The Filters We Need With Digital...

Started Oct 5, 2008 | Discussions
Joseph S Wisniewski Forum Pro • Posts: 34,130
The Filters We Need With Digital...
2

Today, I encountered three different dpReview threads with statements along the lines of "you don't need filters with digital", or "the only filter you need is a polarizer, the rest can be done in post processing. So, for the opposing point of view, some excerpts from an article I'm writing on filters and digital. The dpReview 6000 character limit is forcing me to break it into sections in an unnatural way that interferes with the flow of the material. My apologies for that...

The “Big Six” filters

That’s what I call a small selection of filters that are useful to most photographers, and that you cannot adequately replace with digital techniques...

One - The Polarizer

This is so obvious I shouldn’t need to get into "why" you need it, but I’m me, and that means I’m going to talk about it anyway. Any time light moves from air to a transparent substance, some of the light doesn’t penetrate into the transparent substance and is reflected away. Whether the light hits water on a lake, the natural oil on human skin, clear cellulose and wax on plant leaves and flowers, lacquer on a car or a guitar, or glass on a building, there are reflections. The reflections are “white light”; they “fill in” the color and reduce saturation. They reduce the detail visible under the clear substance. The blue of the sky is also polarized, and a polarizer can deepen the blue, and keep it from blowing out and rendering your sky a cloudless white or a drab gray.

You can fight this with post processing, but you won’t win. When you boost saturation, you fix the things that were "robbed" of contrast, but you also oversaturate the things that weren't suffering from contrast robbing reflections. And you can’t replace the lost detail.

Two - The 80A "Color Balancing" Filter

Most cameras have sensors that are "daylight balanced". They have nice, balanced red, green, and blue channel responses in neutral colored scenes lit by daylight. They achieve their incandescent white balance by amplifying the blue channel over two full stops relative to the red channel. That adds a great deal of noise to the blue channel, so you see some pretty ugly shadows. It also makes it very easy to blow the red channel, especially when shooting red dominated subjects (human skin, cosmetics, and fall colors near dusk and dawn when the light is warm).

Using an 80A will often let you get an interior architecture image in a single shot that would have taken multiple shots and HDR to do otherwise. It also makes it much easier to shoot incandescent or candlelit scenes without blowing the red channel.

Three – The Neodymium Enhancing Filter

Sensor manufacturers (like film manufacturers before them) spend a lot of effort trying to get the red, green, and blue filters in the camera to do a tolerable job of seeing colors the same way a human eye sees them. Normally, this is a "good thing", it reduces an annoying phenomena we techno-geeks call a "failure in observer metamerism", where colors that look identical to one "observer" (a human) look different to another observer (a camera, for example). The neodymium filter disrupts the nice "mimic the eye" characteristics of a sensor, and causes large-scale failures of observer metamerism. Neodymium (sometimes called “didymium”) does it in a way that is very pleasing in a landscape or fall color photograph: browns that would be identical in the picture (or to the eye) suddenly separate, with one turning red, another going yellow.

Again, this cannot be done in post processing, because without the filter, the camera sees all those browns as identical in hue. There's no way Photoshop can know to turn one brown into red, while another, apparently identical brown should be colored yellow, and a third identical brown should be left as "brown". Same thing happens in other colors, seemingly identical oranges separate into deeper oranges, reds, ambers, etc.

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Rahon Klavanian 1912-2008.

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Ciao! Joseph

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OP Joseph S Wisniewski Forum Pro • Posts: 34,130
The rest of the "big six"

Four - The "soft focus" filter

Using a Gaussian blur can only make a good-looking soft focus effect on things that are not overexposed. For my own soft focus work (and the majority that I see from other photographers) the "prettiest" soft focusing is the glow surrounding blown highlights: candle flames, sparkling dew on flowers, the catch-lights in a woman’s eyes, the glint of jewelry. You can't get that right in PhotoShop.

A soft focus filter in front of the lens gives you a glow with size and density that are proportional to how “blown” the blown area really is. So the glow around candles, specular reflections, water drops, etc varies with the brightness and the size of the blown area. And the transition from blown to not-blown on skin is much more natural with a filter or lens than with a PS blur. You can get this same effect with the “soft focus” lenses offered by Nikon, Canon, and Sony, but that’s an expensive route taken only by serious soft focus aficionados. The Tiffen soft focus or “center spot” (a personal favorite) or Zeiss Softar are much less expensive than a soft focus lens, and you can use them at a variety of focal lenths.

