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Thread started 12 Sep 2019 (Thursday) 14:42
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-= 90D owners unite! Discuss and Post Photos

 
FrankKolwicz
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Apr 15, 2020 16:39 as a reply to  @ post 19046044 |  #1711

Follow-up to Dirty Contacts?

Yeah, it really does look like dirty contacts, probably on the 600.

I had some nice cloudy weather this morning, as opposed to that harsh sunshine yesterday, and I did some more tests on birds that actually show where the focal point is: ducks on water - the ripples often show the plane of critical focus or the width of the area between obviously soft focus zones, front and back. The latter is often easier to see and I look for the width of the sharpest zone to include the location of the single focus point that I almost always use. The bright cloudy weather allowed exposures at ISO 1600, f/11 and 1/500th second - pretty normal for my location over the greatest part of the year. Of course it gets a lot dimmer, but this is my default setting.

For analysis of focus accuracy and precision I used the lens wide-open, f/4 to f/8 depending on which teleconverter or none.

Working with a high-contrast test target in my back yard at a distance of about 40 feet (~12 m) yesterday I picked an MFA of -15. Today, working at varying distances up to about a couple of hundred feet (?m) I refined the setting to -18, but variation is so great that the exact number is meaningless. Also, note, that these subjects are 3-dimensional, not the flat plane target, so there's inherent variability of the spot the AF decides to select.

Sampling my saved image files (10-15% of the several hundred) showed considerable variation of the critical focus plane for easy subjects (ducks with good contrast and large features), just as I got yesterday in full sun. About 50% of the image files I consider as sharp as can be expected, the rest are just a bit off, but probably printable with some extra work. That is far better than the 1-10% I'd gotten previously, when the camera insisted on back-focussing, no matter what I did. And, again, closer subjects yeilded more images with better focus accuracy and wide-open aperture was useable, too.

In summary, what I think is going on is that there was a communication fault between the lens and the camera body which caused the AF to fail to recognize setting changes for micro-focus adjustments and that cleaning the contacts solved that problem.

However, it also looks like the 90d's AF system is only marginally accurate when used with my very long focal length lens and telextender combinations (1344 to 1920mm, effectively, and f/5.6 and f/8 wide open) , allowing the plane of critical focus to wander around the aimed point excessively, yeilding only about 50% critically sharp images under conditions that should have yeilded better than 90% critically sharp, as my other Canon EOS bodies have done. The 50% number is for good to excellent light and subject matter only, one would expect that the AF will perform much worse when even darker conditions or dark, low-contrast subjects get involved.

YMMV! Shorter forcal lengths are easier to stabilize and wider maximum apertures give the AF system more light to work with, so don't compare apples to oranges.

I am well aware that there a lots of other things that effect AF performance that are outside of it's ability to remedy, like atmospheric disturbance and the 3-dimensional shape of my subjects. These things have been accounted for in my analysis, as best I can.




  
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Archibald
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Apr 15, 2020 19:59 |  #1712

FrankKolwicz wrote in post #19047136 (external link)
Follow-up to Dirty Contacts?

Yeah, it really does look like dirty contacts, probably on the 600.

I had some nice cloudy weather this morning, as opposed to that harsh sunshine yesterday, and I did some more tests on birds that actually show where the focal point is: ducks on water - the ripples often show the plane of critical focus or the width of the area between obviously soft focus zones, front and back. The latter is often easier to see and I look for the width of the sharpest zone to include the location of the single focus point that I almost always use. The bright cloudy weather allowed exposures at ISO 1600, f/11 and 1/500th second - pretty normal for my location over the greatest part of the year. Of course it gets a lot dimmer, but this is my default setting.

For analysis of focus accuracy and precision I used the lens wide-open, f/4 to f/8 depending on which teleconverter or none.

Working with a high-contrast test target in my back yard at a distance of about 40 feet (~12 m) yesterday I picked an MFA of -15. Today, working at varying distances up to about a couple of hundred feet (?m) I refined the setting to -18, but variation is so great that the exact number is meaningless. Also, note, that these subjects are 3-dimensional, not the flat plane target, so there's inherent variability of the spot the AF decides to select.

Sampling my saved image files (10-15% of the several hundred) showed considerable variation of the critical focus plane for easy subjects (ducks with good contrast and large features), just as I got yesterday in full sun. About 50% of the image files I consider as sharp as can be expected, the rest are just a bit off, but probably printable with some extra work. That is far better than the 1-10% I'd gotten previously, when the camera insisted on back-focussing, no matter what I did. And, again, closer subjects yeilded more images with better focus accuracy and wide-open aperture was useable, too.

In summary, what I think is going on is that there was a communication fault between the lens and the camera body which caused the AF to fail to recognize setting changes for micro-focus adjustments and that cleaning the contacts solved that problem.

