AF speed D700 slower than D3? how come ?

Started Aug 7, 2009 | Discussions thread
Marianne Oelund Veteran Member • Posts: 7,353
Steady state speed

Gabriele Sartori wrote:

I can see that you are very competent but how can you be sure about that? Unless you have the microntroller code of what Nikon is really doing or the schematics showing a regulator in the middle a close loop control like that might be be influenced in speed by the PWS. The nominal battery voltage may be the same but it could be that we have a voltage drop due to the limited current provided by the single battery. How did you measure that?

You're thinking about power supply regulation, whereas I was referring to the steady-state motor speed while it's slewing. I haven't looked at supply voltage to the lens motor, and that's not necessary for this purpose. The measurement is simply focus slew rate, and it doesn't change whether I am using a freshly-charged 11.1V EN-EL4 battery in the grip, or an almost-drained 7.4V internal EN-EL3 battery. In fact, the speed was very slightly faster with the lower-voltage source.

All the self tuning close system like this that I designed in my career potentially could have been influenced by power considerations, indeed we were taking precautions to minimize that, usually you go big with capacitors and traces to avoid that. These servos in certain condition can drain a lot of power.

Those are all transient current considerations. I was only looking at steady-state speed, not start/stop edges where peak currents occur. The slew times from minimum focus to infinity focus are rather long, and easy to measure accurately.

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