Longer Exposures For More Saturation and Luminosity

I just posted this as a response to a question about one of my photos over on ESS. Thought it might be of interest to y'all.

In situations involving low levels of light it can often be beneficial to obtain a longer exposure to allow the sensor/film more time to absorb the color and glow. There can be a lot of color and light bouncing off clouds and hills that our eyes can't pick up. Cameras are able to "see" into low light scenes by leaving the shutter open and collecting more light. If I really want to pull as much light and color from a scene as possible I'll often use an ND along with my usual filter stack and also set the ISO on my camera down to 50 in order to extend what was already going to be a long shutter speed. The two photos above were taken one right after the other, the first at 6 sec @ f/20, ISO 100 with a 3 stop GND. The second was taken at 30 sec @ f/20, ISO 50 with a 3 stop GND and a 3 stop ND. Quite a difference 24 seconds of shutter time can make.

Interesting.

I was going to ask this same question over on ESS as to why you used one in that situation. As Mark H. says, interesting. I wonder if part of the increased saturation could be due to a color cast (in this case magenta) introduced by the filter itself??

Mark W. - that is a good question. I use Singh-Ray ND filters and according to all their beta and what Galen Rowell and a bunch of other top shooters claim, they are the most color neutral ND filters out there. That certainly doesn't mean that they have absolutely no color cast...and in this case I like the result regardless of where it came from. That being said, the effect of longer exposures can be seen without any filters at all. I often shoot on the edges of dark, when there is barely a visible glow to the eye. Two to ten minute exposures without any filters will often yield all kinds of amazing colors I didn't know where there. Marc Adamus has a 10 or 15 minute exposure image that I really like of after glow on a peak in the Sierra that he made when it was all but dark.

I remember reading an article by Darwin Wigget that discussed his use of a 5ND filter to increase exposure time and realize greater saturation of colors. I believe the article is on the Singh Ray web site.

As you begin to step away from the natural/accurate rendition of a scene through the use of multiple filters, do you then enter the realm of photo art?

Interesting, but how does diffraction affects the sharpness of the image if you stop down to f/20 or even smaller? (I assume you work with Full Frame) I know it depends on sensor/film size what the min aperture can be in order to deliver a sharp picture => the larger the film/sensor the smaller the aperture can be.

Interesting... At low light levels, the "signal" to your brain from your eyes is dominated by the luminance receptors (rods) while at high light levels the signal to your brain is dominated by the color receptors (cones). That is why moonlit scenes appear silvery, or why you see in black and white when there is very little light. When the light level is high, you see in color because you get more input from your cones (which come in varieties sensitive to red, green, and blue wavelengths). The camera will pick up color information at low light levels, though. This explains why evening/morning photos pick up color information that you could barely see or didn't see at all with your eyes.

But that doesn't explain the difference in saturation between the two photos. The light can change drastically in a matter of seconds as distant vapor or dust clouds move in or out of the direct path between the sun and your subject, filtering the light in different ways, yet there appears to be something more going on with this long exposure technique.

Hey, both are really beautiful photographs, by the way.

Cool - this is giving me way more food for thought than I expected.

Carol - I'm going to hunt down the Darwin Wigget article. He has a way with figuring this stuff out. I'll post a link if I find it.

Benjamin - For most of my "art photography" I'm fine calling it photo art or photo illustration or whatever because I'm more concerned with creating an impact and expressing my vision of the scene than worrying about if my image is true to the experience of others. In fact, I want my photos to be a departure from what most people experience. I want them to be challenged/excited/confused/intrigued/inspired by what they see. If I was really trying to be true to what my eye saw, it would actually be somewhere between the two images above, so the camera didn't match my eye in either case. If you get down to the root of the thing all photography is actually a separate view of reality anyway. Cameras don't record an image the same way the eye/brain does, so a photo is always an interpretation. Type of film/white balance setting, choice of lens, angle of lens, depth of field, exposure, dynamic range, perspective, lens distortion/aberration/flare, selective framing and shutter speed are all ways that cameras "see" differently than people...no filters needed. Our brains don't see blurred water, but that doesn't mean that it doesn't look like that on the right time scale. Increasing saturation with the use of a longer shutter speed doesn't mean that color isn't there, just not the way that we see it. Filters and other techniques are extensions of what the camera does by itself. If filters, or Photoshop, or fog or crinkled up cigarette wrapper can help an artist achieve his artistic vision, then I'm all for it. That isn't to say that untrained or unrestrained use of any of the above can't produce some cheesy and just plain bad photography.

