Since a few years ago, I had been using an excellent process to fine tune my lenses. It is a painstaking exercise, but nevertheless a very very useful and critical thing to do on a periodic basis.
Recently — I felt the need for a faster way to do this. This past christmas, when Michael Tapes announced the new Lens Align Mark II at a new price, I couldn’t resist it.
Just to show how useful this little gadget is, I decided to go back and tune my lenses again. I found myself in surprise when all my lenses needed a slight tweak again. Here is a shot of my lens align shot with 50mm f1.4 lens:
The product itself comes shipped in a manila envelope. It is fairly easy and straightforward to set it up. It is very well made . Once you assemble it, you can either mount it on a tripod (It has a tripod mount socket) or in my case, since I do have a drafting table — was able to set it up on it. For added benefit, I did add a level to check the accuracy as well (See above image with arrow pointing down). The next thing to do is set up your camera on a tripod, level it accurately (Fortunately on a D700 — you have a built in vertical horizon tool). I set the camera up to the same height as the center of lens align.
With the aperture opened up all the way (f1.4 on my 50mm f1.4 lens) I took a test shot. Oh, BTW — I did use a cable release and had set the camera to shoot in Live View mode (for fine focusing — with magnification).
Here is an example of the image after AF Fine tune (it took several iterations to finalize the exact number. In my case, it was –4. This of course varies between camera to camera and lens to lens. So, this above number for AF Fine tune is just for my camera and lens combination. Once you set this number up, the camera remembers it and every time I use this lens, my fine tuned adjustment is automatically used.
A note about using Live view for adjustment: On my D700 (most likely on other cameras as well) , the Live view mode uses a different technology (contrast based auto focus) as compared to the normal auto focus (phase detection auto focus). While the phase detection AF is faster and generally accurate, the contrast based AF (although slower) can deliver more accurate focus. The above process is nothing but to calibrate your phase detection AF with your more accurate contrast detection AF. You can read up more about the AF detection systems here. BTW — Most of the point & shoots have contrast based AF, since it is more economical to mass produce this.
Here is an example of the results after AF fine tuning. Warning: Once you tune your lenses — there is no going back! You will invariably do this every time and for all your lenses! Here is a shot of my son after alignment:
This was a hand held shot, shot with the just tweaked Nikon 50mm f1.4 lens at f2. Sharpened with R-L Deconvolution technique (no output sharpening, just capture sharpening). I think I can count the number of eyelashes if I spend a bit of time…which I am not going to do. If you wish to see the full image — click here.