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-   -   Si2k without anti-aliasing filter. (https://www.dvinfo.net/forum/silicon-imaging-si-2k/537043-si2k-without-anti-aliasing-filter.html)

Bob Hart October 6th, 2019 06:27 AM

Si2k without anti-aliasing filter.
This is a long shot given the time since the SI2K was subsumed by the 4K+ evolutions.

Has anyone operated the camera with the anti-aliasing filter removed in order to chase some more "apparent" resolution. If so, what did you do about the IR filter?

The SI2K has its combined IR/anti-aliasing filter mounted in a small circular metal holder. The SI2K with the stock filter was a little inclined towards IR contamination of the image with weak greens, more so with ND filters in the path.

If anyone went this route, any advice on a suitable IR filter glass, brand, model number would be appreciated.

Why am I asking? The Blackmagic "big" URSA 4K, which took over from my SI2K has laid down for the count and affordable product support is not there to be had. I am going back to the older SI2K camera as I can't afford anything else presently.

With a speedbooster for the Blackmagic Pocket cam in the optical path, the practical utility of the SI2K camera is extended, even if it is not 4K.

The image lacks that bit of crispness folk seem to expect these days.

Bob Hart October 14th, 2019 08:21 AM

Re: Si2k without anti-aliasing filter.
With just a plain IR filter in the throat of the camera, no anti-aliasing filter and the 35mm to 2/3" Speedbooster optic in play, the setback required to adjust for the thinner piece of filter glass is considerable.

If there is an apparent resolution improvement, it is very subtle. The anti-aliasing filter must have been well matched. Still it can be made to work and seems to hold good for the 14mm wide-angle Sigma-for-Nikon lens.

Daylight tests tomorrow. It is not 4K but it will do for now, seeing as how Blackmagic's URSA 4K has gasped its last.

Bob Hart October 15th, 2019 05:13 AM

Re: Si2k without anti-aliasing filter.
For what it is worth, here is a link to a short clip with the following items in the image path :-


I may also try a contrast filter which I have tried in the path previously with the IR filter to build the filter thickness as infinity focus is a whisker out of reach without skimming a trace more material off the rear of the speedbooster body.

You can blame me for the blue hue. I am partially red-green colourblind. The SI2K look files are no longer supported by edit software. The raw image is very flat and takes a lot of dragging up and saturation range runs out. There is likely a way to do it but I am no colour-grader or editor. I was also unable to export the timeline at original resolution but the lower 1920x1080.

Bob Hart October 20th, 2019 01:46 PM

Re: Si2k without anti-aliasing filter.
1 Attachment(s)
I have been revisiting the uncompressed .siv files. They were an impossibilty with the P+S recorder but it seems that the faux-cinemascope cropped image demands less data. I though there might have been a chance they would work but it seems not so. The buffer indicator does not register when recording a .siv file but the recorder stops and concludes the file at about 1.1Gb.

I managed to get a still image out of it.

The optical path was :-

Nikon 50mm f1.4 lens.
Metabones Speedbooster.
IR filter. ( No OPLF).
Formatt Hitech NC8 filter (behind the IR filter).

This is an attempt to gain a little more sharpness in the image, also trying out a rumoured part of the ARRI Alexa secret sauce which apparently involves a contrast filter close to the sensor.

I acknowledge the generosity of the optical filter manufacturer Formatt Hitech who laser-cut some small NC8 panels for me.

The image was lifted and graded by a BGOBG method as I could not find the "RGB parade" (adobe premiere speak) in DaVinci Resolve which I am trying to learn. As I am partially red/green colourblind it has come out a bit red it seems.

Bob Hart October 22nd, 2019 11:25 AM

Re: Si2k without anti-aliasing filter.
1 Attachment(s)
For those who are curious, here is an outdoors image shot with the the following :-

Voigtlander-for-Nikon 40mm f2 lens.
Metabones Speedbooster for BMPCC modified to IMS-Mount.
IR filter near sensor.
Formatt Hitech NC8 filter panel added close to sensor.
-3db video gain.
Exposed to suit default look. ( Rec709 ).
Shutter 1/100th sec.
ARRI LOG to Rec709 3D LUT added in DaVinci Resolve.
No other grading.
Exported to H264.
Opened in Premiere Pro CS6 and frame exported.

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