Understanding the Low-Pass Filter Effect Cancellation Issue: What You Must Know About Canon’s Two New 50+ Megapixel Camera Bodies

[Arthur Morris]

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Canon’s Two New 50+ Megapixel Camera Bodies

Many of you have read about the two new Canon 50+ megapixel bodies, the Canon EOS 5DS DSLR and theCanon EOS 5DS R DSLR. The two cameras look, sound, and pretty much are quite similar. I have withheld commenting until now because I did not have a good–heck, I did not have any–understanding of the single difference between the two bodies, that being the Low-Pass Filter Effect Cancellation.

From the 5DS R Overview

Low-Pass Filter Effect Cancellation

Low-pass filter effect cancellation takes full advantage of the 50.6MP sensor, delivering greater detail and even higher resolution images than those of the 5DS.
As that is the elephant in the closet and because I was unable to find anything definitive anywhere online, I wrote the always brilliant Rudy Winston. Below I share his e-mail with you. My brief comments follow.

By e-mail from Canon’s Rudy Winston:

Hi Artie,

The basics are as follows…

1. Canon’s engineers believe strongly that a low-pass filter is an important aid, IN GENERAL, to image quality with digital SLRs. We’ve had one in-place immediately in front of the image sensor on all previous EOS D-SLRs to date.

2. Low-pass filters basically attack problems with false colors and especially occasional moire patterns that can arise when fine, repeating patterns (think of the weave in some fabrics, for instance) begin to line-up with and approach the size/frequency of the patterns of pixels on an image sensor. Low-pass filters work by spreading the incoming light by the width of approximately ONE PIXEL horizontally (left and right), and a second low-pass filter layer does the same vertically, splitting it up and down.

3. This scattering of light in effect produces a slight blurring effect (usually easy to correct with slight Unsharp Mask-type sharpening in the computer, after the fact, or judicious use of the in-camera sharpening via Picture Style control). But the by-product is far less tendency to give psychedelic-looking moire patterns with certain subjects, in certain conditions (and of course, you never see these moire patterns in the viewfinder, before the fact).
(Note: To learn more about moiré and see two good example photos, click here. Moiré is rarely a problem for nature photographers. There are many pronunciations: “mwahr” is the most common and the most widely accepted.)

4. The filter array that includes the two different low-pass filters mentioned above is a part of the optical system, even though it’s sandwiched right up against the front of the imaging sensor. The total filter array includes at least one layer of IR-absorbing glass, a dichroic mirror layer to reflect infrared and UV illumination, and what they call a phase plate, which changes the polarization of incoming light into circular polarization. In other words, it’s a pretty sophisticated optical sandwich, even though to the naked eye it appears as a super-thin layer of glass in front of the sensor.

5. All that said, it is true that if we were to remove the low-pass filter component, in theory, we’d have the potential of greater initial, out-of-the-camera sharpness in many situations. And, it’s definitely true that the moire pattern risk mentioned above won’t occur in the majority of images, unless you were shooting things like fabrics or products with very fine, repeating line patterns on a regular basis. (For the type of bird imaging you normally do, or most landscape applications, I’d guess the risk of moire is pretty much nil most of the time.)

6. As a parenthetical note, these moire patterns, IF they do occur, can usually be moderated or even eliminated in some cases with various image-editing techniques… Photoshop gurus have a multitude of them, and some RAW file processing software now contains anti-moire tools for these occasions. Still, it’s an extra step — sometimes a fairly sophisticated set of them — to reduce or remove moire completely from an image, if it does occur.

7. Because the afore-mentioned low-pass filter array is a part of the optical path, you can’t just remove it — you’d change the effective length of the optical axis, and have to re-design the entire camera body slightly, including the AF system’s optical path, to accommodate such a change. Since Canon made the strategic decision to offer TWO high-resolution cameras, a different technique was needed to achieve removal of the low-pass filter effect, without upsetting the optical system within the camera body. And, without the expense of (in effect) having to design an entirely new camera from scratch, with slightly altered internal dimensions.

8. All that said, here’s what Canon has done: they need two low-pass filter layers in-place to preserve the same optical length within the body. The traditional EOS 5DS of course does just that, with Canon’s typical low-pass filter approach. With the EOS 5DS R, they also have two low-pass filter layers in-place. The first scatters the incoming light by spreading it vertically, similarly to how it’s done in the standard 5DS camera. But the next low-pass filter layer bends the incoming light VERTICALLY again, in the reverse direction — back to ONE single ray path, so the scattered light is effectively “un-scattered” and re-focused into a single optical beam. Thus, the low-pass filter effect is “cancelled.”

