Tag Archives: How To

Lens AF Calibration explained

What follows here is taken from Brani Srnec’s educational segment on lens autofocus as presented at the March, 2016 meeting.


Contents

1.  Why to Calibrate
2.  How it works
3.  Calibration naming conventions
4.  Calibration tools
5.  Getting ready – what do we need?
6.  Camera settings
7.  Calibration steps
8.  Calibration tolerance values
9.  Prime vs Zoom lens calibration

1. Why to Calibrate

  • There is some tolerance in AF during manufacturing process
  • To get the best possible sharpness from your lens
  • To get familiar with your lens sharpness, focusing speed, accuracy, bokeh and other aspects
  • Calibration is a complex process
  • Slight autofocus issues will be more noticeable when using high resolution cameras and/or lenses with very shallow DOF (f1.2-f2.8)
  • Useful for portrait, event, wedding photographers, not so much for landscape, architecture…
Calibration 1
Example of Front Focus on a 50mm f1.8 lens. Notice that the sharp area is in front of the 00 target point.
Calibration 2
Example of adjusted focus with the same 50mm f1.8 lens after adjusting the lens calibration by +9 in the camera settings.
Calibration 3
Example of a front-focusing 50mm f1.8 lens. Auto-focus thinks it is in focus, but the image captured by the sensor is not in focus.
Calibration 4
Example of adjusted focus with the same 50mm f1.8 after adjusting the lens calibration by +9 in the camera settings.

2. How it Works

Good news:

  • The process is safe and any changes are reversible
  • No physical adjustments = no damage to the camera or lens

Bad news:

  • AF adjustment is not available in every camera
  • Calibration requires a calibration tool, time and patience
  • Calibration is lens-camera specific. Only one value can be stored for a specific lens/camera combination
  • If you use more cameras, you need to calibrate the same lens for each camera
  • You can save up values for different lenses (even values for the same lens combined with a teleconverter)

3. Calibration naming conventions

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

![AF Fine Tune screen on Nikon](AF-Fine-Tune-screen-on-Nikon_thumb.png AF Fine Tune screen on Nikon)

Calibration 5
AF Fine Tune screen on Nikon cameras
Calibration 6
AF Micro Adjustment screen on Canon cameras

4. Calibration tools

http://regex.info/blog/photo-tech/focus-chart/

Focus Calibration Tool – Free Download


Calibration 8Focus Calibration Tool – ~$2.56 from eBay


Calibration 9

Focus Calibration Tool – Focus Pyramid – US$24.95 from Amazon.com (currently unavailable on amazon.ca)


Calibration 10Focus Calibration Tool – LensAlign MkII – ~$169.14 from Amazon.ca


Calibration 11

Focus Calibration Tool – Datacolor Spyder LensCal SLC100 – $82.79 from Amazon.ca


Calibration 12

Focus Calibration Tool – automated calibration software – US$134.88 from BH Photo Video


Calibration 13

Focus Calibration Tool – Sigma USB Dock – for use with specific Sigma lenses – US$59.00 from BH Photo Video

5. Getting Ready

Yo will need:

  • Calibration tool
  • Tripod
  • Plenty of natural or artificial light
  • Tethered shooting helps to review results much faster than loading test shot to the computer and more accurate then reviewing in the camera

6. Camera Settings

  • Manual mode
  • Manual WB
  • ISO between ISO100-400
  • Shutter speed at least 1/250
  • Aperture wide open (smallest f stop)
  • Centre focusing point and AF On
  • IS/VR on the lens Off
  • Viewfinder grid On helps to level camera
  • Timer On/Exposure Delay Mode On/Cable shutter release/Mirror Up On

7. Calibration Steps

  • Place calibration tool on a flat well lit surface
  • Put camera on a tripod in a distance you normally use the lens
  • Some sources recommend about 25 times the focal length of the lens (e.g. 85mmx25=2.1m) [Source]
  • Level camera with the centre of the focusing point
Calibration 14
Position of camera relative to the focus calibration tool. The distance to the tool will vary with which lens you are calibrating.
  • Take a test image and evaluate focus accuracy on the monitor screen at 100% view
  • When the lens Front focuses, dial “+” number in the camera AF Adjustment menu
  • When the lens Back focuses, dial “–” number in the camera menu

