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Olympus phase detect strips showing up in E-M1 video


Andrew Reid
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If Olympus is using sensor focusing the way Canon is then I doubt there will be any firmware fix.  When taking photos, the camera can take a sensor reading for focus (throw out that data), focus, then take a reading for an image.  It all happens fast.  In video, I do not believe this can be done.  What Magic Lantern does for the Canon's is take the RAW sensor reading straight from the sensor (actually only 36MB/S on those cameras worth, between the sensor and LiveView).  On cameras where there is sensor-focus, like the T4i or EOSM, the pixels that are used for focusing appear "hot".  Most of them are in the red channel (sensels) and usually create, after debayering, "pink dots".  

 

On the Olympus, and all cameras that output compressed videos, focus dots generally don't appear because the compressor probably throws out their information, and a lot more besides.  

 

Fortunately, I, and others before me, have been able to create software the smartly interpolates around these focus pixels IN RAW because we're dealing with the RAW data.  Unfortunately, cameras can't write 1080 RAW frames using current camera IO and most SD cards.  In other words, the only way I can see fixing this problem is if the Olympus camera could write out the RAW data, which would be about 90 megaBYTES per second.  Then you could fix the phase-detection pixels in post.

 

While we're also on this subject, I have my suspicions about sensor stabilization.  It's interesting that the GX7 has a max ISO of 3200.  I believe it is possible they achieve stabilization by shorting the read time of each pixel when the camera detects movement.  That is to say, the camera makers may be putting in features that appeal to people who don't know any better.  I'm not surprised you caught them with their pants down :)

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It's unfortunate however in that the video mode has an unusual bug.

 

These strips are surprisingly large and visible to the naked eye on the sensor.

On the vast majority of shots they never show up. It only seems to be a problem when pointed directly into the light.

 

 

To me that sounds like it might be just an internal reflection rather than an actual bug software/hardware bug. 

 

A kind of a glare reflection which appears only during very specific circumstances; when bright enough a spot light source is shining straight into the sensor from a specific (low) angle, and then the shiny surface of the sensor gets reflected back to the lens, and then some of the lens surfaces or a filter surface (or some other reflective surface) will produce this ghost glare. I've seen something (kinda) similar happen before, under certain circumstances. The easiest way to minimise it was to use a lens hood.

 

I'd try reproducing that scenario with different bright lights straight into the lens from varying angles, trying to create various glares on purpose, and then experiment with different lenses, filters and perhaps even the Speed Booster, if possible. Chances are the stripes will only appear with certain lens and light angle (and colour) combinations.

 

It it really is what I believe it is, I believe it will make no difference if it's a still photo or video. The reflection may just be easier to spot and reproduce in a video clip.

 

Well, just a thought, might be worth investigating.

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The problems of shooting 30p in PAL-land are often discussed but in my experience are not really an issue. The problems of mixing frame rates & problems of flicker with lighting are grossly over rated when shooting HD. I think that most of the Old Wives Tales go back to Interlaced SD & problems with conversions between PAL & NTSC (or vice versa).

 

Both FCP & Premiere Pro easily handle different frame rates dropped onto the same timeline & I assume that any other decent NLE will do the same.

Any problem with flicker from lighting is because of shutter speed not frame rate so even to be on the safe side if you are shooting 30p use 1/50.

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I think that most of the Old Wives Tales go back to Interlaced SD & problems with conversions between PAL & NTSC

 

 

Hardly an old wives tale.  It's hard science.  PAL and NTSC have to/had to use a frame rate that synchronized to the alternate current that powered the televisions.

 

Now that analog is over, that old tech problem isn't much an issue for editing, as you can use whatever frame rate you desire (I still wouldn't mix and match frame rates that can't be equally divided) ... but if you shoot 60p under artificial light in a country that doesn't use 60 hz power line frequency, you gotta do as you suggested:  adjust the shutter to match the frequency of the power supply.

 

It all kind of goes back the the AC/DC feud between Edison and Tesla.  

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There are several posts in this thread stating that they haven't bought an OM-D because it doesn't have 24/25p because they believe that it is an issue. I am just pointing out that with HD it is not the problem that everyone imagines because their thinking hasn't been updated since analogue PAL/NTSC days. In fact the Old Wives Tale about mains flicker with 60Hz & PAL or 50Hz with NTSC was always wrong as it was the shutter speed causing the flicker & not the frame rate.

