Pros and Cons of Liquid Crystal Filter Technology?

[Thomas B.]

Hello everyone

As more and more LC filter products are announced/launched throughout this year, I would like to learn more about this technology.
Although this tech has been around for quite some time - remember RED's Motion Mount or Tilta's TE-ND, which, if I remember correctly,
never made it to market (color shift?) - manufacturers seem to have only recently solved the issues from seven years ago.
RED's eND PL Mount and Sony's built-in automatic eVND are among the latest developments in this area.
Tilta's announced 4" x 5.65" matte box friendly eVND solution is also worth a look.
...and just in case you missed it, electronic diffusion filters (repeatable, exactly adjustable diffusion) have been announced as well.

While searching for an LC filter solution for EF-mount lenses, I was quite surprised to see KipperTie announce three new filter products,
two of which use LC technology:

LCminiND (eVND) for Canon's EF-RF drop-in filter adapter,
Revolva LC cartridge (clear + eVND)
Strata Electro (compact, motorized clear + solid ND swap)

Actually, my favourite is the Revolva LC cartridge as it makes Revolva extremely versatile. Kudos to KipperTie for developing
new products for Revolva.

But coming back to the topic of this thread - as good as this technology may seem nowadays, I found it difficult to get information about
how these products work and more important - what the downsides of eVND filters are (so, when not to use an eVND).

AFAIK, Liquid Crystal Tunable Filters (LCTF) are being used in scientific narrow-/broadband imaging applications
(to block unwanted wavelengths), so I assume that eVND filters are based on the same technology (maybe different designs)
to equally tune/regulate the transmittance to prevent color shifts and IR contamination.
The light passes a (linear or circular?) polarizer to uniform the angle of the light hitting the liquid crystal fluid.
The alignment of the LCs can be changed by the voltage applied, so in our case, if no voltage is applied,
the LC fluid is absorbing the light (no transmittance) and the more voltage is applied, the higher the light transmittance.
And for the diffusion filter mentioned above, the glass looks clear at no voltage and the diffusion gets stronger the more voltage
is being applied. Apologies for mistakes and misinterpretations, corrections are welcome.

The advantages (especially in regard of KipperTie's upcoming products) are:

- 2-7 stops of ND in one filter
- repeatable, seamless and precise tuning of the optical density
- fast switching time = near zero delay
- very consistent color rendition through the whole range of optical density
- only a minor color shift towards magenta between clear and the eVND
- remotely controllable via app

The disadvantages...
...well, I didn't find any information about when better not to use electronic VNDs.
It would be really helpful if manufacturers like RED / KipperTie and/or people who have experience e.g. with RED's eND PL Mount could
share their knowledge, findings and recommendations in this forum.

So, my concerns/questions are the following:

- Since LC tech works with polarized light, can light sources (e.g. sunlight) entering at certain angles cause (partial) color shift
or a sort of vignetting??
- Color shifts when filming LCDs at certain angles?
- Possible artifacts and color shifts in conjunction with other (CPL-) front-mounted filters?
- Do LC fluids deteriorate in neutrality / optical density or transmittance after time and if yes, in what timeframe?
- Can LC fluids take damage when pointed at the sun sporadicly?
- How does the filter behave when using below the recommended operating temperature (slower switching time or not uniform density?)
and can the LC fluid take damage in such cases?
- Can dead pixels/segments occur, or are eNDs one big adjustable segment? I suspect that eDiffusion filters are divided into
several segments to obtain a homogeneous diffusion pattern.
- Are the LCs being aligned at a certain frequency and if so, could this cause flicker issues (shutter speed / artificial light)?

...and here some KipperTie eVND related questions:

- As these filters are powered separately and not through the lens mount (probably to avoid issues in camera/lens communication),
is there a power priority cirquit, e.g. if the tiny internal battery dies, can the filter still be powered via USB-C only?
- Is the internal battery user-replaceable?
- In terms of back focus shift, I expect KipperTie is putting a lot of effort into getting it right for the Revolva LC and Strata Electro,
but what when using LCminiND and Canon's clear drop-in filter? Is the LCminiND "optically matched" to Canon's clear filter to some extent?

Many thanks in advance to everyone who helped clear things up.

 

[Phil Holland]

About to hop on a plane, but I'll swoop in and discuss a few things. Full disclosure, I have been testing LC-Tec eND filter technology for a long, long time now.

The first thing to understand is all Neutral Density solutions, front of lens and rear of lens have pros and cons. Glass, eND, VND, etc. On top of that unique implementations of these technologies may also create interesting issues.

