do image stabilisers decrease image quality?

[Hillsilly]

Is there ever an advantage in turning IS off?  (Ignoring tripod mounted cameras and assuming a sufficently fast shutter speed for a sharp photo.)  I often see it stated that it results in sharper images, but my experiences have been inconclusive.  Any thoughts?

[Mt Spokane Photography]

Hi,
    IMHO, every element added will decrease IQ by a bit, so a lens without IS will have slightly better IQ than lens with IS (when both lens are from the same generation and same grade) under perfect shooting condition.

So you believe a lens with one element is sharpest?  Maybe one with no elements is the ultimate?

That would be so. Looking through a hollow tube will always give you the clearest sharpest image. You can not improve the light when it is in it's near perfect unrestricted form.

If you believe that, then why buy a lens?  You can get a sharp image without one?  Why don'y you start selling them, you can sell sharper lenses for just the cost of a roll of toilet paper.
Multiple lens elements do, in fact correct the various abberations that come from just one element.  Thats why the lenses that are sharpest have multiple elements.
Your theory seems pretty badly flawed when compared with the real world.

Exactly what do you think lenses do?
They take the pure raw light and the bend it, skew it, rearrange it then focus it.
Multiple elements correct the aberrations that the first few elements create. Multiple elements are used to put the light back in the arrangement it started with. It doesn't improve what is natural.
Without one element the light isn't flawed, it isn't until light hits the glass that it changes and bends and compresses.

Weixing is partially right, in that when it touches the first element something is lost. Every element it touches after it looses something, but the following elements are putting it back in the right order for focus. Put enough elements in a lens the light will never make it through.

Yes, something is lost, and it is light. 
But ...  does IQ get worse with each additional element, as he said?  If so, why not a 1 or a 2 element lens?  IQ should be much better than those 22 element lenses - less CA, sharper, less distortion, etc - Really ??  Where are those one or two element lenses with superior IQ, or for that matter, 5 element lenses?
Its a nice theory, but the best lenses with the best IQ have many elements, and they do lose light, but not all that much.  The 9 element 85mm f/1.8 has a Tstop of 2, so it loses 0.2 stops in the glass.  The 20 element 70-200mm f/4L IS has a Tstop of 4.6, so it loses 0.6 stops.  20 elements, and it has suburb IQ and sharpness! 
So, how many elements until you lose a stop?  Maybe 30 some elements?  Your worry that light won't make it thru a lens due to the number of elements seems a bit far fetched.

[Mr Bean]

My feeling is that IS would affect IQ as the lens or lenses in the IS unit are moved off center, to negate movement of the photographer. This process of moving the lenses off axis in the optical path would have been "allowed" in the design, but it'll be a case of "....the lesser of 2 evils".

[PackLight]

 
Yes, something is lost, and it is light. 
But ...  does IQ get worse with each additional element, as he said?  If so, why not a 1 or a 2 element lens?  IQ should be much better than those 22 element lenses - less CA, sharper, less distortion, etc - Really ??  Where are those one or two element lenses with superior IQ, or for that matter, 5 element lenses?
Its a nice theory, but the best lenses with the best IQ have many elements, and they do lose light, but not all that much.  The 9 element 85mm f/1.8 has a Tstop of 2, so it loses 0.2 stops in the glass.  The 20 element 70-200mm f/4L IS has a Tstop of 4.6, so it loses 0.6 stops.  20 elements, and it has suburb IQ and sharpness! 
So, how many elements until you lose a stop?  Maybe 30 some elements?  Your worry that light won't make it thru a lens due to the number of elements seems a bit far fetched.

It is more than just light lost, it is the quality of the light itself, how the light breaks down going through the lens.

It does get worse with each element, because each progressive element corrects one problem and adds another, or not depending. If the lens has 20 elements the last element corrects flaws made through one or more of the previous 19. It will never be perfect and each element takes away, even if it is slightly. There is more lost than just light and loosing a stop, that is why we look for other flaws in our IQ other than just sharpness or quantity of light. No doubt the L lenses deliver great IQ with multiple elements, but it doesn't change that fact that a bit of quality is lost with each element.

