Seventeen and a half years ago I started manufacturing and selling a special rare-earth glass filter, which I called "The Enhancing Filter" ®.

"The Enhancing Filter" ®. also has a chemical misnomer name of "didymium" glass. However, there is no chemical element called didymium, as was thought to be the case 100 years ago. It was later discovered that "didymium" was really a mixture of neodymium (Nd) and praseodymium (Pr). These two elements, when melted in a glass, are the essential ingredients of my Enhancing Filter. The ratio of the two elements is important and their concentrations are also important. A stronger version of my regular Enhancing Filter is called the Super Enhancing Filter which can make fabulous pictures.

I found out that my Enhancing Filters were fantastic for photographing: fall colors, sunsets and sunrises, red barns, some portraits, western scenics and slide copying. The filter enhances reds, oranges, some yellows and pinks but not blues, greens or whites to any extent. The effect of the filter also depends on the color film being used. I personally use 35mm Kodachrome KM (ASA 25) or 120 EPR Ektachrome (ASA64) and Kodak 6117 Ektachrome (ASA64) for 4" X 5", 5" X 7" and 8" X 10". These are "neutral" films. Films with a strong warm or red bias may not work well with my filters in certain situations. In my filter directions, I give specific instructions for using my Enhancing Filter with color negatives. The filter factor for all color films is 2X or one stop.

The Lanthanide series of elements, in the chemical periodic table, includes 13 true rare earth elements plus four associated elements ie: scandium (Sc), yttrium (Y), lanthanium (La) and erbium (Er). Lanthanium (La) and yttrium (Y) are glass formers, i.e.: they can be used instead of silica sand in some glasses, especially true of lanthanium (La). The 13 true rare earth elements have very similar chemical and physical properties. These rare earth elements were finally chemically separated and purified in quantity, as a result of a special wartime project at Iowa State University. Four of the true rare earth elements have very strong absorption bands, these include: neodymium (Nd), praseodymium (Pr), holmium (Ho) and erbium (Er) (possible filter elements). Unfortunately, holmium (Ho) and erbium (Er) are truly expensive. In my Enhancing Filters, which contain neodymium (Nd) and praseodymium (Pr), a number of weak and strong, sharp absorption bands are present in the ultra-violet, visible and infared spectral regions. The strongest absorption band is in the yellow-orange region and it is this band which causes most of the beautiful enhancing effects, especially for fall color.

I personally melted 150 rare earth glasses of many compositions with some very unusual effects, erbium (Er) glasses have a beautiful golden pink color. I couldn'’t melt the glasses with sufficient optical quality but some of the effects I discovered were unexpected. Some of the other true rare earth elements have sharp, but weak, absorption bands and some of them have strong emission bands. Europium (Eu) is used in the red phosphor of color TV sets. Europium (Eu) glasses also fluoresce strongly in ultra-violet light.

I am a retired glass research chemist and it took me nearly 30 years of knowing about "didymium" glasses before I actually used them to take pictures. This type of rare earth glass has been known for about 70 years, but was used only for various scientific purposes. I was aware of these uses, but it took a series of events and observations before I started taking pictures with it. Cerium (Ce) was the clue for me that got the filter idea to be developed. I was an optical emission spectroscopist and noted a large amount of cerium (Ce) present, as an impurity, in a batch of "didymium" glass that Corning Glass Works melted. I knew that cerium (Ce) was a strong UV absorber. There was a glass from Corning that contained cerium (Ce) and manganese (Mn) for strongly absorbing the UV (as in sunglasses). I later obtained some "didymium" glass in the form of eye glasses and decided to use them as sunglasses. I was driving through Vermont in fall color season, and the fall color seemed beautiful. I took off the glasses to look at a map and the fall color faded and was drab (past due fall color). I put on the sunglasses again and saw the beautiful fall colors again. I even tried holding the glasses in front of a small Leica lens but it was too awkward to use.