Five - The Neutral Density Filter

Many people like the look of a stream, waterfall, fountain, or brook with the water blurred into a soft "cotton candy" substance, flowing over rocks and plants. To do this, you have to shoot with a long exposure (anywhere from a second or two to a minute or two). In daylight, there's just too much light to do that, even at ISO 100 and f22, the longest exposure you can use is 1/50 sec. The "neutral density" lets you shoot much longer exposures. You can also use this technique to "blur away" all the moving people and vehicles in a street or architectural scene. Architectural photographers have been doing this for decades.

One "digital way" to emulate the neutral density long exposure technique is to shoot a whole bunch of those 1/50 sec exposures, then blend them together so that they "average out" to a much longer exposure. But that means taking 20 shots just to get one view of a waterfall. Recompose, and that's another 20 shots. It gets boring after a while...

Six - The "Split Grad"

OK, the big “buzz” these days is HDR, “High Dynamic Range” techniques of taking multiple exposures, and combining ones that get the highlights right with others that get the shadow detail. But light that “scatters” in a lens (our old enemy “veiling flare”) can cause the highlights of a sunset to “fill in” and destroy the shadow details. The filter that is part clear and part neutral density can “hold back” the highlights so that they can’t damage our shadows.

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Rahon Klavanian 1912-2008.

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Ciao! Joseph

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OP Joseph S Wisniewski Forum Pro • Posts: 34,130
A Note About Filters

The biggest problem with filters is that they're just like tripods, lens hoods, and remote releases: in order receive all their benefits; you have to carry them and use them...

That's why I'm going put in a plug for these “newfangled” filters with coatings that are supposed to "repel water, dirt, and finger prints”. I thought it was a silly gimmick, but the first time I tried one of the B+W "MRC" (multi-resistant coating) filters, I was hooked. The MRC coating works so well at repelling dirt that I'm likely to open my filter wallet and find all my polarizers and 80A filters clean and ready to go, so I use them more frequently. Even if they're dirty, I know they will clean up easy. With my older Hoya and “pre MRC” B+W polarizers, I would look at it them, see they were dirty, and knowing how hard they were to clean, I'd sometimes feel a bit too lazy to clean it "today", and so, choose to do without...

Filters need to be clean. Anything held away from the lens by a filter has a lot more effect on the image than it would if it were sitting directly on the surface of the lens. This applies to dust, dirt, water splashes, and fingerprints. It even applies to small amounts of damage, small scratches or chips. They all do less damage to the image if they’re on the lens than if they’re on the filter. So, whatever filter you use, it must be clean.

There’s a bit of common advice: buy filters to fit your biggest lens, and use “step-up rings” to make them fit the rest of your lenses. Unfortunately, this hits you twice: it’s more work, and it typically means you can’t use the “best” lens hood, the one built to match a lens. So the “buy big and adapt” advice sets you down a path where using the filters is more work, and therefore, you use them less often. Buy the filters that you use most often in sizes to fit all your lenses, and only screw with adapters (pun intended) for the more esoteric filters.

For example, the majority of my lenses use 77mm, 62mm, or 52mm filters. So I have two good 77mm polarizers, a 62mm, and a 52mm. Same with the 80A filters, two 77, one 62, one 52. Two each of the expensive 77mm filters? It’s worth it to me, because that lets me have both the 24-70mm f2.8 and 70-200mm f2.8 ready to go, I can swap lenses without having to swap the filter from one to the other. The less commonly used filters are more “unique”, I don’t have duplicate 77mm enhancing filters, and the soft focus are a real mixed bag…

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Rahon Klavanian 1912-2008.

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Ciao! Joseph

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OP Joseph S Wisniewski Forum Pro • Posts: 34,130
The “Non-Filter” You Need, and the Filter You Don’t

The Lens Hood

While technically not a "filter", the lens hood improves your fall color shots dramatically. Even when you think you've got no light directly hitting the lens, there's always "stray light" that scatters inside the lens and produces "veiling flare" ("all over the image" flare, instead of streaks and spots of flare). If the stray light is clean and bright, the veiling flare simply erodes your contrast. If the stray light bounces off grass or leaves or has a lot of blue "sky light" in it, it tints your image most annoyingly. And since that tint is strongest in the shadows, it can be very hard to fix in post processing.

The Protection Racket

Well, what about the “protection” filter: be it the traditional “UV” or “haze” filter, or a so-called “digital” filter? The camera store salesman told you that you need one. He may even have said you won’t get a warranty if you don’t have one (a lie the smarmiest sales people have been using for decades).

