As photographers, we tend to believe what camera manufacturers tell us. Why, generally, would we question something as supposedly simple as the accuracy of shutter speeds? Well, it turns out we should in certain situations.
Specifically, I’m talking about the 30 second maximum shutter speed manufacturers tout without invoking Bulb mode. Secondarily, the 15 second shutter speed as well.
What am I going on about?
I admire good wide field astrophotography. I admire good deep sky astrophotography, as well. That requires a lot more equipment than many of us have. The beauty of our galaxy is something to behold. A well made picture of a starry night sky, the Milky Way, or a colourful star trail are wonderful to look at and remind us of our own insignificance in the grander scheme. Or, our true significance from the standpoint of climate change and that we may not have scenes like this if we continue on our current path.
When doing night sky photography we tend to use longer shutter speeds. For star trails, or timelapse videos, we want as little a break between exposures as possible. This makes our star trails appear continuous when we blend the images and it makes our timelapse videos seamless as they track time.
I’m a Nikon user. Many Nikon cameras now have a built in interval timer, or intervalometer. A built in interval timer is fairly common now in other manufacturers also. This, one would think, makes the process of doing star trails, or timelapse videos simpler than if an accessory interval timer had to be used.
I had not done much night sky photography for many years. Actually since before I switched to Nikon and shot with Canon. Over the past number of months I’ve had the opportunity and have experienced some frustration with the Nikon interval timer; both in my D800 and my two Z6s. What I’ve found out may be of interest to you, too.
The interval timer in Nikon cameras requires that the shutter speed be included in the interval. If you want a 30 second exposure with 1 second in between, you set the interval timer to 31 seconds. Which is what I did. Problem? It didn’t work. I got 1 exposure every 61 seconds.
I tried 32 seconds. That didn’t work either. But 33, or 34 seconds did work. This was very odd.
Using an interval of 1 second worked…. BUT… if I set the camera for 999 (the maximum) exposures, it would stop after about 30 minutes.
I tried to do some research online. Maybe I was doing something wrong. I wasn’t. The Nikon interval timer has to include the exposure time. Why didn’t 31 seconds work?
Next, I made the mistake of posing the question on a photography discussion board. These places are the great wasteland of photographic detritus. They really should be avoided at all cost if you value your sanity. Anyway, responses ranged from ‘uhhhhh… dunno’ to ‘well it should work’ to ‘uhhhh…. dunno.’ One bright soul chimed in to say that it needed to be longer than 31 seconds because the camera needed time to write the image to the memory card and that takes time. Recall my earlier comment about the great wasteland that is online discussion boards? That idea is utter nonsense. It’s nonsense because today’s advanced cameras can fire off full resolution RAW blasts at anywhere from 5-12 fps for 7-15 (maybe more) shots before filling the buffer. A single exposure every 30, or so, seconds isn’t going to bog the camera down for 3, or more, seconds.
After not, unsurprisingly, finding an answer on the Internet, I set about with some more experimentation.
Camera makers universally note the maximum 30 second shutter speed before Bulb mode. Dropping back, the next full stop down is the 15 second shutter speed. That’s a problem though. It is a problem because neither of those fit the natural progression of full stops. The natural progression would be 1, 2, 4, 8, 16, 32.
What is a photographer do to with this conflicting information? Testing.
I timed both the 15 and 30 second shutter speeds. The 15 second speed was actually 16 seconds and the 30 second shutter speed was actually 32 seconds. This fits the natural progression, despite being labelled as 15 and 30 respectively. Woohooo! The in between speeds are accurate, it’s just those two full stop speeds that are off.
This now explains why the interval timer needs to be set to at least 33 seconds.
I also shoot with a couple Fuji cameras and tried this with my X-T1. Fuji engineers seem to be better than Nikon engineers because the 30 second shutter speed is 30 seconds. There’s even a countdown timer on the LCD so you know. The 15 second speed is also 15 seconds. With the Fuji this is less important because the interval you set is the actual interval between shots and doesn’t include the shutter speed. Note to camera manufacturers: THAT is how interval timers SHOULD work.
What about other makes? I had a friend try with his Canon camera. Lo and behold, 30 seconds was actually 32 seconds. I asked another friend to try with one of his Sony A7 variant bodies. Same thing. 30 seconds was, in reality, 32. I don’t know anyone who shoots with M4/3 cameras, or other lesser used manufacturers so wasn’t able to have testing done with other makes.
What does this all mean? It means that if you’re shooting long exposures, using an interval timer and your camera requires the shutter speed to be included in the interval, you will need to increase the interval time by a couple seconds to account for the inaccuracy of camera software engineers.
Oh! Why did 1 second work with the Nikon but stop after about 30 minutes?
Using a 1 second interval, and setting the number of shots to 999, the camera will take an exposure every 33 seconds as you want it to. Here’s the rub…. the computer inside the camera is still counting 1 shot every second, so over 33 seconds it has, essentially counted 33 shots. What’s 999 divided by 33? Yes, that’s right, grade 3 math served you well, it’s 30. It’s actually 30.272727…. but we won’t quibble about that fraction of a minute.
Happy interval timer shooting!
