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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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  #31  
Old 9th April 2016
TonyR TonyR is offline
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Re: Using C-AF with moving subjects

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Originally Posted by Miketoll View Post
Surprised by this as I always thought that it was only SLR's that suffered from back focus (or front focus) because of the use of a mirror for viewing requiring a separate focusing array and the different light path not quite matching the light path to sensor.
In other words I would appreciate an explanation of how the back focussing can arise seeing the PDAF sensors are actually on the sensor used for the image. Not that I am doubting you, I just don't understand unless there is an actual fault with the PDAF sensors themselves.
Having the pdaf sensors on the imaging sensor elimitaes one form of error. Namely, having the pdaf sensors inaccurately positioned in the camera. But the len's AF motor is told to move to a certain position by the AF algorithm and there could be a calibration error in this part of the system. I presume this is what happens and why Olympus provides an AF adjustment mechanism for the pdaf sensor array.

cdaf just keeps hunting until maximum contrast converges so it wouldn't make any difference to that. pdaf isn't a completely open-loop system but presumeably does less back and forth than adaf...

... as I understand it .
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  #32  
Old 9th April 2016
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Re: Using C-AF with moving subjects

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Originally Posted by TonyR View Post
Having the pdaf sensors on the imaging sensor elimitaes one form of error. Namely, having the pdaf sensors inaccurately positioned in the camera. But the len's AF motor is told to move to a certain position by the AF algorithm and there could be a calibration error in this part of the system. I presume this is what happens and why Olympus provides an AF adjustment mechanism for the pdaf sensor array.

cdaf just keeps hunting until maximum contrast converges so it wouldn't make any difference to that. pdaf isn't a completely open-loop system but presumeably does less back and forth than adaf...

... as I understand it .
Thanks, sort of understand!
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  #33  
Old 10th April 2016
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Re: Using C-AF with moving subjects

OK, I withdraw my claim that my 300mm has a back focus issue! At least, if it does back focus, it doesn't seem to make any difference in practice.

I have done some more tests on a target at 15m. The target is a white piece of paper with ink lines on it in lots of directions.

What actually happens in a burst using Sequential-H and C-AF (9-area) is that, after initial lock (beep plus appearance of green rectangle), the focus racks back and forth giving a variety of degrees of out-of-focus fuzziness. The degree to which thois happens seems to vary with the amount of contrast in the subject. Initially, using just a cross on the paper, this racking back and forth was quite severe. Adding more lines at more angle seems to help.

So in my previous test looking at the radio tower, I probably fooled myself as the images at the end on the unadjusted burst just happened to be much worse than the images at the start of the burst with the adjusted focus.

So, what's going on? I don't know . I have tried shooting with focus adjustments of 0, -1, -2, -3, and -4 and I can't really tell the difference between any of them. One thing I do find strange is that, viewed on the camera or on Olympus Viewer (in the properties section) some of the images are labelled as having a focus adjustment. In Olympus Viewer, the field is called AF Focus Adj. But most of the photos are not labelled in this way. And it is random within a burst where the labelled images are. My guess is that images get labelled in this way when the image is recognised to be in focus or when focus is achieved using pdaf only. However, some labelled images are out of focus.

All in all, testing on a high-contrast stationary target was pretty disappointing. Focus varies from image to image, particularly when the subject has less contrast. After fiddling with lots of settings, I seem to get better results with Release Priority C set Off and with the frame rate for Sequential-H reduced to 7 frames per second (or lower).

Given that black ink lines on a white sheet of paper is probably as high a contrast target as one can get, it is no wonder that my experience with birds was rather poor, especially with the white egret against a pale sky as shown earlier in this thread.

I had hoped that the 300mm might be more reliable for C-AF due to the subject filling the frame more, but this appears not to be that case. Any other tips for a frustrated birder?
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  #34  
Old 10th April 2016
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Re: Using C-AF with moving subjects

Interesting but very disappointing Tony. This is why I will not even consider buying this lens until Olympus bring out a body that will give reliable C-AF. I will stick with my Canon gear for moving subjects like birds, motor sport and even horse jumping at an amateur level.
When I tried my 40-150 Pro for horse jumping where the horse was fairly frame filling, not moving at any great pace and on a predictable course the EM-1 still could not manage despite it being a bright sunny summers day with masses of contrast. Some shots were pin sharp, many were not quite sharp and some were so far out as to be almost unrecognisable as a horse and rider. High shutter speed was used so it was not subject movement. I would have done better pre-focussing on the jump in S-AF.
So it seems that the EM-1 is just not up to the task of C-AF so as I said earlier no 300 Pro for me. Sad.
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  #35  
Old 10th April 2016
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Re: Using C-AF with moving subjects

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Originally Posted by TonyR View Post
After fiddling with lots of settings, I seem to get better results with Release Priority C set Off and with the frame rate for Sequential-H reduced to 7 frames per second (or lower).
....
Any other tips for a frustrated birder?
Tony,
I think that reducing the frame rate for SeqH & C-AF makes good sense. I did this last month when I took the Flying Scotsman photos.

