CYL-Filter – Moiré and aliasing filter for HD DSLR video

[Update 2016, 16/4   – See this new blog article for latest developments on an adjustable anti-aliasing, anti-Moire filter method and DIY details.]

Manufacturing is currently on hold, summer 2014. I hope to return with a version 2 of the filter method with highly improved means of estimating the optimal filter strengths for different image sensor and lens configurations.

This is an experimental moiré and aliasing filter (CYL-Filter) fitted into a standard filter frame (size 49, 52, 55, 58, 62, 67 and 72 mm). See more info about the this filter method in the earlier posts, here and here.  If interested, please contact me directly via the contact form at the end of this post, and I can give you more information about the filter.

Update May 2013

I have been working and elaborating to survey the possibilities with this  antialiasing filter method for DSLR videoing.  Here is the latest development status:

– I have included 72mm screw frame filter sizes, and I’m working on also to include a 77mm frame.

– Now possible to get CYL-100, in addition to CYL-25, 50 and 75.

– Working on improving the filter mount, E.g. to allow ND filters to be mounted on top of the filter with the screw frame. It is generally not possible now, since the filter glass curves out. Mounting the ND filter ‘under’ the antialiasing filter will increase the distance to the camera front lens and generally lead to more image distortion for the higher filter strenghts (see below).

– Below is a new equi-performance curves chart for the antialiasing filters. This gives an overview of the working range of the different filter strenghts. As it can be seen, the working range is restricted and requires control of aperture and focal length. Keeping the lens setting on this curve will produce the optimal anti-aliasing effect. When moving outside the curves, it is not really possible to achieve the desired effect, ei. either too sharp or too blurred. That means, for longer zooms, above 55mm the image will typically get too blurred, and at super wide angles below it will get too sharp (unless very large aperture). In many cases it will be required to use a ND filter to keep a sufficient large aperture at daylight, wide angle shots, -if not going to higher shutter speeds. To use the filter, it is recommended to run the camera with a fixed aperture and fixed focal length for each shot.

Working range for antialiasing filter CYL 25, 50, 75 and 100

– Performance on full-frame systems. I still only have theoretical calculations, but planning to do tests soon. The figure below shows the estimated working range for a full-frame sensor (basically a scaling of the previous figure). The full frame system needs a larger blur radius since the pixels are more spaced. That sets higher requirements to the filter and it may also lead to more edge distortion, however I will try to carry out real tests as soon as possible.

Different CYL filter strengths working range estimated for antialiasing on Full-frame sensor

– Distortion. In the beginning I did not notice this when using the CYL75 with (18mm and DX size sensor), however this optical antialiasing method produceses a distrinct distortion (45 degree squeeze), when the filter cannot be ultimately close to the camera lens. It is hardly noticalbe for cyl 75 and below. On CYL100 is can be more visible, especialy on wide angle shots and full-frame systems. I have measured the effect in this case to be in the order of 2-4% of at the corners. The most important factor is to get the filter close to the camera lens. To do that may also vary from amongs different lens types. Im working on optimizing and testing the filter lens to minimize this. I will do more tests on different lenses.

I think improving the aliasing performance in HD DSLR videoing is a great way to improve the overall video quality, and to get smooth, detailed, noise-free and better colored images. At first glance, the filtered image may look more soft, but quickly one will realize that the original sharpness was artificial and not representing real details. This is most visible on direct moiré artifacts, but this is just a symptom of the aliasing going on in any picture frame. Antialiasing will increase the information used for each image. It is a digital challenge for DSLR’s. In the mean time optical antialiasing filters may be the best method.

Antialiasing CYL-filter Specifications:

• Method for reduction or elimination of moiré and aliasing artifacts caused by line-skipping (horizontal) on DSLR camera systems
• Through-out tested on Nikon d5100 + 18-55 mm kit lens
• Works by a controlled introduction of blur to reduce moiré artifacts for HD DSLR video by using an astigmatic lens. The blur depends on focal length and aperture according to the table below.  See more [here],
• Available in strengths CYL25, 50, 75 and 100
• Standard screw-on filter frame (sizes 49, 52, 55, 58, 62, and 72 mm)
• High quality optical filter with AR coating
• Filter frame has alignment marks for correct rotation
• Download user guide Here

(update: A newer version of this figure can be found above) CYL filter method – working ranges. Filter strength vs. aperture and focal length. As measured on Nikon d5100 (DX sized sensor)

To work optimally, the filter needs to be aligned and rotated correctly relative to the image sensor, as indicated by white lines on the frame. So, the filter is ideally suited for lenses, which has a fixed, non-rotating front element. However, as long as the rotation is small (which is the case with the Nikon 18-55 kit lens – rotating only about 10 degrees for the normal focus range), or using fixed focus, it is still highly applicable.

At the moment the filter has only been tested extensively with the Nikon d5100 camera, and particularly with the kit lens (my current preferred setup). No tests on cameras or lenses by Canon, Sony and other brands,  so I cannot guarantee the anti-aliasing and moire effect for these systems yet.

However, as long the moiré problems arises from the use of the horizontal line-skipping, the direct optical blur effect of the filter should be the same on all cameras. It is rather a question of how much blur that is needed for the various cameras, chip sizes, crop factors and how the internal image processing methods. In this respect, the values of the table (found here) may need to be multiplied by a factor to fit camera models different than the Nikon d5100.

To get more information, contact me directly on this form

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