Beginner Portrait Lens Guide

What lenses to choose, and why- with a video demo!

By PF Staff in Gear Guides on Jun 11, 2013

Today, we would like to discuss what types of lenses you should look at if you're interested in portrait photography.

Those of you who are just starting out likely own the DA or DA L 18-55mm kit lens that comes with most Pentax DSLRs.  The kit lens is like a swiss army knife, as it can be used for a variety of purposes, but it doesn't shine in any particular area except for versatility.

When it comes to portraiture, one can do much better than the 18-55mm.  A good portrait lens should have the following characteristics:

1. Smooth Out-Of-Focus Background Rendering

When shooting portraits, most of the time you are interested in isolating just the face of your subject.  Details in the background can prove to be distracting and thus ruin the overall appeal of the photograph.  Therefore, the ideal portrait lens should feature a fast aperture such that the background can be blurred nicely.  The maximum aperture of the kit lens isn't large enough to accomplish this, but lenses with maximum apertures anywhere between F1.2 and F2.8 should work wonders.

Lenses are never as sharp at their widest aperture setting as when stopped-down.  However, while some lenses are very poor wide-open, others actually hold their ground quite well.  When choosing a kit lens, you should therefore look for one that is acceptably-sharp when used wide-open.

It is also important to keep in mind that each lens renders out-of-focus areas (also known as bokeh) differently.  This can be attributed to a number of factors, including the optical design and number of aperture blades.  Bokeh is a highly-subjective matter, so if the first lens you pick up doesn't work for you, simply try another.

2. Low Distortion

Distortion occurs when lines that are straight in real life are not portrayed as such in a photograph.  It is difficult to design lenses that are distortion-free, as complex optical designs are needed to accurately project the image onto the flat surface of the camera's sensor.  Zoom lenses generally exhibit much more distortion than prime lenses, so your best bet it so pick a fixed focal length lens for portraiture.

To make matters worse, there exists a second type of distortion called perspective distortion.  Have you ever taken a photo of a skyscraper and noticed that the base appeared much wider than the rest?  This phenomenon happens simply because objects that are closer to you appear larger when projected onto a plane, even if they're same size in real life.  How does this apply to portrait photography?  Well, if try shooting portraits with a wide-angle lens, you will have to stand very close to your subject in order to get a smooth background.  This proximity will introduce perspective distortion that would affect the appearance of facial features and even the overall shape of the face.  Therefore, the focal length of your portrait lens should be long enough to allow you to keep your distance while still being able to obtain smooth backgrounds.  On APS-C cameras, focal lengths of 50mm - 60mm are ideal for this purpose.  On film or full-frame cameras, the traditional portrait lens is an 85mm.

3. Minimal Aberrations

You don't want artifacts such as chromatic aberrations, flare, or vignetting to make their way into your portraits.  In general, the more complex an optical design is, the more prone it is to various aberrations.  Lenses with poor coatings or no hood are susceptible to flare or ghosting, so they should be avoided. Normal and short telephoto lenses generally don't exhibit very many aberrations because their designs don't require any optical "magic".  Again, this is why lenses in the 50mm - 85mm range are so well-suited for portraiture.  Longer telephoto lenses would have more aberrations, or the might simply be too heavy or difficult to handle.

So, to sum things up, here's what we are looking for in a good portrait lens:

• Fixed focal length
• Between 50mm and 85mm (normal to short telephoto)
• Fast aperture and nice bokeh
• Sharp wide-open
• Modern lens coatings

Although there are many lenses that satisfy all of these criteria, the most important aspect of a portrait lens is without a doubt its ability to render smooth out-of-focus areas.  Therefore, we've prepared this short video showing you what you can accomplish with a fast DA 50mm F1.8 lens (known for having good bokeh) compared to the Pentax 18-55mm kit lens:

If you currently just have the kit lens are are looking to step up to a fast portrait prime, here's a list what is currently available for Pentax:

In addition to these modern lenses, you could also opt for a more affordable legacy lens, such as a Pentax-M or Pentax-A 50mm. 

Some photographers use fast telephoto zooms (such as the Pentax DA* 50-135mm or a 70-200mm) for portraiture; if you would like advice on what lens is best for your particular needs, please post a thread in our SLR lens forum!