IS = 3 stops?

I was looking at the 24-105L 4.0 IS that will be coming with my 6D as soon as I pull the trigger and order it. It says that the IS is the equivalent of 3 stops. Am I correct that 1 stop = .4 as far as aperture goes? If so then 3 stops would make it the same as a 2.8 without IS?

3 stops slower shutter speed hand held. From my experience I get 1-2 stops slower shutter speed, I think 3 is kind of generous.

Stops are a measurement of shutter speed as well as aperture say your shutter speed is 1/200 1/100 is a stop less, 1/50 is 2 stops, 1/25 would be 3 stops.

firemanchip wrote in post #17365434
I was looking at the 24-105L 4.0 IS that will be coming with my 6D as soon as I pull the trigger and order it. It says that the IS is the equivalent of 3 stops. Am I correct that 1 stop = .4 as far as aperture goes? If so then 3 stops would make it the same as a 2.8 without IS?

Aperture stops aren't linear as you suggest. They're actually logarithmic, with each step being 1.4x greater (or less) than the next. 3 stops from f/4 would be f/1.4. But what that 3 stops equivalent really means is that you can change the shutter speed to allow 3 stops more light through during the time the shutter is open, since you can't make the lens aperture 3 stops bigger. So instead of using an f/1.4 lens at a hand-holdable 1/60 sec., you'd be able to slow your shutter speed of your f/4 lens, used wide open, to around 1/8" without bad motion blur. That's if you can hand-hold reasonably steadily at 1/60 sec., and don't have other shake frequencies that might get in the way of that.

firemanchip wrote in post #17365434
I was looking at the 24-105L 4.0 IS that will be coming with my 6D as soon as I pull the trigger and order it. It says that the IS is the equivalent of 3 stops. Am I correct that 1 stop = .4 as far as aperture goes? If so then 3 stops would make it the same as a 2.8 without IS?

The three stops of IS refers to shutter speed, not aperture. Each doubling or halving of shutter speed is equal to one stop. Each stop doubles or halves the amount of light reaching the sensor. If for instance you are using the 24-105 on a full frame body the minimum suggested shutter speed when hand held is generally considered to be 1/focal length. On a crop frame body it would be 1/focal length x 1.6. If you are shooting at lets say 50mm, on a FF body your minimum suggested shutter speed would be 1/50 second and on a crop frame body it would be 1/80 second. IS helps you achieve sharp images, of static subjects only, at even slower shutter speeds hand held. One stop of IS at 50mm would allow you to get a sharp image at 1/25 second. Two stops at 1/13 second and three stops at 1/6 second. on a crop body using the minimum suggested 1/80 second, one stop would be 1/40 second, two stops would be 1/20 second and three would be 1/10 second. The 1/focal length starting point is somewhat arbitrary since some people can hold their cameras with far less movement then others at slower shutter speeds. And finally, the amount of IS specified for a specific lens is usually somewhat higher than can be achieved by most people. But, it has nothing to do with the aperture setting except that slowing the shutter speed allows light to pass through the aperture for a longer period of time.

firemanchip wrote in post #17365434
I was looking at the 24-105L 4.0 IS that will be coming with my 6D as soon as I pull the trigger and order it. It says that the IS is the equivalent of 3 stops. Am I correct that 1 stop = .4 as far as aperture goes? If so then 3 stops would make it the same as a 2.8 without IS?

- Aperture controls Depth of Field (DOF).
- IS has zero affect on Aperture - F2.8 is F2.8, F4 will never be F2.8 in terms of DoF just because the lens is stabilized
- IS is really about one thing in my opinion, and that is letting you handhold long focal length lens at lower shutter speeds
- this of course raises the question, with your 24-105 lens, when the lens is at 70 - 105, are you going to be taking pictures of things that aren't moving or are moving slowly that you can utilize slower shutter speeds
- since you are getting a 6D with a 24-105 all purpose lens, my guess is the answer to that is going to be yes - i.e. some walk about travel stuff (buildings don't move), portraits at 70 - 105mm at F4 and 1/30 SS, and walk about video (this is a great Full Frame all purpose video lens)

- since the general quoted formula of setting your minimum SS = 1/Focal Length and 1/105 (the longest of your 24-105) is either 1/100 SS or maybe 1/120 (lets assume this), then 3 Full Stops (which equals 3 doubling or halfings of light) equals (1/120 -> 1/60 -> 1/30 -> 1/15) - therefore, if the claim by Canon of the IS's ability on this lens is accurate, you can expect to be able to take a reasonable picture of a still subject at 1/15th SS when shooting at 105mm.

- if this claim is correct, then this is a very good thing because if the light was not great and 1/120th SS required 12,800 ISO to have good exposure (a very noisy ISO), then by moving the SS to 1/15th, you would be able drop the ISO from 12,800 to 6,400 to 3,200 to 1,600 - and at ISO 1600 and 1/15th or ISO 3,200 and 1/30th you are going to get a way better picture (less noise) than at ISO 12,800 and 1/120th SS which you would likely have needed to use with a non-IS lens

Not a good comparison but 3 is too good to be...
1 and a half to 2 sounds more real.

I actually decided to do a test with this lens (24-105L)

- I set the lens to 105mm
- I placed a bottle of skin cream 9 feet away
- the back of the bottle has lots of lines with very small type font on it
- with the IS in the OFF position, I set the SS to 1/125 on my 7D2
- the small font is not tack sharp (when fully zoomed in) at this SS but it is 'close'
- I then placed the IS in the ON position
- I then tried the same picture at 1/60, 1/30, 1/20, 1/15
- I would say that Canon's 3-Stop statement is mostly true but maybe not quite the Full 3-Stops but it is close
- For sure the picture at 1/20th was basically as sharp with IS ON as it was at 1/125 with IS OFF


I will also add that the IS enabled me to take a picture with an 'acceptable' ISO 2000 vs 10,000 (deliberate not great lighting indoors in a corner) and thus IS really provides real world benefits for the average person shooting in available lighting when indoors or at night.