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Olympus OM-D E-M1 The first Micro Four Thirds camera that offers phase detect focusing so you can use Four Thirds DSLR lenses normally as well a Micro Four Thirds lenses.

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Old 4th April 2016
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Using C-AF with moving subjects

I've followed the posts on this forum concerning the disappointing success rate when C-AF (and other moving objects) for ages before actually trying it for myself.

Having recently attempted to use C-AF + SeqH (with a 3 x 3 focus box) seriously I tried to analyse my results:

It seems that C-AF works just as it says on the tin but:...
....(my) expectations of this function are unrealistic.

When I reviewed shots taken with C-AF + SeqH from the EXIF data it is apparent that once the C-AF has acquired 'focus lock' it uses the same initially selected focus point for the entire sequence of images.
This means that, when using a long telephoto lens, if the subject occupies only a small area of the total scene shown in the EVF - as is the case with distant BIF - then unless your panning skills are really good, whenever the subject moves off the AF point which was auto-selected at sequence start the image is likely to be OOF.
In reality this is partially mitigated for distant BIF because the depth of field will be reasonably large.

Since the E-M1 in C-AF SeqH mode uses only 37 widely-spaced PDAF points, the probability of a fast moving, distant subject staying on the same selected AF point throughout a sequence is quite low. Hence the disappointing success rate.

Given the above it would seem that what is needed for good results is not merely many more active focus points but actually for a feature more akin to C-AF+TRACK working in SeqH mode and handing-off the selected AF point to an adjacent point which has detected a matching PD as the image sequence progresses.

In summary, if the E-M1 successor merely provides more PDAF sites but continues only to use the initially selected AF point during a sequence of C-AF SeqH shots the perceived in-focus success rate may not be substantially better than at present.

Any views on this?
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Old 4th April 2016
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Re: Using C-AF with moving subjects

A 4 year old post, but still relevant:

http://www.dpreview.com/forums/post/50099629

"Like it was said and proved many times here, Olympus C-AF really works great with the right settings techniques. I've done it even with the E-620 and 40-15mm MKII with good results, but with the E-5 and the 35-100 it was superb."

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Old 4th April 2016
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Re: Using C-AF with moving subjects

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Originally Posted by Gwyver View Post
When I reviewed shots taken with C-AF + SeqH from the EXIF data it is apparent that once the C-AF has acquired 'focus lock' it uses the same initially selected focus point for the entire sequence of images.
Are you sure it is always using the same focus point? I looked at some of my bursts and it looks like it does change. Below is a screen capture x 3 from Exiftool (GUI) and I don't understand the info about the 'AFPointSelected' but it does appear to change in the 3rd shot of the sequence:

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Re: Using C-AF with moving subjects

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Originally Posted by Bengeo View Post
Are you sure it is always using the same focus point? I looked at some of my bursts and it looks like it does change. Below is a screen capture x 3 from Exiftool (GUI) and I don't understand the info about the 'AFPointSelected' but it does appear to change in the 3rd shot of the sequence:
Andy,
Yes definitely the same selected focus point in all the 25+ shot sequences I tried.

You can see the relative position of the selected focus point using the (for PDAF) the second table in this post:
http://e-group.uk.net/forum/showthre...t=focus+points

The % numbers show the position across from left/up from bottom on the image where the selected focus point occurs.
The other numbers in these tables show a position in a range 0-255 across/up - so these indicate the size & location of a rectangular region of the image where focus points are active.
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Old 5th April 2016
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Re: Using C-AF with moving subjects

This is terrible! There was me thinking that in Sequential-H all I needed to do was keep the subject in the PDAF array area. This explains a lot! It is nigh on impossible to keep a bird under one individual focus point. No, correction, it is impossible!

I have been out today with the 300mm and mc-14 and I have not done very well with moving subjects at all. Hmm...

Having read this thread this morning, I did try using Zoom-AF (5x) with sequential-H to get a single, larger focus area. I tried it on a Lynx helicoptor that was flying overhead. At the time, I thought it didn't work, but looking at the images on the computer, it appears to have focused on the step of the helicopter in each frame so maybe it is worth more investigation.

The trouble with Zoom-AF is that initial focus acquisition is very dodgy. You can see the focus hunting in and out for a few seconds. However, once you start shooting, the pdaf array does appear between frames so perhaps it works. I'll try it again.
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Old 5th April 2016
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Re: Using C-AF with moving subjects

I don't have an E-M1 and I don't often attempt to shoot BIF but as a birder I would offer the following observations in an attempt to help.

The manual for the E-M1 (in common with all the OM-D cameras) says on page 57.
" SeqH. Focus,exposure and WB are fixed at the values for the first shot in each series." From memory of past discussions on the subject (going right back to 4/3 cameras as well) it is suggested that this is due to limitations of the lens mechanism being able to move quickly enough to be able to change focus reliably at rates of 10fps or so. For SeqL the manual refers to the use of different modes of AFL (page 102) which may be worth exploring.

