Fixing Front and Back Focus

LensAlign MkII

The LensAlign MkII focus calibration tool is the new and improved version of the original LensAlign, featuring a mechanism that makes it very easy for you to properly align your camera with the focus-indicating ruler.  The ruler itself has clear markings that make it easy to detect any misalignment.

What's in the Box

In the box you will find 10 things: assembly instructions, the tripod mount, the standard ruler, and 7 reinforced cardboard pieces used to build the LensAlign setup.  On the back of the box you will find some oversimplified instructions on how to use the system.

If you want to really experiment with the effects of depth of field or need to use the system at longer distances, LensAlign also offers an optional 32-inch extended ruler for the MkII system:

Assembly

Assembly of the LensAlign system will take you at most 10 minutes, as the instructions are simple and more or less self-explanatory.  One thing worth noting about this system, however, is that once it's assembled, it really doesn't like to be taken apart.  Unless you're extremely careful, you'll quickly start seeing wear-and-tear around the attachment points of the individual components.

Here are some photos of the completed system.  As you can see, the creators have made it quite easy to replace the standard ruler with the extended one:

Usage

Using the LensAlign system to check your lenses is very simple, as it should be.  First, position the LensAlign on a flat surface, or mount it on a tripod.  In both cases, you must make sure that it's completely level.  The former may be more difficult than it seems, as the LensAlign doesn't include a bubble leveler (whereas the Spyder LensCal does).  If your tripod doesn't have one either, consider gluing one to your LensAlign yourself instead.

Once you've positioned the LensAlign, mount your camera on a tripod make sure the height is the same as that of the LensAlign.  Point your camera at the left side of the system, and try to have it be as parallel as possible to the target.  Important: make sure your tripod is sturdy enough that your camera doesn't move relative to the lens align as you're making focus adjustments in the meny.

If you just want to check for front-focus or back-focus, minimize the distance between your camera and the LensAlign while still being able to see the entire unit in your viewfinder.  Select the largest (i.e. wide-open) aperture setting on your lens.  If this test reveals no problems and you have second thoughts, you can always try increasing the distance to see if this will reveal any problems (this is where the extended ruler would come in handy).

Finally, finely adjust the position of your camera so that you can see straight through the "True Parallel Alignment" area on the left side of the LensAlign.  Via live view, you should be able to see through both the center target and the smaller target to the right of it (i.e. whatever is behind the LensAlign will be visible), and the red ring of the center target should be perfectly centered inside the opening.  Make sure your center AF point is aligned with the center of the target in the viewfinder. 

Once you've got your camera aligned, all you need to do is take some test photos!  Before each test, reset your lens's focus so that the camera has to do a little bit of work to lock on.  Try starting your lens at both infinity and minimum focus, and repeat each test a couple of times.

As a reminder, make sure that your lens's aperture is set to the widest setting (i.e. wide open, or the smaller aperture number: F1.4 in this case) and that you are focusing using the viewfinder, not live view.

What to Look For

The LensAlign as seen by the camera being tested. (Lens: FA* 85mm at F1.4)

If your lens is correctly aligned, after focusing, the zeros on the ruler should be the sharpest, and the numbers above it should be equally blurry.  The same goes for the bold line beside the red square.

No Adjustment Needed

Below is a close-up of what the ruler will look like if your lens is good to go.  Note that depending on your lens, the depth of field may be wider, and thus you may have to look beyond just the big 0 and 4's.

Front-Focus

In this photo, the lens is exhibiting front-focus, and you would need to apply a negative AF adjustment in your camera.  Keep on subtracting one until the photo looks like the above.

Back-Focus

Here, the lens is exhibiting back-focus, and you would need to apply a positive AF adjustment in your camera.

As you can see, the LensAlign's ruler is quite good at making AF adjustment problems discernible!  Read on for an overview of the Spyder LensCal.