Photography - Knowledge

Parfocal Vs. Varifocal Lens: What is the Difference and Does it Matter!

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Zoom lenses undoubtedly rule in the world of photography. If you are familiar with cameras and lenses, you must have heard the terms parfocal and varifocal. You may know that these terms are used to describe the lenses but are you aware of what these terms mean? If you are new to the world of photography, you might not know anything about it.

But, if you have been clicking pictures with a professional camera for some time now, you would know that the varifocal lenses have been designed for SLR cameras and capturing stills. The parfocal lenses, on the other hand, have been designed for broadcast and cinema.  

But, why do you need to use different lenses when varifocal can capture amazing stills as well as videos? What is the difference between them? Okay, so both parfocal and varifocal are two different kinds of zoom lenses which are based on if or not the focus is maintained as you change the focal length. Let's dive into the complete details of the lenses.

Introduction to Parfocal and Varifocal Lens

Well this is a type of lens which remains in focus even if the focal or magnification length is changed. This is convenient and also offers the advantage of allowing precise and accurate focusing at a maximum focal length. It also allows you to zoom back to a focal length that’s shorter so as to compose the image. 

Most of the high-end broadcast cameras and some of the cinema lenses are conventionally parfocal as changing the focus is a huge part of the creative process and blurry photos are a big no!

The easiest way in which you can determine if your lens is parfocal is by simply comparing it with the live-view.

  • Set a frame and focus using peaking or live view. 
  • Once done, take a video or a still.
  • Now, once you have done that, instead of using peaking or live view, zoom in and focus to the best of your capability and then zoom out to your original frame. Now take a video or a still. 
  • Compare both of them at 100%.

This can be easily done on a DSLR.

The difference would be noticeable to you even on the lenses which are supposed to be parfocal. Try from different angles, across varied zoom ranges, from the front and back, different focal points, frame size and apertures. 

To be honest, only a perfectly curated optical design can be a true parfocal lens which is favorable for most of the situations. 

parfocal lens
Parfocal Lens- Uncompromising Focus (source)

What is the Meaning of Varifocal?

Theoretically, a varifocal lens can be used for shooting both videos and stills. Most videographers, you would notice tend to use varifocal only because of the fact that they are comparatively cheaper. 

With the varifocal lenses, just as you zoom the lens, you are varying the focus. Any kind or amount of recomposition would end up changing the focus. It is for this reason that these lenses were designed for the purpose of still photography. Most of the affordable and the so-called zoom lenses (particularly true in case of fixed lens camera) are basically varifocal.  

The reason as to why they are popular is because of the fact that they are quite practical because of the auto-focus and also because the processor of the camera can adjust the lenses automatically so as to keep it in focus when changing the focal length. This is what makes the operation kind of indistinguishable as compared to the parfocal DSLR lenses. 

Varifocal vs. Parfocal Lenses

Let us see the comparison both of the lenses so as to see the difference between them.  

1. Lens Breathing 

Lens breathing is one of the major differences between both the lenses. With the parfocal lenses, the lens breathing is quite minimal. As you keep focusing in and out, you would hardly notice any changes in the size of the image. 

However, the varifocal lenses breathe significantly and this can, therefore, bring about a change in the size of the image as you adjust or change the focus. The edges of the frame would tend to shift. This could be jarring to the viewer while you are pulling the focus in a video. Therefore, the parfocal lenses have been designed in such a way that it can almost eliminate the focus breathing. 

lens breathing
Minimal Lens Breathing (source)

2. Focus on the Subject 

Just as the name suggests, the problem with the varifocal lenses is that when you zoom the lens, you end up varying the focus. The lenses were particularly designed for the purpose of photography and not for maintaining the focus on the subject all through the zoom range. 

A parfocal lens, on the other hand, is one with which you can easily zoom in and out of the subject. The focus will remain as it was where you had set it. In this case, readjusting would not be required as you keep zooming in and out. 

Parfocal lens vs varifocal lens
See the Difference of Parfocal and Varifocal (source)

3. Zoom Ratio 

Another way of describing the focal length’s range in a varifocal or parfocal lens would be the zoom ratio. This ratio is of the longest and shortest focal length of the lens. The main aim should be to understand the operating range of a certain lens and how the image can be affected because of this range. 

Also, most of the parfocal lenses have a zoom ratio of 3:1. It has been noted that lenses which have a zoom ratio of 1:1, 2:1 and 3:1 have comparatively better quality than that of the higher lens ratios. This is because they offer chromatic aberration. This means that the these lenses are much better as their aberration is lesser as compared to the zoom ration of 4:1 or even higher. 

The major difference between both of the lenses is related to focusing. A varifocal lens can turn out to be a more affordable and favorable option if you are going to be setting up the camera in one place and then remain at the exact same focal length. However, you need to switch to a parfocal lens if the subject isn’t going to remain constant. 

Zoom Ratio
Difference of Zoom Ratio (source)

How Useful is a Parfocal Lens?

The parfocal lenses are most useful when the work involves taking videos. It is because otherwise, it would actually be pretty awkward to continuously keep moving the focus as the zoom changes. It is for this reason that most of the high-end lenses are made parfocal. There are a few parfocal lenses of Canon which work great for the purpose of taking videos like the Canon’s 70-200 f/2.8 Non-IS. Also, the Panasonic 7-14 f/4 is also a great option.

Now, you must have noticed that the modern DSLR lenses have autofocus and therefore do not require parfocal. The focus of these cameras is faster than what you could adjust with your thumb and wrist. But then when it comes to capturing great quality videos, the parfocal lenses are still an excellent asset.

Imagine a situation, you are on the set and the operator would quickly be able to zoom into the subject, then focus and again zoom out. All of this has to be done within the span of a few seconds for getting that accurate focus. In situations where you are shooting documentary or an action sequence, a parfocal lens would be beneficial. 

The zoom lenses used for cinematography need to have the parfocal ability so as to be of any practical use. When the focus is adjusted manually by a focus puller, it is nearly impossible to remain that way while zooming.

Theoretically, this might be possible; however, if the subject moves or if the camera moves, there are way too many variables that would need correction consistently. 

Summing Up 

With the evolution of technology, DSLR’s definitely have gained quite impressive video capabilities. The thin line between video and a still camera has almost diminished. However, the line between the still and video lenses is still there. If you would like to shoot amazing quality videos, it is not just the kind of lenses that you should focus on. There are several other essential factors that need to be looked at. 

Now, the question is should you really be getting a parfocal lens or not? Well, you might consider getting it if it is ergonomically equal to the varifocal lens. The best way to find that out is by testing it out yourself. This way you would be able to judge what would be the best option for you. Now that you have understood the difference, find out which lens you should use for street photography.

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