UV/IR Filters

Contents

  1. Introduction
  2. The UV/IR Filter
  3. Lens Coding
  4. Cleaning UV/IR Filters
  5. Benefit of the M8
  6. How About the M9?
  7. And on Film?

Introduction

When the Leica M8 came out, it was quickly discovered that Leica's well-intended design backfired on them a bit. The idea was to eliminate the AA, or anti-aliasing filter from in front of the sensor. This has the immediate benefit of making for sharper images. The downside is an increased likelihood of moiré - which is an interference pattern in higher frequency areas of an image (for example, fabrics). Certain software can fix this during post-processing. The best software to do this at this time is Capture One.

That's the good news. Leica also made the IR, or infrared filter thinner than normal for the same reason. On the M8, it's practically non-existent. The problem here is that light in the infrared spectrum will reek havoc on your colors in certain situations. One example is synthetic black fabrics (among others). What ends up happening is that certain materials will take on a sickly purple/magenta color. Another issue is foliage and vegetation, which takes on a yellowish cast. The real downside is that there's no real way to fix this in post-processing as with moiré other than to convert your image to black and white. it is even said that this effect is desirable when you intend on shooting black and white... But for color? No good. Naturally, the issue made waves and Leica ended up getting an earful from M8 owners. The solution was to offer everyone that registered an M8 camera with Leica two UV/IR filters free of charge, in a diameter and color (silver or black) of their choosing. At this time, even if you've picked up a brand new M8 sitting on a dusty shelf - the camera has effectively been discontinued - as has the free UV/IR filter program.

Without a UV/IR filter, you need to be careful of what you shoot - which isn't as easy as it may sound, as you never know when the "magenta issue" will strike. This was taken at dusk outside... That magenta sleeve up top is supposed to be black! Notice also the funny yellowish cast to the grass:

The UV/IR Filter

What is it? Just as the name implies, it filters ultraviolet and infrared light at certain frequencies, albeit through interference on the part of infrared. It's this interference filtering that gives the filters that shocking red and cyan coloration when held at the right angles. The ultraviolet part is like any other UV filter.

There are several manufacturers that make such filters, and Leica does not make their own. No one knows for sure, but there have been various rumors as to who actually makes them. Hoya is one guess - we know they're of Japanese origin at least. But it's not really important. Two other popular manufacturers are Heliopan and B+W; they label these filters of the "486" type.

Which should you choose? Each has pros and cons. What all of them suffer from is a bit of flaring/ghosting when strong point light sources are present in the frame - such as street lights at night. What can happen is "green blobs" appearing in your image. If you're shooting in such situations it's really just best to remove the filter, and indeed - in many such cases it won't have any effect on the image anyway. Failing that, you can sometimes "heal" or "clone" out the blobs during post-processing if you must use a filter (or are too lazy or it's inconvenient to remove it).

Leica

Leica offered silver and black version of their filters for the usual sizes used in their lenses. The frame was made of aluminum, and as such have a light feel to them. They work, though they perhaps flare the most. They're also rather pricey for no other reason than being Leica branded. The one filter to watch out for is the 43mm. It has a non-standard thread pitch - it's .75mm rather than .50mm. Fine if you're using an old Leica lens - but decidedly not if you use anything else. In practice, you can screw the filter onto the lens up to a point where the threads begin to bind. Absolutely do NOT go further than this, or you'll strip the threads. Often, however, this will be enough to hold the filter well enough for everyday use.

Heliopan and B+W

Heliopan and B+W filters are essentially identical and differentiate themselves as high-end filters. The frames are made of brass and anodized, which gives the filter a solid, heavy feel. Brass is used to help prevent binding of the filter when screwed onto a lens. The glass used is also very high quality Schott optical glass. Finally, the anti-reflective coatings by both of these manufacturers are among the best in the world. In practice, they tend to work better than the Leica-branded filters - but are by no means immune. What's especially nice about these is that they're much less expensive than the Leica filters.

