8, repeat the shutter press 3x, then finally to f22 and press the shutter 3x.  That would give me a nine stop range of the same image at different exposure settings.  It goes without saying here that in such scenarios, you would want to:

  • Be shooting on a tripod
  • Be using a remote release (or timer)
  • Be using mirror lockup
  • All other settings remain constant
  • and that lighting conditions aren’t changing appreciably
  • You are set to manual focus
  • Your lens is set to its hyperfocal distance

Things that are problematic with bracketing in aperture priority are:

  1. Your depth of field is changing considerably as you move from f2.0 to f32.o so much of what is out of focus at f2 will be considerably sharper at f32 even though you are set at your hyperfocal distance.
  2. Lighting conditions will change.  Unless you are in a studio environment and flash is the only light source, ambient light is constantly changing,and this will have an impact on your exposure values.  Granted if you move quickly and methodically, this can be minimized, but due to the ever-changing values of light, this is something to consider!
  3. Weather conditions will change.  The scene that was perfectly still 30 seconds ago while you did the first bracket may not have perfect stillness for the second bracket set.  Changes in wind speed, direction, and intensity can blur things like flowers, branches, grass, and even some objects that you otherwise would consider fixed.  (Ever see a lamp post in a strong gusty wind?  Or a street traffic signal?)

Any other mechanics, pros and cons or points of discussion I missed here?  Feel free to chime in with your thoughts on bracketing exposures based on apertures.  Don’t forget to tune in tomorrow too for the backeting exposures on shutter speed, along with its pros and cons.  Happy shooting and don’t forget the Twitter v bloging poll from yesterday!  If you’ve already voted, tell a friend!

The Power of Action

Jason6 Comments

Until this last weekend, I had very limited experience with astrophotography.  The concepts and techniques of the field are well documented, and I have read several articles on the subject.  What this last weekend demonstrated to me, (and what I often tell everyone who reads this blog), is that there is no better way to learn something than to just get out and do it!  This is the power of action!

Over the course of a pleasantly long weekend with my wife, we had an opportunity to view an absolutely breath-taking night sky, without the pollution of light interference.  The pure darkness of the mountains, coupled with the lack of urban and suburban sprawl, revealed the brilliance of the night skies to me.  As I shared the moment with Tracy, a part of me finally caved and said “Sorry, but I’ve got to take a picture of this!”  Admitting defeat as a camera widow, she went inside, and I tried to recall the articles with their knowledge:

  • Tripod (critical for stability!)
  • Shoot wide (calls for fewer adjustments during long exposures which also means longer shutter speed allowances)
  • Shutter release (never release the shutter manually on such scenes – increases too much vibration)
  • In camera noise reduction…(long exposures tend to create noise as a consequence)
  • Higher aperture (for greater depth of field)
  • And then there was something about the shutter speed…no more than…what?  I could not for the life of me remember!

So, with the digital mantra in place, I tried many different exposures.  My first attempt was a 30 second exposure at f8.0 and ISO 100.  The on-screen results were not that great.  So, I took things to the extremeon my next shot, 30 second exposure, f8.0 and ISO 3200.  The result:  I saw stars on screen!  Excited at the prospect ofcapturing the scene, I promptly returned to the secluded getaway mentality, forgetting the cardinal rule of digital:  to shoot many, many shots, and at many, many settings.

What I also forgot is that in astrophotography there are more than the above considerations to take into account.  After getting home and realizing my blunder, I re-read the articles and remembered that as a general rule, ISO should never go above 800, and because the earth is always moving, you should never shoot an exposure longer than 5-10 seconds, because stars will blur by then.  (As was evidenced during post processing…)

So, the result was nothing too rewarding.  Certainly nothing that will get me fame in fortune in National Geographic or anything like that.  I did manage to massage something close to what we saw with some post work (including some serious Noise Ninja assistance, drastic curves adjustments, the glowing edges filter, and a little black and white conversion, just for starters…

Night Skies

While the end result is “not too shabby”, it certainly is nothing like these stellar (literally and figuratively) shots from Astropix.com I must admit that I am now considering adding to my gear collection, and that I need to refresh on the techniques of astro-photography, the best method for learning is to simply get out and shoot.  Want to capture the light?  Then here’s teh call to action, because it is, after all, the only way to capture the world around you in images!

For those interested in learning more about astro-photography, here’s a couple resources I’ve got in my bookmarks (how I wish I had my computer with me at the time!):

If anyone has their own links, resources, tips, tricks, suggestions, and ideas for astrophotography, feel free to share them in the comments.  In the meantime, thanks for stopping in and we’ll see you back here again tomorrow.