This article is about why you need or don’t need Kinefinity’s new OLPF. To put it fairly simple; a OLPF filter reduces the chances to get moire artefacts (aliasing)
The new OLPF (Olpf FF3) for the MAVO LF doesn’t replace the original OLPF that ships standard with the camera. But instead has to be seen as an alternative. For those who are familiar with the Arri Alexa you will notice that the new OLPF by Kinefinity is pretty close in terms of resolving power and lack of aliasing issues.
All Bayer sensors can produce color moiré and aliasing. The term Moire is mostly referring to a very high detailed repetitive structure like in fabrics.
So Moire is not really the issue but instead the challenge. If one is talking about Moire issues in digital sensors they often refer to the colour pollution that happens due to the BAYER colour filters. Aliasing is referring to a sensor issue mostly happening in diagonal lines that are unable to be resolved correctly.
Wiki: aliasing is an effect that causes different signals to become indistinguishable when sampled
To keep things simple and straight Moire and Aliasing are basically the same, Moire is the input and Aliasing is the output.
Aliasing in Photography
When the sensor’s sampling rate is high enough, which equals as a very high pixel count, aliasing is less likely. That’s why medium-format cameras with up to 80 megapixels and today’s high-pixel-count DSLRs and mirrorless cameras can do away with the olpf filter—the sampling rate is so high that moiré and aliasing are minimized. They mainly appear in subjects such as cloth textures and distant skyscrapers with lots of windows. Photographers are lucky in that regard, with the simplicity of only having to process one image, and don’t have the moving artefacts of moire/aliasing issues like in cinematography its easy to overcome these issues with some simple photoshop plugins.
Thats why we see for instances NIKON releasing two versions of their camera, one with the OLPF installed one without. Installing a OLPF is not a simple procedure, due to refraction in the OLPF filter the Flange distance changes thus the lens mount has to be adjusted accordingly.
OLPF Filters Explained
An OLPF (optical low-pass filter), sits over the image sensor and does away with aliasing—artifacts that occur when you sample the real world with a fine grid of pixels. Conventional Bayer image sensors add color moiré to the mix, since each pixel “sees” only red, green or blue. (The missing colors are provided to each pixel via interpolation using data from neighboring pixels and complex proprietary algorithms; this “demosaicing” process also creates color moiré.)
A typical OLPF filter consists of a top layer, which slightly displaces the image horizontally, an infrared filter and ultra violet filter to eliminate unwanted infrared radiation and a bottom layer that slightly displaces the image vertically. This blurs the image’s high frequencies (fine detail) at the pixel level, reducing moiré and artifacts. But it also reduces sharpness at the pixel level. So the name OLPF (optical low pass filter) comes from the fact that it sets a certain threshold for frequencies to pass through while others (high frequencies) are blocked.
Aliasing in Cinematography
It seems that most cinematographers aren’t concerned with sharpness. Sharpness is only one of the many optical parameters that brews the image. When cinematographers describe sharpness they mostly do so in an esthetic manner and less in a technical matter. When Roger Deakins says for instance that he prefers MASTER PRIMES over ULTRA PRIMES because they are sharper, he’s wrong. Yes MASTER PRIMES are sharper but not combined with an digital Arri ALEXA. When projecting lenses on a lens projector we clearly see that the MASTER PRIMES are a winner in terms of sharpness, but this gain is eased out with the introduction of the OLPF.
The ARRI ALEXA (benchmark in cinematography) features quite a low pixel pitch , and cinematographers are also striving to have zero aliasing issues, and are okay with lower sharpness. Thats why the Arri Alexa features one off the thickest OLPF filters from all existing cinema camera models. Too much sharpness stands in the way of transforming an image and create a layer of mysterie. In a way its funny ans absurd to see that;
If lens designers are able to add this extra level of sharpness by making sure that even the highest frequencies pass through that these same frequencies -that took so much effort to capture- are filtered out by the OLPF.
For filmmakers occupied with landscape , the techniques for reducing and eliminating moiré are academic. Because landscapes largely consist of such irregular patterns, you’re unlikely to encounter much aliasing at all. So, for the typical outdoor shooter, the OLPF filterless or low density OLPF cameras should be valuable tools, delivering fine definition and lots of landscape detail.
An easily overlooked issue OLPF filters introduce is called Smear. Basically with wide angle lenses, the corners of a sensor are projected in a much steeper angle than the centre of the sensor. This leads to all kind of issues because a light ray under such a steep angle is traveling a longer distance through the Olpf and is messed up.
Thats what introduces corner softness and colour shifts. To overcome this issue, we need light rays that are leaving the lens much more in parallel. The only way to achieve this is to enlarge the entrance pupil of a lens and shorten up the distance from entrance pupil to the sensor. Previously the so called ‘flange distance’ was dictated by the mirror and shutters in analogue cameras. Now that these are erased in modern camera designs we can create new lens mount designs with much bigger ‘throttle’ and shorter ‘flange distances’ enabling lens designer to create lenses that are much more ‘telecentric’.
Arri introduced the LPL mount that has a larger throttle than the PL mount and a shorter flange distance (same as Ef mount), but compared to for instance NIKON Z, the LPL Arri mount is still a pretty conservative design. Currently the only LPL mount lenses are the ‘Arri Signature primes’. If you have the funds to buy or rent these and you have a Kinefinity camera in your posession than we suggest you buy our Kinefinity LPL kinemount in our shop.
OLPF’s and the MAVO LF
Can we eliminate Aliasing completely? NO SORRY this can’t be done with traditional CMOS sensors.
But we can reduce the chance to almost zero. But everything has a price, if sharpness is your middle name, and clients expect high sharpness without the ugly post-production sharpness effects, you have to compromise.
Therefore to our believes the OLPF that standard ships with the Kinefinity MAVO LF has an OLPF that balances between sharpness and aliasing reduction. The Mavo LF(with its default Olpf) can reduce very sharp images, especially paired up with lenses like the Sigma Art series or other modern lens designs.
Under most circumstances, especially when (soft) vintage lenses like Anamorphic lenses are deployed, chances are very small to introduce moire artefacts. But when working in a high contrast tv studio combined with sharp lenses with lots of high detailed objects (fabrics, etc.) chances to introduce moire artefacts are much bigger opposed to them who shoot a lot of nature, or other more organic objects.
The choice to upgrade to the new OLPF FF3 mostly is up to your preferences, theres no GOOD or BAD.
If you work as a cinematographer and doing a lot of narrative work we highly suggest the OLPF FF3. If you do a lot of high contrast high detailed object shootings where aliasing is completely unwanted then go for the Olpf FF3. If sharpness is the least important thing in your work as a cinematographer and your fighting against it then upgrade to Olpf FF3 as well.
But if you shoot a lot of nature, or you are a big fan of vintage lenses with lower sharpness (and you want to retain as much of the lens character), or an allround shooter: Then please first try the standard OLPF and do some tests and see if you really need the new OLPF FF3.
Never mislead yourself, doing tests yourself is the only way to find out what filter fits your way of shooting the best!
Please note that the OLPF FF3 is user replacable, and takes 20 minutes by a skilled camera man to replace, so choosing one OLPF over the other is not definitive. Check the OLPF FF3 out here