Photography - Knowledge

Understanding Lens Calibration: A Fix to Blurry Photography

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We have all at some point or the other been let down and gotten frustrated over the sharpness of an image. Correct focus is vital for the serious photographer. You can name elements such as composition, lighting, action, and emotion, but without focus, all seems to be lost in vain. The higher the use of our lenses, the more important is the need to properly maintain them. Among the most enigmatic camera maintenance procedures is Lens Calibration.

What does the lens do?

Lenses are optical devices that can transmit and reflect light, causing convergence of the beam onto a photographic medium wherein the image is then captured. They are very precise instruments which are constructed under the strict laws of optics to create sharp and crisp images. Over the passage of time, a lens’ precision can get compromised leading to images being slightly out of focus. Soft images can be a cause of multiple issues, some which are indicative of a fault in the camera or lens, others which may require just a change of technique or settings. 

Today’s cameras and lenses are constructed with certain tolerances which technically should fabricate sharp, in-focus photographs, but there is the chance of certain combinations being slightly out of alignment. This could of course be blamed on excess motion or a too slow shutter speed, but these progressive cameras should be able to autofocus in an instant. Hence, in case of all your settings being correct, the shutter speed is fast enough to capture the action, but you are still dealing with photographs that are lacking sharpness, one must consider the possibility of your lens being out of alignment with your camera. Just a slight fraction off from the manufacturer’s citing can make a world of difference to your blurry photos fix. 

While it is true that the majority of lenses don’t come automatically calibrated to your camera body, however, with the newer high-end cameras of now, an autofocus micro-adjustment feature is included which enables you to calibrate each lens separately. This calibration information is then stored within the camera itself so that your camera will remember each lens and adjust accordingly.

Lens Calibration is an important step towards getting the real world precise representation of the real world in the photos.

Why Calibrate? 

The one stop solution to blurry images is calibration. But why should you calibrate? The fact behind this is that even the precise camera manufacturers can make the grave error of calibration tolerance! And that’s the reason why we focus on calibrating for picture perfect photos.  

Calibration is camera and lens specific. This means that in case you have multiple cameras and lenses, you will have to fine tune autofocus on each camera and for each lens that you own. There are various factors such as sample variation, manufacturer defects, improper shipping and handling and insufficient quality assurance testing/tuning which can all negatively impact the autofocus precision. 

Most of the modern DSLRs and mirrorless cameras have a setting which will allow for the camera focus to compensate either for back-focus - when the focus is shifted behind your subject or for front-focus - when the focus is shifted in front of the subject. Most of the front and back focusing lens problems are common to human error. In case you are using a wide open aperture and you are handholding the camera, simple breathing or even rocking back and forth can throw you off your focal plane. 

Lens calibration
Importance of Calibration (source)

While the increase of megapixels in our cameras have a quite a few advantages, what it also does is expose potential focus problems. Therefore, the need for a properly calibrated camera setup is even more important today than ever.

Below are a few pointers which will make you consider the ‘why’ of calibration:

  • There will always be some tolerance in AF during the manufacturing process.
  • In order to get the best possible sharpness from your lens
  • In order to get familiar with elements such as focusing speed, lens sharpness, accuracy. Bokeh and other aspects. 
  • Minimal or slight autofocus issues will become more noticeable in case of using high-resolution cameras and/or lenses with very shallow Depth of Field. 
  • It is useful for events, wedding photography, portraits but not so much in the case of architecture or landscape. 

Camera V/s Lens Calibration

The calibration process of fine tuning autofocus operations so as to capture crystal-clear, macro shots is known as AF micro-adjustment. Lens calibration through physical adjustments to its internal components is a task reserved for experienced lens technicians as the lenses are required to be disassembled, tuned and then reassembled. Should a lens need a physical calibration it is strongly advised to send the lens to the manufacturer, instead of damaging the camera with risky DIY methods and voiding the warranty. 

How Does Calibration Work?

Each camera has particular settings which enable compensation for either back focus or front focus. The process of compensation can be performed in small incremental steps, typically from 0 to -20 and +20 in steps of 1. This allows for precise fine tuning of autofocus system. 

