So, what is the reciprocal rule?
The reciprocal rule simply states that if you are shooting handheld then your shutter speed should be equal to or faster than 1 over your focal length.
So what does this mean?
If your focal length is 50mm then your shutter speed should be at least 1/50th of a second. Likewise if your focal length is 200mm then your shutter speed should be 1/200th of a second .
As you can see the wider/shorter the focal length, the lower you can set your shutter speed to without risking shake and reduction in sharpness…
…and the opposite is true for narrower focal lengths. So the narrower/longer the focal length the faster your shutter speed needs to be.
Don’t forget the crop factor. It’s important!
the rules above are easy enough on their own. For any camera that has a full frame sensor you can just use it directly and not need to worry about anything. But if you have a crop sensor(and pretty much every entry level DSLR will have one), then you need to remember something!
On a camera with a crop sensor the actual focal length is different to the lens that is attached. For example on a Canon EOS 200D/ Rebel SL2 the crop factor is 1.61. What this means is that any lens that is attached to that camera needs to have the focal length multiplied by 1.61.
The Crop factor example…
So lets continue with the example of the Canon 200D.
With a 50mm lens attached it is equivalent to having a focal length of 80.5mm ( 50mm*1.61= 80.5mm) .
So it is actually as if you have a 80mm lens.
This is why you may notice that if somebody with a full frame camera is shooting with the same lens as you they seem to get more in the frame than you if you are using a a camera with a crop sensor.
Sensor type: Full frame
Crop Factor: n/a
Lens: 50mm lens
Equivalent Focal Length : 50mm
Sensor type: Crop Sensor
Crop factor : 1.61
Lens: 50mm lens
Equivalent Focal Length: 80.5mm
The above example shows how the same lens DOES NOT result in the same focal length and look all the time.
How to use the reciprocal rule in action?
With photography you can’t just learn from reading. You need to learn by doing or seeing. So I’m going to give you an exercise to do with your DSLR.
1. First find out if your camera is a crop sensor or full frame.
2. Once you have done that then choose a lens to attach.
3. Now work out your equivalent focal length if it is a crop sensor camera.
We will assume you are using 50mm. But anything can work here.
4. Now work out the shutter speed value needed using the reciprocal rule.
So if it is a full frame you should have 1/50th of a second…
Now take a picture of some text in a book , not too close and not too far away. About an arms length will do.
Now take another picture with a shutter speed half as fast but from the same spot and distance. so if you used 1/50th of a second. Now use 1/25th of a second.
Just for good measure try one with a shutter speed faster than your original. e.g. if you used 1/50th try using 1/80th.
LOOK AT THE RESULTS. What did you see? Was there a difference?
It’s always important to put theory into practice because results can vary. Maybe you have steadier hands than the average individual.
Whatever the case I’m sure this tip will help you as as a useful benchmark for your shutter speed for hand held shots.
DON’T forget this…
remember that this rule is just a general rule as a guideline and works for still or slow moving objects. If you are only relying on this for your shutter speed selection you could be in trouble!
Think of this situation. You’ve got the minimum shutter speed value using the reciprocal rule and you’ve come to a speed of 1/80th…
…But your subject is a car moving at 30mph.
Clearly this is not going to work. your subject is simply moving too fast to be sharp and in focus.
In these situations if you want to freeze the subject in frame you will need a higher shutter speed. But if you are at the limits with available light, then you might drop your aperture to a wider f stop or bump your ISO up higher.
This would allow your camera to let more light in and still expose right while increasing the shutter speed. Or you could even use artificial light if you have access to that.
Although if you’re out on a bright sunny day you should be fine.
We hope this helps!
– PhotographyPursuits Team