↓ “-” back focusing

↑ “+” front focusing

  • Take another image and repeat the first or second step until the sharpest part of the image is the one you focus on
  • Don’t forget Refocusing between shots (I used my hand to put in front of the lens to force the focusing system to refocus and then I focused back on the target)
  • Take notes
  • When you think you are done, take plenty of test images to confirm your AF adjustment decision is correct
  • Take your gear for a real test outdoors. Try different distances and see if you are getting good and consistent results.
  • Periodical recalibration is recommended (once a year should be fine)

8. Calibration Tolerance Values

  • The maximum AF adjustment is +-20 increments
  • If you find that every lens you test is back/front focusing by about the same amount, it is possible that there is actually problem with the camera AF system instead of the lens AF
  • If you find that a lens needs adjustment more than 20, the lens probably needs a physical adjustment done by professional service

9. Prime vs Zoom lens calibration

  • Calibrating Prime lens is relatively easy, because you calibrate AF for only one focal length.
  • Calibrating Zoom lens can be a challenge, because you can experience different results at different focal lengths

Example:
My 70-200mm lens front focused
At 70mm it needed +1 adjustment
At 200mm it needed +7 adjustment

Problem:
you can save only one adjustment value in the camera for a specific lens. This adjustment is then applied for all focal lengths. However, there are some cameras that can save two values for one lens.

Solution:
Using average of the AF adjustment values. In my example +4. Using AF adjustment value of the focal length you use the lens most often. In my case I use the lens the most often at 200mm, so I would save +7.

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Lethbridge Photo Lab Tests

Photography can be simplified into three very basic parts. Capturing the photo, processing or manipulating the photo, and printing the photo. We have near total control over the first two, but when it comes to having our images printed we usually rely on outside sources to take our photo and present us with an accurate representation. Sadly, it doesn’t always work in our favour because we don’t have the control over the final outcome. It becomes a case of trial and error to arrive at a result we are happy with. The various sources to have our images printed here in Lethbridge can provide us sometimes vastly different results.

So, to take some of the guess work out, Brani has gone to the various photo printing shops in town to get prints made of the same set of images. What follows is the result of his work. These prints were presented at our December 2015 meeting to allow members to inspect and see the differences first-hand. Read on and you’ll see Brani’s personal findings and how the images were judged by the members at the December meeting.

The Test Images

Test Criteria

  • Price
  • Processing Time
  • Convenience
  • Staff Experience
  • Print Handling
  • …and most importantly, Quality

Tested Photolabs

Paramount Printers was approached, but they do not do photo printing. Likewise, Shoppers Drug Mart was to be included but they print off-site and generally have  7-10 day turnaround which did not fit with the timeframe of this test.

Prices

Photo Lab 12×18 8×12 10×12 6×8 or 5×7 4×6
Costco $5.99 2.49 $2.49 $0.27 $0.10
London Drugs
(20% discount)
$14.99
($11.99)
$7.99
($6.39)
$5.99
($4.79)
$1.69
($1.35)
$0.39
($0.31)
McBain Camera
(10% discount)
$17.95
($16.16)
$5.99
($4.79)
$5.99
($4.79)
$5.99/$1.49
($4.79/$1.34)
$0.39
($0.31)
Walmart $6.97 $3.57 $1.77 $0.10
Paterson $13.50 $6.00 $5.00 $3.00 $0.96
Kopiko $3.75 $3.50 $1.75 $1.75 $1.25

Results

The three sample images were submitted to the photo labs with instructions that the images not be colour-corrected/balanced in any way.