On a broader perspective regarding BIF, if a bird is so distant that it only occupies an area similar to or less than a 3X3 group target it will be difficult to obtain focus in all but the brightest conditions and even then will be hampered by atmospheric effects etc. You need to be near enough to get nearer to a "frame filling view" to get a worthwhile image and this needs some skill and knowledge of fieldcraft and panning etc. Olybirder's recent post http://e-group.uk.net/forum/showthread.php?t=41748 has some apposite comments on this as well as some examples of what can be achieved. We think of a 300mm (600mm effective) focal length lens as being "really long" but the view it gives is only approximately the same as an ordinary pair of 8 times magnification binoculars ( 8 times means the subject appears 8 times nearer ). A birder looking at "distant" birds will use a telescope with 20-60 times magnification and this, at the higher magnification part of its range will be severely affected by haze/dust etc in the atmosphere.

If you haven't seen it before this Olympus Asia document http://asia.olympus-imaging.com/prod.../feature5.html gives some illustrations which suggest that they expect the subject to occupy a significant portion of the frame. Interestingly it also says that with the latest firmware updates C-AF +Tracking will work in SeqH at 9fps and can be used for "animals in the wild" so it might be worth trying this.

Not sure if this helps you, just my thoughts.

Regards.
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Old 6th April 2016
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Re: Using C-AF with moving subjects

Quote:
Originally Posted by PeterBirder View Post
...
If you haven't seen it before this Olympus Asia document http://asia.olympus-imaging.com/prod.../feature5.html gives some illustrations which suggest that they expect the subject to occupy a significant portion of the frame. Interestingly it also says that with the latest firmware updates C-AF +Tracking will work in SeqH at 9fps and can be used for "animals in the wild" so it might be worth trying this.

Not sure if this helps you, just my thoughts.

Regards.
Peter,
I've just read the asia.olympus link you posted. I think it is well designed 'marketing speak' and you have to be careful to avoid thinking that it means what you would like it to...
It doesn't actually say "C-AF + Tracking" - it merely talks of using C-AF at up to 9fps for tracking moving objects. This is only a plug for the increase in usable frame rate introduced in f/w version 3.

What seems to be meant by "tracking" in this webpage is that the AF will change as the target moves nearer/further away (which is what C-AF is supposed to do!) It does not indicate that AF will be maintained if the target moves around significantly within the frame.

In the image examples for C-AF, the bullet train remains in the pretty much in the same relative position within the frame - so it's not apparent that the selected focus point moves during the sequence, and
the train remains sufficiently distant from the camera that the DOF would mask precise AF discrepancy.

I fully agree that getting your (moving) subject to fill as much of the frame as possible is highly desirable and enables C-AF to perform optimally - particularly if there is good light and the subject has good contrast (as per Jim Ford's post). Often our ambitions and these optimal conditions do not combine

As I said in the OP - it is easy to have unrealistic expectations (of the C-AF capabilities).
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Old 6th April 2016
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Re: Using C-AF with moving subjects

Just a quick follow up to my thoughts on using Zoom-AF to get a larger single focus area. It doesn't help. Once focus is acquired in C-AF, the original point continues to be used throughout the burst as Chris (Gwyver) found in the OP.

I tried C-AF + Tr a bit yesterday but was unconvinced by its usefulness but I think it might deserve more effort. In Sequential-H, the PDAF array is visible between shots so the improved C-AF should be available.

I only kept half a dozen BIF shots freom yesterday from a couple of hundred. This was about the best. A slow moving heron at about 30-40m.



And this is terrible. Shot at 1/3000 sec. What's going on here? Very heavy crop.

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Old 6th April 2016
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Re: Using C-AF with moving subjects

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Originally Posted by Gwyver View Post
....(my) expectations of this function are unrealistic.
To me that should depend on where you came from. It is not unrealistic to expect a newer camera model of the same E System to perform better that the older version.

Your findings do not surprise me. The current development of AF with a mirrorless camera by Olympus does not work as well as the system they previously had, E5 IMHO.

The following articles explains why.
http://www.clarkvision.com/articles/...rless-cameras/

http://www.clarkvision.com/articles/...and.autofocus/

The on chip pase detection comes with a small loss in image quality because it has to use pixels that would other wise have been used to provide detail in the final image.

