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Author Topic: Does IS make bokeh busier/less smooth?  (Read 3818 times)

sunnyVan

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Does IS make bokeh busier/less smooth?
« on: July 09, 2013, 10:43:13 AM »
I realize it's unfair to compare the bokeh quality between 135L and 70-200 f4. Not until I got my 135L did I realize how busy the bokeh my tele zoom produces. My question is whether it is due to  the use of IS. I've heard someone mention that turning off IS on 70-200 2.8 would make the bokeh smoother so I would wonder about the same on my f4 IS. My preliminary conclusion is that the bokeh quality is the whole point of having a prime and it is irreplaceable by a tele zoom.
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Does IS make bokeh busier/less smooth?
« on: July 09, 2013, 10:43:13 AM »

Pi

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Re: Does IS make bokeh busier/less smooth?
« Reply #1 on: July 09, 2013, 11:13:54 AM »
It is mainly due to a different lens design. IS can change the image slightly but it cannot make your 70-200 like the 135, even both at f/4. Try it.

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Re: Does IS make bokeh busier/less smooth?
« Reply #2 on: July 09, 2013, 11:29:43 AM »
Bokeh is not affected by IS, it is determined by the lens design.  Typically, prime lenses will be better than zooms.

sunnyVan

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Re: Does IS make bokeh busier/less smooth?
« Reply #3 on: July 09, 2013, 11:36:53 AM »
It is mainly due to a different lens design. IS can change the image slightly but it cannot make your 70-200 like the 135, even both at f/4. Try it.

I'm not trying to make my tele produce the same bokeh as the 135L. If I could, there would be no place for the 135L in my bag. I'm trying to see if turning off IS would make the bokeh improve somewhat on my zoom. And if IS does have an impact on bokeh quality (a hypothesis), why bother having it if I consistently use at least 1/125 shutter speed?  And people say they want a new 135L with IS, if the hypothesis stands, wouldn't that mean the bokeh quality won't be the same as the original 135L?
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sunnyVan

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Re: Does IS make bokeh busier/less smooth?
« Reply #4 on: July 09, 2013, 11:41:03 AM »
Bokeh is not affected by IS, it is determined by the lens design.  Typically, prime lenses will be better than zooms.

I see. That's what I thought. Thanks.
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Re: Does IS make bokeh busier/less smooth?
« Reply #5 on: July 09, 2013, 11:51:03 AM »
I've seen some nasty "bokeh" out of the 70-200 f/2.8 IS II and 100L, but that is usually when the shutter speed is slow, so I do think that IS can make it worse under certain conditions.  The IS can only compensate at the targeted focal length, so objects at other distances may be moving more with IS than without it.  Good technique/keeping the camera/lens as still as possible seems to help because IS is not as active.  Longer exposures with wind-blown trees lead to a similar effect.  I don't recall encountering bad bokeh in good light (i.e. less than 1/1000s)

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Re: Does IS make bokeh busier/less smooth?
« Reply #6 on: July 09, 2013, 12:40:33 PM »
I think a good question in general is whether there is any change in IQ when the IS elements are shifted to compensate for motion.
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Re: Does IS make bokeh busier/less smooth?
« Reply #6 on: July 09, 2013, 12:40:33 PM »

sunnyVan

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Re: Does IS make bokeh busier/less smooth?
« Reply #7 on: July 09, 2013, 01:14:31 PM »
I think a good question in general is whether there is any change in IQ when the IS elements are shifted to compensate for motion.

It's a good question but different from the original one I asked.  In my case the primary subject looks perfectly sharp with IS on. The background under some circumstances would look a little nervous,  a little busy. 

