Micro-Contrast versus Moiré. The grudge match.

If you want the objectively sharpest photos you can make you'll need to do all the regular stuff well (tripod, best aperture, perfect exposure, etc.) but you'll also need to consider the camera sensor you're putting at the ass end of the lens. 

You find that the sensors are more than just sensors. They are packets or layers of material. There are IR filters, Bayer color screens, and our favorite whipping boys, the anti-aliasing filters. These AA filters step in at certain frequencies of the detail spectrum to soften or disrupt overly sharp images hitting the actual sensor (which has a screen over it) and causing odd color and line artifacts in your final image. The thinner or weaker the AA filter the sharper your final images, and especially the fine details in those images. And, of all the parameters in your camera AA filters are one of  those things that you can't change (well....  you can but....good luck!).

If you mostly photograph images of landscapes, naked people and organic stuff you'll probably never see the unwanted effects of a thin or weak AA filter. Even though weaker filters pass through a lot of detail and make everything you shoot look sharper. Where the weak AA filters stumble is in the rendering of fine, repeating fabric, clothing made with artificial fabrics and things with screens. You don't think about the bad effects of the detail rich/weak AA filters until an image bites you on the butt. The basic problem is two screens (one on the sensor and one in mostly repeating fine patterns such as textiles; especially in man made materials...) that interfere with each other to create bigger patterns.

And bite you they will. The  usual culprits, which cause much conflict and ill will, include wedding dresses, cheap dinner jackets (especially those made with Rayon or other poly and particularly on dark lapels), other fabrics with very fine patterns, and fine blond hair. Many of the things you might find on a real, paying job. And once those conflicting patterns find there resonate frequency then resonate they do.

There are workarounds for moiré if you see it while shooting. These include shifting your focus to make whatever is experiencing moiré slightly out of focus (out-of-focus being its own moiré filter...), using a diffusion or soft focus filter in front of the lens, or just changing your camera to subject difference until you find a sweet spot that gets ride of the weird color infested patterns which are the trademarks of two intersecting interference patterns.  One pattern might be the regular, almost invisible screen pattern of whatever weird cloth wedding dresses are made or and the other one is the Bayer color screen on top of your camera's sensor. When the two interfere with each other the problems erupt. An AA filter on the sensor tries to muss up the optical frequency ( and amplitude of line pairs) delivered to the sensor to make sure there's no interference. But it comes at a cost of super fine detail in your photos. 

The problem was wide spread when sensors had very low resolutions because more and more patterns in day to day life were near the same frequency (repeating pattern line width) as the sensor and there was much more interference. As sensors became available with higher and higher resolutions smaller and smaller subsets of external frequency content were excited into existence. But a basic rule was that the higher the resolution the less frequently the interactions occurred.

Now let's think about compromise in photography. Or what photography delivereth and what photography taketh away. 

You can now buy lenses with incredible resolution. Lens makers are designing lenses now to work with 50, 60 or even 100 megapixel cameras. The issue? The sharper the lens the more likely it is to excite smaller and smaller optical frequencies and to create specific areas of moiré. Add a super high resolving lens to a very weak AA filter that most think they want and, when it comes to fabrics, screens, halftone screens, fine hair and other repeating patterns and you'll spend more of your short and rapidly vanishing life force trying to fix things in post. Mainly because the patterns will be too small to see well in your camera's finder but will become readily apparent when you go pixel peeping at 400%.  Ouch. 

It's a sad blow considering that most of us feel compelled to achieve images with stratospheric sharpness. 

I write about this today from sad, very recent, experience. I was shooting portraits in a studio at f5.6 with an 85mm f1.4 Sigma Art lens attached to a Panasonic S5 camera. Panasonic and Leica have both made cameras whose sensors are covered with weak AA filters in order to deliver higher amounts of fine detail. And it's great until a subject is rendered super-sharp and the subject happens to be wearing nylon, rayon or some other variation of polyester cloth. 

Several of my subjects were wearing just that. And several of my subjects ended up "wearing" a good amount of moiré which was NOT visible in the EVF at the time of exposure. (And remember, the EVF or live view finder is also screen based...). There are workarounds but they add to one's workload. 

Still, this is the first time in about a year that I've seen a moiré pattern end up in one of my photos. Usually we're shooting people wearing natural fabrics which tend to be less uniform in their spatial frequency and much less prone to the effect. And it does show up on most things that themselves don't have repeating patterns. Like landscapes, human skin and other favorite subjects. 

It's a sad fact that, in some instances, your camera and your lens can be TOO sharp. 

In a related subject, a sensor in a high res camera can be covered with too efficient an anti-aliasing filter. Sony cameras in the A7 series are legend for using a very thick filter pack which doesn't really have a bad effect on very modern tele-centric designed lenses but the filter packs in their cameras are thick enough to effect the corners and edges of many, many legacy lenses --- particularly wide angle lenses that were designed for rangefinder cameras that had fairly short lens flanged to film distances. There are many wide angle lenses (mostly from 35mm on down) that were designed to be of high performance on Leica rangefinders but which toss in the towel on some Sony cameras. 

It's always a trade-off. Leica's SL cameras have sensors whose AA filters are designed (weakened?) to work well with older, wide angle legacy lenses. But you have to be careful with the 24 megapixel models if you photograph known moiré subjects because the very thing that makes the camera's sensor work well with legacy wide angles is the same compromise that makes the wrong mix of subjects and sharpness illicit stronger moiré effects. 

Funny to think that less sharp, lesser performing lenses might be just the thing you need for photographing that special bride. Or that executive with the rayon suit. Or that priest with a polyester black shirt....

Good luck out there. Moiré will bite you when it's least expected and least wanted. 

A note to friends who are in the market for new phones. There is no "free phone" contract. The vendors give you something with one hand (a "free" iPhone) and make up the cost with the overall expense of a calling plan in the other hand. Wanna new phone for less money? Just pay out of pocket for the phone you want and then shop around for the best plan for you. If you are budget strapped and of a certain age you probably don't need a plan with infinite minutes, international coverage and all the bells and whistles. You'll just be throwing away money if you don't need a lot of that stuff. Get the basics covered. Having a more cost effective calling plan certainly won't interfere with the photography features of the new phone. 

But really, if you can afford a new, top of the line phone you can afford whatever calling plan you want. Alternately, if you can't swing the price of the plan you need you probably can't afford the new phone either. 

Just sayin.