I don't use common "protective" filters in the studio unless we're doing explosions or liquid splashes. (I lead an interesting life). I don't use them outdoors unless we're in a blowing sand or water spray environment, and sometimes, I don’t even use them in the nasty environments. My lenses are more exotic and expensive than those of the average photographer. I don’t “baby” the gear. I take good care of it, but it goes all over the place: into industrial, urban, and wild places.

At some point in time, you have to sit back and say “how serious am I about photography. Am I out to spend years at this and come back with the best lenses, cleaner and less scratched than anyone else’s, or am I out to come back with the best pictures, sharper, with less flare and more contrast, and more sellable than anyone else’s?”

Even the best and most expensive filters have parallel planes; light bounces back and forth multiple times between those planes and cause more internal reflections than the curved surfaces of the glass lenses. Some of this leads to “scattering” of light, reducing contrast. Some of the bouncing causes ghosts and lens flares. Even the best filters degrade the image. That's one reason why camera manufacturers now use permanently mounted “meniscus” (curved) protectors on their expensive long telephotos. These curved protectors don’t cause as many problems as a flat filter.

So, if you're competent at cleaning lenses, you're likely to get better pictures without filters, even in the most hostile conditions.

Safe In The Hood

So, how do you “protect” a lens? The best way is with a decent lens hood. The hood that’s made by the lens manufacturer to match a particular lens is typically very rugged, and it matches the focal length of the lens so that you get the maximum amount of flare protection without vignetting (dark corners in the image). Those filters securely “lock” to bayonets on the lens front, and you don’t need to unscrew the hood, screw on a filter, and screw the hood into the filter. The hood acts like a great big “bumper”, protecting the lens from fingers (or larger body parts), branches, or anything that might bump into the lens, or that you might bump into.

An aftermarket screw in metal hood or “snap in” metal or hard plastic hood is also excellent protection.

Given a choice between two different protection systems, I’ll pick the hood, which always improves the image, over the filter, which always degrades the image, every time.

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Rahon Klavanian 1912-2008.

Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed.

Ciao! Joseph

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OP Joseph S Wisniewski Forum Pro • Posts: 34,130
Filters That Didn’t Make The “Big Six”

And, of course, there are filters that us really "off the wall" folk use, but they're not really "big six" filters...

Seven - The "Strong UV" Filter.

Modern lenses (especially complex zooms with 15-25 coated elements) and modern sensors (with built in filters) stop as much UV as the traditional "UV(0)" or "haze" filter. And sensors aren’t as sensitive to UV as film was. So, you don't need them to eliminate "haze" in photographs, even when you're shooting at high altitudes. The “traditional” use has passed away...

But there are situations where a stronger UV filter is useful. If you shoot where there are blacklights (nightclubs, concerts, or my own work with body painting) the strong UV filter keeps the blacklight from casting a purple glow on things that aren’t supposed to be glowing, increasing the dramatic look on the things that should be glowing. It really does help. The stronger UV filter is typically called a “UV(1)”, “Haze 2”, or “B+W 415”.

Eight - The “IR Blocking Filter”

Back when I shot primarily with the Nikon D100, the “IR blocking filter” or “hot mirror” was a “must have” filter. Early cameras let invisible infrared “contaminate” the visible colors.

· Blacks, browns, and dark grays tended to get magenta tints. This was most visible in dyed cloth, but also frequently visible in human hair and animal fur.

· IR penetrates the surface layers of human skin, so an IR sensitive camera emphasizes veins. The IR penetrates to reveal blood “pooled” under the surface of the skin, resulting in a “blotchy” skin appearance.

· And IR contamination also makes green plants look a less healthy “brownish” green, makes clouds look pink, etc. and in general increases the amount of work you have to do in post processing to get colors “right”.

But these days, all modern cameras (with one notable exception) have IR blocking filters good enough to eliminate all these problems. So, unless you own a Leica M-8, or you love an older camera like a Nikon D100 or D2H, you do not need to worry about the IR blocking filter.

Nine - The IR and UV Filters

These are not IR and UV “blocking”, they are filters that appear to be solid black because they block all the visible light and only let through invisible infrared or ultraviolet. The effects can be spectacular, the amount of work required surprising, and they require careful attention to choice of camera and lens to get the best results. Only mentioned here because what they do can only be done through real filters, not post processing.

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Rahon Klavanian 1912-2008.

Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed.

