Tag Archives: anti-aliasing

Sigma brings back the moiré

3 Feb

I believe I’ve written on this subject before. DPReview just exclusively announced the results of DxOMark testing of the Sigma 85mm f/1.4 “Art” lens, announcing it to have achieved a perfect 36 “perceptual megapixels” on the Nikon D810’s 36 megapixel sensor. It therefore sort-of-ties with the Sony FE 90mm f/2.8 macro lens, which achieved 42 perceptual megapixels on a 42 megapixel sensor.

Discussion immediately broke out on whether the Zeiss Otus 85/1.4 or Nikon 105/1.4 provided nicer bokeh and whether this was, in fact, more important than sharpness. The Zeiss, in particular, is almost tied with the Sigma for sharpness, and like it excels in many other technically measurable characteristics. The Nikon may be half a step behind, and in fact has a focal length of 94.8mm vs. the Sigma’s 79.9mm, so is more comparable than it sounds at first.

But back to my original point, which is the following:


Excerpt from DPReview sample image no. 30, of the Sigma 85mm samples.

That’s right, moiré. It is a physical certainty that if the sensor has no anti-aliasing filter on it, and the lens outresolves the sensor, you will see moiré on certain subjects (you can find technical details of moiré and aliasing on the Wikipedia pages, moiré pattern and Nyquist frequency). Many manufacturers have dropped the anti-aliasing filter to squeeze more resolution out of their images and as a small cost-saving, or installed a second filter that cancels the first (slight cost increase). Wisely, Canon added the 5Ds without the R to their line-up, which cuts back on moiré much better than the 5Ds R.

In Nikonland, it seems the highest resolving lenses and highest resolving sensors do not make a good pair. That being so, should we buy high resolution cameras at all, and what other choices do we have? Both the Nikon D600 and D610 have weak AA filters (link in Polish) – a bad idea for a lower-resovling camera as the range of lenses that outresolve it will be greater.

Pentax now releases its cameras with an AA filter that works up to shutter speeds of 1/1000s – presumably adequate for most portrait work, and hopeful that anything you’ll want to shoot above that shutter speed will be moving so fast that aliasing is not likely.

In spite of this, Pentax remains, as of this writing, a stalwart of compact lenses that value bokeh over resolution – partly, perhaps, owing to the fact that some of its lenses have been available for quite some time.

It’s well known that Tamron and Pentax have been sitting in a tree lately, and so it is fitting that Tamron somewhat recently launched a line of f/1.8 primes – more compact than the competition’s f/1.4 standard. DxOMark allows comparing Tamron’s 85mm lens with Zeiss’ Otus and Milvus, for instance, and there’s hardly a hair between them. Most surprising perhaps is the performance of the Milvus at less than half the price of the Otus.

Incidentally, while the three aforementioned lenses max out the D800E’s sensor at 36 perceptual megapixels, Sony’s new Gold Master 85mm lens reaches no more than the same value – 36 P-Mpix on an AA-filterless 42 megapixel sensor.

It’s worth asking therefore whether the trend for the second half of this decade is going to continue with lenses increasing in size, resolving power, and price, as exemplified by the Art and Otus, or a reconsideration of traditional values.* If the former, I hope consumers will be asking for strong anti-aliasing filters, and that camera makers, in spite of mobile phone cameras nipping at their heels, will grant that gift.

*An opportunity, perhaps, for Chinese lens makers trying to push into the market.

Update 7 February 2017: For differences between the Art and Otus, check out Roger Cicala’s blog post.


Why high resolution cameras don’t need an AA filter

17 Dec

Disclaimer: Unfiltered truth ahead.

Digital cameras used to have a problem, which was that their lenses were so sharp that images would show moire or aliasing if there wasn’t an additional anti-aliasing or low-pass filter placed directly in front of the sensor to add a small amount of blur. Side effects of this filter include a small reduction in light transmission and a slight distortion of the colour distribution.

As camera sensors got to around 16MP APS-C or around 40 MP full frame, it became apparent this problem wasn’t so much of a problem any more. Glass quality generally wasn’t good enough to still cause moire and other aliasing at this tight packing of Bayer array and photosites. The lenses themselves served as AA filters, and throwing in an low pass filter on the sensor only made images blurrier, without any particular benefit. So some smart executive or engineer at Nikon said, “let’s ditch the thing and see if our customers like it”. And the customers came, and they saw that it was good, and they bought it.

Around the same time, some Pentax execs likewise came together and said unto each other, “let there be unwavering sharpness”. But knowing full wele that the Nikon gods had spread their bets across two models, one with and one withoute AA filter, the good sirs of Pentax did likewyse, and thus there came to be the K-5 II and IIs, made in the D800E’s image.

So there you have it: the story of why you can buy a D800E or K-5 IIs without regret. And how, as an engineer, you can do something for very good reasons and completely fail to communicate this to the customers. Probably because upper management told you to keep your trap shut about the sharpness of the lenses. And the fact that the Ricoh GR and Fujifilm X100S take sharper pics than your monster-tea-bagging SLR.

So there you have it: the reason you can leave that K-3 AA simulation switched off, save battery power, and never worry. Woohoo!

What’s the deal with the Pentax K-50?

23 Jun

In a strange reversal over the general feeling when the K-30 was released (“what does the K-5 offer over the K-30 that justifies the higher price?”), everyone is now asking what Pentax’ new K-50 offers over predecessor K-30, and whether indeed these are just firmware updates rather than “real” improvements.

