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Canon 1/Focal Length


Sooty_1 4 1.3k 203 United Kingdom
24 Jan 2013 1:17PM
It's only a guideline. Some can handhold slower, some can't. And it depends on many variables .... Focal length, subject, steadiness, if your using a support and so on.

Treat it as a guideline rather than gospel.

Nick

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pulsar69 10 1.6k 6 United Kingdom
24 Jan 2013 1:21PM
We are not talking about photographic guidelines to which most of us are aware, we are talking about the inbuilt formula of Canons cameras which works out the shutter speed required for a shot bu using the 1/focal length assumption derived from older 35mm days ..
blastedkane 9 66 2
24 Jan 2013 1:23PM
I think I sort of agree, the rule is a "rule of thumb" so it may be a guide, but that means that it may not be appropriate for everyone.

If I am right the OP was referring to the traditional view of best shutter speed to focal length (and physical size) of the lens and if this is the case then the best thing to do would look at shooting in TV (Shutter Priority) and allow the camera to determing aperture (unless you want to go completely over to manual).

You can then see what your personal best SS is (i beliseve that we all have a slightly different Shutter Speed that we can hand hold to). Jut put yout lens on the camera and then hand hold and shoot a series of frames from 1/30 to 1/500 in 1 stop intervals (1/30 1/60/ 1/125 1/250 1/500) allowing the aperture and the iso to automatically adjust. Once all images have been taken then import to the computer and look at some of the small details to see where there is no camera shake. THis would be your optimum SS for that lens. then repeat with any other lens.
mikehit e2
5 7.1k 11 United Kingdom
24 Jan 2013 1:30PM
As you see above, some people disagree that the 1/f does not need to be changed for APS-C.
I would bet that most people most of the time cannot get a sharp photo at 1/f.

According to this article, the in-camera auto-ISO calculation on the 7D uses a minimum shutter speed of 1/2xf so in fact it is 'playing safe' with regards shutter speed
http://www.dpreview.com/articles/0206161199/an-in-depth-discussion-of-m-auto-iso-for-canon-slrs
pulsar69 10 1.6k 6 United Kingdom
24 Jan 2013 1:45PM
thats a good article actually a lot of useful explanations in it
keithh e2
11 23.4k 33 Wallis And Futuna
24 Jan 2013 2:21PM
I was referring to the maths pertaining to focal lengths not how low can you go maths.
mikehit e2
5 7.1k 11 United Kingdom
24 Jan 2013 2:34PM
And the maths are driven by the perception of how sharp the photo looks. And given that perceived sharpness is dependent on image size, magnification (which istelf is dependent on sensor size) and viewing distance the formula will change if any one of those changes.
keithh e2
11 23.4k 33 Wallis And Futuna
24 Jan 2013 7:03PM
The focal length of a lens does not change regardless of the sensor it is put in front of.
pulsar69 10 1.6k 6 United Kingdom
25 Jan 2013 12:01AM
No it doesn't correct , but does how much that lens moves in correlation to the size of the sensor behind it matter ? Human hand held speeds are limited and a smaller area with which to work within creates more movement outside of it ?
keithh e2
11 23.4k 33 Wallis And Futuna
25 Jan 2013 6:38AM
The movement is the same. If I move my finger in front of a sheet of A3 paper and then a sheet of A4, the movement is the same.
25 Jan 2013 8:45AM
The maths actually supports the perception, if you use it to answer the right question.

If you use a 70 mm lens on full-frame and APS-C, your hand-shake produces the same movement of the image at the sensor (like keithh’s finger over the A3 or A4 page). But since you’re magnifying the APS-C image by about 1.5 × more to get your final displayed photo, any shake is that much more obvious. To reduce the blur caused by shake to the same acceptable level, you’d need to use a faster shutter speed on APS-C.

But, and it’s a big but: the above comparison is not one that photographers are concerned with. If you use a 70 mm lens on full-frame, the only sensible comparison on APS-C is a lens that would take a similar photo, i.e. one of about 45 mm. Using a 45 mm lens on APS-C gives the same photo as 70 mm on full-frame.

And when you compare 45 mm on APS-C to 70 mm on full-frame, it turns out you need the same shutter speed for the same standard of acceptable sharpness. The 70 mm lens on full-frame produces 1.5 × more hand-shake blur at the image on the sensor, but that’s exactly cancelled out by the 1.5 × greater magnification of the APS-C image at printing (or viewing on a display, etc.).

