# shutter speed 'rule of thumb' on digital

Discussion in 'Australia Photography' started by Bigpond, Sep 11, 2005.

1. ### BigpondGuest

The old rule of thumb of using a shutter speed of at least the same as the
lens focal length (ie using 1/200 sec for 200mm focal length) when hand
holding works well for 35mm (the exception being if you have an IS lens).
What happens in digital format? I.e if you have a 200mm lens on digital do
we still use a 1/200 shutter speed or do we have to apply the rule to the
effective focal length (given the cropping factor of 1.6) and use a shutter
speed of at least 1/320 sec?

Bigpond, Sep 11, 2005

2. ### POTD.com.auGuest

In terms of the old rule (ignoring individual skill levels and the use of IS
etc) yes you need to apply the x-factor.

POTD.com.au, Sep 11, 2005

3. ### RobGuest

Why its the same focal length lens?

rm

Rob, Sep 11, 2005
4. ### PoxyGuest

Not by the rule. If you have a 200mm lens on a a digital, it's effectively a
320mm lens (or whatever is relevant to the particular camera) and behaves as
such in terms of magnifying camera shake

Poxy, Sep 11, 2005
5. ### Justin ThymeGuest

Stopping perceptible hand movement is based on a typical amount of hand
movement and the field of view in the image, not on the actual focal length
of the lens.
To explain why this rule of thumb works for the 35mm equivalent length,
rather than the actual length, it's math time.
Let's assume that for acceptible sharpness, the camera has to move by less
than 1/1000th of the image size during the exposure (in reality it is an
even smaller amount, but this will do for the purpose of this example). With
a 50mm lens on 35mm, the field of view is 47degrees. So during the exposure,
the camera must move by less than .047 degrees to give acceptible sharpness.
The rule states that 1/50sec would be the longest exposure, so we can assume
that we have hand movement at a speed of 2.35degrees/sec. If we are using
the same 50mm lens on a 1.5x crop factor DSLR, the field of view is now only
32 degrees, so we need a hand movement of less than .032 degrees. The speed
of hand movement is still the same, so in order to have a fast enough
shutter to make the camera move by only .032 degrees during the time, we
need a shutter speed of 1/(2.35/.032) or approx 1/75sec. Since the 50mm lens
has an equivalent focal length of 75mm, we see that to get the same
sharpness, the shutter speed has also increased to 1/equivalent focal
length.
If the above still doesn't make sense to you, think of a digi-compact, that
typically has a real focal length of 4-12mm, with equivalent focal length of
35-105mm. If you think you can handhold at full zoom with a shutter speed of
1/10sec, you're dreaming. You actually find that 1/100sec is about the
limit, as predicted by the 35mm rule of thumb.
Of course some people are steady handed enough to go much slower than the
speeds predicted by the rule of thumb, and other people's hands are quite
shaky and need faster shutter speeds.

Justin Thyme, Sep 11, 2005
6. ### POTD.com.auGuest

With a 1.6x camera you have captured the image on a smaller sensor, this
means that it has to be enlarged more than an image captured with a FF
sensor/film to get to the same size print. This additional enlarging (1.6x)
also enlarges the blur due to camera shake and makes it more noticable, so
adopting a 1.6x FL guideline puts it on par with original 1x guideline.

POTD.com.au, Sep 11, 2005
7. ### RobGuest

So its Ok to hand hold my 6x17 90mm lens at 1/20th !

Rob, Sep 11, 2005
8. ### POTD.com.auGuest

That all depends on how large you intend to print it!

POTD.com.au, Sep 11, 2005
9. ### Bruce GrahamGuest

yes, if you want the same results as a 35mm handheld snap

Bruce Graham, Sep 11, 2005
10. ### Andrew WellerGuest

Hi Bigpond,

It is a rule of thumb so your mileage will vary depending on the circumstances.

If you are going to pixel-peep or print large prints you will want a really sharp image.

If you want a really sharp image, you're best to use some camera support anyways.

If they're just snap-shots, then you will care less.

If you're shooting fast moving subjects, it will depend on whether you want motion blur, panning etc.

The lens or camera may well have IS (Canon) or VR (Nikon) or any number of anti-shake technologies inside it - depending on what you are shooting, this may or may not help.

A direct translation of the rule of thumb would mean that you would take the equivalent field of view of the 35mm lens (assuming print sizes were all the same) - ie. for a 1/200s shutter speed the FOV from a 200mm focal length lens on a 35mm camera would be the same as the shorter 200mm/1.6 - a 125mm focal length. (this is because the field of view is the dimension mostly likely directly related to the blur induced by the camera shake). It depends on the distance to the subject, the context, etc., as to how noticeable the blur is in reality - hence this is a rule of thumb.

[which is the same as your interpretation essentially]

Other things affect how noticeable the blur is too - the lighting, the DOF, etc.

The anti-shake lenses, however can make a considerable difference - I often shoot in low light situations (music concerts etc.) and often shoot at 1/20s with a 200mm IS lens and get away with it about 1 time in 2.

This shot was taken at 24mm, f/2.8 1.0s, EOS 20D handheld (body propped against a post).

Rules of thumb need to be applied to your situation: the steadiness of your shooting, the smoothness of your shutter release action, your intended use of the image, the subject detail you want to keep, etc.

Ciao for now,
Andrew - who wonders why anyone would use a nick so like the BigPong ;-)

At last! Affordable Adventure Photography Tours.

Andrew Weller, Sep 21, 2005