A true crime mysterZ...

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beatboxa Veteran Member • Posts: 7,760
A true crime mysterZ...

There's a recent thread that brought something up I remember observing when the Z's first came out, but that I de-prioritized and eventually forgot about...

It's a mystery, and perhaps the usual suspects (Horshack, JimKasson, bobn2, many others I missed) or any other private-I...or private-Z...can chime in on.

Here's the skinny:

  • When one presses the shutter button with a Z lens mounted, the Z lens will snap its aperture blades. At least on the original Z6 (and I'd assume Z7). Not sure about the II's on latest firmware.

More specifically:

  • The aperture blades snap to somewhere between F/2.5-2.8.
  • This occurs even in silent shutter mode
  • This only occurs on Z lenses. Not on FTZ.

In other words, if you have an F/1.8 lens and you keep it wide open, when you take the shot, the aperture will quickly stop down to ~F/2.5, then open back up & take the shot. If you stop the lens down to F/4 and press the shutter button, the aperture blades will open up to ~F/2.5 then close down & take the shot.

So now, onto the mystery:

  • Why?

I said this in that earlier linked post, but I suspect this is due to Nikon reusing its code / logic from its RGB sensors in the Z cameras. Let's be real: Nikon did not redo everything from scratch in order to build the Z's out. That's a LOT of work (even if it would be better performing to start from scratch). Instead, I think they started from what they already had and then adapted & tweaked it. And over time, they will rearchitect or tweak further. The Z9 could be a major architectural change, even if it's all under the covers and the interface looks the same.

DSLRs have 3 distinct sensors:

  • Imaging sensor, for actual exposure / taking the picture
  • RGB sensor for metering, white balance, tracking
  • AF module for PDAF

I suspect for the Z's they leveraged the following:

  • (Menus from their DSLRs)
  • Imaging from their DSLRs
  • Live view preview from their DSLRs
  • Autofocus & tracking from their Coolpix & Nikon 1 (<< probably the most modified)
  • Exposure metering, white balance, & subject recognition from their DSLR 180K RGB sensors

I suspect that the AF was probably heavily modified, but the others were just tweaked a bit. I also think the recent firmware update was essentially tweaking this last RGB (subject recognition) part of the code up to deal with higher resolution. So in general, it seems the Z's do leverage a very DSLR-like modular workflow of:

  • Live view until the shutter button is pressed...
  • then RGB metering/subject ID step, with a quick, line-skipped sensor scan
  • then the shot

So why is this relevant? Because I believe that F/2.5 number contains a clue. F/2.5 is just about where the viewfinder of a DSLR is set to all the time (maybe a bit faster, but then reduced to F/2.5 after accounting for the pellicle mirror loss for the AF). Meaning the RGB sensor of a DSLR also expected F/2.5. Any metering it did was a calculation from this 2.5. So if a user set the aperture to F/5.0, the RGB / metering would say "OK, when we shoot, the exposure will be 1 stop slower."

And I think it is possible that the Z's leverage this same RGB logic (or similar). And this is why they snap the aperture--they need to first get a quick peek so that the virtual RGB process can do its thing before the shot.

Of course, this doesn't explain the discrepancy between Z's & F's. There does appear to be some different mechanism when an FTZ is used vs. when a Z is used (and also keep in mind that most F-lenses have slower, less accurate spring-loaded apertures). Perhaps they were ok skipping a step for F's at the risk of accuracy (assuming the latest from the rendered live-view as opposed to a raw, clean measurement for the photo). I can think of a few tests I will run--namely capture comparisons on F vs. Z, leveraging picture controls too. Or maybe all of this is wrong, and the real reason is just some coincidental electronic pulse.

That's why it's a mysterZ. And it will remain that way until we figure it out.

Casio Exilim EX-Z9 Nikon Z6
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