When it comes down to it, buy whatever filter meets your needs - be it "keeping it all Leica" or managing expense or even matching a silver Leica filter to a chromed-ring lens such as the Zeiss ZMs. They all do the same thing. There has been some debate as to whether there's any optical/visual difference when using a non-Leica filter. The thought is that Leica tuned the M8's firmware to the specific characteristics of their filters. This is most likely true, of course. But when you compare images shot with different filters - the difference is slight, if any - and it may even just be psychological. In certain cases, you might not have a choice as to which filter to choose simply because of the fact that Leica made filters only in sizes that their lenses use! So if you have an odd size, you simply must use an alternative.

Lens Coding

One problem you now face is the potential for "cyan corners." With a UV/IR filter on an un-coded lens (coded meaning having a 6-bit code on the flange) might give you what are effectively cyan-tinted corners to your image. This is due to the UV/IR filter and the way it affects light traveling through the microlenses and onto the sensor. These microlenses are angled more towards the center the further out you go from the center of the sensor - which is why it's in the corners. Note also that the wider the lens, the more likely you'll see this effect. The angle of the light rays in the corners and edges become more extreme and thus exacerbate the problem.

The solutions are to either code your lenses, or correct the images during post-processing. If you have lenses from Leica, you can have them code them for a nominal charge, requiring a round trip to the service center. The problem comes should you have third-party lenses like Zeiss ZMs, Voigtländer or others as Leica won't code them for you. You can either hand-code them yourself (which also applies to Leica lenses) using a template (e.g. D-Coder) and a Sharpie marker, or have the flange machined by a competent machinist. One such person is Jon Milich and you may even have heard of his work, the "Milich adapter." In the case of permanent coding, six pits are milled into the flange and either painted white or black to denote "off" and "on" respectively. To save time and expense and code them yourself with a marker, you can emulate this by just drawing a dark black stroke at the appropriate position(s) - white not generally being necessary. There are downsides to hand-coding. First and foremost, it's a temporary method as the mounting and unmounting of lenses will wear the mark off and it will need to be reapplied occasionally. Second, third-party lenses might have a screw positioned right where the code needs to go. Often a dark enough mark will still work, but if it's supposed to be white you'll likely need some paint on the screw.

Read more about Leica Lens Codes in our comprehensive article.

The next option is to fix this during post-processing. The easiest way to accomplish that is by using the CornerFix application. You basically take a reference photo of a neutral background with your particular lens, with the filter attached. This will give a clean image from which the application can generate a reverse image - which when combined - will neutralize the discoloring. It's an extra step in post-processing so you might want to re-consider coding the lens, but it's not that big of an inconvenience - and CornerFix works in batch mode. Did we mention it's also free?

Cleaning UV/IR Filters

Some people have expressed concern over cleaning these filters, as they're not quite like normal UV filters. They have a slight "tooth" to the interference side, and the coatings can be a little funny. So if you're used to breathing on a filter and wiping it with your t-shirt and having issues... This might be why.

You really should be using a better method to clean your filters - and any optics - if you have the choice. The preferred method, using a fresh lens tissue and cleaning solution will usually result in a clean filter and no issues (e.g. smudging, scratching, etc.). Formula MC is a great product that's been around for decades and works on all filters, multi-coated or not. It comes in a small dropper bottle that you can keep in your bag and lasts a long, long time.

Benefit of the M8

One good thing to come out of this increased infrared sensitivity for M8 shooters - is that the M8, obviously perhaps, makes a great camera for shooting infrared! Fit an 072 filter on the lens and try some landscapes shots for an eery, other-worldly effect. It's easier on the M8 than most other cameras exactly because of this.

How About the M9?

When Leica went back to the drawing board for the M9, they took into consideration the backlash over the previous design as used in the M8. The IR blocking filter in front of the sensor was made a little thicker, more effective. Their goal was to still maintain the highest level of image performance but address the IR problem. So again, it's a bit of a compromise. The M9 fares a lot, lot better than the M8 and typically doesn't require a UV/IR filter except in extreme cases - as it's not immune. You could still use UV/IR filters with the M9 with no ill effect, but we'd recommend against it if for nothing else than the flaring issue and the debatable point of image degradation.

And on Film?

Do not use UV/IR filters with film. With color film you may get weird effects, though with black and white you should be okay. But there's really no point with film.