Living in a part of the world where lens to body calibration is not possible I was really happy when micro-focus adjustment, MFA, was introduced in dSLRs and it was a major decisive factor for me to change cameras yet another time.
Unfortunately MFA can be quite frustrating and time consuming if you do not rely on a solid method. Iâ€™ve been myself quite close to buying focusing system products but I just couldnâ€™t justify the cost.
I have since found 3 reliable and free methods to adjust the focus of my lenses
Method 1: Sharper is bigger
In short this method relies on the fact that a sharper image will yield larger file size.
You will need for this a target with a lot of patterns and details I simply printed this resolution chart on A3 paper.
- Make sure your target is completely flat
- Set your camera on tripod with MLU 2 second timer or remotely triggered
- Set your camera to be perpendicular to the target
- Let your target fill the frame
- Set ISO to be in max 400 (lower is actually better)
- Set your lens to its widest aperture
- Set your image quality to fine large JPG or RAW
For a corresponding micro focus adjustment value
- Defocus your lens completely
- Focus using 1 shot Auto focus
- Take the shot.
- Repeat from step 1 twice
- Pickup larger file size between the 3 delete the others
- repeat the whole process for another micro focus adjustment value
Finally the value giving the bigger file size is the best one for this lens.
Of course you donâ€™t have to do this for all available values you can quickly check first using live view what range is giving the best autofocus results and use the above for fine tuning.
Method 2: MoirÃ© interference pattern
I wouldnâ€™t know how to explain this from a technical perspective but the idea is to focus on an LCD screen (not a paper) and pickup the micro focus adjustment value giving the most moirÃ© interference pattern, the whole procedure is explained in details at northlight-images and reference images can be found here and here.
Method 3: DIY Focus charts
These are actually
cheap free alternatives to the products you can find on the net. All you have to do is print the focus chart, do some folding and then test the accuracy of your autofocus system.
Here you are no longer relying on file size but on a ruler to know if you have any front/back focus issues.
2 charts are available for free download and use, the first provided by focustestchart.com with full and detailed instructions, the other is curtsey invisicord.com (also available in .doc format), also with instruction of use.
Well hope this well give you more confidence next time you are trying to calibrate a lens.
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