Correcting Ultra-Wide Angle Lens Keystoning
Correcting Ultra-Wide Angle Lens Keystoning
by James A. Rinner
The ultra-wide angle lens for the landscape photographers are those heavy pieces of glass that we just can't leave at home! They can capture dramatic skies like no other lens in your collection. The problem with them is a distortion called keystoning where the pitch angle of the camera causes vertical objects to lean toward the center of the image.
Below is a typical example of keystoning that plagues me when using an ultra-wide lens. The lens is a Panasonic 7-14mm (14-28 35mm equivalent) zoom lens used on an Olympus OM-D.
|Here is the original image with the lens pitched upwards to capture the dramatic evening sky. Notice how the power lines and towers pitch inward.|
With the original image above I am going to show you three different methods to lessen or remove the keystoning effect from the image. I am using Adobe Photoshop CS6.
Method 1: Using the Clone Brush and Content Aware Healing Brush
With some photographs, like the one above, you can easily remove the most obvious subjects (the power towers and lines) in the image by the simple act of cloning. I personally like using a Wacom Intous tablet but this can easily be performed with a mouse. When cloning/healing the different areas of the image make sure you choose from areas close to the part you want removed to keep the tonality smooth. Also be careful not to introduce repeated patterns into your image. Below is the finshed photograph with the power lines nd towers removed.
|As you can see the simple removal of the lines and towers has greatly reduced visual keystoning but the image still retains the keystone effect in other portions of the image.|
Method 2: Using Lens Correction or Perspective Control
What do you do if there are more obvious vertical objects in the scene that you don't want, or can't remove?
***To use the Lens Correction Filter do not use the automatic lens correction filter but the one accessed by pressing Shift+Control+R (in Windows version).***
Now go the "Custom" tab and slide the vertical perspective slider to the left (minus) direction till your vertical objects are once again vertical. Since I am shooting with an ultra-wide zoom even moving the slider all the way to the left (-100) my vertical objects are still keystoning. Click OK and return to the main Photoshop screen. Make sure you create new layers so you can see your progress. This also allows you to go back to various steps if you need to tweak something.
|So here is the I got with -100. Notice the power lines and towers still have some keystoning effect.|
I made the following final adjustments where I needed another -67 in lens correction.
Now I make my final vertical perspective correction and click OK for the corrected image.
Final results of the two consecutive lens corrections.
I could then remove the power lines if I wanted to but I decided to leave them because they add depth to the image. The image no longer has the keystone affect but you can see that I lost some of the image on the side. How do we keep all of the image and lose the keystoning affect? By using Photomerge!
Method 3: Automate Photo Merge
This next process has to be preplanned at the time of exposure. Because I am an old school photographer I shoot about 95% of my landscape work in manual mode. This is essential for this process. If I was to shoot these images in an automated mode on my camera the two images could have different exposures which would be very obvious in the merging and could cause some extra work trying to balance the images.
I take one photo (the one I used in the previous example) showing all the sky that I want to include. The next image is taken with the horizon in the center of the frame. This removes any keystoning effect.
Below you can see the two images I want to use in Adobe Bridge.
Having selected both images in Bridge I open them up in Adobe Camera Raw (you can also open up jpegs in ACR) and at this time I am only going to remove chromatic aberration and perhaps add a little sharpening. It is important that whatever you do on one image you do the same on the other so choose the "Select All" button in the upper left corner. Save these files. You can also skip this step and go straight to the next step and work on tweaking the final image later.
|Adobe Camera Raw (ACR)|
Now the fun! Go back to Photoshop and under FILE choose: Automate then Photomerge. The following screen will come up.
|Then browse for your files, select Auto (default), Blend Images Together (default) and Geometric Distortion Correction. Press OK.|
Wait a few moments for Photoshop to do it's magic and here is the result. If for some reason Photoshop has trouble aligning the images correctly you may have too many programs running. This is a major power process so close anything that is not needed and it should look something like this.
|Isn't this cool?|
What Photoshop has done is take the two images and created two layers. Below are the separate layers.
|This layer was created from the original "sky" shot.||This layer was created from the "horizon" shot.|
The next step you should do is duplicate both layers and the merge the two duplicate layers. This will allow you to work on them as one layer. Once that is done you can then crop the image to your liking.
|There were a few spots in the sky that I wanted to keep so the crop had a couple of empty areas on the bottom.|
Using the clone brush I fill in the blank areas being careful to make sure there are no repeated patterns.
|This is a seamless merge with no keystoning. It has a full, normal looking sky with out any unwanted cropping that usually happens when using vertical perspective control!|
|Original.||Original with power lines and towers removed.|
|Original using a double lens correction.||Photomerge with two images specifically taken for process.|
I hope you enjoyed this article. I am sure there are many more ways to accomplish this but is the processes I like to use.
The views and opinions expressed in this article are those of the author and do not necessarily reflect the views and opinions held by dpreview.com or any affiliated companies.