IS and "stops"

[MDesigner]

Question: when the manual for my IS lens says that when IS is enabled, it approximately gains you 4 stops.. does that mean if I'm at f/5.6, turning on IS will approximate a shutter speed that would've been chosen for f/1.4?

 

[reg]

No - it lets you handhold LONGER, it doesn't make shutter speeds SHORTER. I think I have a little chart somewhere...

Edit: Well, NO, I don't. But I do have this:

As a result of the 3–4 stops slower shutter speeds allowed by IS, an image taken at 1/125 second speed with an ordinary lens could be taken at 1/15 or 1/8 second with an IS-equipped lens and produce almost the same quality. The sharpness obtainable at a given speed can increase dramatically.

 

[MDesigner]

Right.. I know it doesn't make the actual shutter speeds faster. What I mean is, when they say IS gains me 4 stops.. if I'm at f/5.6, does it shoot as if I were at f/1.4? And of course I don't mean DOF or any of that..

 

[reg]

No, it doesn't. It shoots as if you were at f/5.6, 1/8 second exposure, but had taken a Valium beforehand.

ALL it does, is make shots that would have been shaky and blurry before, crisp and clean.

But I don't need it to make me a taco, so I guess it does its job well.

 

[fredpb]

IS or VR does not change camera settings or "operation".

If you are shooting a low light subject, the lens corrects a certain amount of movng or vibration. That is the action of IS.

This elimination of some movement, like camera shake or unsteady hands at 1/10 second....without IS you would shake enough to lose sharpness or you may blur the picture. With IS the camera corrects the shake for a sharper picture.

The number of stops you get is iffy. The more you shake, the less "stops" you get. IS has it's limits.

You could say you would get the results of 1/250 for a picture when the camera speed is really 1/30th.

 

[MDesigner]

Hehe.. I think I'm failing to communicate clearly. And yeah..English is my first language

I fully understand IS doesn't change any of the operations such as shutter speed, aperture, etc. I know exactly how it works. The manual says it can gain you around 4 stops. I understand that's not REALLY adjusting your aperture.. it's a "simulated" gain of 4 stops. My question was.. what do they mean exactly by "4 stops"? If I'm shooting at ISO800 1/4" @ f/5.6, and I THEORETICALLY have a 4-stop gain.. then what exactly in my stats above (ISO800 1/4" @ f/5.6) has changed?? If someone tells you you just got +4 stops... what does that mean?

 

[elemental]

Hehe.. I think I'm failing to communicate clearly. And yeah..English is my first language

I fully understand IS doesn't change any of the operations such as shutter speed, aperture, etc. I know exactly how it works. The manual says it can gain you around 4 stops. I understand that's not REALLY adjusting your aperture.. it's a "simulated" gain of 4 stops. My question was.. what do they mean exactly by "4 stops"? If I'm shooting at ISO800 1/4" @ f/5.6, and I THEORETICALLY have a 4-stop gain.. then what exactly in my stats above (ISO800 1/4" @ f/5.6) has changed?? If someone tells you you just got +4 stops... what does that mean?

If I understand correctly, it means that it simulates the stability you would have with a four stop faster shutter speed, so your picture is as "stable" and sharp as a shot at 1/60. Think shutter speed, not aperture. Four stops seems like a pretty big gain, but then again the whole "rating by stops" thing is pretty gimmicky anyway.

 

[MDesigner]

There we go. That's the part I don't understand..actually, two big questions have been buzzing around in my head lately:

1) Why do people use the term "stop" to refer to either shutter speed, aperture, or exposure compensation? If someone says "bump it up by 2 stops," how the heck do I know what they're talking about?
2) What unit of measurement is a "stop"? If someone gives me a shutter speed like 1/200, and says "add 3 stops"... what is that exactly?

With apertures, I think I know the order of stops, for the most part.. f/1, 1.4, 2.8, 4, 5.6, 8, 11, 16, 22, 32, etc. So f/11 + 4 stops = f/2.8. But what about shutter speeds?

 

[ANDS!]

Hehe.. I think I'm failing to communicate clearly. And yeah..English is my first language

I fully understand IS doesn't change any of the operations such as shutter speed, aperture, etc. I know exactly how it works. The manual says it can gain you around 4 stops. I understand that's not REALLY adjusting your aperture.. it's a "simulated" gain of 4 stops. My question was.. what do they mean exactly by "4 stops"? If I'm shooting at ISO800 1/4" @ f/5.6, and I THEORETICALLY have a 4-stop gain.. then what exactly in my stats above (ISO800 1/4" @ f/5.6) has changed?? If someone tells you you just got +4 stops... what does that mean?

It's probably not even referring to aperture, but shutter speed. Stops are genernally reserved for aperture value, but they can also refer to shutter-speed values. Or they could be referring to both.

 

[MDesigner]

Here's a good example of what's confusing me:

From another thread..

You CAN leave the polariser on all the time, but it will (for an average CPL) cut off 1 stop of light, or halve your shutter speed (unless you're using flash).

What is "1 stop of light"?? -1EV? A 1-stop reduction in aperture? (going from f/5.6 to f/4)? I just don't get it..

 

[rob40wilson03]

I took the original post to mean: "what is the numerical value of a stop?" for example, is one stop equal to one sequential change in aperture value?

im afraid i dont have a great answer for it though

 

[kundalini]

It's a very confusing subject, so don't feel bad. Pick up the book Understanding Exposure and it will help a lot.

 

[MDesigner]

Thanks, kundalini. I'll definitely pick that up.

 

[BoblyBill]

The rule of thumb is if you have a lens zoomed to 300mm you should not have a shutter speed slower than 1/300 (i.e. 1/8 or something like that). Now a stop is an increment of exposure. Lets say that you have a 100-400L IS... With IS off, you could shoot a scene at 400mm with a 1/400 of a shutter speed with no camera shake hand held, but what they mean by four stop gain would be you could shoot all the way zoomed out with at 400mm and maintain a sharp result at 1/25 (four stops below 1/400) as a shutter speed. So on your lens whatever it is, you should be able to divide the max and minimum mm by 16 and that should be your slowest shutter you could hand hold a shot without camera shake.

 

[BoblyBill]

Wow... a lot has occured since I started my little explination...

A stop could mean:
a change in aperature
a change in shutter
a change in ISO

You have the aperature part down.
A one stop change in shutter is a double of the shutter speed... so 1/30 to 1/60 would be one stop difference.

A one stop change in ISO is a double of the ISO... So 100 to 200 ISO is one stop.

So if someone tells you to stop down by three stops lets say and you shot the picture with these settings: f/11 1/125 and 800 ISO. You could one change the aperature to f/4 or the shutter to 1/15 or the ISO to 100 OR you could change the apt to f/8 the shutter to 1/60 and the ISO to 400 to stop down 3 stops.