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Canon 1/Focal Length


pulsar69 10 1.6k 6 United Kingdom
24 Jan 2013 11:07AM
Has anyone ever come across software hacks or anything else that allows the altering of this age old equation in Canon cameras ? Or does anyone else think its time that this was added to the cameras as an option to change to 1.5 or 2 x focal length ? Is it really that difficult or do camera manufacturers want to hide behind it cloaking the performance of their cameras ?

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mikehit e2
5 7.1k 11 United Kingdom
24 Jan 2013 11:22AM
Are you talking about the 'crop factor'?
pulsar69 10 1.6k 6 United Kingdom
24 Jan 2013 11:32AM
No the 1 / what your lens is at setting ie if your shooting at 70mm the camera will presume 1/70 is fast enough for a good shot !
pulsar69 10 1.6k 6 United Kingdom
24 Jan 2013 11:32AM
Although crop factor does come into it aswell as the equation is somewhat out on a crop body so not sure if that is changed with a crop sensor ?
mikehit e2
5 7.1k 11 United Kingdom
24 Jan 2013 11:36AM
OK - its the supposed shutter speed limit of handheld shots. I am not sure what they would change in the software - what are you referring to in Canon cameras?
keithh e2
11 23.4k 33 Wallis And Futuna
24 Jan 2013 11:38AM
You are still shooting at 70mm regardless of the crop factor.
mikehit e2
5 7.1k 11 United Kingdom
24 Jan 2013 11:42AM

Quote:You are still shooting at 70mm regardless of the crop factor.

The logic goes that the handheld limit for a 70mmlens on 35mm camera is 1/focal length. If that same lens is put on a APS-C body and you take the same shot (same framing) and view at the same physical size, the APS-C image is being magnified 1.5 times more so any camera shake is more evident. So to get the same acceptably sharp shot, the shutter speed need to be faster: not 1/70 but 1/105.

To my mind, there are far too many vairables (conditions, technique, profusion of AF lenses etc) that make the formula increasingly redundant.
pulsar69 10 1.6k 6 United Kingdom
24 Jan 2013 11:43AM
I believe high end Nikons allow you to tweak this equation allowing for a sharper shot ... most often i find that while 1/focal is fine for a static object i dont photograph many static scenes , so rather than manual and shutter priority modes it would be a lot easier if there was a simple option to just jump to telling the camera i want it to double it to 1/2xfocal so i am more likely to get the sharp shot and be able to do it at speed , i just cant understand why such an option is not available even with a 5k 1Dx ?
keithh e2
11 23.4k 33 Wallis And Futuna
24 Jan 2013 11:44AM
Nope. 70mm is 70mm. The fact that you are only viewing a portion of the image produced by that lens is immaterial.
24 Jan 2013 11:51AM
I think the OP may have been referring to the equation Canon cameras seem to use when in auto-ISO mode. If so, then if the formula "Minimum Exposure time = 1/focal length" is right for 35mm cameras, then logic would dictate that it should be 1.6/focal length for APS-C. But it isn't.
mikehit e2
5 7.1k 11 United Kingdom
24 Jan 2013 11:57AM

Quote:Nope. 70mm is 70mm. The fact that you are only viewing a portion of the image produced by that lens is immaterial.


In my example, you are not looking at a 'portion of the image' - I was careful to give a situation where you take the same framing with 35mm and APS-C cameras
The formula is to give an image with acceptable sharpness. Do you disagree that the more you magnify an image, the more obvious camera shake becomes - as a simple example, images viewed in the LCD of your camera can look superbly sharp, but when viewed in the computer monitor look awful. The ame applies to sensor size.
pulsar69 10 1.6k 6 United Kingdom
24 Jan 2013 12:03PM
The crop factor issue is one that's always hotly debated as it seems easy to see it from many different angles, in reality if i stick a 24-105 on a 7d and a 5d2 and shoot the same scene at 70mm on both the resulting images will look as if they were shot at different focal lengths although the same. There are many different technicalities involved in that subject and that could turn into another thread Wink

I was really interested in peoples views on whether the 1/focal length foundation is really redundant know in this digital age with all the advances in iso capabity etc isn't it an option we should be able to configure ?
keithh e2
11 23.4k 33 Wallis And Futuna
24 Jan 2013 12:11PM
The maths doesn't change. What changes is your perception of it.
rhol2 e2
3 321 1 United Kingdom
24 Jan 2013 12:11PM

Quote:You are still shooting at 70mm regardless of the crop factor.
The logic goes that the handheld limit for a 70mmlens on 35mm camera is 1/focal length. If that same lens is put on a APS-C body and you take the same shot (same framing) and view at the same physical size, the APS-C image is being magnified 1.5 times more so any camera shake is more evident. So to get the same acceptably sharp shot, the shutter speed need to be faster: not 1/70 but 1/105.

To my mind, there are far too many vairables (conditions, technique, profusion of AF lenses etc) that make the formula increasingly redundant.



I agree on this one, why some people try to stick to the convention I'm not sure, in these days of improved High ISO performance ,which allows higher speeds.

Having said that, unless subject movement is an issue, IS can of course allow lower speeds

Not having IS available, I generally use the highest speed possible for the given circumtsances.. I would not trust a fully Auto mode to do this however.

Program Mode can be useful, though,with programme shift available to make quick adjustments of the sort mentioned above...
mikehit e2
5 7.1k 11 United Kingdom
24 Jan 2013 12:56PM

Quote:The maths doesn't change. What changes is your perception of it.


As far as I am aware, there are no maths. The 1/focal length rule is not a mathematically derived function but is a rule of thumb found by hard experience as a rough-and-ready measure. In that respect the rule is all about perception, not maths.
IME you still need very good technique to operate at 1/f.

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