When Olympus promote the max fps - this is just another marketing plug (similar to boasts about pixel count) and must be based on a number that is on the edge of the possible. If you back off from the max of 10fps to 9 or 8 then this should be increasing the time for the C-AF to operate by 10 or 20+ percent - so hopefully it should give better results. (The secondary benefit is that it takes longer for the image buffer to fill up.)
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  #36  
Old 10th April 2016
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Re: Using C-AF with moving subjects

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Originally Posted by Gwyver View Post
Tony,
I think that reducing the frame rate for SeqH & C-AF makes good sense. I did this last month when I took the Flying Scotsman photos.

When Olympus promote the max fps - this is just another marketing plug (similar to boasts about pixel count) and must be based on a number that is on the edge of the possible. If you back off from the max of 10fps to 9 or 8 then this should be increasing the time for the C-AF to operate by 10 or 20+ percent - so hopefully it should give better results. (The secondary benefit is that it takes longer for the image buffer to fill up.)
I am sure you are right, it should help.
However when I was so disappointed with the C-AF with my 40-150 Pro my setting was 6fps and the nine box focus area. I think Olympus need far more PDAF focus points plus have cross types if possible or at least some horizontal and some vertical along with a new set of algorithms. Sony are beginning to get there, admittedly on a bigger sensor which I imagine gives them more scope for manoeuvre so it can be done.
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Old 10th April 2016
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Re: Using C-AF with moving subjects

Its not the lens that delivers the C-AF performance. Mirrorless cameras cannot currently compete with floppy mirror cameras and the explanation for this is very clearly set out in the Clarkvision articles. Its not just a EM1 problem but with all mirrorless cameras.
http://www.clarkvision.com/articles/...rless-cameras/

This does not mean that the 300mm f4 lens is not worth buying or that C-AF is of any use. There are situations to use C-AF with birds. I like to use C-AF with birds in tress for instance. By half pressing on the shutter button in C-AF with single point focus I find I can get good focus on birds with complex backgrounds by gently moving the lens around the bird.
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  #38  
Old 10th April 2016
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Re: Using C-AF with moving subjects

I know it is not the lens but the body. For me it is not worth spending 2000 for a lens that with any of the bodies available will not do what I want it for. If in the future Olympus bring out a body that will give me good C-AF then I would reconsider the lens.
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  #39  
Old 15th April 2016
kbouk kbouk is offline
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Re: Using C-AF with moving subjects

Quote:
Originally Posted by TonyR View Post
OK, I withdraw my claim that my 300mm has a back focus issue! At least, if it does back focus, it doesn't seem to make any difference in practice.

I have done some more tests on a target at 15m. The target is a white piece of paper with ink lines on it in lots of directions.

What actually happens in a burst using Sequential-H and C-AF (9-area) is that, after initial lock (beep plus appearance of green rectangle), the focus racks back and forth giving a variety of degrees of out-of-focus fuzziness. The degree to which thois happens seems to vary with the amount of contrast in the subject. Initially, using just a cross on the paper, this racking back and forth was quite severe. Adding more lines at more angle seems to help.

So in my previous test looking at the radio tower, I probably fooled myself as the images at the end on the unadjusted burst just happened to be much worse than the images at the start of the burst with the adjusted focus.

So, what's going on? I don't know . I have tried shooting with focus adjustments of 0, -1, -2, -3, and -4 and I can't really tell the difference between any of them. One thing I do find strange is that, viewed on the camera or on Olympus Viewer (in the properties section) some of the images are labelled as having a focus adjustment. In Olympus Viewer, the field is called AF Focus Adj. But most of the photos are not labelled in this way. And it is random within a burst where the labelled images are. My guess is that images get labelled in this way when the image is recognised to be in focus or when focus is achieved using pdaf only. However, some labelled images are out of focus.