A single lens that produces an image with little or no flaw is possible. The human eye has only one lens. Glass and Crystal lenses abilities are flawed in comparison.

[Frodo]

"Its a nice theory, but the best lenses with the best IQ have many elements, and they do lose light, but not all that much.  The 9 element 85mm f/1.8 has a Tstop of 2, so it loses 0.2 stops in the glass.  The 20 element 70-200mm f/4L IS has a Tstop of 4.6, so it loses 0.6 stops.  20 elements, and it has suburb IQ and sharpness!  "

Not sure that's correct. The first thing is that just because a lens says "1.8" or "4" does not mean that it is 1.8 or 4 in an optical sense.  Just like 70mm on the 70-200mm is not actually 70.

Secondly, a 1.8 lens with a T-stop of 2 is a loss of 11%, whereas the f4 lines with a T-stop of 4.6 loses 15%.  A loss of a full f-stop represents a 40% difference between f number and T-number, so the first lens loses about 0.27 of an f-stop and the second about 0.37 of an f-stop.

But my nit-picking aside, in principle you are right, extra elements will absorb or reflect more light, reducing the light passing through the lens, just not as much as you suggest.  Others have commented on how extra elements can correct distortions and improve IQ.

[sanj]

Sanj, how could it do anything to IQ? It is a mechanical device outside of the row of elements in the lens, it is not optical.

The only way it would affect optics is if it doesn't work properly.

But really this thread is about a non issue. There is no IS vs non IS lens that Canon makes that would be equal, those that are close the IS version is superior to the Non IS version.

I don't know but am trying my best to understand!
I bought the X100 and asked the Fuji 'guys' about IS and this is what they said:

Hello Greg and Billy.
Great video, great camera! Mine will be with me end of this month...!!
Could you please educate me on one point:
Why is incorporating Stabilization into the camera a bad idea: Does it:
a) Increase costs?
b) Increase size?
c) Reduce quality?
Asking because I am sure ISO 400 results in better quality than ISO 3200 (which 4 stops stabilization would provide.)
I understand that u guys strongly believe that this camera does not require IS but my question is: HOW CAN IT HURT?
Sanjay Gupta 1 year ago
   Reply
A) Yes, B) Yes, C) Yes as the ability for customization of the lens to the sensor would not be possible (well at least cost effective). I believe in I.S. however not so much with a 35mm equivalent lens. Especially the quality of ISO settings up to 3200 and a fast lens should allow for decent shutterspeeds for most situation. Others, use a tripod, or enable the flash.

Fuji Guys - X100 Frequently Asked Questions	Small | Large

[PackLight]

But my nit-picking aside, in principle you are right, extra elements will absorb or reflect more light, reducing the light passing through the lens, just not as much as you suggest.  Others have commented on how extra elements can correct distortions and improve IQ.

I am not sure how much I suggested, I didn't put a quantity to it. Maybe the difference is small and slight but it is still there.

Extra elements do not improve the quality of the original light. They correct the flaws of the other lenses. The additional elements improve the IQ and flaws in the light that was created by other lenses. Just because a lens has 20 elements doesn't make it a superior lens by quantity only, it is a lens that took 20 elements to get the IQ back to a usable form.

The elements do more than absorb and reflect, it also breaks down the light. It alters the colors that you will get. When comparing lenses it is common to talk about chromatic aberrations, sharpness, color, distortion and flare. All these items have an impact on IQ, and I haven't seen a lens made yet that took 100% of these lens created aberrations out.

