Category Archives: Technique

Technique

Exposure Blending – A Quick Overview

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(This is a slightly modified version of something I wrote as part of a discussion on Google+)

The author of the post that I read before writing this mentions two alternatives for dealing with dynamic range issues in landscape scenes – the use of graduated neutral density (GND) filters or the use of a similarly-named post process technique in Lightroom. (Similar processes are available in other software including Photoshop/ACR.) Another alternative is to use HDR (High Dynamic Range) techniques that allow computer algorithms to combine source images in ways that are not the same as what I describe in this post. I almost always use a different approach, exposure blending, and I’d like to share a few ideas on this topic.

When the scene contains an extremely large dynamic range – a common situation in landscape photography – it is possible to end up with shadow areas that are nearly black and devoid of detail, along with bright areas that are blown out and also completely lack detail. (The latter is especially an issue with digital capture in which overexposed areas can simply become pure white. Film failed more gracefully in this situation.)

One traditional method for dealing with such scenes is to attach various types of graduated neutral density (GND) filters to the front of the lens. These filters include a clear area and an area darkened by a few stops. A typical use might be to position the dark portion over the sky and the clear section over a darker foreground, effectively reducing the dynamic range of the light reaching the sensor by reducing only the brightness of the sky. With film, especially positive transparency film, this was just about the only realistic way to handle the situation in many cases.

A second method is to make a single exposure and use features in Photoshop/ACR, Lightroom, or other software to simulate the effect of the GND, lightening (or darkening) a portion of the photograph. This can often help quite a bit when it comes to balancing out dark and light areas in the image, and the fact is that most savvy landscape photographers do this sort of thing and more in post. But it has its limits. For example, darkening a bright area cannot put detail back in blown out areas, and lightening underexposed shadows can lead to problems with noise and posterization. The bottom line is that this technique works well when the overall range 0f brightness in the scene does not exceed the dynamic range of the camera – here it may be used to adjust the relative levels of the areas – but it does not work well when the dynamic range is actually too great for a single normal exposure.

There is a third method, sometimes called exposure blending, that can often be used when making the exposure. The idea is to make more than one exposure, with each exposure optimized for different parts of the scene by varying shutter speed, and then selectively blend the two exposures during post-production.* Two exposures are sufficient in almost all cases, with one for the shadow detail and the other for highlight detail – though in very complex or wide dynamic range situations more exposures can be used. Continue reading Exposure Blending – A Quick Overview →

Commentary, Equipment, Technique

Very Basic Filter Advice for New DSLR Shooters

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(This article has been slightly updated since it was originally posted.)

Earlier this morning I replied to a question about filters from a new DSLR owner who wondered which filters he “had to get” to use his new camera. I realized that this sort of question comes up from time to time, and I thought that the answer might be useful to others. So here it is!

With DSLRs there are typically four types of filters that most people might consider. You do not necessarily need filters – it is a question of shooting preference and some stylistic issues.

“Protective” filters

Some believe or have been told that they need so-called “protective UV filters” on their lenses. The thought is that these filters will protect the front element of your lens from possible damage, and there is an old school notion that reducing UV (ultraviolet) light will improve certain types of photographs. DSLRs are not sensitive to UV light  in the way that film was, and there are some compelling arguments against using filters for protection in normal shooting. My thoughts on this are posted elsewhere on this blog.

I must acknowledge that opinions vary on this issue, and that this discussion (oddly, but like those about certain other photography equipment issues) can become rather heated. I don’t use protective filters. Others do. You’ll have to weigh the arguments yourself on this one.

Circular Polarizing (“CP” or “CPL”) Filters

Contrary to what you may think, CPL filters are generally not simply placed on the lens and left there, but they may be added occasionally for certain shots and in certain conditions. You do not necessarily need them, but in some situations they are useful. There are several things that they can do:

  1. In some photographs they can increase the contrast between things like clouds and sky, possibly producing a more dramatic photograph. This does not always work – it depends on things like the angle of the sun and the nature of the sky. It also does not work well on very ultra-wide-angle lenses. You almost certainly would want to use this effect sparingly, since it easily become a cliche.
  2. The CPL can control or reduce reflections from things like the surface of water or windows. It can also be useful in some situations for reducing the reflections from shiny foliage. Some find the CPL useful for photographing waterfalls and cascades.
  3. The CPL can also function as a stand-in neutral density filter when you want to use a slightly longer exposure time or a larger aperture.

In the first two cases, you rotate the filter to control the effect. There is usually a small dot on the edge of the filter and you can maximize the filtering effect by rotating in 90 degrees away from direction of the sun.

Neutral Density (“ND”) filters

These filters simply darken the image by some number of stops, ranging from one stop to as much as 10 stops. ND filters allow you to use a longer exposure and/or a larger aperture in conditions that might otherwise not allow this. You might do the former to allow motion blur, for example with photographs of water or clouds. You might to the latter to limit depth of field in very bright conditions. (As noted above, a CPL can stand in for a mild ND filter in some cases.) Contrary to some claims you will read, they do not really alter the overall brightness or color balance of photographs at all. (The very dark 9- and 10-stop filters can produce an unwanted color shift.) Most photographers starting out will not need neutral density filters.

