It's fair to say that AF accuracy is something the drives me nuts and has done for years. I've tried numerous methods including angled rulers, keyboards, a toy cat and even the computer based Reiken Focal software of which I have the full pro version.
During this time (and it has taken a lot of it) I've learned a few things, including the following:
As you can see from the table, I tested three bodies with two teleconconvertors (Nikon TC-20e III and Kenki 1.4), plus two Nikon 70-200 2.8 VRII lenses. That's 18 permutations so it took a while. I initially went through the lot with the Reiken software but I wasn't completely happy with the results, so the next day I brought out the cat!! I find these stuffed toys really useful as you can aim at the nose and when you look at the results the fur gives a good idea of where the sharpness is.
I set cat at around 20' away for the 70-200 and 70-200+ Kenko 1.4. The 70-200+ Nikon TC20e III was about 30' away from the camera. I put two small figures next to the cat, one about an inch in front of, and one about an inch behind the cat's nose. I put the 500w security light next to the cat. I metered the cat and put the cameras on a tripod in manual mode and tethered them to Lightroom via digicam control. I only used the digicam control software as Lightroom tether is unreliable for me. I then took shots of the cat using its nose as the target.
Having set everything up I fired the camera from the PC at various AF fine tune settings until I was happy with where it's focussing. The figures next to the cat help to tell if you are back or front focussing. I've set everything with a bias to focus slightly to the back as this seem more useful for real life situations. By this I mean the nose is in focus as is one inch in front of it and three inches behind.
I've included my table of results which gives an indication of how widely the settings vary. I've also included some cat pictures, although you need to see them at full resolution at 1:1 to make a judgement.
I now need to go and use them to see how they fair in the field.
During this time (and it has taken a lot of it) I've learned a few things, including the following:
- When you AF fine tune the lens, it is focus tuned for that camera to subject distance and if it's a zoom, for that focal length as well. The further from the subject the less you will notice it as the depth of field increases, but you need to be aware or you will tune a lens at ten feet and then try it in your hand at five feet and wonder why it's slightly off. Therefore try to tune lenses at a typical distance to the intended use. I know that last point is difficult. With regards to focal length, I tend to use a setting just shy of the long end as this is where you have least depth of field and as such the tuning is more accurate.
- Use a bright light for AF consistency. I use a 500w security light very close to the target.
- Boy does the D800 have mirror slap. I was doing two D7100s and a D800. Initially I was using 1/80 sec shutter speed but noticed the D800 shots at 400mm focal length and 25' from the target where blurred unlike the 7100s. I increased to 1/400 sec and the problem disappeared. This movement was on a Manfrotto 055 tripod with heavy duty 3 way head.I will never go out again without mirror lock up.
As you can see from the table, I tested three bodies with two teleconconvertors (Nikon TC-20e III and Kenki 1.4), plus two Nikon 70-200 2.8 VRII lenses. That's 18 permutations so it took a while. I initially went through the lot with the Reiken software but I wasn't completely happy with the results, so the next day I brought out the cat!! I find these stuffed toys really useful as you can aim at the nose and when you look at the results the fur gives a good idea of where the sharpness is.
I set cat at around 20' away for the 70-200 and 70-200+ Kenko 1.4. The 70-200+ Nikon TC20e III was about 30' away from the camera. I put two small figures next to the cat, one about an inch in front of, and one about an inch behind the cat's nose. I put the 500w security light next to the cat. I metered the cat and put the cameras on a tripod in manual mode and tethered them to Lightroom via digicam control. I only used the digicam control software as Lightroom tether is unreliable for me. I then took shots of the cat using its nose as the target.
Having set everything up I fired the camera from the PC at various AF fine tune settings until I was happy with where it's focussing. The figures next to the cat help to tell if you are back or front focussing. I've set everything with a bias to focus slightly to the back as this seem more useful for real life situations. By this I mean the nose is in focus as is one inch in front of it and three inches behind.
I've included my table of results which gives an indication of how widely the settings vary. I've also included some cat pictures, although you need to see them at full resolution at 1:1 to make a judgement.
I now need to go and use them to see how they fair in the field.