LC-Tec's eND is generally very good and allows for finite tuning between stops in subtle increments, something glass filters can't do. Also, since this is a Liquid Crystal based technology, you don't get some of the issues that occur with Variable ND filtration. Lots of pros. However, depending on the lens design itself you may see color shift specifically in corners, but potentially more than that. In the case of RED, since the eND "talks" to the camera, they can compensate any potential color shift, but not necessarily the magenta/green you may see in the vignette or field.

To answer some of the specific questions. I have not detected any noticeable shift after prolonged use. You won't see dead pixels as that's not how the technology works. The material is positioned via charge universally. Since they are static when adjusted, they don't have an impact on frequency/flicker. I haven't had issues pointing into the sun, but I'm also not pointing into the sun for many hours when testing.

I have yet to see any KipperTie eND filters, so hard answers aren't going to happen yet. I know the Strata Electro was going to take external power, but I wouldn't put it out of the question to be powered through the mount somehow. Back Focus on these, unknown just yet.

RED's eND PL Mount comes with a matched pair of Clear and eND Cartridges that are very, very precise. Downside to the Mount is having to swap cartridges to go from eND to Clear. XL allows for that in body as there is space there to handle that physical mechanism. KipperTie may allow for that capability via the Mount/Adapter. The killer implementation would be to have that controlled via the camera menus and RED Control if that handshake can occur.

 

[kukras33]

Hello everyone

As more and more LC filter products are announced/launched throughout this year, I would like to learn more about this technology.
Although this tech has been around for quite some time - remember RED's Motion Mount or Tilta's TE-ND, which, if I remember correctly,
never made it to market (color shift?) - manufacturers seem to have only recently solved the issues from seven years ago.
RED's eND PL Mount and Sony's built-in automatic eVND are among the latest developments in this area.
Tilta's announced 4" x 5.65" matte box friendly eVND solution is also worth a look.
...and just in case you missed it, electronic diffusion filters (repeatable, exactly adjustable diffusion) have been announced as well.

While searching for an LC filter solution for EF-mount lenses, I was quite surprised to see KipperTie announce three new filter products,
two of which use LC technology:

LCminiND (eVND) for Canon's EF-RF drop-in filter adapter,
Revolva LC cartridge (clear + eVND)
Strata Electro (compact, motorized clear + solid ND swap)

Actually, my favourite is the Revolva LC cartridge as it makes Revolva extremely versatile. Kudos to KipperTie for developing
new products for Revolva.

But coming back to the topic of this thread - as good as this technology may seem nowadays, I found it difficult to get information about
how these products work and more important - what the downsides of eVND filters are (so, when not to use an eVND).

AFAIK, Liquid Crystal Tunable Filters (LCTF) are being used in scientific narrow-/broadband imaging applications
(to block unwanted wavelengths), so I assume that eVND filters are based on the same technology (maybe different designs)
to equally tune/regulate the transmittance to prevent color shifts and IR contamination.
The light passes a (linear or circular?) polarizer to uniform the angle of the light hitting the liquid crystal fluid.
The alignment of the LCs can be changed by the voltage applied, so in our case, if no voltage is applied,
the LC fluid is absorbing the light (no transmittance) and the more voltage is applied, the higher the light transmittance.
And for the diffusion filter mentioned above, the glass looks clear at no voltage and the diffusion gets stronger the more voltage
is being applied. Apologies for mistakes and misinterpretations, corrections are welcome.

The advantages (especially in regard of KipperTie's upcoming products) are:

- 2-7 stops of ND in one filter
- repeatable, seamless and precise tuning of the optical density
- fast switching time = near zero delay
- very consistent color rendition through the whole range of optical density
- only a minor color shift towards magenta between clear and the eVND
- remotely controllable via app

The disadvantages...
...well, I didn't find any information about when better not to use electronic VNDs.
It would be really helpful if manufacturers like RED / KipperTie and/or people who have experience e.g. with RED's eND PL Mount could
share their knowledge, findings and recommendations in this forum.

So, my concerns/questions are the following:

- Since LC tech works with polarized light, can light sources (e.g. sunlight) entering at certain angles cause (partial) color shift
or a sort of vignetting??
- Color shifts when filming LCDs at certain angles?
- Possible artifacts and color shifts in conjunction with other (CPL-) front-mounted filters?
- Do LC fluids deteriorate in neutrality / optical density or transmittance after time and if yes, in what timeframe?
- Can LC fluids take damage when pointed at the sun sporadicly?
- How does the filter behave when using below the recommended operating temperature (slower switching time or not uniform density?)
and can the LC fluid take damage in such cases?
- Can dead pixels/segments occur, or are eNDs one big adjustable segment? I suspect that eDiffusion filters are divided into
several segments to obtain a homogeneous diffusion pattern.
- Are the LCs being aligned at a certain frequency and if so, could this cause flicker issues (shutter speed / artificial light)?

