If you’ve ever read any introductory material on photography, you’ve probably seen the hand holding rule of thumb. The rule of thumb suggests that to avoid camera shake, the shutter speed should be at least 1/focal length of the lens or faster. So for example, if you’re using a 100 mm lens, you need a shutter speed of 1/100 second or faster.
This article was originally written in spring of 2011. At that time, the Nikon D800 hadn’t been announced, and camera resolutions were still very much in line with the capacities of the film that preceded them. However, since then sensor resolutions have increased, and the rule of thumb has needed to evolve.
A Bit of Background
The catch for the digital photographer, is that the hand holding rule of thumb was developed for 35 mm film cameras. Moreover, as far as I can tell, it was developed empirically with film, and not from some first principals. Because of this, for the modern digital photographer the traditionally hand holding rule of thumb runs in to problems.
To start with, many digital photographers use cameras with frame that’s smaller than the traditional 36 x 24 mm of film. Because the frame is smaller, the image has to be enlarged more when it’s viewed (compared to a “full frame” sensor), this makes camera motion more visible in the resulting images.
Even for those shooting with a “full frame”, or 36 x 24 mm sensor, the rule of thumb is often insufficient now too. In his article Film versus Digital Information, Dr. Roger Clark estimates the digital equivalent resolutions of several film stocks, the bets of which topped out at around 16 MP for a 36 x 24 mm frame. Incidentally, his estimates correspond well with my experiences in scanning and processing film too.
However, many full frame digital cameras now are shooting at more than twice that resolution, with many of the higher end ones approaching 50 MP (which puts them on par with 6 x 4.5 cm film stocks). With these higher pixel pitches, photographers can crop more and print larger than they could in the past, again magnifying the blur caused by camera motion into something that’s visible.
The short of it is that with modern digital cameras, we need to consider the applicability of the old 1⁄focal length rule for our images.
The New Digital Rule of Thumb: Double the Focal Length
Easily the simplest solution is to just double the shutter speed. This is the solution I currently recommend, and use, due to the increased resolution of modern cameras.
By doubling the shutter speed, you halve the distance the camera can move due to shake.
While shake is linear, sensor resolution (in, e.g., megapixels) is a square of that. So in halving the distance, you quadruple the resolution the sensor can be before it starts showing shake the same way, at least at the pixel level.
This should provide a good rule of thumb for full frame cameras up to 65–80 MP, and APS-C cameras up to 28–36 MP, and FourThirds cameras up to 16–20 MP.
|Format||Safe Resolution (MP)|
|Full Frame / DX||65–80|
|4/3 and M4/3||16–20|
I’ve seen this work out in practice too. With my old 23 MP EOS 5D mark III, I could reliably use the old 1⁄ focal length rule of thumb and get pixel sharp images with un-stabilized glass. However, when I upgraded to a 30 MP EOS 5D mark IV, I found that more often than not images would be marred with camera shake using that old rule of thumb.
I now always use double the focal length as my hand holding speed with any modern cameras.
As a second data point, I found that some Nikon photographers had similar problems when moving from the 16 MP D4 to the 36 and 46 MP D810 and D850.
Crop users will still have the same penalties, for the increased enlargement and typically smaller pixel pitch. In fact, as things currently stand most APS-C cameras top out at 24 MP, and Micro Four Thirds cameras at 20 MP. Both of which work well with the double the focal length suggestion.
For Posterity: Cutting it closer
The following has been adapted from the original version of this article back in early 2011. Due to increases in sensor resolution, I don’t recommend this practice anymore. However, it’s still valid in some cases and can be helpful so I’m including it in this updated article.
Doubling the shutter speed, has two main advantages:
- It makes the math easier. Doubling a number is a lot easier than trying to multiply by 1.5 or 1.6.
- It builds in some extra cushion for most cameras, making camera shake even less likely.
However, it also means you’re giving up potentially precious shutter speed for the sake of safety. Let’s be honest here, it’s not when we’re metering 1/500 with a 50 mm lens that we care about camera shake. It’s those cases where we’re trying to get every bit of shutter speed in the dark and still have a sharp picture. In these situations loosing 1/3 to 2/3rds of a stop using an overly safe rule of thumb can be a problem.
There is a tidy solution though…
For Posterity: Use the Camera as a Calculator
Due to an amazing twist of luck, there’s a way to use the camera as a calculator and get values that have less margin for error, but should still work. The trick works because sensor sizes correspond very closely to fractional-stop exposure increments used by the metering systems. Whether that was a consideration when the camera companies were picking sensor sizes, I don’t know, but it’s certainly very useful.
By dialing in exposure compensation to adjust the meter exposure, you can quickly see if the meter exposure is fast enough to meet the suggested rule of thumb.
Here are the adjustments either working up from the old hand holding rule of thumb or down from the recommended new one.:
Here are the adjustments:
|Format||Crop Factor||Adjustment From
1⁄ 2x focal length
|Nikon DX, Pentax, & Sony APS-C||1.5x||-1/2 (or -2/3)||1/2 (or 1/3)|
|Four Thirds / Micro Four Thirds||2x||-1||0|
Working this way you can quickly check when you’re in the danger zone, without spending a lot of time trying to figure out what the exact numbers are. Even better, it becomes second nature to do it in your head, once you become familiar with 1/3rd stop shutter speed steps between say 1/30 and 1/250 and you’re not memorizing anything that isn’t generally applicable anyway.
Putting it into practice:
Meter the scene.
Dial in the exposure compensation from the list above.
Read the shutter speed listed:
- If the shutter speed is faster than the focal length, you’re good.
- If not you’re in shaky image country.
That’s it, no math, no multiplying, and no memorizing equivalent focal lengths.
For example, suppose you’re using an EOS-1D and have a 85 mm lens on it. Looking though the viewfinder and you see the metered shutter speed is 1/100. One click of negative exposure compensation, 1/3 Ev, and the camera meters 1/80 now. 1/80 is right on the line and I know from experience not quite enough for me to be comfortable assuming the image will be shake free.
As another example, suppose you’re using a 7D with a 24 mm lens and the meter is showing a 1/40 shutter speed. Since it’s an APS-C (1.5/1.6 crop) camera, dial in -2/3 Ev, or 2 clicks on the rear dial. The meter will show 1/25, which larger than 24, so you’re good shake wise.
The nicest part of this technique to me, though, is that it doesn’t require doing mental math or trying to memorize something that isn’t generally applicable (i.e. 35 mm equivalent focal lengths). Shutter speeds are something that you either can see in the viewfinder, or will eventually memorize simply though experience using and seeing them. Once you’re familiar with the shutter speed steps, it’s possible to check yourself without even adjusting the camera’s settings and do so intuitively.
Finally, this technique is applicable as long as you can translate a crop factor into fractional stops. For example, if you ever find yourself shooting medium format, you can take the rule with you, using +2/3 for 645-format (~1.6 x larger frame than 35 mm / FX digital) to the same effect.