Graduated Neutral Density (GND) filters

These filters are darker on one half than the other, with the clear and darker sections separated by an area of relatively smooth gradation whose width may vary. The dark section may reduce the light by two or three exposures. An example of their use might be a scene with very bright sky and darker foreground – the filter is lined up so that the graduated section is on the horizon and the darkened section covering the sky. Although screw-in versions of these filters are available, their usefulness is very limited. More common are large rectangular versions that are attached by means of a holder in front of the lens and then positioned manually. This is a fussy bit of business, and if you are new to this it is quite unlikely that you want to “go there” at this point. (I have heard some argue that they should be called “gradated” rather than “graduated” neutral density filters. I may be dense, but I’m, uh, neutral on this question. ;-)

Filter Alternatives

Today we can emulate the effects of most filters in software. In most cases this gives us more options and greater control than attaching filters to the lens at the time of exposure, and it also means less gear to carry. The circular polarizing filters is an exception, in that you cannot really emulate its ability to control reflections using photography post-production software.

Bottom Line

In my opinion, if you just got your first DSLR and suddenly find yourself in the mood to start buying lots of accessories… hold off on getting filters for a while. Not everyone needs them, and at first you can probably do everything you need to do without adding this additional complication. Eventually, once you become more comfortable with your camera, the filter that is most likely to occasionally be useful to you is perhaps the circular polarizer since it is useful in several different ways and because its effect is generally not one you can duplicate in post-processing.

G Dan Mitchell is a California photographer and visual opportunist whose subjects include the Pacific coast, redwood forests, central California oak/grasslands, the Sierra Nevada, California deserts, urban landscapes, night photography, and more.
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Text, photographs, and other media are © Copyright G Dan Mitchell (or others when indicated) and are not in the public domain and may not be used on websites, blogs, or in other media without advance permission from G Dan Mitchell.

Commentary, Site News, Technique

A Question: Data or Not?

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Until recently I included some basic exposure data with each of my daily photographs, listing the camera and lens used, the focal length, ISO, aperture, and shutter speed. When I switched to a new blog format a week or so ago, I made a few other changes at the same time. One of these was to eliminate the technical shot data from the posts.

To explain my thinking a bit, there were two reasons behind the decision. First, the shot information included links to a vendor with whom I had an affiliate relationship. The equipment listing allowed me to help readers who were looking for the very equipment that I used to make the shots to locate it online and make a purchase through this vendor. When the vendor abruptly cancelled its affiliate relationships with all California-based blogs at the end of June, it obviously no longer made sense to include those links. Second, I like to think that there are more important things about the photographs than the aperture, shutter speed, and camera/lens used to make them. In some ways, I have always thought it was just a bit odd that photographers have historically often included this technical information – while musicians rarely list the instrument they play and I’ve never seen a painting include data about the brand of brush used to make it! :-)

However, I get email. And several readers have very politely asked what happened to the exposure information, and some have asked that I again include it.

What do you think? Would you like to see it included again? Let me know by leaving a comment on this post. Thanks!

Commentary, Ideas, Photograph Exposed, Technique

A Photograph Exposed: A Tale of Light

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(“A Photograph Exposed” is a series exploring some of my photographs in greater detail.)

On the weekend of June 18-19 of this year I made a point of getting to Yosemite so that I could photograph the high country on the first day that Tioga Pass Road was open for the season. On a shoot like this, my subjects range from some that I planned to shoot ahead of time to some that were completely unanticipated. Among the many things that might affect my decisions is the light itself, and this is a story about that light… and perhaps a few other things, too.

I had driven to the park very early on Saturday morning and after photographing straight through the morning I finally made it over the pass and headed down to Lee Vining Canyon to find a campsite for that night. After getting up at 3:30 a.m. and driving to the Sierra from the SF Bay Area and then shooting all morning, I was exhausted! I pulled into the first available site, paid my fee, and promptly fell asleep in the car for perhaps an hour. When I woke up I set up my camp and at about 3:00 or so headed down to Lee Vining to get some “dinner” – on “photographer time,” dinner tends to either be very early or very late, and on this day I made it early so that I could be back up in the park well before the “good light” started.

Heading back up to Tioga Pass after my mid-afternoon dinner, I had a few subject ideas in mind. Tuolumne Meadows itself was one possibility, and I knew that I wanted to watch for any cascades or creeks that would be flowing in the spring snow-melt conditions. Tenaya Lake was another possibility, and a client’s interest in photographs of Mount Conness had me thinking about the possibility of a photograph from Olmsted Point that included ice-covered Tenaya Lake and this peak. Continue reading A Photograph Exposed: A Tale of Light →