Need help with polarizing techniques

[karl_kaboom]

Complete novice requesting advice from a pro. I'm going to be tasked with photographing a very large number of antique advertising items. They consist primarily of 3 subject types: Lithographed tin serving trays approximately 12-14" in diameter (as per below example), large flat tin advertising signs approximately 36-48" in either dimension, and paper lithographs framed behind glass approximately 36-48" in either dimension.

Camera: Canon SX40HS.

Conditions: Interior only, under controlled lighting, with tripod.

My question is concerning the elimination of glare from the light sources, which in my case, is two 105 watt lights (marked "105W 5500K 110V 60Hz") inside two 19x19" soft boxes on stands.

Taking advice from online sources, I did the following: Put two 19x19 polarizing sheets in front of my two light sources, set them at 45° to the subject, and used a circular polarizer on the camera lens. These are the specs of the polarizing sheets I used: "Transmittance: single(43%); parallel(38.1%); crossed(0.056%). Color: neutral gray. Polarizing efficiency: 99.9%".

As expected, the sheets and lens filter did eliminate all glare, but created a new problem. I immediately realized that virtually every subject that I need to photograph features a speckled, vibrant, almost glittery gold color that was apparently quite popular in circa 1900 advertising items. The polarizers seem to kill this vibrant gold color right along with the glare.

To see the affect that the polarizers are having on this vibrant gold color, see my two examples below -- one taken without the polarizers (and, hence, with two glare spots), and one taken with the polarizers. Look, in particular, at the phrase "Beer, Ale and Porter" in the lower right corner of the tray. The polarizers have almost completely blotted out the vibrant gold tone.

Can someone please educate me as to how I can fix this problem, i.e. specifically, 1) eliminate glare, but 2) do not blot out any of the other vibrant colors in the subject.

FYI: Setting the camera at an angle to the subject in order to eliminate glare is not an option in my case. These will need to be 90° straight-on shots.

Thanks in advance for your help! Please, no guesswork. I'm tapped out on time and resources. I need experienced insight. Thanks!

 

[tirediron]

Have you tried adjusting the degree of polarization on the CPOL (rotating it)?

 

[Derrel]

I actually prefer the specular highlights on the rim of the serving tin; the highlights add depth clues. The gold glittery paint gets its allure FROM reflection of non-polarized light...polarizing the light basically ruins the entire effect of the paint they used to draw the eye.

Eliminating ALL reflection is not the best strategy...it robs the items of dimensionality. As human observers, when we look at a two-dimensional representation of a three-dimensional item, we gauge shape by reflection! ELiminating ALL reflection makes things look flat, and dimensionless.

 

[minicoop1985]

My advice: if you aren't using them, get a pair of softboxes. That should help your shadow situation a lot. I use a pair of softboxes and a CPL, no polarizing sheets. I do agree with Derrel and tirediron-spin the polarizer (it will spin without unscrewing) while looking through the viewfinder to get the image you want with just the right reflections. You may need to do some slight editing to bring the colors back to how they were before they were shot.

 

[Big Mike]

I'd suggest the book 'Light: Science & Magic'.

What you can learn in that book, is that to avoid seeing your lights (direct reflection) on the surface of your subject, you need to identify your 'family of angles' and ensure that your lights are outside of it.

FYI: Setting the camera at an angle to the subject in order to eliminate glare is not an option in my case. These will need to be 90° straight-on shots.

Yes, the camera should be perpendicular to the flat object, but your lights don't have to be. If the surface is quite flat, then all you have to do, is move the lights far enough away from the camera's position, that the reflection doesn't show up.

The problem comes when your subject isn't just flat, but has other angles & surfaces, which have their own families of angles. It becomes next to impossible to keep your lights outside the families of angles, which means that if the subject does have properties of 'direct reflection', that you will see a reflection, one way or another.

You certainly are onto one way of getting rid of the reflection, by polarizing the light at the source and at the lens, but as you are seeing, reducing too much direct reflection (either polarized or ordinary) can tend to take away the 'essence' of the material that you're shooting. In other words, the glare that the viewer sees in the photo, is what tells the viewer what the material is.

So rather than trying to completely eliminate the direct reflections, you can try to control them so they look more pleasing. It's important to realize that they are 'direct' reflections of your light source(s), so if you change the shape and/or relative size (size and proximity) of your lights, you will change how the direct reflections look.

For example, you could use very large umbrellas or softboxes, or you could use large diffusion screens, or a light tent. You could bounce the light off of surfaces like reflectors or walls, and have those as your light source for the subject. We call this 'filling the family of angles'. As you make the light source larger, the glare on the material will get bigger and spread out, which usually looks less offensive than a bright blob of reflection. This isn't always ideal though, because even spread out, that direct reflection will tend to compete with the 'diffuse reflection', which is where we see the color. So the you end up trading reflective blobs for lackluster color.