Finally, in the fall of 1980, I went to Vermont with a hand-made Series 7 Enhancing Filter that I made without any experience in grinding glass into circles. I got simply beautiful pictures there as well as a favorite fall scene near my home in Michigan. I showed the results to some local photographers and the "Enhancing Filter" business was on its way.

I had never manufactured anything for other people before but I had made a lot of camera gadgets for myself. I made up a set of slides showing filter effects as a camera club program which was very well received in my area. In March 1983, I wrote a big article about my Enhancing Filter in Modern Photography from which I got over 1,000 filter orders from all over the world and my filter business really took off.

Due to my limited manufacturing facilities, I primarily make series filters as they use 6" X 6" glass sheets most efficiently. Thus I make series 5, 6, 7, 8, 9 and even 4". I also make Cokin A/P, 2" X 2", 4" X 4", 4" X 5.65" (pro-movie size) and 6" X 6". At times, I make 82, 95 and 105 mm round filters on a custom basis. Series 7 is the most common filter I make and it has interchangeable mounts of: 46, 49, 52, 55, 58 mm and Hasselblad (Bay 50) and series 8 filters have interchangeable mounts of: 58, 62, 67 mm, Bay 60 (72 and 77 mm in some cases). I make filters for Stereo Realist, Widelux, flash gun filters, large format to 11" X 14", pro-movie (16 and 35 mm), some pro-video, microscope, slide copy and enlarging lenses (for Cibachrome printing).

Some filter mounts for very old cameras or certain Leica lenses can be a problem. Generally, I have been able to fit almost any camera lens within reason. I also make several sizes of rear-of-lens filters for big telephotos eg 300 mm f 2.8.

The cost of the filter is proportional to the area of the filter and any scrap it generates. I have used the same glass source for over 17 years with great results. 40% of my cost of the regular Enhancing Filter sheets I buy (6" X 6") is in the cost of the precision grinding and polishing process. This is not true of my various rival manufactures.

I was the first person to name the Enhancing Filter and the first person to sell this type of filter for normal photographic use. I will list some of my more important filter customers: University of Michigan, University of Minnesota, University of California, Panavision, Kodak, Polaroid, David Muench, Daryl Benson, Pete Turner, Eric Meola and Gene Ahrens.

If any of the people reading this communication are interested in an Enhancing Filter or filter information, please call me at (248) 356-3918 or write me at:

In turn I will send a price sheet, instruction sheet, filter chip and, if possible, an original Kodachrome KM slide set showing a scene with no filter and with an Enhancing Filter. I sell filters all over the U.S. and Canada, as well as overseas. I generally don'’t stock many filters, so if you have a big trip planned, please let me know ASAP as it can take up to 4 to 5 weeks turn-around time after I order glass.

Related Links:
Enhancing Filter user notes..
Filter FAQ and links

Related Postings

>Having not used one, I wonder if these filters add an unreal look to  images.
>I shoot Velvia and certainly don't want to oversaturate colors to an
>unrealistic degree. I know how some of you feel about Velvia, so I don't
>need to hear cynical or sarcastic comments about my film preference.
>
>Have you found these filters useful or interesting for any other
>applications other than fall foliage and the like? Any other comments are
>appreciated.
>
>Thanks,
>Michael

I use a Howard Ross normal Didymium intensifier and find it works best with Kodachrome. It works with Velvia with the right subjects, but if you include sky, you will often get a pinkish or purple cast. If you are shooting slot canyons, red rock formations or fall foliage you can get spectacular results - the intensifier works to intensify reds and oranges. The Howard Ross intensifier ( even the normal one) is quite a bit stronger than others I've seen on the market, so it really intensifies reds. The stronger version he sells is too much for me. It's a good filter to use when you need to shoot in the high sun and it's fun to use when you want to introduce reciprocity failure by taking long night shots and really skewing colors. Another fun filter is the Cokin P173 blue/green polarizer - but thats a different story.

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