There’s a significant focusing problem that many Canon and Nikon DSLRs and some mirrorless users face. However, it’s not the end of the world; there is a workaround that can help you get the shot.
It’s something I take for granted. I’ll admit that it was a mistake of mine not to think about it beforehand when I was working with a group of photographers, most of whom had Canon and Nikon DSLRs. I had forgotten because it was an issue I had not faced for over a decade. While I set up my camera and pressed the shutter release button to take the above minute-long shot, the others started pointing out they were having difficulties. Their problem was due to the autofocus restrictions and lack of vision through the optical viewfinder when shooting in the dark or with an ND1000 filter.
To understand the focusing problem my clients faced, we’ve got to look at why there are drawbacks with DSLRs especially. It’s a drawback that modern mirrorless cameras should not have, although some still do.
The above images show the difference between a 1/400-second and a 10-second exposure.
Understanding Focus
The following explanation is both a very simplified and broad generalization; there are exceptions to this overview of the focusing problem.
Most DSLRs have two separate focusing systems.
Phase Detection
Although it sounds like technobabble from a sci-fi movie, the concept of phase detection is simple.
On old film SLR cameras, a split screen could be seen in the center of the viewfinder. If you pointed your camera at, say, a thin, vertical post, and the lens was out of focus, the post would appear to line up above and below the split. However, when out of focus, the post above and below the split would not align. In other words, it would be out of phase. The top and bottom halves of the post would appear too far and left, respectively, if focusing too near, and the reverse if focusing too far.
A DSLR works similarly but electronically. The camera splits the subject into two images and, when aligned, the lens is correctly focused. Looking through the viewfinder, you should see the focus points that usually illuminate when you half-press the shutter button.
That is all very fine if focusing on a vertically oriented subject. However, when aiming at a narrow horizontal subject, a horizontal sensor struggles as it cannot see the misalignment. Similarly, a vertically aligned sensor would struggle to focus on a narrow vertical subject. One way to get around this is to rotate the camera when focusing.
Some models look solely for that misalignment across a horizontal or sometimes vertical plane, but more advanced cameras look for both horizontal and vertical misalignment. These are called cross-type focus points. This configuration makes them more accurate than single linear sensors because these types of autofocus points use two sensors in a + shape. Consequently, they can detect changes in two dimensions instead of one.
Generally, the better the camera, the more focus points there will be, and more of those will be cross-type. An online search will soon give you this information for your camera. Cross-type focus points are more accurate even in low light because they can detect changes in two dimensions. Moreover, they make compositions easier because you can compose shots freely without being subject to the shape or orientation of the subject.
The big advantage of phase detection is that it is fast. The camera can tell which way the misalignment across that split is. Consequently, it knows whether to focus nearer or farther.
Contrast Detect
The second type of focusing system is contrast detection. That comes into play when you use the Live View screen at the back of the DSLR. When a lens is out of focus, both whites and blacks become a mushy gray. Then, as the lens comes into focus, the contrast gradually increases until it reaches maximum.
Contrast detection is much slower to focus because the camera does not know whether the lens is focused too near or too far. However, it is more accurate, especially when focusing close to a subject.
Keeping Us in the Dark
Can you see the issue with both systems? They require the camera to be able to see the subject. If it is dark, or you have an ND1000 filter attached to the camera, it will struggle. Both systems need to see the subject to be able to focus on it.
That was the main problem we faced when I was with the photographers shooting with their older DSLR fitted with ND 1000 filters. Moreover, they could not see through the viewfinder. Even when using Live View, the cameras could not display the subjects.
The way around it is simple: remove the filter, compose the shot, focus on the subject, switch the camera to manual focus, and carefully reattach the ND filter. If you face the same issue at night, use a bright torch to illuminate the subject, focus, and then switch to manual focus mode.
The Big Advantage of Some Mirrorless Cameras
If you have read my articles before, you will know I shoot with an OM System OM-1 Mark II. I sometimes take some of its advanced functionality for granted and assume others' cameras have the same facilities. For example, it uses an advanced metering system that combines phase and contrast detection. That, along with its stacked sensor, makes the camera far superior at focusing in the dark or when using the ND1000 filter compared to many other models. I was quite happily shooting long exposures while the others were struggling.
Furthermore, for exposures over six or seven stops beyond its maximum 60-second exposure in M (manual) mode or B, A, S, and P modes, it’s still possible to autofocus and preview the final exposure through the viewfinder, even with an ND1000 filter fitted. Some other advanced cameras can do that too, but many are limited to a 30-second exposure.
However, the OM-1’s night vision mode further enhances the images. Consequently, I can see the foreground details when it is much darker, and a longer exposure is necessary.
Not only that, but the entire viewfinder is entirely covered by the hybrid cross-type phase-detect and contrast-detect focus points, which means I can focus on subjects right at the edges and corners of the frame.
So, if you are in the market for a camera and want to do nighttime photography, it is worth checking what the camera can do. Ask your search engine, “Does the (Insert camera name here) have a night vision mode?” Or, “Can the (insert camera here) viewfinder allow you to see through an ND1000 filter?”
Better still, take an ND1000 filter to the camera shop, attach it to (or hold it in front of) the lens, and see if the camera can focus through it.
In Conclusion
Although mirrorless camera sales have overtaken those of DSLRs, there are a lot of hobbyist and enthusiast amateur photographers using older DSLRs. I suspect there are still more DSLR users out there than those of us who use mirrorless; there were a lot of DSLRs sold during the heyday of digital camera sales. Those older cameras can still take good pictures, but they will struggle in low light or with an ND1000. However, there are ways around it, and some mirrorless cameras will have problems too.
Perhaps you are thinking of buying an ND1000 filter. If you are, then please read my recent review of Urth Filters that I used in all the shots in this article.
If your camera has one of the focusing issues I mentioned, I hope the workarounds will help. Or are there other methods to overcome the issue that you have employed? Or, you could treat yourself to a new camera with better low-light functionality. Start your replies below with “Dear Santa.”
Never had any problems focussing with a nd1000 filter on my EOS R, even with the 17-40 with an 6 stop gel filter combined with my ND1000 screwed on it. The R has the advantage of having 5655 focus point all over the sensor. My old 6D had just one cross type focus point. But than Canon is very good at focussing in low light.