Another way to go, would be to use very hard light (small and or far away). This would make the direct reflections smaller, maybe to the point where they aren't as offensive. Or, maybe just to the point that they become very easy to edit out in post production.

 

[karl_kaboom]

Hey everybody. Thank you so much for the insights! I will respond to each comment separately below so that I can get a little tighter on my exact situation. But first, just so that the original post doesn't get lost in the conversation: my goal is to find a pro's trick to remove glare, but keep other colors fairly well intact. More detail below...

Big Mike: Thanks. I'll get a look at that book. I very much appreciate your explanation of "family of angles". Of course, I was hoping for a magic bullet that would cover me in all situations. But I guess that was a bit naive. Still, I need to try to maximize my ability to handle every glare situation wisely with the tools available. I will be photographing in people's homes, and will get "one shot" in these situations. So I must be armed with the best knowledge and tools that a novice can get.

You said, "If the surface is quite flat, then all you have to do, is move the lights far enough away from the camera's position, that the reflection doesn't show up." Problem with that: Since, I'm photographing in people's homes, I won't usually have the option of moving lights very far away, or removing the subject from the wall. This is especially problematic for large lithographs under glass. I have to be prepared to handle the situation as it is presented to me. Hence my need to have other tricks in my bag.

I fully agree, glare is not objectionable in all situations, and even desirable in some. But, in my present situation, I need to be able to remove glare if/when necessary without removing other colors. Example: There is nothing worse than a lithograph framed behind glass that has white glare bouncing off the glass. There is nothing aesthetically pleasing about that. Again, I need a tool to kill that glare, but keep the sparkly golds so common on these lithos. That is the essence of my question. Another example: A great many of the trays (with multi surfaces) that I will photograph have writing and/or imagery in virtually every location, including rims, etc. The primary purpose of these photographs is not necessarily aesthetic, but educational, as in a catalog. Thus, if/when glare interferes with the subject matter, I must know how to remove it. When a particular subject allows for one or two spots of harmless glare, like Derrel said, that's not necessarily a bad thing. But there will be situations where there is nowhere to "put" the glare without blotting content. I need an appropriate tool in my tool box for those situations.

One more question for you Big Mike: One of the problems that I have had with moving the lights to minimize the glare (or control where it lands) is that I then often find the light source causing inconsistent tones across the image, i.e., bright at the top, dark at the bottom, etc. Can you speak to that briefly? Again, these are photos for catalog-type use, where literal relationships of colors are important for informational purposes. In other words, I wouldn't want to create a false gradient of color with my lighting that isn't on the original.

tirediron: Yes, I use the circular polarizer and rotate it until it has eliminated the glare that I need to eliminate. But, of course, when the glare disappears, so does the gold. Hence the problem.

Derrel: I agree, glare is not objectionable in all situations, and even desirable in some. See my response to that above. In some situations, I simply need to be able to eliminate the glare. Period.

minicoop1985: Yes, as stated, my light sources are two 19x19 soft boxes. I do understand that editing the photo in photoshop afterwards will be required to fine tune the colors. No problem there -- except with than darn gold. Look again. No way I can easily recreate the glitter from dead flat brown -- especially when that gold appears in minute details throughout the subject, on dozens of subjects. Look, for example, at all the lettering on the right hand side of my example shots. Every single bit of it is trimmed with gold, which all disappears with the polarizers.

Thanks again, all. Now that I've rudely nitpicked it to death, any more help/advice? It is truly appreciated!

 

[Derrel]

One of the problems that I have had with moving the lights to minimize the glare (or control where it lands) is that I then often find the light source causing inconsistent tones across the image, i.e., bright at the top, dark at the bottom, etc. Can you speak to that briefly? Again, these are photos for catalog-type use, where literal relationships of colors are important for informational purposes. In other words, I wouldn't want to create a false gradient of color with my lighting that isn't on the original.

When a light source is CLOSE to a subject, the degree of light fall-off over very small distances is VERY great. When the light source is farther away, the degree of light fall off over short distances becomes almost inconsequential. This is due to something called the inverse square law.

If you are suffering from visible fall-off to the degree that it looks like a gradient, then the light source(s) is/are far too close to the subject, and an easy "fix" is to increase the distance of the lights from the subject.

As the light is pulled farther and farther away from the subject, the falloff in intensity across distances from side-to-side or top-to-bottom becomes basically irrelevant.

 

[Big Mike]

You said, "If the surface is quite flat, then all you have to do, is move the lights far enough away from the camera's position, that the reflection doesn't show up." Problem with that: Since, I'm photographing in people's homes, I won't usually have the option of moving lights very far away, or removing the subject from the wall. This is especially problematic for large lithographs under glass. I have to be prepared to handle the situation as it is presented to me. Hence my need to have other tricks in my bag

I didn't necessarily mean that the lights had to be 'far away', what I meant was that they could/should be radially further from the camera's perpendicular position. Imagine a clock. If the subject is at 12:00 and the camera is a 6:00....i meant that the lights should not be a 5 & 7, but could maybe be moved to 9 & 3 (still pointed at 12).

