I feel misled: Panasonic 20mm f1.7 II AF is SO SLOW!

Started 5 months ago | Discussions
Anders W
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Re: I feel misled: Panasonic 20mm f1.7 II AF is SO SLOW!
In reply to TheEngineer, 4 months ago

TheEngineer wrote:

Anders W wrote:

There is no evidence whatsoever that the 20/1.7 has greater difficulty locking focus than other lenses in apples-to-apples comparisons (same light conditions, same AF target, same target magnification).

Sorry, but thats just not true.

You call yourself TheEngineer. So have you tested it under carefully controlled conditions as I have? If so, where's your evidence?

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micksh6
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Re: I feel misled: Panasonic 20mm f1.7 II AF is SO SLOW!
In reply to Anders W, 4 months ago

Anders W wrote:

micksh6 wrote:

Why do you feel mislead? Of course it's slow and it has been shown here long time ago. You just needed to look at the right tests:
http://www.dpreview.com/forums/post/52045407
http://www.dpreview.com/forums/post/52049352

A "controlled" test can also show that 20mm focuses much slower than other lenses and hunts more often too. It's not needed to refocus from close-up to infinity in order to see that. These tests show refocusing between about 5 and 7-8 feet.

Those tests are not controlled. They are biased in ways and for reasons spelled out in the thread to which you link. That's why they are not the right tests.

The "bias" reasons were spelled in regards to first test (more than a year old). This is why I linked to a second test (9 months old) with corrected conditions, so all that bias stuff is no longer relevant.

When you reviewed the second test you couldn't come up with any bias arguments, only with minor nitpicking about viewing angle. These nitpickings were pointless because anticipating these I did several tests with slightly different angles and they all showed the same results. Here is your last post in that discussion: http://www.dpreview.com/forums/post/52056626

The test is as right as it could have been. Any more "controlled" test would also be less relevant because it would have to use artificial conditions, having nothing to do with real shooting.

Your test is a good example of irrelevant test because now you always have to add disclaimers like "when refocusing between 0.75m and infinity". Why didn't you test a real life scenario - refocusing between approximately 5 and 7 feet, like I did?

Your ending word was basically that "If you want to make one lens look like it would be more prone to hunting than other lenses, it's very easy to arrange that by means of any of a large number of seemingly minor side conditions".

It could be so, and that's where statistics comes to play. More and more people find that 20mm is slow comparing to other lenses. Nobody appears and says that 20mm is faster than recent primes such as 17mm F1.8 (especially that 17mm), both 25mm, 45mm F1.8. Isn't that telling something?

The best what people can say about 20mm AF speed is "it's fast enough for me" or "about as fast as some other lenses I own". And this also should have raised "where's your evidence" questions that you ask everyone who claims that the lens is slow, if you weren't so attached to this lens, of course.

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Anders W
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Re: I feel misled: Panasonic 20mm f1.7 II AF is SO SLOW!
In reply to micksh6, 4 months ago

micksh6 wrote:

Anders W wrote:

micksh6 wrote:

Why do you feel mislead? Of course it's slow and it has been shown here long time ago. You just needed to look at the right tests:
http://www.dpreview.com/forums/post/52045407
http://www.dpreview.com/forums/post/52049352

A "controlled" test can also show that 20mm focuses much slower than other lenses and hunts more often too. It's not needed to refocus from close-up to infinity in order to see that. These tests show refocusing between about 5 and 7-8 feet.

Those tests are not controlled. They are biased in ways and for reasons spelled out in the thread to which you link. That's why they are not the right tests.

The "bias" reasons were spelled in regards to first test (more than a year old). This is why I linked to a second test (9 months old) with corrected conditions, so all that bias stuff is no longer relevant.

When you reviewed the second test you couldn't come up with any bias arguments, only with minor nitpicking about viewing angle. These nitpickings were pointless because anticipating these I did several tests with slightly different angles and they all showed the same results.

No they were at the same angle but with different framing of the target.

Here is your last post in that discussion: http://www.dpreview.com/forums/post/52056626

Exactly.

The test is as right as it could have been. Any more "controlled" test would also be less relevant because it would have to use artificial conditions, having nothing to do with real shooting.

Your test is a good example of irrelevant test because now you always have to add disclaimers like "when refocusing between 0.75m and infinity".

That disclaimer is not some kind of artifact of my testing. It describes the boundaries within which the 20/1.7 will focus about as fast as other lenses. I did another test before that where I had the minimum distance at 0.5 meter rather 0.75 meter. When refocusing from infinity to 0.5 meter, you start seeing a difference between the 20 and other lenses although not a very large one. When you go from the minimum focusing distance (0.2 m) to infinity or the reverse, the 20 takes about twice as long as other lenses.

Why didn't you test a real life scenario - refocusing between approximately 5 and 7 feet, like I did?

The reason why I chose 0.75 meter and infinity for one of my two test scenarios is explained above. I don't think there is any particular pair of distances that can be considered more real than others in this case. Why, for example, didn't you test refocusing on a target at the same distance as I did? Refocusing on the same target happens, I would think, quite frequently in real shooting.

Your ending word was basically that "If you want to make one lens look like it would be more prone to hunting than other lenses, it's very easy to arrange that by means of any of a large number of seemingly minor side conditions".

It could be so, and that's where statistics comes to play.

Rather, that's where confirmation bias comes into play.

More and more people find that 20mm is slow comparing to other lenses.

What do you know about that? I might as well say, based on a number of posts other than mine in this thread, that more and more people come to about the same conclusion as I. In reality, all we know is that perceptions are widely different.

