How to make a Lens Distortion Target for evaluating your lens distortion and how to 'measure' it in Photoshop or Lightroom.
How to make a Lens Distortion Target
One of the common imperfections of photo lenses is distortion, specially with wide-angle lenses. In this video, I show how you can build a lens distortion test target. I'll also explain how you can get a simple, if not very accurate, measure of distortion using either Photoshop or Lightroom.
You can download the target png file I designed for this purpose HERE. (You can do 'Right Click -> Save Link As' to save the file to a local folder).
Print the target at 20x30in size using a printing service such as Costco in the US or use your home printer if it can print this large.
Here are links for the materials I used from Amazon:
- 1/2in Thick 20x30in Foam Board (only pack of 10 available at time of writing in Amazon. Search for single units instead when available)
Print and Spray Adhesive
You will need something rigid and very flat to later hold the target. For this purpose, I bough tick 1/2 inch foam board as it is lightweight and relatively inexpensive.
Photos of this size, normally come in a roll from the photo center. In order to flatten the surface, lay the foam board and possibly some weights over the print and let it sit for a few hours. This should reduce curling significantly and will make it easier to glue to he foam board.
Sraightening the Print
Before using the spray adhesive, prepare the work surface by protecting it with paper or plastic bags. Make sure to shake the adhesive can well before using. Spray the foam board thoroughly, trying to distribute the glue as evenly as possible. Cover the foamboard with the target print making sure that the two are very well aligned with each other.
To use the target, I recommend that you mount it on an easel as shown here. Use a level to ensure the target is aligned vertically.
Position your camera to fill the frame with the target and take some tests shots.
Camera Mounted on Tripod
The figures below show the lens distortion compensation sliders for Adobe Camera Raw and Lightroom respectively. Refer to the video for more detailed instructions on how to correct distortion with these programs.
Adobe Camera Raw Distortion Compensation
Lightroom Distortion Compensation
By noting how much adjustment was required in the compensation slider, you get a practical and simple measure of the amount of distortion in your lens. Note that this method may not work with lenses exhibiting a more complex distortion pattern (moustache for example). However, for most common lenses, this method should work well.
Comments, questions, suggestions? You can reach me at: contact (at sign) paulorenato (dot) com