What’s wrong with electronic variable NDs

[Run&Gun]

Plural (more than one camera) vs. blanket (all cameras). For example, the Alexa Studio does not have a full spectrum ND and is stated as having color shifts: http://cinematography.net/ir-grabs/ir-grabs.html (F55 and 65 stated as full spectrum; note color shifts on these NDs). Quick search didn't find F55 internal ND examples- have you specifically tested yours (might not be noticeable for everyday shooting)?

I only found this out by doing a deep dive color analysis for skin tones (google: Filmic Skin C300 II, for more info). It's not an issue, just something I observed from real-world testing; perhaps a few hundred Kelvin- easily fixed with WB or in post. It appears lower cost NDs shift light at different frequencies (colors) non-linearly, so it's not possible to fully correct with a simple WB adjustment. Apparently it's a complex problem, otherwise Canon could build in auto-compensation when the internal NDs are engaged (or perhaps Sony did a better job with software correction). Colors are jumping all over the place with these NDs as well: https://nofilmschool.com/2013/08/true-nd-filter-color-shift-test

Given the lack of true color calibration for current cameras systems (all the way to the top), everything is ultimately adjusted in post (getting computer and monitor systems accurately calibrated is another issue).

I'm sorry, but that still reads like a generalized statement. Had you said "some cameras", that would have been more clear. Not being argumentative, just saying'...

ALEXA's don't have built-in ND(AMIRA's do) and ND, especially inexpensive filters, but also expensive well-known brands, can be all over the map with color shift and IR. I don't have the "it's good enough" philosophy, but when I said I have no issues, I meant that I have not seen anything visually objectionable(like noticeable IR pollution or color shifting) on my calibrated monitors, not on scopes. That's arguably all subjective, but so much of what we do it is.

 

[jcs]

I'm sorry, but that still reads like a generalized statement. Had you said "some cameras", that would have been more clear. Not being argumentative, just saying'...

ALEXA's don't have built-in ND(AMIRA's do) and ND, especially inexpensive filters, but also expensive well-known brands, can be all over the map with color shift and IR. I don't have the "it's good enough" philosophy, but when I said I have no issues, I meant that I have not seen anything visually objectionable(like noticeable IR pollution or color shifting) on my calibrated monitors, not on scopes. That's arguably all subjective, but so much of what we do it is.

If the statement was a patent claim (language as mathematics: Boolean algebra) it would not cover the "all" scope. Sure, adding 'some' would be more clear. The Alexa SXT Studio they appear to be referring to has an internal motorized ND filter (ARRI might want to proofread their page regarding the ND strength): http://www.arri.com/camera/alexa/ca...xa-sxt-studio/subsection/sxt_studio_features/

My point was that non-variable NDs (glass or glass with film (composite)) may not necessarily be better than something based on liquid crystal if it's possible to create a solution which effectively doesn't polarize light. Internal solutions can be part of the color science in software, since the system knows what filter is active and the associated MTF, along with the OLPF, CFA, sensor behavior, etc.

 

[Run&Gun]

You're right, JCS. The SXT Studio does have a built-in, single density motorized ND filter.

And yes, i agree that manufacturers should be able to optimize their built-in ND systems to perform "flawlessly" in their cameras.

 

[bob'slaststand]

If it was polarized some FS7 or FS5 user somewhere on a sunny day with the electronic ND on must of tried to use a polariser, surely. A search of “Sony electronic ND and Polarizing filter” or “FS7 mark 2 and Polarizing filter” gives no complaining or questioning results that I can see.

But Sony’s info video on their electronic ND sounds suspiciously like their admitting it’s polarised and the few descriptions I can find of how it works show the light to be polarised, no magic box, no secret source filter after the LCD’s to somehow depolarise the light.

And Panavision also, no mention of polarisation. Just we’re really good at colors blah blah. I’d mention it. Cinema5D seems to think that they don’t polarise.

Just to get rid of the suspicion I’d like to hear Sony or Panavision say it somewhere. Or have an FS7/FS5 user tell me that a polarizer works fine with his or her electronic ND.

 

[jcs]

Placing a high-quality circular polarizer in front of an LCD screen only causes a color shift (appearing as a warm/cool WB shift) when rotating the filter, vs. going darker. Rotating a linear polarizer (sunglasses) in front of an LCD goes darker. Rotating a variable ND (linear + circular polarizer) the LCD screen goes darker, and if the outer ring is rotated (controls filter level), the LCD stays dark while everything around the LCD varies in brightness.

Thus adding a typical circular polarizer to an electronic LCND would potentially cause a WB/color shift, which may not be noticed vs. making things dark or adding dark streaks, which would be noticed.

Digging deeper leads to quantum physics and the nature of photons as spiraling wave-particles*, one of the more popular topics on dvxuser

* "If it's a wave, what's the medium??", another fun topic for debate (aether, quantum field theory, etc.).