Help... ursa mini 4.6k FPN? With footage uploaded

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mike8418

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Help... ursa mini 4.6k FPN? With footage uploaded

PostSat May 04, 2019 10:54 am

Hi everyone, many thanks for stopping by and help! I've just bought a second hand ursa mini 4.6k, which is out of warranty, and noticed there might possibly be a fixed patterned noise issue (vertical blue lines in shadow area, IRE>20). Here's the Prores HQ footage straight out of the camera, these footage are all taken after the black shading calibration, firmware 4.4, and with detail sharpening turned off.

Download link:
https://mega.nz/#F!HggHAYDA!t7QNrBWleQTNsB2D-_ieIA

I do understand I have underexposed the picture a lot, and I should never underexpose that much when filming. But I am just purposefully testing out the camera's limit so to learn to use it properly when working on paid gigs. From the scope, once it's hitting below IRE 20, I can see that the vertical blue lines easily. So my question is:

1. Is these vertical blue lines normal? If not, will blackmagic support repair it even it's not in warranty? Will it be expensive? Or should I just return the camera to the seller?

2. If the of vertical blue lines noise is normal, what should I do to minimize the issue? Expose carefully and crash anything under 20 IRE to the black? Light anything needed to be black above 20 IRE? Use Davinci Resolve to De-noise when needed? Any other tips and tricks?

Many Thanks again everyone!
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mike8418

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Re: Help... ursa mini 4.6k FPN? With footage uploaded

PostMon May 06, 2019 4:51 pm

Please also find a quick black test I have done with my ursa mini 4.6K
Have edited without doing any color correction, grading and changes, only added some text on it.
I put a body cap on, and recorded a few seconds of black in different ISO, before and after the black calibration. Thank you!

Download link
https://mega.nz/#!WoZ2kawT!rk_MkkxZWF9v ... uzMUyJvT9M
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rick.lang

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Help... ursa mini 4.6k FPN? With footage uploaded

PostMon May 06, 2019 7:02 pm

Mike, you should upgrade the camera firmware to release 4.8. Significantly underexposed footage does suffer from fixed pattern noise on that sensor. There’s a huge thread on the forum on FPN, but you’ll grow a grey beard before getting through FPN threads here.

I think you’re doing things right so try bring more light to the scene as appropriate or crushing the blacks a little in post. Avoid ISO 1600 like the plague if your light is too low unless you like noise. ISO 800 and boosting one stop in post is better. Some scenes can actually be brought up four stops, but no guarantee that works in every situation subject to your aesthetics.

And a recommendation that you use False Colour to evaluate your exposure range. Read about it in the camera manual, but generally if you see purple in False Colour, that may not come out well in the end unless it’s something you know should be black or near black. Blue using False Colour is usually fine in post. If your scenes are very dark grey to very light grey you’re very safe. Yellow is likely going to be good and red might be clipping. Middle grey will be pink and green is still very usable.
Rick Lang
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mike8418

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Re: Help... ursa mini 4.6k FPN? With footage uploaded

PostTue May 07, 2019 10:11 am

Many Thanks for your help Rick! Will definitely try firmware 4.8! And thanks for the tips as well!
More light, avoid ISO 800 and 1600, study the manual and use false color to judge exposure! They are all great tips and methods to deal with the low light issue of my ursa mini.

So basically, I have two choice here, based on the black test and other samples I have uploaded, if you were me, would you send the camera back to BM support for re-calibration? Or just keep it as it is? Compared to yours ursa mini, is the FPN of my ursa mini worse or similar?

I have contacted BM support, they refuse to acknowledge the FPN issue, stated "did not found a serious FPN", but they said that I could still send the camera back for re-calibration, then again stated "If your camera is too old, CMOS may aging and will not help significantly after recalibration." They quoted USD 100 for re-calibration. So, if you were me, would you take the bet and try send the camera back for re-calibration? Or just keep it as it is?
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Robert Niessner

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Re: Help... ursa mini 4.6k FPN? With footage uploaded

PostTue May 07, 2019 7:27 pm

Mike, I had a look at the sample you supplied and compared it to some ISO1600 low light footage I took with my UM46k in 2017. Yours look far worse than mine. I don't have any blue lines, just a slight amount of FPN barely visible.

But you have to make sure you did the black shading the correct way.
Remove the lens and put the BMD protection cap onto the camera mount.
Let the camera warm up for around 15 minutes.
Then start the black shading.

Black shading won't do anything to FPN, it solely calibrates the black levels.
Hope this helps with the blue lines.
Robert Niessner
LAUFBILDkommission
Graz / Austria
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mike8418

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Re: Help... ursa mini 4.6k FPN? With footage uploaded

PostWed May 08, 2019 5:28 am

Hi Robert, many thanks for taking the time to look at my sample footage and comparing it with yours...! Glad to know that the FPN I have is far worse than yours, it makes me want to take the chance and send back the camera to re-calibrate more.

Thanks for the reminder about the importance of doing the black shading in the correct way!
Although I'm quite sure I have done the black shading calibration the exact same way you've mentioned, I'll give another try tonight so to double confirm.

Many thanks again for your help Robert!
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rick.lang

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Re: Help... ursa mini 4.6k FPN? With footage uploaded

PostWed May 08, 2019 5:06 pm

Mike, note I said to avoid ISO 1600. Shoot ISO 800 and boost one stop in post will give better results.


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Rick Lang

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