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It Works, But Do You Really Need It?
on January 22, 2014
There is this little voice in the back of my head that kept asking, is my camera achieving precise autofocus? I don't have to wonder any more, the answer is yes; and well I don't need this device any more. The good news / bad news, after spending a morning messing around with setting this up, taking pictures and evaluating focus points; both of my lenses focus perfectly - no adjustment was necessary. The biggest culprit to missed autofocus is not that the autofocus system is not calibrated, but the camera choosing the correct autofocus point.
Until I used the SpyderLensCal, I would have never been satisfied that my camera was focusing correctly. I had absolutely no reason in the world to believe there was something wrong, just this doubt in my mind. When I discovered that my camera has the micro focus adjustment capability, I wanted to test my lenses. Now that I've done the test, well I feel kind of silly.
Here are the cameras that have micro focus adjustment (March, 2014 update, as listed by DataColor at the time of this review - see comments, there are more sony cameras than listed here)
Canon (50D, 7D, 5DMkII, 5DMkIII,1DMkIII, 1DMkIV, 1DsMkIII, 1Dx, 1Dc)
Nikon (D7000, D300, D300s, D700, D800, D800E, D3, D3s, D3x, D4)
Sony (A850, A900, A77)
Olympus (E-30, E-620, E-5)
Pentax (K-20D, K-30, K-5, K-7D, K-2000/K-m, K200D, 645D, K-x)
The caveat with this adjustment is, if you are using a kit lens, don't bother with this target. The depth of field on a kit lens at f 3.5, 4, or 5.6 is so great - even at 200mm, you will never ever see a need to adjust the focus plane. This target is really only useful for f2.8 and above lenses. And frankly, it is only useful for 70mm and longer. I suppose it could be useful for macro lenses, except that the tolerances at incredibly close focus distances are so critical, I'm not sure you can align the target and your camera correctly to reliably do this test.
The procedure is simple but painful. Essentially you set up the target parallel to your film plane, with the camera exactly centered in front of the target. You need to be about 50 times the focal length away from the target (so with a 200mm lens, that means about 10 meters, or 30 feet). The camera has to be on a tripod and the target on something very stable - a table or another tripod. The target needs to be lit fairly brightly - a flashlight will do the job (color balance and even lighting is irrelevant). Set the camera to ISO 200 (you want a sharp grain free image) and the largest / finest Jpeg image you can dial in (yes you can mess around with Raw if you like, but you already knew that - and it doesn't really improve the test other than to add an extra step at the computer). Set the camera to aperture preferred and set the lens to the widest aperture. Now comes the critical piece - you need to set your camera autofocus to a single center spot and use pinpoint if your camera has that setting (some cameras can use a wider or narrower square for focusing). If you allow the camera to choose the focus point, it will focus on the front edge of the target and it will look like your lens is way off. There is one positive thing I learned about my camera, even though it lit up with the focus point on the center of the target, it actually focused on the front edge of the target. Put the center focus spot exactly on the tiny square target next to the 0. Now move the focus to infinity, press autofocus, and take a picture.
Now comes the painful part. On the camera LCD you can vaguely check your work. Because the target image will be fairly small, you'll have to blow up the playback to maximum size. At this point, basically check to see if you can read the numbers and lines clearly (you didn't get camera shake and the exposure was somewhere near right). If all looks good, repeat the image two or three more times (each time rack the lens to infinity focus). With those three or four images, now go to your computer and look at the image. You will have to blow the image way up to see the lines. You are looking for the one line that is the sharpest. If the 0 line isn't the sharpest line, then you need to do the micro focus adjustment on your camera. I would suggest changing it a lot at first so you can see the difference (this is a bit like when you make adjustments with Photoshop, first go big to see the effect, then go back and tweak it to the subtle change you really need). After making the adjustment, take more pictures.
Now you probably see why a really solid tripod is critical (you are going to do a lot of removing and inserting your memory card), and why it is critical to set the target on something solid.
In the end, if you find out your lens was focusing one direction or the other by a half an inch or an inch - well that's good news; you made the adjustment and now can rely on autofocus in those critical situations. If on the other hand you find out everything was just right, well this was a futile exercise. Remember, this test doesn't tell you anything about the quality of your lens, it only tells you if your lens can autofocus accurately.
Some tricks I learned while setting this up. Don't over think the set up. If the target is a little bit crooked, it isn't going to make a lot of difference (the 0 line and the focus target are right next to each other, you'd have to be a long ways off crooked for that to matter. Make sure you get your tripod perfectly level - the bubble in the exact center of the bubble level. Match the camera and target height as best you can. Ultimately I switched to Manual on my camera and bracketed the exposure several stops. I was using a flashlight to light the target and the target image size was so small, the evaluative exposure was way off. Don't mess around with lenses less than f2.8, this isn't worth it.
When I consider the cost of my equipment (a Canon 7D, with 70-200mm f2.8 II and 24-70mm f2.8 lenses) and the cost of my time missing focus, this device isn't terribly expensive. Now that I've found out my camera focuses correctly, well this is a waste of money. I'm not sure I'll ever use it again.
I find it very difficult to figure out who would really benefit from this device. In some roundabout way, a professional might find it useful if they have three or four bodies, and several f2.8 lenses. Unfortunately for Datacolor, those people already belong to the professional camera services of their brand of camera and the manufacturer does this adjustment for them (Canon has this service for gold and above Canon Professional Service members). A cleaning and calibration provides exactly this service.
There are ways to build this device yourself for virtually no money. They aren't terribly hard to do if you are a little bit handy. After I've used this commercial device, I'm not sure I would be happy if I'd spent a day building one myself. I really think this is a solution looking for a problem.