Ciao! Joseph

http://www.swissarmyfork.com

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nokem
nokem Contributing Member • Posts: 729
Good summary.

In fact the only filter I use is the 80B. BTW I always enjoy your posts.

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Shoot.

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rc53 Contributing Member • Posts: 562
Re: Good summary.

Indeed, but I've never heard of

The Neodymium Enhancing Filter

Could you expand, please?
--
Bertie

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Diopter
Diopter Senior Member • Posts: 2,830
With all respects...

With all respects and attention to your recommendations, I observe, that many very experienced photographers do not experiment with the filters at all. They accept the "naked truth" as it is coming from the light and technology.

In analog times they never used even a light-orange to enhance the sky, because they saw how it affects contrast, and tonality of greens ( in b&w - of course).

With critical relations of the sensor and optics resolution today, I would be very very careful. Most filter vendors still offer a huge selection of filters designed 10 -20 years ago. You must see a ctrong and credible note, stating that the filter matches today's standards of resolution. Even ND (neutral density) filter intended to protect your lens against elements, may actually ruin it's critical properties, costing you a grand extra.

Do I discourage anybody to experiment with any filters? Not at all. Play with Cokin, pantyhose, and vaseline. Just know, what you are doing.
(-)

Angular Mo Senior Member • Posts: 2,454
Re: The Filters We Need With Digital...

great info, thank you.
--
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tak44 Regular Member • Posts: 123
Re: Filters That Didn’t Make The “Big Six”

Thanks for taking the time and trouble to make this very interesting and informative post - which I have printed out for reference.

As one of the R/G colour-blind minority (and therefore with greatly enhanced metamerism) I wonder if the Neodymium filters would make my colour photos more interesting (to me at least) by making colour differences that I cannot otherwise detect become visible? Perhaps analagous to the effects of red/green/yellow filters in B/W photography?

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Paul Beiser Regular Member • Posts: 353
Re: The Filters We Need With Digital...

Thanks, Joe - great info, appreciate your taking the time to help us all.

Bob Sal Senior Member • Posts: 1,529
Re: The Filters We Need With Digital...

A more complete list of filters for digital cameras would be:

1: UV filters. The optics and sensors in a digital camera do not completely block all UV and a loss of sharpness due to UV rays as well as the bluish tints in distance scenes (especially at altitude) are eliminated by using a UV filter.

2:Protection filter. Absolutely crystal clear glass with no color (other then the coating) to protect the lens from damage from blowing sand and dust and smoke, fingerprints, etc. While a hood may protect from oblique directions a filter protects from damage from things coming directly towards the lens.

3: Skylight filters: Adds a pleasing warmth to shots when desired.

4: Polarizing filters. Normally circular for DSLR type cameras.

5: ND filters to reduce the overall amount of light in a scene (a polarizing filter can be used if it blocks the desired amount of light.

6: Graduated ND filters. To selectively reduce the amount of light to bring the scene into an acceptable contrast range.

7: IR filters. To photograph scenes or objects under IR radiation.

8: UV filters. To photograph scenes or objects under UV radiation.

Both of the above types are opaque to the human eye and the camera must be used on a tripod.

9: Digital filter. Camera sensors are effected by both UV and IR radiation. The Digital filter blocks both types of radiation and passes only visible light. This results in cleaner blacks, whites, reds, blues, browns, etc. Its' use results in greater separation between colors (easily seen on a histogram). This filter also totally eliminates the "M8 bug". It can not be used with lenses shorter then 28mm. It works thanks to its' dichroic coatings and is not made from a special type of glass.

10: Close-up lenses. To shorten the focal length when your lens will not let you focus close enough. Better methods with a DSLR are by using extension tubes or bellows but those will require an exposure change.

Other useful lens gadgets are:
Step-up rings to allow one size of lens accessory to fit all lenses.
Lens caps
White balance caps

Special effects filters (double exposure, fog, soft focus, etc. (many of these effects can be done in post processing but it is faster to do it at the time of shooting).

An effective lens hood. A lens hood that does not vignette at a lens' widest focal length is not providing any protection at the longest. Conversely a lens hood that works effectively for a long focal length will vignette with a wide focal length.

To overcome this either an adjustable hood or a compendium bellows lens hood is required.

Franka T.L. Veteran Member • Posts: 8,143
In fact , all the old favorite still work fine

And its not just those that get mentioned. I frequently work with color filter on my DSLR ( and not just for B&W ).