Stefan - I often worry about diffraction degradation with small apertures, and yes, the problem is worse near the outer edges of wide angle images...so full frame sensors and extra wide lenses are particularly susceptible. However, all of photography is compromise. Sometime I'm willing to give up some DOF to maintain the best sharpness. In this case, I was willing to give up some sharpness to obtain a longer shutter speed. The above image is an unsharpened crop from the full res image. Hard to say how much distortion there is, but however much it is minor and I think it was a fair trade.

Mike - I obviously need to do some more reading on the topic, but my understanding is that color and light both behave in a similar way when contacting the sensor (since they are really both the same thing). In strong light the sensor can capture a proper exposure and saturated color with a very short exposure time. As light fades a longer exposure is needed, but with enough time the sensor can collect the light necessary to produce an image brighter than it actually appeared to the eye. By the same token, if that light has a color cast, a long exposure allows the sensor to collect enough colored light to create an image that appears more saturated than it would to the eye or with a faster shutter speed. Not sure that makes any sense and I'll need to back that up with some research.

Wow - both are beautiful renditions! Sean, I am on the brink of purchasing a Singh-Ray graduated neutral density filter as well as a neutral density. Do you use a Cokin holder to stack your filters? I'm trying to figure out the best way to do this...

Amy - I do use a Cokin p-holder to hold my filters sometimes (for exposures of more than a minute or so) but I often hand hold them. I have heard that Kevin McNeal has a blog entry on his site about how he holds filter stacks with a rubber band system. I'm going to check that out, because the p-holder isn't a great solution. It is a pain to get set up and it causes a really bad vignette with my 16-35mm lens between about 16-20mm. Singh-Ray makes a variable ND filter that can be adjusted from one or two stops up to, I think, 10 stops. It is spendy, but not as much as if you bought all those ND levels separately. That's next on my list.

Sean - Here is the site for the Darwin Wiggett article I mentioned. (Sorry, but I don't know how to make it link.) Once you get to the site you will need to scroll down to the article called "The Terrific Triple Threat". I remembered it so well because it really sounded like it would produce some great results and as you said, maybe not photojournalist photos, but fine art photos.

http://singhray.blogspot.com/search/label/Darwin%20Wiggett

Just my 2 cents here, I think both images work on different emotional levels. I like them both, but the longer exposure has more impact for me. I definitely will try this technique at the first opportunity.
And to Benjamin, I respect your position and approach to photography, but I do try to create art with almost every shot I take. I know you do too. I hope this forum has room for both preferences. I concede that art to one does not necessarily appeal to the other. It is evident that each photographer has his line in the sand, so to speak, that he does not want to cross because of his likes, dislikes, or even philosophy toward photography. In my mind that is perfectly o.k. We should certainly all be free to express ourselves as we wish. And yes, there is a point for me in my mind where a photographer could go too far to be included in nature photography, but that's just my line, and does not mean it is correct in the next mind.

Sean...this is fascinating, I wonder how much this effect has to do with what went on in the camera vs. what went on in the environment. For example, is a digital sensor non-linear in response to different wavelengths? Might explain luminosity being preserved but color information being radically altered. But that does not compute well considering only luminosity is realyl detected, the bayer sensor + processing provides color info. I can only conclude that the variation in color, while subtle to our eyes and exaggerated in the capture, came from the environment. Of course, easy ways to find out - first off, does film show the same effect as digital? Second, conduct the low light color sensitivity tests in a studio with controlled variables!