So the rule of thumb (1/focal length) applies to equivalent focal lengths, not the actual focal length.

Of course it is just a rule of thumb, not a law of physics. It’s very possible someone could consistently shoot at 1/50th with a 50 mm lens even on APS-C. But that just means they could also shoot 1/50th with a 75 mm lens on full-frame.
mikehit e2
5 7.1k 11 United Kingdom
25 Jan 2013 8:57AM
Not doubting that at all Keith. And no-one is saying that the focal length changes.
But to take your pape example: Movement over A4 sheet gives a blur of 1mm. Movement over A3 sheet gives a blur of 1mm. Expand both images to A2: movement over A4 sheet now gives a blur of 3mm, movement over A3 sheet now gives a blur of 1.5mm.
In other words, the amount of blur (camerashake) is dependent on final magnification.
mikehit e2
5 7.1k 11 United Kingdom
25 Jan 2013 8:58AM
Samuel beat me to it.


Quote:If you use a 70 mm lens on full-frame, the only sensible comparison on APS-C is a lens that would take a similar photo, i.e. one of about 45 mm. Using a 45 mm lens on APS-C gives the same photo as 70 mm on full-frame.

Only applies if you do not change position - for example you have a 100mm macro in your kit bag you will vary position to get a full frame image. Again, the conditions are crucial.
25 Jan 2013 12:40PM
Yes, if for some reason you must use the same focal length on full-frame and APS-C, then you’ll have to use a faster shutter speed on APS-C.

But that’s not strictly comparing like with like. By moving your position you change the photo (unless the subject is a two-dimensional thing perpendicular to the lens axis, like a map on a copy stand). And the 100 mm macro on APS-C has a narrower angle of view than the same lens on full-frame, which is why the safe shutter speed changes.

In fact, true focal length is a red herring. Our real concern is angle of view, and how that compares to the change of angle caused by our shaking hands. As soon as the ratio of the shake angle to the picture angle reaches some threshold, the shake becomes noticeable in the final photo. Naturally, if the lens has a narrower angle of view, our hand-shake – which remains the same – becomes more noticeable.

It’s just a happy coincidence that many photographers have found 1/(full-frame equivalent focal length in mm) to be a minimum safe shutter speed. And the persistence of the 135-format for a century has attuned us to thinking about angle of view in terms of 135-format focal lengths rather than degrees.

This becomes especially obvious with compact cameras. I have a Ricoh with a 6 mm lens (28 mm full-frame equivalent). I can’t hold it at 1/6th of a second without image stabilisation. I can safely hold it around 1/30th.

•••

Back to pulsar69’s original question for a moment. Adding the option to vary this rule of thumb in the camera’s firmware would be a trivial job for Canon (or Nikon, etc.). But for some reason, these tremendously conservative engineering-led behemoths cannot bring themselves to inject such thought and cleverness into their cameras, or to open up the firmware for third-party development. I put it down to lack of real competition.

Alternatively, you could argue that adding features like this would add complexity, and complexity would reduce the usefulness of the camera to the average user, even if it helps pulsar69 in this case. But since Canon and Nikon have merrily added nearly useless features to their cameras for years, with no identifiable concern for the resulting complexity, I wouldn’t believe such an excuse if either of them brought it up as a reason to withhold programmable safe shutter speeds.
pulsar69 10 1.6k 6 United Kingdom
26 Jan 2013 9:19AM

Quote:
Alternatively, you could argue that adding features like this would add complexity, and complexity would reduce the usefulness of the camera to the average user, even if it helps pulsar69 in this case. But since Canon and Nikon have merrily added nearly useless features to their cameras for years, with no identifiable concern for the resulting complexity, I wouldn’t believe such an excuse if either of them brought it up as a reason to withhold programmable safe shutter speeds.



Or maybe you could argue that to remove this age old and redundant formula would force manufacturers to be less frugal with their claims of how great their cameras are , ie auto iso to 51200 etc is not really that if its calculated on a shutter speed thats useless and needs doubling for a sharp shot - that in my mind is where the issue lies - a bit like the new car you drive that does some theoretical 70mpg that you can never reach unless dropped from a plane Wink

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