PhotoWalkPro

I was reading an email that I had received from someone that had purchased my Canon 50D: From Snapshots to Great Shots book and they asked me a great question.  How do you know what F-Stop to start with? This is actually a pretty common question and it’s one that I heard several times over the past couple of weeks while teaching a photography class in Malaysia.  The truth is that there is no simple answer.  A lot of the decision depends on other factors that go in to determining an appropriate exposure setting like; What is the best ISO for the scene? Do I need to use a fast shutter speed because I am going to be hand-holding my camera? How much light do I have to work with? and on and on.

Depending on the subject you are shooting, you will want to vary the amount of depth of field in your image.  Remember that there is only one plane of focus but the depth of field will render a range of acceptable focus depending on the selection of the aperture.  This also has a lot to do with your distance to the subject and the length of the lens.  Wide angle lenses have a greater apparent depth of field due to the wide angle of view, which makes everything look smaller and thus sharper.  Remember that everything looks sharper and more in focus when it’s smaller, which is why I always tell people to zoom in on their LCD screens.  Everything looks great on a 3″ screen.  A longer lens will offer a more narrow field of view and make everything look larger.  Long lenses can also produce a more narrow depth of field than wide angle lenses.

So with all of these things to consider, where does one start?  Well, you could start with your sharpest aperture setting.  This will usually be one of the f-stops in the middle of the range of available f-stops for your lens.  It is also referred to as the sweet spot and it’s usually somewhere around f/8 or f/11.  This doesn’t mean that you should always shoot at f/8.  For example, if I am shooting a landscape or panorama, I will try to use a smaller f-stop (f/16 or 22) to get a greater apparent depth of field from near to infinity.

If I’m shooting a portrait, I will tend to go the other direction by selecting a larger aperture opening (f/4 or 5.6) so I can narrow the depth of field and place more emphasis on my subject while blurring distracting background objects.

It’s possible to see the effects of your aperture setting as it relates to depth of field by using your camera’s Depth of Field Preview button.  Most lenses do not close their aperture down until the moment the photo is captured.  This is done so that you have the brightest possible view in your viewfinder.  When pressed, the DOF Preview button will close the lens down to the selected f-stop and will allow you to actually see how much depth of field you are getting at the chosen f-stop.  It also makes the image in the viewfinder appear darker at smaller f-stops due to the lower amount of light coming in through the lens when it is stopped down.  Note that not all cameras have a DOF Preview button so consult your owner’s manual.

While the DOF Preview is a good starting point, the only way to really determine just what the proper f-stop should be is through experience.  Sometimes it’s a good idea to shoot at multiple f-stops just to see which one you like the best.  Over time you will develop an eye for what will look good with a lot of depth of field and what would look better with just a little.  From that point you will be able to adjust the other camera settings to get just the look you are after.

See, I told you it wasn’t simple,  but with practice, it will get easier.

For a little more on Depth Of Field, check out my post on Hyper Focal Distance.

Related posts:

1. Do you know what Hyperfocal Distance is?
2. Shooting Through the Fences – Better Zoo Photos
3. Some HDR Camera Options
4. Upgrading to a Full Frame Camera? You May Have to Leave Your Old Lenses Behind
5. Is your Focus Letting You Down

This entry was posted on Wednesday, November 4th, 2009 at 12:04 am and is filed under Photography, Tips. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.