While the negative numbers compensate for back focus, positive numbers compensate for front focus problems. To understand it simply, setting a negative number will cause the focused point closer to the camera. Setting a positive number will cause a reversed effect, moving the focused point away from the camera. 

Pros: 

  • All the changes made during the process is reversible.
  • You don’t have to make any physical adjustments, hence protecting your lens from any damage.

Cons:

  • AF adjustment feature is difficult to find in every camera.
  • Calibration process demands time, patience and of course a calibration tool.
  • Calibration is a process which is lens-camera specific. Therefore, for each lens-to-camera combination, you can store only one value. 
  • If you use multiple cameras, then you will need to calibrate the same lens for each camera
camera vs lens calibration
Learn Back and Front Focus (source)

Calibration Naming Convention

As is pretty common in the world of technology these days, there is no standardization of naming things. Well the camera world is no different. Since each company and/or manufacturer comes up with technology that they develop themselves, they prefer to stand different in the land of competition which leads to patented titles and naming rights, most of all which mean almost the exact. 

For instance, while Nikon names the feature as ‘Vibration Reduction’/VR, Canon goes by the name of ‘Image Stabilization’/IS. Ironically, Tamron which is a third party lens manufacturer for both of these companies features the name of ‘Vibration Company’/VC. While they all sport various names, it’s but an obvious observation that the purpose or function is the same.  

If you are looking out for this feature on your device, it’s advisable to keep these names in mind: 

  • Nikon – AF Fine Tune
  • Canon – AF Micro-adjustment
  • Sony – AF Micro Adjustment
  • Pentax – AF Adjustment
  • Olympus – AF Focus Adjust

Calibrate Feature Availability

The calibration feature isn’t readily available on all cameras and is usually sported only by the high end DSLRs. The reason is this feature is considered to be part of ‘advanced’ settings by camera manufacturers. In our current date and time, all entry level, upper entry level and some semi-professional DSLRs do not include this feature.  You can easily check if your camera includes this feature by checking the camera manual. 

Calibrating Prime Vs Zoom Lenses 

A prime lens is a lens that has one focal length only. Prime lenses come in all focal lengths ranging from wide angle ones through to the longer telephoto ones. Calibrating prime lens is relatively easy, as only one focal length requires calibration. They also tend to be easier to calibrate due to fewer moving parts.

A zoom lens is a lens that has a range of focal lengths available to the photographer in the one lens. Zoom lenses have become increasingly popular over the past few years as they are obviously a very convenient lens to have on your camera as they mean you can shoot at both wide and longer focal lengths without having to switch lenses mid shoot. Calibrating zoom lens can pose some difficulty as you might encounter distinct results at different focal lengths. You can stick to these three lenses and work on your shots. 

prime vs Zoom lens calibration
Zoom vs Prime Lens (source)

Calibration Tools 

While one can find multiple methods described online for calibration, we have categorized them into the following three with the pros and cons listed.  

1. DIY Method –

Pros: 

  • These types of calibration procedures are free of cost 
  • If done in the right manner, work perfectly 

Cons: 

  • You might face precision or accuracy problems due to insufficient technical expertise 
  • It takes up quite a bit of time to setup correctly 

DIY methods do not work efficiently in the case of high-resolution cameras.

calibration tools
Easy DIY Calibration Tool (source)

2. Commercial Tools – 

Pros: 

  • A commercial tool will work with any lens-to-camera combination 
  • It can be fairly precise 

Cons: 

  • You will have to shell out few bucks for a commercial calibration tool 
  • It encompasses a fair amount of time for manual adjustments and fine tuning

3. Calibration Software – 

Pros: 

  • Can be of automated or semi-automated in nature 
  • They provide a high precision 
  • It saves time

Cons: 

  • Purchasing calibration software can burn quite a hole in your pocket 
  • The software will only work well with supported cameras
Calibration Tools
Calibration Software (source)