Costco

Pros:

  • Inexpensive
  • Online ordering is available
  • Helpful staff
  • Professional print handling

Cons:

  • Must have a Costco membership card
  • Cannot do matte and glossy prints on the same order. Would have to place two orders.
  • Minor cropping of 0.25cm was applied to both 12×18 prints
  • All prints had a minor greenish tint
  • The B&W print lost shadow detail
  • The colour print lost highlight detail

London Drugs

Pros:

  • Online ordering is available
  • 20% discount for Lethbridge Photography Club members
  • Helpful staff
  • User-friendly software at the in-store kiosks
  • Professional print handling
  • Prints had good tonality

Cons:

  • Visible banding or ‘ribbing’ pattern in 4×6 prints
  • All prints had a strong magenta tone

McBain Camera Store

Pros:

  • Online ordering is available
  • 10% discount for Lethbridge Photography Club members
  • Helpful staff
  • Professional print handling
  • White balance was correct for all prints

Cons

  • The most expensive even after the 10% discount was applied
  • Both glossy images were printed on semi-gloss paper
  • Instructions to print the Colour Test Image and Colour Calibration Image on glossy paper was not followed, they were both printed on matte paper
  • B&W print was printed “true archival matte paper” which  caused very low contrast in the image
  • It is recommended to discuss the best paper selection for a print before placing an order

Walmart

Pros:

  • Inexpensive
  • Correct white balance and good tonality in the Colour and B&W prints

Cons:

  • Online upload is not available
  • Kiosk software is not user-friendly, some machines were broken and some freezing, causing line-ups and customers frustration
  • Staff inexperienced and unhelpful
  • Cannot do matte and glossy in one order
  • Unprofessional photo handling, leaving fingerprints on prints, rolling prints in a plastic bag
  • One glossy image order was printed on a matte paper
  • All prints were over-sharpened
  • 5×7 print had a green tint

Paterson Photography

Pros:

  • Online upload via Dropbox or email available
  • Helpful staff – Image and paper proof before print available
  • Professional Print Handling
  • Custom size printing
  • Variety of photo paper
  • Correct WB of all prints and good tonality on 12×18 prints

Cons:

  • Business hours are Monday to Saturday,  10am-5pm; however, they may be closed during business hours without notice (it is good to call before to make sure someone is there)
  • 8×6 print was overexposed and highlights were completely lost. Upon revisiting the lab and having the image reprinted on a lustre paper, the tonality was good.

Kopiko

Pros:

  • Inexpensive
  • Images can be emailed
  • Correct WB of B&W print

Cons:

  • Unprofessional photo handling, leaving fingerprints on prints, handing prints in a plastic bag
  • Using uncalibrated printers
  • Low quality photo paper
  • Minor cropping of about 0.25cm was applied to both 12×18 prints
  • Printer wheels leave visible marks on the prints
  • Very low tonality and contrast in all prints due to low quality paper

Quality

General Problems:

  • Walmart applies automatic sharpening to all prints with no option to select ‘no adjustments’ when placing an order
  • Kopiko uses low quality paper and printing
  • 4×6 prints from London Drugs had a banding or ‘ribbing’ pattern, and all prints had a magenta tint

My Findings and Final Results

Sample_B&W
B&W Test Image (18×12 Matte

Costco:
White balance incorrect (green tint in darker areas), higher contrast (lost shadows)

London Drugs:
White balance incorrect (magenta tint), good tonality

McBain Camera:
White balance correct, extremly low contrast (due to use of “true archival matte paper)

Walmart:
White balance correct, good tonality, oversharpened

Paterson Photography:
White balance correct, good tonality

Kopiko:
White balance correct, very low tonality and contrast (due low quality paper?)

My picks:
Paterson Photography
McBain Camera (assuming they use the proper type of paper)
Walmart (oversharpened)


Sample_Colour
Colour Test Image (18×12 Glossy)

Costco:
White balance incorrect (green tint), overexposed (some highlights lost)

London Drugs:
White balance incorrect (magenta tint), little underexposed (some shadows lost)

McBain Camera:
White balance correct, good tonality

Walmart:
White balance correct, little overexposed (not as much as Costco), over-sharpened

Paterson Photography:
White balance correct, good tonality, contrast was a little low

Kopiko:
White balance incorrect (magenta tint), very low tonality and contrast (due to low quality paper?)