[mb66energy]

I think that there is no simple answer to your question. Trying to break it into different paths:

• IS itself: If well programmed and eqiupped with good actor hardware it will not blurr the image by wrong corrective movements
• IS uses additional lens elements in most stabilized lenses and needs sometimes additional lens groups in the rest of the optical path. The number of lens elements is increased. Optical calculation of such systems is very complex because the moveable lns element has to correct movements correctly and at the same time it has to keep IQ at a high level.
  This splits into to paths:
  
  • If the calculation of the lens is done very carefully, IQ will remain very good.
  • If the calculation is done less carefully or the price limit cuts into optimization quality, IQ will decrease.
• If you have a simple lens design movement of one lens element will give usable results, but I think extreme values of corrective movements will cut into IQ.
• If IS gives you 4 exposure steps, you have 16 times lower movements due to camera shake - if the IS element reduces resolution by a factor 1.2 you will gain roughly 12 times more sharpness in comparison to an unstabilized lens.
• Additional lens elements reduce the contrast of a lens - if you use the same measures to suppress reflections and light scattering on lenses and structural elements. But if you go from 13 lens groups w/o IS to 15 lens groups w/ IS this is a small difference (70-200 4.0 non IS vs. IS). If you go from 6 to 12 groups it might be another thing (5.6/400 vs. 2.8/400 ii).
  On the other hand additional lens elements improve IQ by correcting different aberrations if the calculation is done properly and if there is no strong price limit.

IMO there are applications of IS lenses: If a tripod isn't allowed/appropriate    and   low aperatures are essentially needed to gain enough DOF/the light is limited.
The new 4.0 24-70 IS lens might address these application fields. I think it is a good addition of the EF lens family ... if the quality is phenomenal and the street price will come into the region of the 24-105.

[sandymandy]

100mm 2.8L IS is one of the sharpest lenses out there i think Probably Is can degrade IQ by helping u in situations where without IS u would get motion blur but IS reduces it like 98% for example but not 100%. So thats when it perhaps could cause "worse IQ"

[sanj]

My feeling is that IS would affect IQ as the lens or lenses in the IS unit are moved off center, to negate movement of the photographer. This process of moving the lenses off axis in the optical path would have been "allowed" in the design, but it'll be a case of "....the lesser of 2 evils".

This makes a lot of sense to me!

[neuroanatomist]

A single lens that produces an image with little or no flaw is possible. The human eye has only one lens. Glass and Crystal lenses abilities are flawed in comparison.

It has one structure called a lens, true, but actually the eye can be considered to have at least 4 elements, perhaps better thought of as 4 groups, 3 groups with one element each and one group (the lens itself) comprising multiple elements.  The cornea actually does most of the refracting, but both the aqueous humour and vitreous humour have refractive indices that differ from the cornea and lens.  The lens itself has a refractive index that varies through the structure, and the action of the ciliary muscles changes the shape of the lens, which alters not only the shape of the lens surfaces, but also the differential thickness of the regions of different internal refractive indices.

So if we assume the eye is producing an image with little or no flaws, understand that it's far more complex than a single-element lens.

[PackLight]

A single lens that produces an image with little or no flaw is possible. The human eye has only one lens. Glass and Crystal lenses abilities are flawed in comparison.

It has one structure called a lens, true, but actually the eye can be considered to have at least 4 elements, perhaps better thought of as 4 groups, 3 groups with one element each and one group (the lens itself) comprising multiple elements.  The cornea actually does most of the refracting, but both the aqueous humour and vitreous humour have refractive indices that differ from the cornea and lens.  The lens itself has a refractive index that varies through the structure, and the action of the ciliary muscles changes the shape of the lens, which alters not only the shape of the lens surfaces, but also the differential thickness of the regions of different internal refractive indices.

So if we assume the eye is producing an image with little or no flaws, understand that it's far more complex than a single-element lens.

I would say it is more complex. Compared to Nikon its sensor has about 3x the dynamic range. I wonder how that would rate with DxO.

But I do have to admit it does have flaws, when I turned 50 I had to start using reading glasses. So I guess mine has a 5th element that I use for macro work.

[mb66energy]

A single lens that produces an image with little or no flaw is possible. The human eye has only one lens. Glass and Crystal lenses abilities are flawed in comparison.

