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August 8, 2010

Soft Filters: a Solution for DSLR Aliasing?

I have tried Cavision, Lee, and Tiffen soft filters in an attempt to eliminate aliasing and moire but have yet to find a solution. Now Philip Bloom is reporting (from a user's comments) that Zeiss Softar filters offer a potential remedy for these problems. I'm skeptical, given I've tried a number of similar filters (and the Softars claim to "retain sharpness," which would mean... retaining aliasing), but here's the word from Zeiss:

Unlike most softeners and diffusors the Zeiss Softar attachments are not mass produced pieces of plastic. This is why genuine Zeiss Softar attachments do not lose focus and do not produce unsharp out-of-focus images. Zeiss Softar attachments also do not lose important fine detail like eyelashes. Neither do they lose overall contrast and color saturation, which would result in dull images like the ones produced by so many softeners, ”soft lenses”, and diffusors. However, Zeiss Softar attachments reduce, lower, ”soften” the visibility of skin blemishes and freckles thus easing the life of the portrait and beauty photographer, saving retouching efforts, supporting the acceptance of his or her work and increasing the economic success.

More important than any manufacturer description, however, is what users actually report. So: has anyone out there had success getting rid of the dreaded ugliness demonstrated below? Along with the 5D dropping to 480p during recording, the aliasing issue is my chief DSLR complaint.

By all means, if you've found a way of reducing aliasing and moire, please share!

Your Comment

2 Comments

Wow that picture is amazing, I have never seen it that bad. I ran a bunch of moire pattern tests today that I hope to share tomorrow. I'm still learning that's why I found your blog.

August 11, 2010

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An HD image captured by a higher-than-HD sensor will require that lines be either dropped or averaged. Since averaging adjacent lines takes tons or processing power, it is not currently possible for standard video frame rates (24 - 60 fps).

The most common method is line skipping, like on the 5D, where only every 3rd or 4th line is read. This is EXACTLY what is causing the moire and anti-aliasing problems.

One camera has a novel approach: Don't skip lines, but just use the 1080 lines in the middle of the sensor! The moire bands disappear, and the camera can run lightning fast by bypassing all of the extra processing. So far this has only be seen in the "crop mode" of the Panasonic Lumix DMC-GH2 and it seems to be a very workable method of getting clear, non-moire images at standard framerates.

Basically, this carries the baggage of a "small sensor" including a strong lens focal length conversion factor, and the current biggie - deep depth of field.

Since the low light benefits of large sensors are lost by straight row skipping (and averaging requires so much processing power) I think the only real loss in using a small or cropped sensor for VIDEO is the DOF issue.

Current DOF adapters (35mm lens adapters with ground glass elements) bring their own share of drawbacks (light loss, moving parts, extra wires and power supply, additional weight and expense, etc.).

It seems like all we need now is some outside-the-box thinking on getting shallow depth of field (when desired) while using small sensors.

p.s. Reducing the vertical scan height of sensors also drastically reduces CMOS sensor "rolling shutter" effects as well.

August 29, 2011

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David James