[CarlJF]

I didn't noticed problems with af with non IS lenses. When I bought my 70-200mm f4L IS lens, I rented also for 3-4 days the non IS version of the lens. Both worked the same, the only difference being at low shutter speeds. With the IS version I could shot at 200mm and a shutter speed of 1/40s. With the non IS version I needed at least 1/125s to take a sharp image.

Also, when panning, the IS version allowed me to use shutter speeds of 1/25s, 1/40s.

I didn't noticed any lag regarding af when IS was on or off. At shutter speeds faster than 1/500s the IS seems to slow the af a little bit.

Thanks Dan. This is in line with what I heard from other shooters and what I explained above. Although on paper an optical IS could provide some benefits in AF performance, they aren't noticeable in real world usage.

So, to answer the OP question, the claim that optical IS "enhances the ability for precise focusing and exposure metering" is mostly marketing gimmick or some kind of myth propaged again and again on the internet. So, if someone buy an IS lens, they should do it because they want to be able to shoot at lower shutter speeds, not because it will improve the overall performance of their AF and exposure systems.

[Rondec]

I doubt there is much difference. There are some folks who say that with stabilized lens that the image the auto focus sensor sees is more stable and it will be more accurate. It might be true, but certainly it isn't a huge difference.

As far as hand holding 5 second shots with Olympus, my guess is that it is hit or miss. Depends on how stable you are naturally, how much you are supporting yourself and how much coffee you had to drink earlier in the evening. If I want that sort of exposure I'm going to bring a tripod along.

I also am not shooting in that shutter speed very often. I find that typically you either have better or worse light than that. If it is night time, shutter speeds are getting up to 10 to 30 seconds easily, while sunset you can typically do less than 1/10 second pretty easily and have good results.

[BrianR]

As far as hand holding 5 second shots with Olympus, my guess is that it is hit or miss. Depends on how stable you are naturally, how much you are supporting yourself and how much coffee you had to drink earlier in the evening. If I want that sort of exposure I'm going to bring a tripod along.

I also am not shooting in that shutter speed very often. I find that typically you either have better or worse light than that. If it is night time, shutter speeds are getting up to 10 to 30 seconds easily, while sunset you can typically do less than 1/10 second pretty easily and have good results.

Don't concentrate on the "5 seconds" claim concentrate on "in-body stabilization coupled with in-lens stabilization". From the looks of the Olympus reviews, it's a real improvement over their in-body stabilization on its own. If this let you extend your sunset hand holding a few more minutes, that's good isn't it? I'm not sure why there should be resistance to this as a Pentax option (outside of the unknown R&D costs and probable lens price/weight increases).

I still prefer a tripod and/or artificial lighting, but I wouldn't say no to more stabilization.

[Kunzite]

With apologies if I'm repeating what was already said.
I've seen this claim on DPReview, usually some Canon user bashing Pentax' SR, or some clueless "internet expert" proving that he doesn't know what a SLR is. What I didn't see is any sort of proof.

First, the only way for SR to impact precise focusing and exposure, given the SLR design, is by using processing power. Since both the PDAF system and the metering system are independent, and fixed in relation to the camera body - there is otherwise no difference if the camera has a SR system or not.
I'd say the (negative) impact is negligible, if any. After all, we've seen improvements in AF speed as Pentax started using the SR.

About the OIS helping significantly with the AF, if it was true we would have proof - Canon and Nikon users observing a decrease in AF speed just by turning the IS/VR off. Same lens, same camera: it would be trivial to test. We have no proof of a positive impact, at least in normal situations.
Note: I'm talking specifically about the AF speed, not about easier hand holding. And of course the example with the plane is about hand holding. In very low light, close to the working limit, I have to keep the camera very stable so it will lock on the target instead of hunting; this is an edge case where OIS might help. This is still about hand holding.
By the way, I briefly tried OIS with Pentax, and my K-5 didn't focus like a D4

As for metering: I don't buy it. Given the working range, and how the metering system has a much coarser resolution than the imager, I don't see why we would get gross errors attributable to camera shake.
Long exposures are a red herring in this case; the exposure system works down to -3EV regardless of which ISO (and corresponding aperture and shutter speed) you're using. No matter what you do, you cannot convince the metering system to take seconds for a reading.
The actual proof of an impact would be in weird inaccuracies happening only when hand holding, but not with the camera on the tripod. I never noticed the metering going crazy in low light.

---------- Post added 12-10-17 at 02:16 AM ----------

As for "Why VR is built into the lens", the answer is obvious: because Nikon (and Canon) introduced stabilization before digital, with their film SLRs. There simply wasn't any alternative to OIS: moving the film to correct camera shake was not a practical option.
When digital came, their choice was already made.

---

Last edited by Kunzite; 10-11-2017 at 04:17 PM.

[Dan Rentea]

Thanks Dan. This is in line with what I heard from other shooters and what I explained above. Although on paper an optical IS could provide some benefits in AF performance, they aren't noticeable in real world usage.

