What is the DataColor LensCal
The DataColor LensCal is a device which you use to calibrate your lens and ensure it is focusing correctly. Although the majority of lenses are calibrated in the factory, there is still the occasion whereby you maybe experiencing situations where the lens does not appear to be focusing on what you believed it should have been.
From my experience, issues can occur whereby the lens is focusing slightly in front (front focusing) or slightly behind (back focusing) from what we intended when making the exposure.
What do you get in the box
The SpyderLensCal comes in flattened form in a retail pack.
A base plate, with tripod attachment and bubble level.
A square chequered focus pattern.
There is a ‘quick start guide’ online outlining the steps you take to perform the adjustment, but no software or any thing else to guide you. You are going to need to find out how to set individual AF adjustments on your own camera. and yes, this does mean reading the manual…
Setting Up The DataColor LensCal
Setting up the LensCal is very straight forward, simply raise the target area and clip the ruler into position . It is important that the LensCal is perfectly straight and to help you achieve this, a small bubble level is located on the base.
The DataColor Lenscal can either be positioned on any flat surface such as a table top or fastened to a light stand or tripod using the standard 3/8th tripod thread located underneath the LensCal device.
Using the SpyderLensCal
You need a camera that supports AF adjustment.
I found it best to attach the device to the top of a tripod, and use the bubble level to level everything up. It’s important to get things lined up carefully and you need to be square on to the target.
To eliminate any camera shake at all, I used the Mirror lockup mode on my Nikon D3s and also a remote cable release. I used Manual exposure mode so that my exposures were consistent but I see no reason why Aperture Priority mode or even program mode could not be used. The ISO on the camera was set to 200 to ensure I got the cleanest image possible. Performing the tests in good light also helps in obtaining a reasonable high shutter speed.
Testing The DataColor LensCal
When setting things up, I make sure that the centre AF point is selected and that it is focusing on the centre of the target.
The ‘quick start guide‘ suggest taking photos and zooming in with the rear screen to view the ruler and see whether the front or rear section is sharper.
If the numbers below the Zero mark front are sharper, then the lens is ‘front focusing’ and If the numbers above the Zero mark front are sharper, the lens is back focusing.
Personally, I found it easier to take the photograph and then view it on the computer screen at 100% rather than on a tiny LCD screen on the camera.
Camera To LensCal Distance
The suggested distance between the camera and the lensCal device is 25 x the focal length.
25 times the Focal Length of the lens under test (25xFL), which resolves to 8.2 feet per 100mm of Focal Length. It is not critical that the distance be precise, although the closer the distance the more critical it is. In general +/- 10% is fine.
For example, for a 200mm lens, 200mm = 200/100 x 8.2 = 2 x 8.2 = 16.4 = 16 feet is OK
To simplify even further, think about it this way – take the focal length and move the decimal point 2 place to the left:
100 becomes 1
200 becomes 2
50 becomes .5
25 becomes .25
Then shorten 8.2 to 8 and multiply:
100mm = 1 x 8 = 8 feet
200mm = 2 x 8 = 16 feet
50mm = .5 x 8 = 4 feet
25mm = .25 x 8 = 2 feet
Making The Adjustments
If you need to make adjustments, you can use the camera’s adjustment procedure to alter it. Please read the camera manual to find out how to do this
In the end, I decided to just take a series of photos at microadjust settings of +20, +15, +10, +5, 0, -5, -10, -15 and -20 and see what they looked like.
After taking the series of images, I processed them in Adobe Lightroom (with no sharpening or noise reduction) and cropped out just the target. I then viewed each individual photograph at 100%.
Out of all the lenses I tested, I found that my Sigma 100mm macro lens was back focusing which is something I have been concerned about for sometime now and also my Nikon 24-70 f/2.8 was slightly out according to the LensCal.
Cameras with only 1 setting for a zoom lens.
Some cameras may only allow you save one AF adjustment per lens so in the case of a Zoom lens the best approach is to calibrate it at 1 focal length.
Using a 70-200 zoom lens as an example.
The best way to approach the issue of a zoom lens with a camera that only stores 1 AD Adjust setting, is to test and adjust (if necessary) at the 200mm setting. Then test at 70mm and see how the AF is performing. Since there is more DOF at the 70mm setting (unless you are very close) usually there is enough margin for error that any difference in how the AF performs at the near and far range of the zoom. To summarize, generally test and set at 200mm, and then do a quick check at 70 mm at the appropriate shooting distance.
If the AF Adjustment at the extremes of the lens are very different, then you will have to make a decision either to go with one or the other (depending on your shooting needs), or use them both at different times, when using the lens for different purposes. If both ends must be right, then the lens will have to be serviced by the manufacturer to bring the short and long end of the zoom into proper calibration. (Check with the service center to see if this is possible for your specific lens).
Microadjustment definitely works if your lenses need it, however at the back of my mind, I do wonder just how many people really do work that requires such precision set-up.
The times I’m really picky about detailed focus is in my product and still life photography especially where depth of field can be shallow so I really need to nail that focus.