It has one structure called a lens, true, but actually the eye can be considered to have at least 4 elements, perhaps better thought of as 4 groups, 3 groups with one element each and one group (the lens itself) comprising multiple elements.  The cornea actually does most of the refracting, but both the aqueous humour and vitreous humour have refractive indices that differ from the cornea and lens.  The lens itself has a refractive index that varies through the structure, and the action of the ciliary muscles changes the shape of the lens, which alters not only the shape of the lens surfaces, but also the differential thickness of the regions of different internal refractive indices.

So if we assume the eye is producing an image with little or no flaws, understand that it's far more complex than a single-element lens.

That's what I  thought as I read the comment, that the human eye is a single lens construction. I would prefer to see it as a 4 element - 1 group system but that might be a matter of taste.

There are two further reasons why the eye doesn't compare to photographic lenses:

• The eye has optimum quality only near the image center where the spatial resolution is maximal and  spherical aberration or CAs arent a problem. The image borders are optimized for faster "frame rates" and only B&W ...
• The brain corrects the raw data from the retina and adds fragments of detailed information from the image center (while scanning our surroundings) to give us the perception of a detailed larger picture with corrected perspective.
• EDIT: Image stabilized by coupling the eye to the vestibular system to keep the direction during slower motions + soft tissue between eyeball and bones to damp higher frequency motion.

[Mr Bean]

Regarding the title of the post:
I think people are getting a little caught up on the number of lens elements in the optical path, which is really a separate issue to how IS works (in Canon lenses at least). Yes, IQ is affected by the number of lenses in the path, but bear in mind that multiple lenses are used to correct multiple optical issues. If you didn't have those lenses, then spherical or CA (or other issues) would degrade the quality. Its a balance.

IS on the other hand, is done by moving an element or elements on and off axis. This is going to create aberrations such as astigmatism. The effect would be much greater in lenses that are fast, as the latitude for astigmatism would be much smaller.

As an example, for those who wear glasses, hold them an inch or 2 in front of your eyes and move them around. As you will see, the image moves accordingly. This is, in effect, the same approach as IS in a Canon lens. Pushing it further, while holding the glasses in front, move the glasses so you are looking through the outer edge, not the center. In some cases, the IQ will drop, and the image blurs. This is the extreme example of an off axis lens.

[Mt Spokane Photography]

 
Yes, something is lost, and it is light. 
But ...  does IQ get worse with each additional element, as he said?  If so, why not a 1 or a 2 element lens?  IQ should be much better than those 22 element lenses - less CA, sharper, less distortion, etc - Really ??  Where are those one or two element lenses with superior IQ, or for that matter, 5 element lenses?
Its a nice theory, but the best lenses with the best IQ have many elements, and they do lose light, but not all that much.  The 9 element 85mm f/1.8 has a Tstop of 2, so it loses 0.2 stops in the glass.  The 20 element 70-200mm f/4L IS has a Tstop of 4.6, so it loses 0.6 stops.  20 elements, and it has suburb IQ and sharpness! 
So, how many elements until you lose a stop?  Maybe 30 some elements?  Your worry that light won't make it thru a lens due to the number of elements seems a bit far fetched.

It is more than just light lost, it is the quality of the light itself, how the light breaks down going through the lens.

It does get worse with each element, because each progressive element corrects one problem and adds another, or not depending. If the lens has 20 elements the last element corrects flaws made through one or more of the previous 19. It will never be perfect and each element takes away, even if it is slightly. There is more lost than just light and loosing a stop, that is why we look for other flaws in our IQ other than just sharpness or quantity of light. No doubt the L lenses deliver great IQ with multiple elements, but it doesn't change that fact that a bit of quality is lost with each element.

A single lens that produces an image with little or no flaw is possible. The human eye has only one lens. Glass and Crystal lenses abilities are flawed in comparison.

I think your theory says it all.  A 20 element lens has lower IQ than a 10 or 7 or 3 or one element lens.
The only problem cones in the FACT that actual measurements disprove it.