Terminology question: Canon 100mm Macro lens

[Panchdara]

Looking thru the Canon 100mm F/2.8 IS USM instruction manual there is a paragraph under the features section: The Image Stabilizer provides the effect of having a "shutter speed about four stops faster" during normal shooting. (Based on [1/focal length] second). To prevent blur caused by camer shake.. shutter speed should be recipocal of current focal length (100mm I presume?) [1/focal length] or faster.

As a newbie, I am a little confused. I am thinking speed as in time when it comes to shutter speed and apature 'speed' when it comes to size of opening (and f-stops), but mot shutter speed in terms of "stops")??? Or am I just not seeing the forest thru the trees?

I hope this makes sense.

[digirebelva]

The "1/focal length] second" basically means that shutter speed should be equal to or greater then focal length...i.e. for the 100mm lense shutter speed should be 1/125 of faster to prevent camera shake from being seen in the image. Now the cavet..there is some disagreement on this as to whether or not it holds true but on a crop body camera with its 1.6 crop factor that lens effectively becomes 160mm. (no it doesnt magically make the lens have a greater reach) v/s it being an actal 100mm on a full frame body. So with that in mind then the rule may or may not be 1.6/focal length so shutter speed would need to be 1/250 or greater. My suggestion would be to test this theory yourself to determine what is acceptable to you..

[andys101]

Originally Posted by digirebelva

The "1/focal length] second" basically means that shutter speed should be equal to or greater then focal length...i.e. for the 100mm lense shutter speed should be 1/125 of faster to prevent camera shake from being seen in the image. Now the cavet..there is some disagreement on this as to whether or not it holds true but on a crop body camera with its 1.6 crop factor that lens effectively becomes 160mm. (no it doesnt magically make the lens have a greater reach) v/s it being an actal 100mm on a full frame body. So with that in mind then the rule may or may not be 1.6/focal length so shutter speed would need to be 1/250 or greater. My suggestion would be to test this theory yourself to determine what is acceptable to you..

Sorry, pardon??

[Elmo]

Due to the higher pixel density on reduced sensors I suggest the faster speed.

But back to the orig question. Both f-stop and shutter speed are directly related. so when you change either you adjust the exposure by the a Stop value. changing from f-4 to f-5.6 is one stop change. Likewise changing from 1/125 to 1/250 is also a change of 1 stop. (half as much light either way) So in the case of an IS lens it allows one to take a picture in an area with x-stops less light.

clearer or muddier??

[Panchdara]

Originally Posted by Elmo

So in the case of an IS lens it allows one to take a picture in an area with x-stops less light.

clearer or muddier??

Clearer me thinks...

Thanks all for your courteous responses... slowly, but surely this dead head will get around the practicalities of speed and stops and hopefully be a productive photographer.

Bestest

[LeeR]

I'm not sure anyone has answered your question in a simple way. What I beleive Canon is trying to tell you is that if you are shooting with a 100mm lens and you normally would not venture below 125th of a second to avoid camera shake, you will now be able to open up to an 8th of a second (four stops) and get the same results you used to get at 125th. That would be pretty impressive because I can't handhold a 50mm lens at that speed without getting camera shake. However, before you accept any paying jobs with your new lens I would be trying this for myself to see my results matched the hype.

[inkista]

One more try at clarification, with lots of numbers this time.

A stop is 1EV. A stop is a doubling/halving of the light, irrespective of which setting the light is coming from. Which means it's a way to equate your iso to your shutter speed to your aperture.

You have to think in powers of 2 (because of the doubling/halving).

-4EV = 2^-4 = 1/16x
-3EV = 2^-3 = 1/8x
-2EV = 2^-2 = 1/4x
-1EV = 2^-1 = 1/2x
0 EV = 2⁰ = 1x
+1EV = 2¹ = 2x
+2EV = 2² = 4x
+3EV = 2³ = 8x
+4EV = 2⁴ = 16x

With iso, you multiply the iso setting by the factor that corresponds to the stops you want to adjust.

To +1EV from iso 400, it's 2x400 = iso 800.
To +4EV from iso 400, it's 16x400 = iso 6400.
To -2EV from iso 400, it's 1/4x400 = iso 100

With shutter speed, it's the same deal.

To +1EV from 1/400s, it's 2x1/400s = 1/200s.
To +4EV from 1/400s, it's 16x1/400s = 1/25s
To -4EV from 1/400s, it's 1/16x1/400s = 1/6400s

So, Canon describes the effectiveness of any particular IS system in terms of stops of the shutter speed you gain (+EVs) over the 1/focal_length rule. Without stabilization, with a 100mm lens, you should be at 1/100s or faster by the rule. But with 2-stop stabilization, you only have to be at 1/100x4 => 1/25s. With 3-stop stabilization, it would be 1/12.5s. And with 4-stop stabilization, it's 1/6.25s. So they say.

You do want to take this number with a grain of salt, and realize that handholding does have a lower bound. It's not like a tripod, and at some point the numbers will refuse to go any lower. The marketing copy on my 24-105L says it has three-stop stabilization, but I can only reliably get two stops out of it, down to about 1/8 of a second, because my personal handholding boundary (without stabilization) is 1/30s.

And last, but not least:

With aperture, stops are not quite so power-of-two simple. This is because of two factors: the f-number of the aperture is a ratio that gives you the diameter of the aperture opening; and the light isn't proportional to the diameter of the opening, but to the area of the opening. Time to remember your gradeschool math.

Essentially, the f-number is the lens's focal length divided by the aperture diameter: focal_length/opening_diameter. The f in f/# stands for "focal length." If you're using a 50mm lens, set to f/2, then your aperture diameter is 50mm/2 = 25mm. But if you're using a 100mm lens, set to f/2, then your aperture diameter is 100mm/2 = 50mm.

This is why we use f-numbers for aperture, rather than the actual diameter measurement--those numbers (and the proportional amount of light we get from the aperture) stays constant across all focal lengths.

But. The light isn't directly proportional to the diameter of the opening. It's proportional to the AREA of the opening. Which is proportional to the square of the diameter (remember πr² from grade school?) So, what's actually doubling between the full-stop f-numbers is the square of the f-number (with all the numbers rounded off).

f/1 => 1
f/1.4 => 2
f/2 => 4
f/2.8 => 8
f/4 = > 16
f/5.6 => 32
f/8 => 64
f/11 = > 128
f 16 => 256

But because of the ratio, this scale is also going the other direction. The lower numbers mean wider openings and more light.

So, to go +1EV from f/8, you use f/5.6
To go -1EV from f/8, you use f/11.
To go +4EV from f/8, you use f/2.