The motto is that

  • A filter modify the light and scene before it even get into the lens

  • PS or any post processing modify the image after the Development ( RAW )

  • You cannot exactly replicate one with the other, although one can emulate somewhat

  • filter can provide a modification to the shooting which PS cannot ( typical case being the ND in brightly lited situation )

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  • Franka -

Bob Sal Senior Member • Posts: 1,529
Re: In fact , all the old favorite still work fine

Franka T.L. wrote:

And its not just those that get mentioned. I frequently work with
color filter on my DSLR ( and not just for B&W ).

The motto is that

  • A filter modify the light and scene before it even get into the lens

  • PS or any post processing modify the image after the Development (

RAW )

  • You cannot exactly replicate one with the other, although one can

emulate somewhat

  • filter can provide a modification to the shooting which PS cannot (

typical case being the ND in brightly lited situation )

-- hide signature --

  • Franka -

That is the beauty of the creative ability that digital and analog allow. You can create by using whatever allows you to get the final result that you desire.

Although the market for traditional B&W filters and warming and cooling filters is drastically reduced today as is the market for special effects filters and lenses like the Softar.

OP Joseph S Wisniewski Forum Pro • Posts: 34,130
Thanks, and about the "The Neodymium Enhancing Filter"

rc53 wrote:
Indeed, but I've never heard of

The Neodymium Enhancing Filter

Could you expand, please?

Certainly.

The Neodymium Enhancing Filter was born about 25 years ago, in the suburbs of Detroit. It's the brainchild of local glass chemist Howard G. Ross. Here's something he wrote about it a long time ago.

http://medfmt.8k.com/mf/filters.html

Basically, neodymium has a very "irregular" absorption spectrum. It absorbs small bands of colors, and lets other bands through unharmed. The band that has the "enhancing" effect is yellow-orange part of the spectrum. That color is common to virtually all plant pigments. Like any color that's common to several things, if you can eliminate it, you increase the differences between those things. In the case of plant colors, eliminating the common yellow-orange makes all the other colors look more lively, and many colors that were "masked" by the yellow-orange are now visible.

There's two downsides to this filter. First, if you white balance for good looking plants, the blue sky will be fine, but you get magenta clouds, so it's not suited for mid day when there are pretty clouds in the sky. At sunset, it does the same thing to clouds that it does to plants, some seemingly identical orange clouds will "divide" into reddish clouds and yellowish clouds, and the sky gets more dramatic.

Second, it tends to push red flowers even farther into the red, so deep red flower, such as certain roses, may look oversaturated and lacking in subtle tonal variations or texture. Not really a problem with wild flowers, though.

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Rahon Klavanian 1912-2008.

Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed.

Ciao! Joseph

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Rumpis Veteran Member • Posts: 3,089
Re: Thanks, and about the "The Neodymium Enhancing Filter"

Thanks for explanation. How to use this filter? How to set white balance not to be in conflict with this filter?

Joseph S Wisniewski wrote:

rc53 wrote:
Indeed, but I've never heard of

The Neodymium Enhancing Filter

Could you expand, please?

Certainly.

The Neodymium Enhancing Filter was born about 25 years ago, in the
suburbs of Detroit. It's the brainchild of local glass chemist Howard
G. Ross. Here's something he wrote about it a long time ago.

http://medfmt.8k.com/mf/filters.html

Basically, neodymium has a very "irregular" absorption spectrum. It
absorbs small bands of colors, and lets other bands through unharmed.
The band that has the "enhancing" effect is yellow-orange part of the
spectrum. That color is common to virtually all plant pigments. Like
any color that's common to several things, if you can eliminate it,
you increase the differences between those things. In the case of
plant colors, eliminating the common yellow-orange makes all the
other colors look more lively, and many colors that were "masked" by
the yellow-orange are now visible.

There's two downsides to this filter. First, if you white balance for
good looking plants, the blue sky will be fine, but you get magenta
clouds, so it's not suited for mid day when there are pretty clouds
in the sky. At sunset, it does the same thing to clouds that it does
to plants, some seemingly identical orange clouds will "divide" into
reddish clouds and yellowish clouds, and the sky gets more dramatic.

Second, it tends to push red flowers even farther into the red, so
deep red flower, such as certain roses, may look oversaturated and
lacking in subtle tonal variations or texture. Not really a problem
with wild flowers, though.

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Rahon Klavanian 1912-2008.

Armenian genocide survivor, amazing cook, scrabble master, and loving
grandmother. You will be missed.