If the IS helps make the subject sharp but I have to sacrifice the smoothness of the background,  I may want to turn IS off and use it very sparingly.  If IS doesn't really do anything to the background I could leave it on at all times. Ever since I have owned my tele I have never turned IS off.
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Re: Does IS make bokeh busier/less smooth?
« Reply #8 on: July 09, 2013, 01:23:32 PM »
Hmmm ... that's the first time I ever heard someone question the quality of bokeh with/without IS ... I'll have to test and see but I don't think IS has any bearing on bokeh.
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Re: Does IS make bokeh busier/less smooth?
« Reply #9 on: July 09, 2013, 01:36:06 PM »
The lens design with IS is a different, there is more glass and air the light has to travel through as with a prime so maybe that is a factor.
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Re: Does IS make bokeh busier/less smooth?
« Reply #10 on: July 09, 2013, 01:38:19 PM »
Talking about nasty bokeh:
The nastiest my equipment has to offer is the 70-200/2,8II with the TC 1,4.
Useful combination for outdoor sports, very good IQ in focus, but.....

No, IS does not have an effect on the bokeh.

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Re: Does IS make bokeh busier/less smooth?
« Reply #11 on: July 09, 2013, 03:09:36 PM »
True bokeh is the result of things being out of focus and is affected by lens design, aperture blade design, etc.

IS addresses blur caused by motion of the camera. It doesn't have anything to do with focus directly.

Not saying you're not seeing what you're seeing, just that it might be a case of the blur rather than the bokeh.
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Pi

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Re: Does IS make bokeh busier/less smooth?
« Reply #12 on: July 09, 2013, 03:14:34 PM »
I'm not trying to make my tele produce the same bokeh as the 135L. If I could, there would be no place for the 135L in my bag. I'm trying to see if turning off IS would make the bokeh improve somewhat on my zoom. And if IS does have an impact on bokeh quality (a hypothesis), why bother having it if I consistently use at least 1/125 shutter speed?  And people say they want a new 135L with IS, if the hypothesis stands, wouldn't that mean the bokeh quality won't be the same as the original 135L?

Well, try it, and let us know. I do not expect too much difference. On the other hand, a lens having IS would have a different design, and this might affect the bokeh visibly.

IMO, the main reason for not so great bokeh with some lenses is because they were optimized for sharpness. This includes some of the 70-200 lenses, the Sigma 35, and the 18-35, and maybe others. There is a well known and easy to google Zeiss document about bokeh and it explains how over- or under- corrected aberrations affect bokeh. 

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Re: Does IS make bokeh busier/less smooth?
« Reply #12 on: July 09, 2013, 03:14:34 PM »

sunnyVan

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Re: Does IS make bokeh busier/less smooth?
« Reply #13 on: July 09, 2013, 04:25:21 PM »
I'm not trying to make my tele produce the same bokeh as the 135L. If I could, there would be no place for the 135L in my bag. I'm trying to see if turning off IS would make the bokeh improve somewhat on my zoom. And if IS does have an impact on bokeh quality (a hypothesis), why bother having it if I consistently use at least 1/125 shutter speed?  And people say they want a new 135L with IS, if the hypothesis stands, wouldn't that mean the bokeh quality won't be the same as the original 135L?

Well, try it, and let us know. I do not expect too much difference. On the other hand, a lens having IS would have a different design, and this might affect the bokeh visibly.

IMO, the main reason for not so great bokeh with some lenses is because they were optimized for sharpness. This includes some of the 70-200 lenses, the Sigma 35, and the 18-35, and maybe others. There is a well known and easy to google Zeiss document about bokeh and it explains how over- or under- corrected aberrations affect bokeh.

Thanks for your input. I will definitely try. I don't expect very much difference either but for the sake of argument I'm going to try without IS for a week and see what I get. I'm open to experimentation. 

I threw the question out there because I thought it's been asked before and I thought there would be a ready answer. 

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Pi

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Re: Does IS make bokeh busier/less smooth?
« Reply #14 on: July 09, 2013, 08:07:16 PM »
I threw the question out there because I thought it's been asked before and I thought there would be a ready answer.

It is certainly and interesting question, especially whether IS would alter the design in a way that would change the bokeh visibly. Unfortunately, we will never now, since the battle now is to beat the competition when shooting charts. Every new version of a lens which does not have higher MTF numbers would be declared a failure by the Internet. And you can't argue with the Internet(s).  ;)
« Last Edit: July 09, 2013, 08:12:43 PM by Pi »

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Re: Does IS make bokeh busier/less smooth?
« Reply #14 on: July 09, 2013, 08:07:16 PM »