I’d like to continue relating my earlier experience of using this software to fine tune focussing of my lenses. I’ll first discuss how precise the measurements are. First, what do I mean by ‘precise’. Well to me 'precision' is the 'ability to reproduce the results'.

Let me draw an analogy. Imagine a shooter honing his rifle's sights on a target. He fires a few rounds and then looks at how the bullets are grouped on the target. For him, a good group would be tight and ‘precise’. A bad group would be spread out all over the target and therefore ‘imprecise’. Please note that precision and accuracy are different. Nevertheless, they are related! It is far easier for the rifle shooter to adjust his rifle sights to achieve bulls-eyes (that is his goal – for him accuracy means hitting the bull's eyesl) if he has a tight precise group. And so it is with this software. How precise are the measurements?

As with the rifle shooter, testing this is straightforward. You need to run FoCal repeatedly and as carefully as you can and then check the output. How consistent are the values? Do the values form a tight group? Let me give you some values I obtained recently:

Results
Lens 1. Fo-Cal Fine Tune Values: +12 & +6. My Comment: Acceptable.
Lens 2. Fo-Cal Fine Tune Values: 0, +1 & +1. My Comment: Brilliant.
Lens 3. Fo-Cal Fine Tune Values: +12 & +11. My Comment: Brilliant.
Lens 4. Fo-Cal Fine Tune Values: +5 & +2. My Comment: Good.
Lens 5. Fo-Cal Fine Tune Values: +4 & +2. My Comment: Very Good.
Lens 6. Fo-Cal Fine Tune Values: +6 & +8. My Comment: Very Good.

Lessons Learnt
1) The results obtained are certainly reproduceable. Note that this reflects the whole technique - this includes how FoCal software is working, me and my camera gear. The reproducibility suggests all are in ‘synch’ and working well. I would conclude the Focal software is reproducible and reliable.
2) Note that here, as the software is reliable, it may be possible just to obtain a single fine tune value and use it. However, it is much better to obtain a few values for each lens and use the average of those values.
3) Here, the fine tune values are all positive indicating that without any adjustments, my photographs would all be ‘front focussed’. As this is so consistent, it suggests that my camera is ‘front focussing’ and could do with slight adjustment. However, the values are within the fine tune value range of -20 to +20 and, as the camera would have to go back to Nikon, I can live with this.

Next I will show you if the x1.4 teleconverter on a lens degrades the image obtained.