Calibration Steps

Now that you are aware of the various methods of lens calibration, let's dive into the easy calibration steps:

  1. Place the calibration tool on a flat, and a well-lit surface.
  2. Site the camera onto a tripod at a distance you would normally use the lens Say about 20 times the focal length of the lens. 
  3. Next, level the camera with the centre of the focusing point. You can check this by clicking any random image and assessing the focus accuracy at 100%view (on monitor screen).
  4. With the lens Front focus, click the ‘+’ number in the AF Adjustment menu of the camera, whereas with the lens Back focus, click the ‘–‘ number.
  5. Repeat steps 1 and 2, for another image till you can focus on the sharpest part of the image.
  6. Remember to refocus between shots. Make your camera understand the refocus concept- place your hand in front of the lens and then move your hand from it. This will help the focusing system to refocus and then focus back on the target. 
  7. Make notes.
  8. When you think you have achieved a decent calibration, go shoot various of test photos to confirm this AF adjustment decision. 

Next, start clicking outdoors and try different distances to see if you are getting flawless and consistent results. You can try outdoor portrait photography, aesthetic photography to become a pro with calibration. We recommend a periodical recalibration, say about once a year should keep it good. 

Calibration Distance

A big factor in the play of the lens calibration process is the variation caused by distance. This means that if the distance between the camera and the subject changes, the focus might be off again. This is caused due to various factors. The phase detects sensors in DSLRs require a great deal of light, which is why all lenses focus wide open, despite whatever aperture you set the lens to. Hence, a whole lot of variables are put into gear - chosen aperture, focus shift, focus distance, etc. 

Add to that, fine adjustments at very close distances that are much more granular than at longer distances. So, the AF fine tuning system isn’t programmed to cope with all these variables all at once, leading to different lens calibration values at various focal lengths, apertures, and camera to subject distances. 

This again can vary from lens to lens. While on some lenses, the difference is too minuscule to notice, on others, the difference is very noticeable.

Calibration distance
Focus and Distance makes the Difference (source)

The Usefulness/Uselessness of Camera Calibration

What is a common observation is that camera calibration only works dependably well at minor adjustments, when it is not acute. In situations where a camera body was to blame, the influence of an extreme tuning did not seem to be so bad, even though it still wasn’t very reliable. At the point where a lens was at fault, hitting above -10 or +10 led to very inconsistent results. 

In case you find that your camera/lens setup is in need of high adjustment values either in the negative or positive, it’s highly recommended that you do not intervene on your own and instead send the gear to the manufacturer for proper tuning instead. It’s probably the reason why none of the current DSLR manufacturers will allow for calibration of values higher than 20. 

Calibration Tolerance Values

The maximum of AF adjustment is +-20 increments. If you happen to find out that every lens you that you test is back/front focusing by about the same time. Then, there are chances that there is a trouble with camera AF rather than the lens AF. Should you find that a lens needs adjustment more than 20, then the lens mostly needs a physical adjustment performed by a professional.

Calibration is a Continuous Process

A fact you will have to make your peace with is that one time calibration isn’t going to tide you over. The autofocus precision will change over time. Various factors could cause this change from normal wear and tear, physical abuse, to changes in temperature. While there are a few who take the process of calibration too seriously by performing it as often as few times a month, a periodical adjustment once a year would also suffice.

The main goal behind performing it at regular intervals is maintenance and upkeep so that the gear performs at the levels it’s expected to. In case you notice any drastic changes in autofocus behaviour and AF adjustment, do not hesitate to take action. It’s always worth the hard work and even spending that money to maintain that standard of crisp and sharp photographs. 

Lens Calibration
Calibration a Continuous process (source)

Wrapping Up

Since every manufacture is different, calibration is a trial and error process. While you could possibly search online for a number of recommendations and approaches to lens calibration, they might not necessarily be the best. What you need to remember is that you need to have a full understanding of all the details of this process, the pros and cons and the resulting outcomes before attempting to decode this feature. Once you get there, it’s not an unsalable mountain, and you will soon have a sharp lens in a matter of minutes! 

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