First of all, the biggest complaint with the K-30, that the default kit pairs a weather-resistant camera with a vulnerable lens, rendering the whole assembly prone to water intrusion, has been addressed: the K-50 comes with a new variant of the 18-55mm design, a light-weight plastic lens (DA-L) that is additionally weather-resistant (WR): the DA-L 18-55mm WR.

Pentax K-50 in white

A white and black Pentax K-50 with the new weather-resistant and colour-matched DA-L (plastic) 18-55mm kit lens. Promotional image from Pentax.

Other than that, the firmware is now capable of correcting “jaggies”, that is, jagged edges that are an aliasing-spectrum phenomenon. Somewhat disappointingly, however, the algorithm is likely to overcorrect in some cases, leading to a loss of jagged detail, e.g. jagged leaf edges. I would personally prefer to have a stronger anti-aliasing filter and not worry about whether some algorithm will delete important detail in my image.

Composition Adjust

The K-50 has inherited Composition Adjust from the K-5 series, but what is it? Composition Adjust allows you to move the sensor around while sensor stabilisation is disabled. This gives tilt-shift to any lens with sufficiently large image circle, or alternatively allows you to stitch images together in post for a very wide-angle image, although not quite rivalling 35mm proportions. Some people just like to have composition adjust so they can make fine adjustments to composition while the camera is on a tripod head that may not be very conducive to small corrections. It is not a feature you’ll be using very often, but it would be nice to have if you can get it for free.

K-50 conspiracy

It seems likely that the K-30 has always been capable of ISO 51200 output in principle, and the K-50 now adds this feature without any known change in the image processing platform or sensor. However, no firmware update is as yet available to enable ISO 51200 output in the K-30. Whether this is an example of deliberate crippling in order to give customers enough reasons to continue buying the K-5 and its successors, or whether Pentax simply considered the addition of ISO 51200 too confusing for people, or the resulting image quality too potentially offputting to those knowing little of digital photography, may forever be unclear to the layperson.

In terms of design, the K-50 returns to shapes that were tried on the K20D, a time when Pentax and Canon cameras looked more similar to each other than they do today. This may be a ploy by Pentax to get the K-50 sold more easily to those more familiar with Canon bodies, but is just as likely an attempt to reach out to the female demographic who may have found the design of the K-30 too edgy and sporty.

Should you consider buying the K-500?

In one word, no. I won’t discuss colour choices, as the matter is very simple (the K-500 comes in one colour, which is black, the K-50 allows many different combinations, depending on your location). But I will address weather sealing.

Pentax K-500

Pentax K-500 promotional image.

Weather sealing keeps spray water, sand and dust out of your camera and lenses. You will need to do less cleaning and maintain your kit in good condition for longer with weather sealing. A weather-sealed camera will also retain its resale value for longer, as dust and moisture can less easily invade the lens and camera. Therefore especially those on a budget should NOT consider buying the K-500 because it will depreciate faster, and you’ll end up losing money. You will be better served to save up for another two months and buy the K-50, and for those who live in the land of plenty, there is no currently publicised reason for buying the cheaper camera.

There is one single scenario in which I can see the K-500 making sense, and that’s if you mostly shoot indoors with cheap lenses and are expecting to get through 100k to 150k actuations relatively quickly, essentially treating the camera as a consumable. If I were in that position, I would get the K-500, but seeing how many actuations are usually left when cameras hit the second hand market, I think this will involve a minute proportion of Pentax’ customership. (You can get the mirror or shutter repaired when either breaks, but for a camera in this price bracket, it may not be worth it.)

That thing about the battery holder

The K-500 is clearly modelled as a spiritual successor of the K-x series, where the K-x and successor K-r were not weather-sealed, and the K-x could only be run with AA batteries, with an adapter being available to do so with the K-r (and K-30). With the new models, the rule is that the K-500 includes only an AA battery adapter and batteries, but no lithium rechargeable, whereas the K-50 includes only the Pentax-label lithium battery, but misses the battery adapter. While the adapter and lithium battery are similarly priced, you may want to try out both to see which suits you better, and if you’re going for the K-50 and want to use AA batteries, you’ll have to factor the extra 55 Euros into your purchase (price correct at time of writing). Generics for either part sell for a few dollars, but may affect the warranty relationship with Pentax; some reports suggest the original Pentax batteries are superior to most if not all generics – blind faith probably plays a role, but if I had to give any advice, it would be to support Pentax and avoid playing a gamble with your camera over 40 dollars. Some generics are more reputable than others. Always read the reviews and let others make mistakes first. The same caveat w.r.t. paying separately for the adapter also applies to the K-30.

Note that the K-50 will come with a charger for the battery. If you don’t already have a stash of rechargeable AA batteries and charger, this will add to the cost of any setup that uses the battery holder. Obviously, if you’re remotely serious about photography, you won’t want to even think about using throw-away AA batteries, as these will quickly get quite expensive and are worse for the environment.

Using AA batteries also apparently reduces continuous drive speed from 6 down to 5 frames per second.


Don’t get too fixated on buying the K-50 rather than the K-30 – they are very close in features and ability. However, you should definitely avoid buying the K-30 with a weather vulnerable kit lens – this alone may justify any price difference you may see between K-30 and K-50 kits!