Every manufactured product has tolerances. You might have the most precise milling machine in the world, but whatever you produce, if you're shooting for 1.00000 in, the resulting product will not be exactly that, it will be off by a small amount. So if you're a high end camera manufacturer, the fit of your lenses to your camera body might vary by a few thousands of an inch. That's enough to affect where the camera actually focuses when you press that shutter release and activate your autofocus.
And it can change. Using your camera, swapping lenses, firing that shutter 50,000 times, it's going to change. If you're at all fussy about it, you're going to want to tune the alignment of your lens and camera body to give you the best possible focus. That's what the LensAlign product is for.
I was given a LensAlign MkII package to evaluate. I made it clear that if I did so, my evaluation would be 100% unbiased, I would report on my experience exactly as it happened, good and bad. I have no interest in this company and/or product, and the device will be going back to them after this is complete. I was not paid in any way for this evaluation.
On a scale of 1-10, 10 being the best, I would rate the product like this:
(a) Not adjusting your lenses........... 3
(b) Adjusting your lenses using a cobbled together setup with a tape measure.......... 5
(c) Adjusting your lenses with the LensAlign product......... 7
(d) Sending your camera and lenses in to a professional to do the job............ 9
Now let me explain, then we'll get into the procedure.
Most people don't have to microadjust their lenses (for the sake of saving typing, I'll just call it 'aligning lenses' from now on. It's actually 'microadjusting the alignment of a specific lens with a specific camera body by using the software in a high end DSLR'). Now why do I say that? Well because most people aren't pushing the edge of the envelope. If you want to focus precisely, you do it manually, not with the autofocus. And the only time it really matters is if you're shooting with a shallow depth of field, and you've damped out all vibration that would affect sharpness, and... you get the picture.
But if you do want that expensive lens to give you the best results with that expensive camera body, well, you're going to want to take the trouble to align it. There are 3 ways to do it. Let me skip ahead to option (d) for a second. Sending it in to the factory or a service shop to do the alignment for you is the best way. When you get it back, somebody with fingers smaller than yours and eyes that work better than yours, and the skill to take apart the camera or lens if necessary, and a machine that probably cost more than your car to do the work, will have done a fine job. He'll probably have taken 2 weeks or more to do it and the bill that he hands you is not going to be trivial, but he'll do a great job.
The question is, what is your time worth? It took me about 90 minutes, from start to finish, to align two lenses with my D300 body. It took me a bit longer than that when I did it a couple of years ago (September 2009. Here's the writeup) and it cost me nothing. I put the camera on a tripod, stretched out a tape measure at an angle, and did pretty well the same thing that I did with the LensAlign product. The results were similar if less precise, but this isn't something a professional or fussy enthusiast would do. It works, though.
The LensAlign product is reasonably professional. It's made of thin plastic, though, and I could see that you might have some troubles with it after repeated use. Assembly is very straightforward, even for a numnutz like me (I don't fix things. If I look at them the wrong way, they break. My aging eyes don't work as well as they used to and let's not get into arthritis in my hands...). I wanted to do it right, so I used the instruction sheet and it still took me only 5 minutes. It's designed to be disassembled so you can transport or store it in an 8x10 envelope. Here's what it looks like when you're done:
Here's the thing. You want that target thing on the left to be parallel with your shutter plane. That way, the scale on the right is the right distance — the SAME distance — when you focus on the target. And if your focus sensor is not exactly in the middle, it doesn't matter because everything is parallel and equidistant.
Here's where I had the biggest problem. Getting it parallel. If you blow up the picture, you'll see that there's a hole in that back panel, in the red dot in the centre of the circle. There's also a hole in the centre of the front target. If you align it so that you can see the back hole through the front hole, through the lens, it's parallel. Oh yeah? HOW? I figured out that if you look through the back hole and move the assembly so that you can see the lens of the camera (which is of course mounted on a second tripod), then it's lined up. But the lens is black... so I tried to fool it by taping a piece of masking tape with an "X" on it to a lens cap... I thought that worked but in the end, it was still off by a bit. You can see red through the target, but not the centre of the hole.
Edit: it works MUCH better in the daylight. It helps when you can actually see the camera.
Here's the next problem: nowhere in the package were instructions on how to do the alignment. Now I've done it before, so it wasn't hard to figure out, but why not put an instruction sheet in the box? I went to the website, and tracked down the instructions. Pretty simple: align the target and the lens, open it up all the way (the lens), shoot a picture using autofocus (remember, the target and the "0" point on the ruler are exactly the same distance away if it's parallel). Blow up the image on your LCD (nah. you're kidding, right? Use the computer, but see the paragraph below on "Tethered"). Find "microadjust" in your camera menu (they don't all have it, only the higher end ones. RTFM). Adjust it and shoot another shot. Keep doing that until you get it right.
Each lens has to be done separately. In fact, a zoom lens at different focal lengths will behave differently. For me, the longest focal length was the most critical, so that's what I based the adjustment on. Here's what I got:
Nikkor 70-200mm at 200mm f/2.8, unadjusted. You can see that it was forward focusing around 3 units (whatever they are) where the arrow is pointing.
Nikkor 70-200mm at 200mm f/2.8 after adjustment. This is set to +12 on a scale of -20 to +20. It's still not perfect, but it's close.
Nikkor 24-120 at 120mm, f/5.6, unadjusted. This is harder to see because the DOF is higher because it's a slower lens. The sharpest focus is around +8, backfocusing.
Nikkor 24-120 at 120mm, f/5.6, after adjustment. It took much less adjustment to align this one, about -5. I probably should hav dialed in -4 or -3 to be precise.
So once you get everything set up, it's a pretty easy task — just shoot and examine and adjust, shampoo, rinse, repeat until you're done. However if you have to take the card out of the camera, load it in the computer and upload the pictures between each shot, it will take you all day. If you're doing this, you have a high end camera. Probably you can shoot tethered to the computer (here's an argument for getting Lightroom!). That's what I did:
No comments from the peanut gallery. Shot with my Blackberry in, like, the dark. I loaned my P&S to Rosa so that's all I had to shoot with. You can see that the camera is tethered to the laptop on the left, the target is under the floodlight that illuminates my artwork on the wall. Not the greatest lighting.
Edit: Here's another shot I did today in daylight with the 200mm, now properly aligned. You can also see that I got the hole in the target properly aligned with the lens so everything is parallel now.
OK. Does the LensAlign MkII work? Yes. Is it worth the $80 list price? Again I'll say Yes, if nothing else than because it's a more professional way of doing things than laying out a tape measure. Should you own one of these? Well if you're fussy and you have a lot of money invested in cameras and lenses, then Yes. Remember I said that usage of your camera, especially if you regularly swap lenses causes things to change. When I did this two years ago, the 70-200/D300 combo needed a setting of +7. Last year after i got it back from Nikon, it went to +15. Now it's at +12. If you're a macro photographer and you're shooting focus stacks with rails, then no. If your thing is landscapes at f/11 on a tripod, then no.
And that's all I have to say about that.