All in all, testing on a high-contrast stationary target was pretty disappointing. Focus varies from image to image, particularly when the subject has less contrast. After fiddling with lots of settings, I seem to get better results with Release Priority C set Off and with the frame rate for Sequential-H reduced to 7 frames per second (or lower).

Given that black ink lines on a white sheet of paper is probably as high a contrast target as one can get, it is no wonder that my experience with birds was rather poor, especially with the white egret against a pale sky as shown earlier in this thread.

I had hoped that the 300mm might be more reliable for C-AF due to the subject filling the frame more, but this appears not to be that case. Any other tips for a frustrated birder?

The focus racks back and forth because camera tries to find the next target... It's how Olympus engineers made CAF routines work, if you try it on a stationary target you will find many misfocus shots but on moving target it's good enough with good light at least with the pro lenses.
Also there are so many other menu parameters as CAF Lock, shutter release priority, EVF mode (high or Normal), L or H mod , fps , small or big 1 focus point or 9 F.P. , etc ... which are engaged with the CAF performance, you have to try them with patient one by one and find the best solutions for you, for different target scenarios.
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Old 15th April 2016
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Re: Using C-AF with moving subjects

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Originally Posted by kbouk View Post
The focus racks back and forth because camera tries to find the next target... It's how Olympus engineers made CAF routines work, if you try it on a stationary target you will find many misfocus shots but on moving target it's good enough with good light at least with the pro lenses.
...
Well, that might be how it works but if it is, it is not very good. There is nothing to say that C-AF requires a moving target.

In my view, what should happen is that the pdaf sensors should assess how the distance to the subject is changing between samples. If that distance is not changing, there is no need to change the focus. If the range is changing, the AF algorithm can calculate which direction to move in and roughly how far. Subsequent pdaf samples will refine the focus.

I would suggest that your description better describes what happens with a cdaf focus system for C-AF. i.e. move the focus a bit and see whether contrast has improved or not. Rinse and repeat...
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  #41  
Old 15th April 2016
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Re: Using C-AF with moving subjects

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Originally Posted by Miketoll View Post
I know it is not the lens but the body. For me it is not worth spending 2000 for a lens that with any of the bodies available will not do what I want it for. If in the future Olympus bring out a body that will give me good C-AF then I would reconsider the lens.
I am also holding off. One thing I have to admit is that all photography equipment is a compromise. But I think that the Olympus equipment is excellent in most other areas of photography apart from nature IE BIF.
Kind regards mike
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  #42  
Old 15th April 2016
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Re: Using C-AF with moving subjects

Has anybody read the link I posted earlier?

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

Jim
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  #43  
Old 15th April 2016
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Re: Using C-AF with moving subjects

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Has anybody read the link I posted earlier?

Jim
Yes! Back when I had the E-3 & 50-200 SWD

I do hardly any moving subjects, but need to develop my technique beyond the "old school" pre-set focus and panning we used with the OM cameras.

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  #44  
Old 15th April 2016
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Re: Using C-AF with moving subjects

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Originally Posted by Jim Ford View Post
Has anybody read the link I posted earlier?

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

Jim
Just re-read it. I'm an EM-1 user and cannot see anything resembling Dynamic area AF in any of the menus, I also cannot see anything that looks like an 11 area function to avoid, are these E5isms?

Or am I missing something as ever?
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  #45  
Old 15th April 2016
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Re: Using C-AF with moving subjects

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Originally Posted by Jim Ford View Post
Has anybody read the link I posted earlier?

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

Jim
Jim, I did read it, and have read it before when you posted it. At one stage with my E3 I even felt I managed to get continuous focus working well enough to capture dragonflies in flight. But it was a lot to change and, I think I set it as a mode. But it was a while back and it wasn't easy or intuitive.

Indeed my user experience is that Olympus design menus and systems badly. The em5 mk2 is a bit better, but it still has too many deep options, which are badly described. And the manual is just as bad.

Recently, my son convinced me to try a Canon. Which I did. Together with a 100-400 mk2 L lens it delivers wonderful continuous shooting. I wanted the 70D rather than the 7D, because of video use, it also had a well designed touch screen and a battery that lasts as long as three Olympus ones.

The first time I used it, set up as it came out of the box on auto it just worked. I ended up with red kites diving at high speed for food on the ground all in good focus. My friend was with me using his em5 and cursing.

I don't want to sell Canon but as someone else said it isn't just the lens it is the body. And I prefer what I have moved to for birds and am getting used to just grabbing shots of things without any hassle.

But having two systems is not perfect.
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