...and here some KipperTie eVND related questions:

- As these filters are powered separately and not through the lens mount (probably to avoid issues in camera/lens communication),
is there a power priority cirquit, e.g. if the tiny internal battery dies, can the filter still be powered via USB-C only?
- Is the internal battery user-replaceable?
- In terms of back focus shift, I expect KipperTie is putting a lot of effort into getting it right for the Revolva LC and Strata Electro,
but what when using LCminiND and Canon's clear drop-in filter? Is the LCminiND "optically matched" to Canon's clear filter to some extent?

Many thanks in advance to everyone who helped clear things up.

If you also want to go to Chernobyl on a tour, then I can recommend you to use this service - https://chеrnobylstory.com/ , because this is the best service to book a tour of the cool place Chernobyl! I used this service myself and I really liked his tours of Chernobyl! So I advise you to try them too!

Great breakdown and questions! LC-based eVNDs are super promising, but yeah, not perfect. Main downsides are:


– Color shift under strong polarized light (like reflections, skies)– Potential issues with CPL stacking (they can fight each other)– Cold temps can slow response time– Some LC filters can show uneven ND if poorly aligned or aged– Risk of flicker with certain shutter/light combos (if voltage modulates at visible frequencies)


KipperTie seems to have tackled many of these well. Still, for mission-critical work, traditional glass ND might be safer. Curious—are you planning to try one of these soon?

 

[andrewhake]

Phil answered it best already, but each type of solution will have pros/cons. The only practical cons I have come across so far with the RED eND PL setup is the price really. That and some non standard PL lenses not fitting with behind the lens systems.

 

[Phil Holland]

KipperTie seems to have tackled many of these well. Still, for mission-critical work, traditional glass ND might be safer. Curious—are you planning to try one of these soon?

I have a fair bit of KT's offerings here from various mounts, Revolvas, and Stratas for several of my cameras. I'll test the new stuff when possible. I'm mostly interested Strata Electro if it does what I'm hoping it does. If it doesn't, I'll be living with RED's eND PL Mount as it does 90% of what is needed and is exceptionally well built.

My last two long shoots, 3 and 2 month long schedules, were entirely on the RED eND PL Mount with various primes and zooms. Worked great. The only thing I want is to be able to electronically go from ND to Clear on the smaller form factor DSMC3 bodies. Ideally powered via the mount itself if possible.

Jarred and a few others know how hard it was for me to choose between the smaller V-Raptors versus the XLs because of this one feature difference, but the smaller form factor is just too useful for everything I do to ignore and I lived with the cartridge. Not a huge deal, heck, I'll still use glass ND in front of the lens, but it's the only real missing link here.

 

[John Marchant]

I'll try and address some of these from a KipperTie perspective - sticking to the facts as I know them.

All of this is specific to our products embodying the LC-Tec electronic ND. It is worthy of note that LC-Tec are several generations into this core technology now and have solved enough of the shortcomings seen in other implementations that I consider it worthy of a place in our brand's products.

There is some effect on polarised light, but it is minor. Most notably some small colour shifts related to z-axis oriented rotation when filming electronic screens. In general however it is not very significant, and the filters retain useful function without bad effects when combined with CPL for reflection control.

Longevity and robustness are not expected to be any kind of issue on a sensible product lifespan. We have earlier generation LC-Tec engineering samples as far back as 2017 which are as good as new.

The filter (including upcoming diffusion iterations) acts a single large piece with no subdivisions, and is not susceptible to localised failure or degradation.

The filters density has a stable neutral state when the charge applied to it is unchanged. It could be driven by a dc voltage to set opacity, but over time this degrades the filter, so instead it is driven by a high frequency AC waveform. This waveform does not induce a flicker at its frequency however, merely sets the shortest system response time (above that of the LC material itself). Temperature does affect switching speed, but only on a scale so short as to have no relevance to an ND product.

On power, for Revolva LC and LCminiND, they are supplied by a custom internal battery of very high energy density. Real world use yields multiple days of run-time on an hour's charge. And yes, you can just plug in to USB when flat and continue - it'll recharge while in active use too.

The filter thickness of the LCminiND is matched to the Canon standard clear, the Revolva LC has a thinner glass for packaging reasons, and a matched clear built-in.

The battery is pretty trivial to replace if you are technically competent, but we designed such that even a very old and degraded battery provides the officially advertised performance.

 

[Thomas B.]

Sounds great! Thanks for your answers.