As for your take on photo "art" - I am totally with you. Frankly, I simply don't get how any photographers believe in any way that what they are capturing is "real". I find that an odd notion - we see differently from any planar sensor, period. We have curved sensors (retina) - that means we perceive angles and distances differently from planar sensors. It's why wide angle distortion exists. Right there, from the outset, cameras see differently. Then there's color - white balance issues aside, the fact that out color sensitivity is dependent on luminosity and contrast...different from a camera. Somehow, people only seem to apply standards of "reality" to color images and not to B/W - and B/W images are manipulated way beyond color images most of the time for maximum impact. I think photographers need to stop kidding themselves and other people stating that their images are "true to what they saw". Even if you did nothing to manipulate your image in any way and tried to be absolutely faithful to what you saw, you can't really. I don't believe it when other photographers tell me that, and I don't say that to people who ask me about mine. I simply say "I'm trying to create a beautiful photograph, not document the beauty of nature."

I've noticed this effect too Sean while taking a long exposure just after sundown, no filters. Far more color than my eyes see. I've also played around with ND's to do this also. Tomas Kaspar pointed it out to me while we were shooting on the coast once. I really like what you did in the second shot.

Kartik - you pose some interesting questions. For this particular image, I think I would have to say that the effect has to do with how the camera is recording the light not the environment since I only added the ND after the most intense visible color had already passed, and I wanted to see if I could get more out of it. So, the visible color was getting less saturated during the time of the ND exposures, not more. It seems like the effect is most apparent with the red end of the spectrum, so perhaps you are correct that sensors respond differently over time to longer wavelengths? However I have also experienced this effect with blues and greens. THIS long exposure image posted in ESS by David Fernandez shows the saturated blue/cyan effect. Here is what Darwin Wiggett offers on the subject in the above mentioned article:

"the 5-stop ND filter creates long exposure times which has two benefits; first it shows painterly blur in any object moving in the frame (swirling tides, running water, blowing clouds) and second it builds up colour intensity especially at sunrise and sunset by allowing colour to wash over the land and sky over time."

Not sure that really tells us much. I agree that your studio test idea would be the right way to get a scientific answer.

I just sent an email to Darwin inviting him to weigh in on this topic, so hopefully he'll have some insight to share.

I think what Darwin is referring to is that with longer exposures, points or areas of color have the opportunity to move across the scene; essentially the difference between a point of color and a streak of color.

In the image on the left, in the distant clouds, you can see parts that are distinctly more colorful than the surrounding areas. In the image on the right, those points are recorded in multiple areas as they move across the scene, more or less "painting" color as they go.

What I don't quite yet understand is how this translates into more saturated images.

It does appear that there is a color balance difference between the two, with the right one being much warmer than the left. Not sure if that's a byproduct of the longer exposure, a different color temp selected by the camera, or processing differences.

I set the color temp to the same for both images. The second image was actually much warmer when using the auto WB setting, so I cooled it considerably and then set the other to match. I don't think that Darwin is specifically talking about moving color as much as an all over color glow or "wash" as he puts it. You should check out the article. He shows several examples and there is certainly an increase in saturation when he puts on a 5ND, even in parts of the image where there isn't any movement of color such as a static, shaded foreground receiving only indirect light. Also, in my image the hills in the BG are evenly and fully lit regardless of the exposure time, so there isn't a change or move in the light or color, but the longer exposure shows a lot more saturation in those hills.

I think you just showed me the reason I want to eventually go FF. With 12MP DX, and diffraction limited to f/11 (my personal hard limit) Having the aperature availability of say f/20 now has another completly new component to it....

Gonna start looking real hard at the D700. Maybe get the AA filter removed instead of going with the 24MP monster when it comes.

We are getting to an arena of choices not as simple as the old days when you just went for the most MP. There are a LOT of factors to consider.

Roman

Sean,

I don't see a polarizer filter mentioned in your first post. Did you not use one? Thank you for sharing this info with us. The difference between the two pictures is stark. If you don't mind, it would be interesting to see a crop of the BG to see sharpness comparison, regarding diffraction.

Jay - No polarizer. The sun was rising directly behind me, so there wouldn't be any polarization benefit in the sky. I could have used a polarizer to cut the reflection from the water surface, but in this case I wanted as much sky color to reflect off the water as possible so I opted to leave it off. The long exposure blur of the waves as they were coming in and out of the FG made it possible to see through to the rocks as if a polarizer had been used.

Above is a crop from the background of the full res file without any sharpening applied.

Looks sharp to me. I'm impressed with the detail front to back at f20. Thanks for posting that and for the explanation.