So, to answer the OP question, the claim that optical IS "enhances the ability for precise focusing and exposure metering" is mostly marketing gimmick or some kind of myth propaged again and again on the internet. So, if someone buy an IS lens, they should do it because they want to be able to shoot at lower shutter speeds, not because it will improve the overall performance of their AF and exposure systems.

I took a few test shots this morning with the IS on and off. I've shot from my balcony an old lady who was walking on the alley. The shutter speed was 1/250s, which is a safe shutter speed at 200mm. To make the test more interested, I asked my wife to take the camera and to turn on and off the IS without telling me. Practically, I didn't knew when I was shooting the old lady if the IS was on or off. I really didn't noticed any difference regarding af speed.

Yes, with tele lenses and fast shutter speeds the IS slows down a little the af speed, but with lenses up to 300mm and shutter speeds up to 1/500s, I doubt that the IS has a notable impact on af speed/precision.

[TheOneAndOnlyJH]

Take a long lens, 300mm or more. Set the focusing on a the central point only. And set the exposure in the spot mode. Look for an airplane above you, high in the sky, at great distance, in the day time, when the sky is blue. Take your Pentax camera, set the focal lenght at max, and take a number of shots of the plane. Maybe you will not see the differences in the very first shots. But after ten or less, you will notice that Pentax beggins to lose the exposure. and sometimes, the focus. In reality, the camera will keep the exposure and focus correctly, but your hands will betray you, and you will lose that small object which give the right exposure and focus, And if you dare to repet this test with a good stabilized lens from Canon or Nikon, anybody will see the truth with his own eyes.

About the OIS helping significantly with the AF, if it was true we would have proof - Canon and Nikon users observing a decrease in AF speed just by turning the IS/VR off. Same lens, same camera: it would be trivial to test. We have no proof of a positive impact, at least in normal situations. Note: I'm talking specifically about the AF speed, not about easier hand holding. And of course the example with the plane is about hand holding.

I'd say hand held is the only way OIS could potentially make a difference in AF speed. If the camera is not moving (tripod) then no lens elements move and there would be no difference between OIS or IBIS. In that case the hand held plane example is relevant, but if you can't track it while hand-holding a Pentax I don't think OIS will be enough to keep the center point on it either. Even if you are good enough to keep the center point on a tiny plane that's so far away that the AF can't keep track of it without OIS... I'd say that's a niche use not relevant to most photographers, and the image probably would be so small you won't see any detail.

I could see OIS possibly being beneficial for multi AF point tracking though. (Possibly, not certainly - I'd be interested to hear if anyone does test this.)

...I really didn't noticed any difference regarding af speed.

Yes, with tele lenses and fast shutter speeds the IS slows down a little the af speed, but with lenses up to 300mm and shutter speeds up to 1/500s, I doubt that the IS has a notable impact on af speed/precision.

Could you elaborate on that further? Does it really slow it down on long lenses / fast shutter speeds? I don't see why fast shutter speeds would affect anything since you should be focused before the shutter even actuates. Does OIS have to stabilize before it focuses? (IBIS has to stabilize too, but from what I remember it stabilizes on startup and is ready to go whenever the power is on.)

[dtmateojr]

IBIS does affect focusing to some extent. Had this issue with my K5. The focus issues happen at higher shutter speeds between 125-320. Possibly because IBIS kicks in when it is not needed. Much like having IBIS turned on when you are on a tripod and the image becomes blurry.

Edit: lens is sigma 17-70

[Kunzite]

I'd say hand held is the only way OIS could potentially make a difference in AF speed. If the camera is not moving (tripod) then no lens elements move and there would be no difference between OIS or IBIS.

That's not what I'm saying - I'm simply differentiating the claimed impact on speed from the basic inability to track the subject. But, of course, it's all while hand holding.
For example, JimmyDranox was talking about tracking the subject using the center AF point and spot metering. Obviously, if you can't keep the AF point on the subject, you're not measuring the AF speed - as the AF won't work (it will try to focus on the sky).
The inability to track the subject using the center AF point and spot metering doesn't exactly depend on the light level anyway.

---------- Post added 13-10-17 at 02:51 AM ----------

IBIS does affect focusing to some extent. Had this issue with my K5. The focus issues happen at higher shutter speeds between 125-320. Possibly because IBIS kicks in when it is not needed. Much like having IBIS turned on when you are on a tripod and the image becomes blurry.

Doesn't sound like a focus issue. SR kicking in when it is not needed won't change the focus at all.

[TheOneAndOnlyJH]

I think we're both trying to make basically the same point.

[Dan Rentea]

Could you elaborate on that further? Does it really slow it down on long lenses / fast shutter speeds? I don't see why fast shutter speeds would affect anything since you should be focused before the shutter even actuates. Does OIS have to stabilize before it focuses? (IBIS has to stabilize too, but from what I remember it stabilizes on startup and is ready to go whenever the power is on.)

Here is what a former Nikon ambassador say regarding fast shutter speeds an Image stabilisation turned ON. I hope I translated right.