However, it also looks like the 90d's AF system is only marginally accurate when used with my very long focal length lens and telextender combinations (1344 to 1920mm, effectively, and f/5.6 and f/8 wide open) , allowing the plane of critical focus to wander around the aimed point excessively, yeilding only about 50% critically sharp images under conditions that should have yeilded better than 90% critically sharp, as my other Canon EOS bodies have done. The 50% number is for good to excellent light and subject matter only, one would expect that the AF will perform much worse when even darker conditions or dark, low-contrast subjects get involved.

YMMV! Shorter forcal lengths are easier to stabilize and wider maximum apertures give the AF system more light to work with, so don't compare apples to oranges.

I am well aware that there a lots of other things that effect AF performance that are outside of it's ability to remedy, like atmospheric disturbance and the 3-dimensional shape of my subjects. These things have been accounted for in my analysis, as best I can.

Thanks for this analysis. It sounds like a lot of work. Focus issues are hard and time-consuming to troubleshoot. So with the cleaner contacts and MFA, will the 90D be usable with the 600?

And BTW, as far as I know, wider apertures focus more accurately for geometry reasons, not because they are brighter.


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DreDaze
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Apr 15, 2020 21:23 |  #1713

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John ­ Sheehy
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Apr 16, 2020 05:37 |  #1714

Archibald wrote in post #19047208 (external link)
And BTW, as far as I know, wider apertures focus more accurately for geometry reasons, not because they are brighter.

It's both, especially in lower light.

There's a downside to the larger apertures, though. When you see a bird in the sky, and then point the lens at it, a larger aperture will blur the bird more, losing it in the sky to greater blur, so you can't get the AF points on the bird sometimes, unless the focus was already close, to begin with.




  
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FrankKolwicz
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Apr 16, 2020 12:27 |  #1715

Archibald wrote in post #19047208 (external link)
Thanks for this analysis. It sounds like a lot of work. Focus issues are hard and time-consuming to troubleshoot. So with the cleaner contacts and MFA, will the 90D be usable with the 600?

And BTW, as far as I know, wider apertures focus more accurately for geometry reasons, not because they are brighter.

Thanks for your reply, Archibald.

Before I respond about useability, at length, please tell me about the geometry of aperture and AF accuracy or provide a pointer to a source. Thanks.

As to the 90d and 600 system: If it didn't have the articulated LCD along with the slightly higher pixel density, I wouldn't have even considered it. That combination solves a lot of problems I have using the 5ds bodies in my restricted workspace (my car).

The short answer is, yes, it is workable, now that the AF problem is fixed.

Specifically, after doing all that testing, I went out yesterday to find some birds and give it an actual field trial to see how productive the camera would be under good average winter lighting conditions: bright overcast verging on patches of blue sky. I found a cooperative Marsh Wren singing away on some cattail seed stalks, "punks" we used to call the stalks, as kids. I converted the 183 image files to DNG and reviewed them in Lightroom (an old version that doesn't handle CR3 files). Of them, I saved 40 using a fairly loose criterion for sharpness (pose and composition trump perfect sharpness). That's about a 20% "hit rate". My long term hit rate, from a general feeling over years of noting approximately what an outing's success rate was, rather than statistics, is about 10% using several different cameras on the same 600/1.4x and 2x extenders. That 20% isn't anything to get excited about, though, conditions were good and the bird was cooperative, but it's about as good as I have ever gotten outside of more controlled conditions and closer subjects.

Saying all of that has led me to think about why my hit rate is so low, compared to manufacturer's claims of AF proficiency. Given that, even under the nearly ideal conditions of a controlled test, I can see regular variation in AF accuracy around the best point in 50% or so of image frames that cause those images to be generally undesirable, the success rate can only go down from there.

When I use my camera system in normal field conditions: for moving, 3-dimensional (not flat and perpendicular) subjects, dark and low contrast birds, relatively dim lighting, active or twitchy subjects, atmospheric distortion, camera shake due to gusty winds, rain and probably some other problems I'm forgetting, it's no wonder I have to make hundreds of images to get anything useable and sometimes conditions really are impossible and I get zero out of a hundred frames. Still, if I could have say 95% AF accuracy instead of 50%, things would be much better and, maybe, a 20% overall success rate would become my new normal.

As always, YMMV, my conditions aren't most people's conditions and I wouldn't be at all surprised that you can do better.




  
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FrankKolwicz
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Apr 16, 2020 12:39 |  #1716

John Sheehy wrote in post #19047340 (external link)
It's both, especially in lower light.

There's a downside to the larger apertures, though. When you see a bird in the sky, and then point the lens at it, a larger aperture will blur the bird more, losing it in the sky to greater blur, so you can't get the AF points on the bird sometimes, unless the focus was already close, to begin with.

I'm not sure what "larger apertures" you mean, I see this with extended lenses that have max apertures of f/4 and f/5.6 (300/2.8 plus 1.4 and 2x) in full sun.