9. The result of this cancellation of the low-pass filter effect in the EOS 5DS R is a slight — but noticeable, in many instances — increase in the overall contrast and sharpness of fine detail, lines, and texture in subjects. Canon is clear that photographers need to understand that a by-product of this is a risk of moire patterns appearing occasionally, and that it’s up to the shooter to work with post-processing to limit this effect if and when it happens. But I have no doubt that there would be a bit more detail and texture in things like feather detail in birds, for example. I don’t want to over-state the improvement in sharpness in the EOS 5DS R vs. the standard 5DS model… you can see it when you start magnifying images and look for it, but it’s not an “in-your-face” type of obvious difference that my Mom would immediately spot when viewing on-screen at 100%.

10. Bottom line: we anticipate that the majority of sales of our 50.6 million pixel camera will be the standard 5DS camera, and that in the eyes of most users, the 5DS R will be seen as something of a specialty version. Buy the latter for the right reasons, and it’ll delight you. We just want all potential buyers, and dealer staff, to understand that along with its added initial image sharpness does come a risk of occasional optical imperfections in certain shooting situations. I’ll finish where I started: overall, Canon’s engineers remain very firm that in their opinion, OVERALL digital image quality is enhanced by the use of traditional low-pass filter design in digital SLRs. We’ll let the market be the ultimate judge!

Let me know if you have any other questions, or if any of this is not perfectly clear. Good questions you ask, and it’s up to us here at Canon to make sure every potential customer understands the answers to them! Be well, stay warm!

— Rudy Winston
Canon USA

Thanks!

Thanks a huge stack to Rudy for sharing his almost infinite knowledge of all things Canon with us.

The Overview and the Specs

You can learn all about the Canon EOS 5DS DSLR by clicking here , scrolling down, and then clicking on the Overview tab or on the Specs tab.
You can learn all about the Canon EOS 5DS R DSLR by clicking here, scrolling down, and then clicking on the Overview tab or on the Specs tab.

My Comments

I will not have any idea as to whether I would want either of these bodies for nature photography until I see some RAW files from each one. I can understand that serious landscape folks and those who make large prints as a matter of course are salivating over the thought of getting their hands on whichever of these bodies they deem to be best.

There are some great features that many might love; each features the new 50.6 megapixel full-frame CMOS sensor that will deliver ultra-high resolution images for large-scale printing and extensive, creative cropping, fine detail mode in Picture Style (I wonder if Arash will like that….), 1.3x and 1.6x crop shooting (I need to learn a bit more about that and will share what I learn with you here at some point), full HD 30p movie capability, a built-In intervalometer and bulb timer, and lots more.
High-speed continuous shooting at up to 5 fps might leave those accustomed to the blazing frame rates of the 1D X and the 7D Mark II feeling a bit sluggish.

Questions and Your Comments

If you have any knowledge of the two new cameras or of any of the related issues, or any questions on the same topics, please do leave a comment. If you ask a question that I cannot answer perhaps other can chime in. And I will reach out to Rudy or to Chuck Westfall and share what I learn with you here.

[arash_hazeghi]

Hi Artie,

Thanks for posting Rudy's comments.

In order to get moire you need perfectly repeating patterns, that usually only exist in man made objects. I would not worry about it for birds. I am going to get the 5DsR as a backup, it is slow compared to the 1DX but the resolution is really nice and it is faster the competition i.e. the Nikon D800 . I think most folks who care about this kind of resolution will probably want their files as sharp as it can be and will opt for the R model.

[arash_hazeghi]

BTW for folks who want understand moire better this wiki article is great.
http://en.m.wikipedia.org/wiki/Moiré_pattern

[Doug Brown]

Thanks for sharing Artie! I wonder what happens to feather detail with the D800E, and if there are any issues with moiré in bird feathers?

[arash_hazeghi]

Thanks for sharing Artie! I wonder what happens to feather detail with the D800E, and if there are any issues with moiré in bird feathers?

Moire in objects that aren't man made is highly unlikely, as the pattern must be perfectly repetitive at high frequency. I wonder if any D800E users have seen it on birds... my Google search returned no results.