OM-D EM-5 - High Iso Banding?

Started May 8, 2012 | Discussions thread
Vlad S
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Re: OM-D EM-5 - High Iso Banding ? - Lighting Pulsations / Scan Rates
In reply to Detail Man, May 9, 2012

Detail Man wrote:

Vlad S wrote:

I doubt that light pulsation itself is the cause.

Why, specifically ? Note that the Shutter Times that were noted to exhibit the problem the most (1/30 and 1/60 Second), are exposure-windows that are directly integer-related to 60 Hz (CPS), or a sub-multiple. We know for a fact that indoor lighting is modulated by 60 Hz AC line currents ...

So are the RF emissions... I do not know exactly how the Live MOS sensor data are read out, but CMOS sensors read it line-by line. If that is the case with the Live MOS sensor as well, then the pulsations would have to occur many times during either exposure or readout. The reason why I thought that high frequency harmonics would not show up in the visible range is that in my personal experience the fluorescent lights glow for some time after the power is cut, so I assumed that this glow would smooth out any high frequencies. This is just an assumption though, so I do not insist that this is the answer, I just thought it was a reasonable hypothesis.

But the electric discharges within the lamp are a source of radio waves, and the oscillators in the ballast also might be a source.

The possiblity of EMI at 60 Hz or its harmonics seems extremely unlikely. Vague theories regarding "radio waves" in the microwave frequencies higher than 2 Ghz (cell phones, Wi-Fi) seem possible, but (likely) a lot more far-fetched, less likely, and thus more nebulous ...

Why are the harmonics in the electronic circuits unlikely? If a circuit resonates at a certain frequency then it will necessarily produce overtones. As far as other emitting devices are concerned, I have not experienced interference from microwaves, but I experienced interference from my cell phone clearly audible on my ipod and care stereo, and by the sound of it I'd say it's higher than 60 Hz. @Ghz and above is just the carrier signal, what you see/hear is the modulation of the carrier, rather than the carrier signal itself.

And, it was you (yourself) in a recent post on this thread who stated that the camera likely is well shielded against the electro-magnetic coupling of EMI . Thus, you are now contradicting yourself ...

It's only shielded if there's no conduit from the outside of the shield. If the signal is picked up by the circuitry in the lens, then it can be transmitted by wires, and if that particular conductor does not have a choke, then the high frequency will pass inside even a shielded circuitry.

What is your own background, knowledge, and experience in analog/RF electronic design, Vlad ?

With the electronic design - just a middle school electronics club. But I do have a couple of graduate level physics courses under my belt, and I studied quantum physics long enough to know properties of electromagnetic waves fairly well.

I really would not like to turn this into "who's stick is bigger" contest. I don't need to be right. I participate in this thread because I am going to get this camera, and I am interested in its limitations. So please don't question my background, if you think that I am saying something wrong just present your argument - that's quite sufficient.

Vlad

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