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It seems a somewhat similar phenomenon is seen in the GH2 camera. As you all know it doesn't have phase detection but I noticed similar but not exact patterns on Griffin Hammond's latest video on his personal channel making a DIY Projector screen. 

 

4:29 mark

 

What can that be attributed to? 

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I noticed all of this weird green stuff going on in some footage I shot over the weekend with my E-M1. Is this the same issue? Shot with the Panasonic 25/1.4.

 

Happened when shooting inside and outside. 

 

http://youtu.be/VlfhZSRqRxI

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I noticed all of this weird green stuff going on in some footage I shot over the weekend with my E-M1. Is this the same issue?

 

Nope. That looks like an ordinary lens/dirt glare.

 

Wipe off all the fingerprint smudges and other gunk off your filter(s) and the front element of the lens with a microfiber cloth, but be careful when doing it. If your filter is clean try another one, or shoot without the filter.

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Nope. That looks like an ordinary lens/dirt glare.

 

Wipe off all the fingerprint smudges and other gunk off your filter(s) and the front element of the lens with a microfiber cloth, but be careful when doing it. If your filter is clean try another one, or shoot without the filter.

 

Thanks, Quirky. Excellent news !!

 

At the time I was using a "Lightcraft Fader ND MK II" on the 25/1.4. It's possible that the incense smoke from the Temple may have clouded the lens causing this but I'm not sure. In any case, I have cleaned the filter and checked the front element. I'll shoot again this weekend and hopefully not see this again.

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That's lens flare.  You can only solve that "problem" by flagging the lens so lights aren't directly shining on the glass.  Or, just not shooting into lights.

 

Also, the next time you direct a movie in the Star Trek franchise you can do that on purpose with Zeiss lenses and everyone will think it's awesome and want to emulate it.

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That's lens flare.  You can only solve that "problem" by flagging the lens so lights aren't directly shining on the glass.  Or, just not shooting into lights.

 

Also, the next time you direct a movie in the Star Trek franchise you can do that on purpose with Zeiss lenses and everyone will think it's awesome and want to emulate it.

 

 

Ok, great … thanks.

 

Will file that tip away for when I'm directing Star Trek 17.

 

My wife and I love Star Trek btw. Currently watching S4 of TNG BD …. Engage !!! 

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Ah yeah, I forgot to add that after checking out the filter and lens surfaces, use a lens hood if possible. Good point.

 

Anyway, I'd say it's still possible that shooting without the filter (or with another filter) may indeed decrease the amount of that lens flare. The two (or four) surfaces of the filter are the first glass surfaces that catch the light coming into the lens, and those surfaces are the most likely to cause additional glare and reflections. Especially the cheapest (and smudgy) ones. Sometimes it can be something as simple as a subtle layer of dust on a filter that haven't been used (and cleaned) in a while, and screwed on the lens in a hurry.

 

I had somewhat similar looking reflections in my shots a while ago, and it was fixed simply by changing the cheapo (and not entirely clean) filter screwed on the top of the lens. I used that particular filter mainly to protect the lens from possible sea water splashes.

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Ah yeah, I forgot to add that after checking out the filter and lens surfaces, use a lens hood if possible. Good point.

 

Anyway, I'd say it's still possible that shooting without the filter (or with another filter) may indeed decrease the amount of that lens flare. The two (or four) surfaces of the filter are the first glass surfaces that catch the light coming into the lens, and those surfaces are the most likely to cause additional glare and reflections. Especially the cheapest (and smudgy) ones. Sometimes it can be something as simple as a subtle layer of dust on a filter that haven't been used (and cleaned) in a while, and screwed on the lens in a hurry.

 

I had somewhat similar looking reflections in my shots a while ago, and it was fixed simply by changing the cheapo (and not entirely clean) filter screwed on the top of the lens. I used that particular filter mainly to protect the lens from possible sea water splashes.

 

I can't use the hood for most lenses as I need to keep the variable ND filter on. Unless you like shooting at f/56, in Hong Kong you need to have one on all the time.

 

I checked the variable nd filter i was using and the front element of the lens and they were all very clean. The sensor seemed fine as well. I will see if this happens again in the next couple of days.

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