  
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John ­ Sheehy
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Apr 16, 2020 13:03 |  #1717

FrankKolwicz wrote in post #19047575 (external link)
I'm not sure what "larger apertures" you mean, I see this with extended lenses that have max apertures of f/4 and f/5.6 (300/2.8 plus 1.4 and 2x) in full sun.

The faster any lens is at a given focal length, the more likely that the subject is completely out of focus when you try to find it through the viewfinder, to track it.




  
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Apr 16, 2020 13:58 |  #1718

FrankKolwicz wrote in post #19047570 (external link)
Before I respond about useability, at length, please tell me about the geometry of aperture and AF accuracy or provide a pointer to a source. Thanks.

I read a cool web page quite a few years ago about how phase detect AF works. It was technical and fairly detailed. Of course I can't find it back now, and I don't recall the details. But basically it said the AF system works by comparing two parts of the image (for each AF point), one from the top of the lens and one from the bottom, and when they fuse, the image is in focus. So it works much like a range finder. Wider apertures give more spread between the two part-images and that is why wide aperture lenses are more accurate, and why it is not so good for smaller apertures (and why the firmware imposes a limit). The following article gives some insights to this.

https://photographylif​e.com …detection-autofocus-works (external link)

Obviously PDAF needs light too, but it functions by geometry.


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Apr 16, 2020 21:00 |  #1719

Ole Blue Mouth!


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Apr 17, 2020 14:26 |  #1720

Help with tracking settings

Shooting Cormorants on a swaying platform with a lot of blowing reed grass!!! Oy!!!!!!

So:
1. I'm set for BBF. If I use single point and acquire focus and then release the BB and wait and in between a reed grass decides to blur stuff, will the shot work, or do I constantly need to bump focus?

2. Using 9 point instead of Single point ? and f11 instead of single point and f9?

3. Setting tracking sensitivity to -1 to try to ignore the blowing grass?

4. Swear and kick something?

What's best?

Also: I'm experimenting with Acceleration of +1 for swallows.

What do you guys do?


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Apr 17, 2020 15:52 |  #1721

cdmazoff wrote in post #19048196 (external link)
Help with tracking settings

Shooting Cormorants on a swaying platform with a lot of blowing reed grass!!! Oy!!!!!!

So:
1. I'm set for BBF. If I use single point and acquire focus and then release the BB and wait and in between a reed grass decides to blur stuff, will the shot work, or do I constantly need to bump focus?

2. Using 9 point instead of Single point ? and f11 instead of single point and f9?

3. Setting tracking sensitivity to -1 to try to ignore the blowing grass?

4. Swear and kick something?

What's best?

Also: I'm experimenting with Acceleration of +1 for swallows.

What do you guys do?

For BBF and a moving target, I always use servo focus, and keep the button pressed while shooting. Even if the subject is stationary I will usually keep the button pressed, because I might be swaying, changing the distance slightly.

And I practically always shoot with a single AF point. I tried using the helper points, and those helping AF points annoyingly focused on the wrong part of the subject. So they were not helping but hindering.

Regarding tracking settings, I go with the defaults because I have no way of knowing what the next situation will require. Anyway, there won't be time to make adjustments when the next opportunity presents. And I wouldn't know what adjustments to make for the situation anyway, because I haven't determined optimal settings. That's because shooting situations don't lend themselves to doing controlled tests to find out what those settings should be.


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Apr 17, 2020 16:24 |  #1722

Archibald wrote in post #19048240 (external link)
For BBF and a moving target, I always use servo focus, and keep the button pressed while shooting. Even if the subject is stationary I will usually keep the button pressed, because I might be swaying, changing the distance slightly.

And I practically always shoot with a single AF point. I tried using the helper points, and those helping AF points annoyingly focused on the wrong part of the subject. So they were not helping but hindering.

Regarding tracking settings, I go with the defaults because I have no way of knowing what the next situation will require. Anyway, there won't be time to make adjustments when the next opportunity presents. And I wouldn't know what adjustments to make for the situation anyway, because I haven't determined optimal settings. That's because shooting situations don't lend themselves to doing controlled tests to find out what those settings should be.

Thanks Archie. I'm always in servo.. And I usually have the BB pressed but I was wondering if removing the thumb would help. I hate that darned marsh grass!!! As for the other settings.. I hear you.


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Apr 17, 2020 22:45 |  #1723

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Post edited 10 months ago by David_Wales.
     
Apr 20, 2020 06:41 |  #1724

Really getting to enjoy 90D since going back to basics, and forgetting everything I learnt on 7D mk2, two different horses for courses.

Photo taken in my garden of Dandelion Seed Head with 90D and EF-S 10-18mm 4.5 - 5.6 IS STM (no macro close-up filter attached):


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Apr 25, 2020 15:08 |  #1725

Anna's Hummingbird


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