My picks:
Paterson Photography (low contrast),
McBain Camera (printed on semi-gloss instead of glossy)
Walmart (over-sharpened)


Sample_Calibration
Colour Calibration Test Image (6×8 Glossy)

Costco:
White balance relatively accurate (little greenish in darker areas and darker reds), low tonality (shadows a little lost)

London Drugs:
White balance incorrect (magenta tint across whole spectrum), good tonality

McBain Camera:
White balance correct, good tonality

Walmart:
White balance incorrect (green tint across whole spectrum), good tonality, over-sharpened

Paterson Photography:
White balance correct, overexposed (highlights completely lost)

Kopiko:
White balance correct, very low tonality due to low quality paper (highlights completely lost, and shadows partially lost)

My picks:
McBain
Paterson Photography (assuming they use the proper type of paper)

Evaluation by Photo Club Members

These are the results from the December, 2015 meeting. Members were asked to rate the images as: first, second, third and worst.

Photo Lab 12×18
B&W
Matte
12×18
Colour
Glossy
8×6
Colour Callibration
Glossy
Costco Third
London Drugs Second
McBain Camera Second First
Walmart First Third Third
Paterson Second First
Kopiko Worst Worst Worst

Other Info

All prints are available to club members for detailed inspection upon request. If you would like to see the prints in-person, please make contact with Brani at contact@lethbridgephotoclub.org


Update – January 2016

As a follow-up to the prints done at Paterson Photography, club member Chris Oates visited with Mike Paterson and presented the following video interview at our January 2016 meeting.

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How to Submit Images for the Monthly Theme

Every regular monthly meeting held by the Lethbridge Photography Club has a theme that paid members are invited to submit one image for (with the exception of June). These images are then evaluated by other members in advance of the regular meeting and their comments and critiques of the submitted images are then read aloud to the membership. Discussion is welcomed and encouraged as the images are presented to the membership at the monthly meetings.

Images are to be submitted via email to theme@lethbridgephotoclub.org typically by 11pm on the Sunday before the next regular meeting.


Image Size

For optimal presentation as our meetings, we ask that images be sized to be no smaller than 1200-pixels on the smallest side. Compose your your image as you wish, but do ensure that the overall size is large enough.

Our digital projector has a resolution of 1920 x 1200 pixels. Images that are smaller than that projector’s resolution will be enlarged when displayed and the image quality will not be optimal.


Evaluation

After images have been submitted, an evaluation meeting is then held the day after the deadline, typically on the Monday before the regular meeting.

We encourage members to attend these evaluation meetings as a way of learning how to critique images and further discussion of photographic technique and vision. Each image submitted is discussed and constructively critiqued. Comments are noted and will be read aloud at the regular meeting when the images are presented to the membership.


Print Themes

While the majority of our monthly themes are digital, we feel that the print is still an important part of photography. We typically have three to four print themes each year.

To participate in our print themes, we have a few guidelines:

  • Be a paid member in good standing.
  • Prints can be any size you like. Bear in mind that larger prints may present better than a smaller print.
  • Prints do not need to be framed. If they are framed, please remove the glass.
  • Whether your print is matted is up to you.
  • Unframed prints should be firmly mounted on a stiff backer board so they can stand upright.

Prints need to be brought to the meeting before 6:15pm so we can get them organized for judging.


Club Year-end – June

Our annual theme for June is an open theme where you may submit images as you please.  For our year-end meetings, we deviate from our usual and accept both digital and print submissions. All submissions will be evaluated by the membership as a whole at the June meeting, with discussion about the images.

We invite you to submit images in any of the four following categories:

  • Print:  Single image
  • Print:  Series-of-Three
  • Digital:  Single image
  • Digital:  Series-of-Three

For the Series-of-Three, the images should belong together. By this we mean belong in the sense that they are of the same subject, subjects that balance, contract, or complement each other.

Print Submissions should be brought to the regular meeting on the third Thursday in June by 6:15pm.

The deadline for digital submissions will be the night before the regular meeting.


Themes for the 2015-2016 Club Year

September 17 – ’Open’
October 15 – Three
November 19 – Memories (prints)
December 17 – Glass
January 21 – Food
February 18 – Old
March 17 – Blue
April 21 – Dreams (prints)
May 19 – Sign of the times
June 16 – ’Open’ (print and digital)

July – no monthly meeting during summer break
August – no monthly meet during summer break


Past Themes

2015 – February – Fire (digital)

2015 – March – Purely Abstract (digital)

2015 – April – Textures (prints)

2015 – May – 10 Second Exposure