Ciao! Joseph

http://www.swissarmyfork.com

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Rumpis

http://foto.pudele.com/ - Low intensity blog about photography, Nikon and some other stuff interesting to me. Just for fun. In Latvian.

OP Joseph S Wisniewski Forum Pro • Posts: 34,130
For color blind people...

tak44 wrote:

Thanks for taking the time and trouble to make this very interesting
and informative post - which I have printed out for reference.

As one of the R/G colour-blind minority (and therefore with greatly
enhanced metamerism) I wonder if the Neodymium filters would make my
colour photos more interesting (to me at least) by making colour
differences that I cannot otherwise detect become visible? Perhaps
analagous to the effects of red/green/yellow filters in B/W
photography?

I imagine it would work exactly that way. Do you know if you've got the red deficient or green deficient variety? If it's red deficient, you're already "shelving" off the low end, and I don't think any filter will help. If green deficient, I can see the neodymium filter helping.

Have you ever simply tried swapping the red and green channels of a picture in Photoshop? I know a r/g color blind individual who does this, and he also sometimes puts both the swapped and original image in an animated GIF. The end result is adding a third factor to perception, some colors "shimmy", some don't.

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Rahon Klavanian 1912-2008.

Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed.

Ciao! Joseph

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OP Joseph S Wisniewski Forum Pro • Posts: 34,130
White balance two ways...

Rumpis wrote:

Thanks for explanation. How to use this filter? How to set white
balance not to be in conflict with this filter?

Well, never set it via a white card or gray card, everything in the picture that isn't white will get green tinted.

There are three things that work.

First, set the white balance without the filter on. It really doesn't shift plant greens or sky blue, and plant reds and yellows are going to shift "away from each other" but be correct relative to a common center. Do this, and skin is going off into the red, if there are people involved.

Second, most cameras will do as well in auto white balance with the filter as they will do without it, so if AWB works well on your camera, go for it.

Third, it actually will work with the Macbeth ColorChecker and profile building with the Fors ACR calibrating action or Pictocolor inCamera. I assume it will also work with the new Adobe profile building tool, but haven't tried it yet.

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Rahon Klavanian 1912-2008.

Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed.

Ciao! Joseph

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stephenmelvin Veteran Member • Posts: 4,547
Neodymium Filter History

Hi Joseph,

Actually, the Neodymium filters go back way longer than 25 years. I'm an avid reader of history, particularly that of u-boats. I was surprised to read the the Germans used neodymium filters with their binoculars to enhance their ability to see signals from Morse lamps from other boats.

I wish I had that book with me, so I could find the passage.

BTW, I was in a building yesterday that made me think of Detroit, only it's much, much closer to home. It was a fun day!

OP Joseph S Wisniewski Forum Pro • Posts: 34,130
Yes, Howard was just the first to use it photographically..

stephenmelvin wrote:

Hi Joseph,
Actually, the Neodymium filters go back way longer than 25 years. I'm
an avid reader of history, particularly that of u-boats. I was
surprised to read the the Germans used neodymium filters with their
binoculars to enhance their ability to see signals from Morse lamps
from other boats.

That, and narrow band filters. I remember some obscure bit of history about this: telegraphers using ultraviolet lights and people receiving them who had had lens replacement surgery. Our lenses block UV, without them, you can see a pretty good way into the UV.

Howard talks about some of the other uses of neodymium glass. He was inspired by neodymium sunglasses to try it for photography. He believes he was the first to do so, and trademarked the name "enhancing filter" for it. Tiffen licensed his trademark, but ticked Howard off by making the filter weaker than Howard liked.

Some other common uses of neodymium included glasses worn by scientific glassblowers, the kind who do "torchwork" or "lampwork". They work by putting glass rods or tubes into the flame of a very hot torch. This is typically done with borocilicate glass. When you do this, the sodium in the glass "flares" bright yellow, making it hard to see what you're working on. The neodymium yellow-orange blocking allows you to see the glass under the "sodium flare".

(I'm a different kind of glassblower, an "off hand" blower, I use a big steel pipe to pull "gobs" of glass from a crucible. That kind of glass has no sodium flare, so we don't use neodymium glasses).

I wish I had that book with me, so I could find the passage.

BTW, I was in a building yesterday that made me think of Detroit,
only it's much, much closer to home. It was a fun day!

Cool.

I am very ticked off about the increased levels of vandalism and looting at the train station here. It's suffered more this year than any other time that I've ever seen.

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Rahon Klavanian 1912-2008.

Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed.

Ciao! Joseph

http://www.swissarmyfork.com

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