"1. Do not leave stabilization on when shooting in good light and the shutter speed is 1/500 - 1/800 or faster. Since the operating frequency of the opto-mechanical system is 500 Hz, exceeding the time of 1/500 s will lead to erroneous results of the stabilization system. It is written in the manual without explaining the cause.

2. Do not shoot faster bursts of 5-6 frames / second with stabilization turned ON. Cause - At the first trigger of the camera, the camera starts to produce vibrations, the Image stabilisation tries to compensate those vibrations, but until it finishes, the camera performs a second trigger, producing other vibrations, and the IS needs to do the compensation calculation again. In the meantime, the camera performs another trigger again ... and so on."

What he wants to say on point 2 from above is that by turning OFF the image stabilisation when you use fast shutter speeds, you get rid of the inability of the image stabilisation system to keep up with the the succession of vibration waves induced by the camera when you shoot in a burst.

[Kunzite]

I think we're both trying to make basically the same point.

That was my point

[Fogel70]

The guy who wrote this article needs some lessons regarding tracking. Or he should visit Grant Artkinson Youtube channel.

I quote from the article from the link you posted "The downside of Single point selection is that if you or your subject moves, even in AI Servo, the camera will likely lose focus. The AF system does no tracking in these modes so its best suited for static subjects or ones with complex 3d surfaces." I used Canon 6D for more than 2 years, I now use a 5D Mark IV and I'm telling you that what this guy said it's far from being true. And I have tons of images to back up my comments, but it's not a topic dedicated to Canon tracking.


---------- Post added 10-11-17 at 04:43 PM ----------

I believe the guy tries to explain the distinction between continuous AF and tracking AF.

Continuous AF tries to keep focus on the the the selected point(s) without any further function trying to keep track of the object in focus. With continuous AF it up to the photographer to track the subject.
While tracking AF use more information of the subject to keep tracking it. FI trying to calculate the size of the subject, the motion of the subject in the VF and maybe even the color of the subject.

Mirrorless cameras may have even more advanced functions for tracking. FI tracking eyes of an model.

I like Oly colors and also the lenses. But the smaller sensor and the EVF makes me skip Oly as a travel camera.

[Dan Rentea]

I believe the guy tries to explain the distinction between continuous AF and tracking AF.

Continuous AF tries to keep focus on the the the selected point(s) without any further function trying to keep track of the object in focus. With continuous AF it up to the photographer to track the subject.
While tracking AF use more information of the subject to keep tracking it. FI trying to calculate the size of the subject, the motion of the subject in the VF and maybe even the color of the subject.

Mirrorless cameras may have even more advanced functions for tracking. FI tracking eyes of an model.

Let's first clarify a few things regarding Ai Servo (AF-C).
1. With only one AF point enabled (spot or single point AF), the camera will focus only where you place the AF point and from there you have to pan or track the moving subject to keep the af on the subject.
2. When you pan or track the moving subject and you have multiple AF points enabled, the focus point can move from one AF point to another in order to keep the subject in focus. But you still have to pan or track the moving subject to keep it in the frame.
3. The EOS iTR (Intelligent Tracking and Recognition) becomes active when you select all 65 point Automatic Selection (or whatever af points has each camera that have EOS iTR). When iTR is enabled you have the option to place the designated starting point over the subject in order to activate the af. The iTR will track the subject as long as you manage to keep any of the 65 AF points on the subject. Automatic point selection is based on sharpness information, color information and face detection information. When it's disabled, only sharpness information is used for af points auto selection. Yes, if you manually select a single af point, then the iTR is disabled. But, like the 3D tracking from Nikon, iTR is best to use it in some situations. Let me give you an example. Let's say we want to photograph horses running on a field. If we have 2 horses that looks the same, camera can get cunfused when you use iTR because the horses color is the same, the faces look the same, etc.

I've talked to a lot of wildlife photographers and 90% of them doesn't use EOS iTR for this type of shooting. They even told me that it slows down a little the af performance. Most of them are using either single point af or the expanded af (1 point with 4 or 8 surroundings) to track birds or animals. EOS iTR is more suited to track athletes or a bride...

[beholder3]

Whatever it is called:

1. "AF-C" just means continuous automatic adjustments of focus plane (distance = z-axis). This is the actual autofocus part
2. "Tracking" means automated framing helper (x-/y-axis) when the photographer is unable to point the camera properly where he should. This is mostly a primitve image recognition topic that switches active AF points when the automated helper thinks the photographer has not kept the subject under the chosen focus point.
3. Beyond these software helpers only Samsung ventured so far. Obviously the high art of image recognition is to step from the "where has the subject wandered" up to the "has the subject done something that is worth triggering the shutter" automation. The NX1 was able to recognize the right moment and then fire the shutter all by itself for a predefined scenario (baseball batting).
   Super primitive versions of this have been around as "smile detection" on cameras, which fired once a person smiled.

[Hidrieus]

I want to thank all for their good will to elaborate and especially Dan Rentea for taking time to experiment also.