Let’s say you just got a new toy – a DSLR body! You are so excited. You wanted this camera to take good portraits of your family. How should you best put that new 50mm portrait lens to work? Well, that is always a tradeoff between sharpness, shutter speed, and bokeh. Let’s look at photos using a Nikon 50mm f/1.8 D lens.
The aperture of 1.8 is fantastic at achieving that creamy blurred background that you used to have to mimic in Photoshop when you used your point and shoot camera. That poor little thing had a maximum aperture around 5! With an aperture of 1.8, you are letting in loads of light and can use a much faster shutter speed to achieve the exposure you want. The faster shutter speed means fewer blurred photos (no camera shake).
In low light situations, this can be crucial. A smaller aperture (bigger number) will let in even less light. You need to keep the shutter open longer to get enough light. If the available light is quite low, this can mean the difference between a handheld shot that is in focus, one that requires a tripod, or looks blurry.
The photo above was taken at f/1.8 with a shutter speed of 1/2000 seconds. Looks good. The blurred background encourages your eye to focus on the beautiful bloom. I always thought you had to shoot literally wide open in order to achieve that creamy background. Today, I proved myself wrong.
f/2.0 1/1600 sec.
Here is the same photo taken with the same overall amount of light. This time the aperture was closed down one stop and the shutter speed was decreased one stop. Still nice bokeh. Let’s see if there’s any difference by closing the aperture one more stop and decreasing the shutter speed an additional stop.
f/2.2 1/1250 sec.
Overall the shot looks pretty similar. Still nice bokeh. What’s your point??? Well, let’s look at closeups of those beautiful flowers.
f/1.8 closeup
Hmm, where did the detail go in the center of the flower? Let’s look at that with an aperture of 2.0
f/2.0 closeup
Wow, the detail looks a lot sharper in this one. Let’s try 2.2.
f/2.2 closeup
Now that’s pretty sharp. Not too much difference between 2.0 and 2.2. At that point it comes down to personal preference. But there was a noticeable jump in sharpness between 1.8 and 2.0.
What does this all mean to you? Although your lens may give you the ability to have a super wide open aperture, it doesn’t mean you’ll get a sharp photo at that setting. In fact, your depth of field may wind up being soooo shallow that you don’t get all your important parts in focus.
Take another look at the top photo. The entire length of the petals is not in focus. Were you really looking for a portrait in which your baby’s nose was in focus but not his ears? You may want that look. It’s quite popular to take a portrait in which only the eyelashes are in super-sharp focus. But, as an amateur, if you don’t want to spend a ton of time in Photoshop sharpening all the eyeballs in your portraits, close down your aperture a bit. You’ll still get the bokeh and a pretty quick shutter speed, and you’ll get a nice sharp photo as well.
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