I like my EM1 for many of the other features that my E5 does not have but for AF with BIF and motor sports it is a real disappointment. I cannot help fear that Olympus will drop the on sensor PDF in future models. I think only the EM1 uses this technology and it has been out for some time now, if it worked or could be developed I am sure we would have seen this on other models by now. Also Oly has effectively ditched the FT lenses now concentrating on mFT, in time there will be no need for PDAF on a mirrorless system..
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Re: Using C-AF with moving subjects

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Originally Posted by birdboy View Post
I like my EM1 for many of the other features that my E5 does not have but for AF with BIF and motor sports it is a real disappointment. I cannot help fear that Olympus will drop the on sensor PDF in future models. I think only the EM1 uses this technology and it has been out for some time now, if it worked or could be developed I am sure we would have seen this on other models by now. Also Oly has effectively ditched the FT lenses now concentrating on mFT, in time there will be no need for PDAF on a mirrorless system..
John
I'm less pessimistic than you about future Olympus developments. They need to improve the BIF (& similar) performance to generate sufficient sales volume of the 300 f4 to recoup it's development cost.
Also, I understand that the latest Sony A7ii cameras have on-sensor PDAF (with rather more PDAF points than the E-M1) and Oly seem to be using Sony image sensors for their high-end cameras.
Hope springs eternal....
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Re: Using C-AF with moving subjects

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Originally Posted by TonyR View Post

And this is terrible. Shot at 1/3000 sec. What's going on here? Very heavy crop.
Tony,
Do you have Release Priority ON or OFF? It seems like the image was taken even though Focus Lock hadn't been achieved.
If you inspect your images EXIF values with a program such as ExiftoolGUI, and examine the Tag named "Focus Process" it should say "AF Used" for the images that look OK,
or most likely "AF Not Used" for shots like your 2nd image. If you have images with "AF Not Used" then you most likely have "Release Priority C" set to ON (it's on Cog C). With "Release Priority" set to ON the camera will take images even though Focus Lock hasn't been achieved. (p94 of the latest edition of the E-M1 manual has a customarily laconic explanation of this setting).
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Re: Using C-AF with moving subjects

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Originally Posted by Gwyver View Post
Peter,


What seems to be meant by "tracking" in this webpage is that the AF will change as the target moves nearer/further away (which is what C-AF is supposed to do!) It does not indicate that AF will be maintained if the target moves around significantly within the frame.


As I said in the OP - it is easy to have unrealistic expectations (of the C-AF capabilities).
Yes, unfortunately you have developed an unrealistic expectation.

C-AF "tracking" is the tracking of the focus distance, also called "predictive tracking" which is possible when you have PD sensors and is what happens in DSLRs as well. A link in the second link that Birdboy posted shows this. http://www.clarkvision.com/articles/...ith.autofocus/

What you are expecting, because of the undefined use of the word "tracking" is subject tracking. Subject tracking for subjects moving laterally or vertically in the frame has to be accomplished by panning and keeping the "focus box" on the subject. The Olympus Dot Sight is an aid to this and this review from Mirrorlessons may be of interest. http://www.mirrorlessons.com/2016/01...-sight-review/

The rest unfortunately is down to practice and skill.

Regards.
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Old 6th April 2016
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Re: Using C-AF with moving subjects

Hi Chris, sorry to disapoint the EM1 does not have the Sony sensor, as they were still dev on chip detection, I believe it was a Panasonic sensor, the EM5 ARE THE ONLY EM's using the Sony sensors without on chip focus detect arrays.

Hopefully the EM1 MARK 2 will have the new Sony sensor.
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Re: Using C-AF with moving subjects

Quote:
Originally Posted by Gwyver View Post
Tony,
Do you have Release Priority ON or OFF? It seems like the image was taken even though Focus Lock hadn't been achieved.
If you inspect your images EXIF values with a program such as ExiftoolGUI, and examine the Tag named "Focus Process" it should say "AF Used" for the images that look OK,
or most likely "AF Not Used" for shots like your 2nd image. If you have images with "AF Not Used" then you most likely have "Release Priority C" set to ON (it's on Cog C). With "Release Priority" set to ON the camera will take images even though Focus Lock hasn't been achieved. (p94 of the latest edition of the E-M1 manual has a customarily laconic explanation of this setting).
I do indeed have "Release Priority C" set to On but that is deliberate and, I believe, the default when the camera is delivered.I have never found "Release Priority C" Off to be a very usable experience! The new pdaf routine (firmare 3 hack!) only kicks in when the burst has started shooting. If the burst pauses due to not being focused, it doesn't seem to be able to get back in focus.

I haven't tried this for quite a while. Do you think it would work better?
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Re: Using C-AF with moving subjects

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Originally Posted by Daveart View Post
Hi Chris, sorry to disapoint the EM1 does not have the Sony sensor, as they were still dev on chip detection, I believe it was a Panasonic sensor, the EM5 ARE THE ONLY EM's using the Sony sensors without on chip focus detect arrays.

Hopefully the EM1 MARK 2 will have the new Sony sensor.
Hi Dave, I know that the E-M1 sensor isn't made by Sony. At the time of writing I had in mind the sensor in the new Pen-F - which I had read somewhere is made by Sony.
As you say, hopefully the E-M1 successor will have an improved sensor with better PDAF support.
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