Category Archives: Equipment

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.

Equipment, Ideas, Technique

Backpacking and Photography

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This is the time of year when many of us find our thoughts turning the the upcoming backpacking season. (My home range is the Sierra Nevada, where I have backpacked for decades.) During the past week or two I’ve seen an upsurge in discussions of and questions about photography and backpacking. Several years ago I began posting annual updates on my approach to photography in the backcountry: “Backpacking Photography Equipment.”

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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, Equipment, Ideas

Myth: Diffraction and Motion Blur Worsen With More Megapixels

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They don’t.

Another post that I wrote just before this one (“Why Your 21MP File “Looks Softer” Than Your 12MP File at 100%“) explains why pixel-peeping* photographers might imagine that cameras with greater photosite density (e.g. – “more megapixels”) might produce “softer” photographs, based on what they observe when they compare 100% magnification images on the screen. These cameras do not produce softer images – the results will either be equal to or better than those from lower photosite density cameras in this regard. You can follow the link to read the original post.

A reader wrote and suggested that perhaps the images from the camera with greater photosite density really are softer, but the cause is a greater susceptibility to diffraction blur or motion blur.

No. Neither is the case.

These are two additional misconceptions that can be fed by (yet again!) pondering 100% magnification crops on the screen without thinking through the actual (non-) effect of what you see there when it comes to actual photographs. Continue reading Myth: Diffraction and Motion Blur Worsen With More Megapixels →

Commentary, Equipment

Why Your 21MP File “Looks Softer” Than Your 12MP File at 100% Magnification

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(Note: 21MP cameras were state-of-the-art when I wrote this. While that is no longer the case, the explanation of the concept still applies to comparisons between more recent higher MP cameras cameras with differing sensor resolutions. And, years later, camera reviewers are still making the mistake that I address here.)

A frequent photography discussion forum meme is that “this old camera with fewer photosites produces sharper images than this newer camera with more photosites. In fact, I have carefully inspected 100% crops from both and the evidence is clear!”

Not so fast.

Let’s imagine that the comparison is being made between the full-frame 12MP Canon 5D and the full-frame 21MP Canon 5D2, both of which I own and use. If you put the same lens on both cameras, set the lens to the same aperture, and point both cameras at the same subject, the lens will project exactly the same image onto the sensors of both. Let’s say that you do this under controlled conditions, and you decide to compare the two captures to see if the 21MP camera is really sharper than the 12MP camera.

You want to compare closely, so you display both images as “100% magnification crops” – portions of the image that show each individual pixel from the original photograph as an individual pixel on your computer monitor. You display the two images side by side and, squinting closely and looking back and forth between the two, you notice that the 21MP original is certainly no sharper than the 12MP original and that the 21MP image actually looks a bit less sharp! You decide that a) higher MP cameras are less sharp than lower MP cameras (you have the evidence!), and/or b) the camera companies are pulling a fast one on us.

You are actually wrong. Dead wrong.

When gazing too long and too intently at a computer screen, it is easy to forget that the real world is not always represented accurately on the screen. In this case, the error is a result of viewing on a computer screen rather than making more realistic comparisons, for example between two prints of equal size. With the screen image comparison, you might overlook a fact that explains why the sharper (or at least equally sharp) camera appears to be less sharp. A look at the above  illustration will help.

The image includes two copies of a full-frame photograph. Think of the one on the left as representing the photograph made on a 12 MP camera (like the 5D) and the one on the right as representing a 21MP camera (like the 5D2). The original 5D image would be 2912 pixels wide, while the original 5D2 image would be 3744 pixels wide. The full-color area of each image represents the part of the original image that would fill the screen of a 1280 x 1024 monitor when the originals are viewed at 100% magnification.

The critical point illustrated here is that the 1280 x 1024 “slice” of the 21MP image shows a considerably smaller portion of the overall image, and in order to fill the same size screen it will have to be magnified more than the image from the 12MP camera. If the two images are equally sharp to begin with, the one that has to be magnified more to fill the screen will lose more of its original resolution because you are looking more closely at a smaller portion of the image.

In the end, if you were to make two prints of the same dimension from the two original full images, the higher MP original would look at least as sharp as the lower MP original, and if you use good lenses and good technique (and print large enough that it makes a difference) the higher MP version has the potential to resolve more detail.

Some related points

A few related notions about sharpness and megapixel resolution also come up from time to time, and those who believe in them can be quite stubborn about their misunderstandings. Here are a couple:

  • Claim: When you move to a higher MP sensor your photos will be more susceptible to motion blur.False. This is not the case at all. If you make otherwise identical photographs with a low MP full frame (or other format) digital camera and a higher MP camera using the same format, prints of the same size from both sources will have exactly the same amount of motion blur. (Technically, the higher MP camera will provide a more accurate image of the blur, but that doesn’t change how much blur there is.) In both cases the blur covers the same percentage of frame width. And, if you are tempted to check 100% magnification crops to prove me wrong, don’t forget what we saw above about looking more closely at a smaller area with the higher MP example. (The good news for the higher MP sensor is that when there is less motion blur it has the potential to produce an even higher resolution image of the subject.)
  • Claim: Because the diffraction-limited aperture is larger when you work with higher resolution sensors, you’ll have more blur at smaller apertures with the higher MP system.False. You’ll have exactly the same amount of diffraction at every aperture. Diffraction is an optical phenomenon that is not affected by the sensor. Once again, if you make prints at some size from otherwise identical frames from a higher and lower resolution system, at every aperture diffraction will affect both the same way. And, again, while the higher MP system is never worse, if you use a very good lens and open up a bit you may get an even sharper image from the higher MP system.

In every case, either the two systems perform the same or the higher MP system is better. There is no situation in which the lower MP system will produce a sharper print at a given size, and there are some in which the higher MP system will make a sharper print… or allow one to make a larger print with the same resolution.

(See related post: “Myth: Diffraction and Motion Blur Worsen With More Megapixels”)

G Dan Mitchell is a California photographer and visual opportunist. His book, “California’s Fall Color: A Photographer’s Guide to Autumn in the Sierra” is available from Heyday Books and Amazon.
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