# IS in prime lenses.



## CJRodgers (Jan 28, 2011)

Hello, 

Im stills saving for my 5dkmii (or mkiii if its on the horizon when i can afford it) and looking at lenses whilst i save. Im will be shooting a fair amount of video with it so i have a few questions about the IS in the lenses. 

For a start how much of a difference does it make? 

Also why isn't there IS in the shorter primes such as the 24mm 1.4, 50mm 1.2 and 85 1.2?. These are three lenses on my short list ( i could only afford one to start with), however are they no good for video without IS? Any one with experience shedding light on this for me would be much appreciated.

Craig


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## NormanBates (Jan 28, 2011)

IS does help, but it is not always essential

it helps most on long lenses: with my t2i, even with a (cheap) shoulder support, I can't take consistently stationary footage with a 90mm; if my lens had IS, the footage would be fine

with a 35mm, the shoulder support is enough, I would only need IS if I wanted to go totally handheld

in any case, it would always be more steady if I could use a tripod, but that's not always an option


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## Leisersan (Jan 28, 2011)

Short lenses generally don't need IS. Long lenses amplify motion, while short lenses minimize it. Try attaching a zoom lens to a camera with live view, and look at the way your hand shakes at the short and long end of the lens.


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## CJRodgers (Jan 28, 2011)

Thanks, yea that make sense. Ill just try keep a bit of money aside for a shoulder rig to hold it then. Dont want to be totally hand held when trying to shoot at low fstops as i can imagine focusing is hard enough without wobbling about too!


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## kubelik (Jan 28, 2011)

CJRodgers said:


> Also why isn't there IS in the shorter primes such as the 24mm 1.4, 50mm 1.2 and 85 1.2?. These are three lenses on my short list ( i could only afford one to start with), however are they no good for video without IS? Any one with experience shedding light on this for me would be much appreciated.



a lot of this is also about diminishing returns.

let's pretend you're shooting in poor light with the Canon 24mm f/1.4 L II, and the 100mm f/2.8 L IS Macro.

without IS turned on in the macro lens, your fastest realistic shot you can grab is at f/2.8, 1/100s. the equivalent shot on the 24mm f/1.4 L II, wide open, is at f/1.4, 1/400s. the 24mm can comfortably go down to 1/24s, at which point you are gathering 4 times the amount of light that the 100 f/2.8 L IS Macro is gathering. thus, the macro lens needs the 4-stop IS to get to the same level of functionality.

adding IS to wide-angle primes would be like M&Ms on your froyo ... it'd be great, but it's not necessary. do you want to pay for the increased cost and weight, when it's already doing what you need it to do? that's the question. and it seems like Canon has determined not enough people are willing to pay the premium for the extra bit of utility


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## Lawliet (Jan 28, 2011)

CJRodgers said:


> Also why isn't there IS in the shorter primes such as the 24mm 1.4, 50mm 1.2 and 85 1.2?.



IS is deliberate decentering, thus introducing the common optical errors as well as artifacts due to the interaction of rays from far of the optical axis and the three dimensional structure of photodiodes. 
Its a trade off between trouble in lens design and the few use cases that would really profit from it. 
For example the moving picture: the IS could dampen x and y motion, but to deal with DOF-shift due to swaying you want a steadycam rig anyways. And if you circumvent this by stopping down you could use an available lens in the first place.
Or for still images: High usable sensitivities, a superclamp with the right stud - one helps to freeze subjects in motion, the other keeps the camera stable enough to actually use the lens wide open.

Granted, a 24-70/2,8IS would be nice, but with very fast lenses you have a weakest link the IS can't deal with.


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## Rocky (Jan 28, 2011)

kubelik said:


> CJRodgers said:
> 
> 
> > Also why isn't there IS in the shorter primes such as the 24mm 1.4, 50mm 1.2 and 85 1.2?. These are three lenses on my short list ( i could only afford one to start with), however are they no good for video without IS? Any one with experience shedding light on this for me would be much appreciated.
> ...


It is always nice to have IS on ANY lens, if it does not degrade the optical performance. There are times that your 24mm is too wide and you need the depth of field. So you may be forced to use your 50mm or even 100mm and stop down to f5.6 or even f8. Under that situation, you will really wish that they have IS.
I can thinks of the following reason why there is no IS on the prime lens shorter than 100mm:
1. To keep the size and weight minimal. That is important for most of the prime lens user.
2. To avoid degrading of the optical performance. The IS will need at least 2 additional Glass(or plastic) wedge in the optical path. This is degrade the optical performance.
3. Design problem. It is already hard enough to design a good short focal length lens due to the distance between the lens mount and the film (sensor) plate to allow mirror movement. Adding the IS optical elements will make it even tougher.


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