The key is to imagine the family of angles.
In the lighting class I teach, I take a laser pointer and hold it right at the camera position. I place a small mirror at each of the corners of a piece of art and point the laser at each corner. Imagine that the laser is drawing a line through space as it leaves the camera position, then reflects off of the mirror at all four corners. Those lines will create a rectangular shape that expands as it gets to the art, and then continues to expand as it reflects off, back into the room. That is your family of angles.

So to keep your lights outside of that family of angles, you have to move the lights more to the side (away from the camera position).

The simple test, is to look at the art (from the camera's position) and move your lights in and out of the family of angles. If you see the light source's reflection coming and going, you will know: 1) that you are dealing with direct reflection. and 2)where you have to put the light so that it's inside/outside the family of angles.

As I mentioned before, this is much more complicated when your subject is 3 dimensional and has multiple families of angles. For for flat art (copy work) it's usually pretty simple.

There is a 'trick' that we use to make this easier. The further away from the art that you (& the camera) are, the narrower that your family of angles will be. Remember the laser....if you are 20 feet away from the art/mirror, the laser's path is at a slight angle to the corner, and at a slight angle back. But if you are really close, then angle is more outward and it then reflects off at the same wide angle, making your family of angles huge...which makes it harder to hide the lights outside the family of angles.

So the tip is to place your camera further away (and thus use a longer focal length lens to fill the frame).

One more question for you Big Mike: One of the problems that I have had with moving the lights to minimize the glare (or control where it lands) is that I then often find the light source causing inconsistent tones across the image, i.e., bright at the top, dark at the bottom, etc. Can you speak to that briefly? Again, these are photos for catalog-type use, where literal relationships of colors are important for informational purposes. In other words, I wouldn't want to create a false gradient of color with my lighting that isn't on the original.

Derrel spoke to this, but to to echo his comments, this is due to the fall off rate of light (reflection from objects characterized by diffuse reflection). The closer the lights are to the subject, the more fall off you will see from side to side. So ideally, you would use two lights of the same design and strength, at equal distances to either side. If you are in a position where you can't place your lights evenly to both (or multiple) sides, then moving the lights further away will help. It will mean that the artwork is not as bright (again, the fall off rate of the light) but you can compensate for that with your exposure settings. (use a tripod so that slow shutter speeds won't cause you blur).

You will find all this information and more, in the book I recommended. Or you could make the trip up to Edmonton to take my lighting 101 course. Six Thursday nights in April/May or three Saturdays in September.

 

[minicoop1985]

One of the problems that I have had with moving the lights to minimize the glare (or control where it lands) is that I then often find the light source causing inconsistent tones across the image, i.e., bright at the top, dark at the bottom, etc. Can you speak to that briefly? Again, these are photos for catalog-type use, where literal relationships of colors are important for informational purposes. In other words, I wouldn't want to create a false gradient of color with my lighting that isn't on the original.

When a light source is CLOSE to a subject, the degree of light fall-off over very small distances is VERY great. When the light source is farther away, the degree of light fall off over short distances becomes almost inconsequential. This is due to something called the inverse square law.

If you are suffering from visible fall-off to the degree that it looks like a gradient, then the light source(s) is/are far too close to the subject, and an easy "fix" is to increase the distance of the lights from the subject.

As the light is pulled farther and farther away from the subject, the falloff in intensity across distances from side-to-side or top-to-bottom becomes basically irrelevant.

This is very helpful information-I did not know that.

 

[karl_kaboom]

Everybody -- Thanks again for your generous insights. You've been extremely helpful. This is a friendly, smart forum! Big Mike -- I ran out and borrowed a copy of Light: Science and Magic from my library, and was instantly convinced I needed to own a copy. Will buy one today. It focuses right on all the very issues with which I've struggled. Thanks so much for that tip. And, BTW, it shows that you have teaching in your blood --

There is a 'trick' that we use to make this easier. The further away from the art that you (& the camera) are, the narrower that your family of angles will be. Remember the laser....if you are 20 feet away from the art/mirror, the laser's path is at a slight angle to the corner, and at a slight angle back. But if you are really close, then angle is more outward and it then reflects off at the same wide angle, making your family of angles huge...which makes it harder to hide the lights outside the family of angles.

This was exactly the type of insight I needed. When I called myself a "novice" I wasn't kidding. The idea of a long focus lens opening up the area where you can place your light sources is a bit of wisdom that I will probably use in half my shots moving forward.

Thanks again, all.