Nobody appears and says that 20mm is faster than recent primes such as 17mm F1.8 (especially that 17mm), both 25mm, 45mm F1.8. Isn't that telling something?

Presumably nobody says so because nobody (myself included) thinks so.

The best what people can say about 20mm AF speed is "it's fast enough for me" or "about as fast as some other lenses I own".

Sure. And I have no trouble agreeing with either of those statements.

And this also should have raised "where's your evidence" questions that you ask everyone who claims that the lens is slow, if you weren't so attached to this lens, of course.

I don't need to ask others for evidence of something I have already shown myself.

Now what about the questions I asked you here:

http://www.dpreview.com/forums/post/53587566

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NZ Scott
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17/1.8 is significantly faster than the 45/1.8
In reply to Anders W, 4 months ago

Anders W wrote:

"Are you claiming that the 17/1.8 is noticeably faster than other modern lenses with similar AF design like the 12/2 and the 45/1.8 included in my test? If so, on what basis do you make that claim?"

Nobody seems to have answered this.

In my experience, the 17/1.8 autofocuses significantly faster than the 45/1.8 under real-world shooting conditions.

I've taken around 5000 photos with the 45/1.8 and 10,000 with the 17/1.8, often switching between the two lenses several times a day.

The difference is especially noticeable in situations that require big changes in focusing distance (ie. from near to far or from far to near) - e.g., when shooting street.

The 45 is occasionally slow enough to miss shots.

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Mark Chan
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Re: 17/1.8 is significantly faster than the 45/1.8
In reply to NZ Scott, 4 months ago

Anders W wrote:

"Are you claiming that the 17/1.8 is noticeably faster than other modern lenses with similar AF design like the 12/2 and the 45/1.8 included in my test? If so, on what basis do you make that claim?"

Nobody seems to have answered this.

In my experience, the 17/1.8 autofocuses significantly faster than the 45/1.8 under real-world shooting conditions.

I've taken around 5000 photos with the 45/1.8 and 10,000 with the 17/1.8, often switching between the two lenses several times a day.

The difference is especially noticeable in situations that require big changes in focusing distance (ie. from near to far or from far to near) - e.g., when shooting street.

The 45 is occasionally slow enough to miss shots.

S

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Scott, same experience here; though I do suspect the focal length of the 17mm makes it easier to focus?

In any case miles faster than te 20mm.

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micksh6
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Re: I feel misled: Panasonic 20mm f1.7 II AF is SO SLOW!
In reply to Anders W, 4 months ago

Anders W wrote:

micksh6 wrote:

Anders W wrote:

micksh6 wrote:

Why do you feel mislead? Of course it's slow and it has been shown here long time ago. You just needed to look at the right tests:
http://www.dpreview.com/forums/post/52045407
http://www.dpreview.com/forums/post/52049352

A "controlled" test can also show that 20mm focuses much slower than other lenses and hunts more often too. It's not needed to refocus from close-up to infinity in order to see that. These tests show refocusing between about 5 and 7-8 feet.

Those tests are not controlled. They are biased in ways and for reasons spelled out in the thread to which you link. That's why they are not the right tests.

I didn't start this thread stating that 20mm is slow, so you might as well tell OP that he is biased and the lens is actually fast.

Don't worry. I already told him what the facts are a couple of times, latest here:

http://www.dpreview.com/forums/post/53583615

Whether you like my tests or not they showed exactly what OP is seing now. Your tests, on the other hand, showed that 20mm is as fast as other lenses.

My tests show exactly that yes, but only under the specific conditions I spelled out in the post where I originally reported my test results as well as in posts where I refer to them, latest in the post I link to above. As you you should be well aware by now, I have no trouble recognizing that the AF of the 20 is slower than that of other lenses under several other conditions. As you can see, this too is clearly pointed out in the post I link to.

The problem with your tests is that they don't show much at all due to unrobust test conditions that make the outcome very sensitive to minor variations along with a failure to control these variations sufficiently well.

BTW, a year ago I replied to your post with test results which you linked today: "the claim that 20mm focuses as fast as other fast primes is just plain wrong and it can mislead people". http://www.dpreview.com/forums/post/51100467

Perhaps, this is why OP feels misled now.

So you erected a straw-man. The unconditional claim made in the passage of yours that you quote is not and was not my claim. What I am, and have been, claiming is summarized in the post I link to above.

I think a curved focus target attributes to slow AF with this lens.

Any lens will have greater difficulty focusing on a curved than a non-curved surface since for the former there is no single point where the entire surface contained within the focus box can be in perfect focus. But on what grounds would the 20 have greater difficulty focusing on a curved surface than other lenses of similar FL?

This is what tests show.

No. For reasons already spelled out above, your tests do not show that and I don't know of any other ones that do either.

Explanation of test results can be a different topic.

One way of putting test results into question is to ask questions about them.

Some time ago I suggested that it might be because of noisy focus motor. Noise is caused by vibration. Vibration also leads to blurred images, and it's much harder for camera to find peak contrast on blurred images. Peak contrast of curved surface is already is harder to determine than of flat surface. And if some contrast samples are impaired by blur this can make AF fail, or it can lead to slow AF.

Have you ever tried focusing the 20 in 14x zoom AF using a remote and watching the screen as you focus? Did you compare with another lens? If so, what did that tell you?

Yes, I did. It told me that I'm not a superhuman. I can't see difference in blurrines on sequential live view frames because the frames are rapidly changing with 60fps frequency. Can you estimate blurriness of individual frames in fast-paced movie sequence? No? Why did you ask this question, then? (you don't have to answer, otherwise this will never stop)

One way to see that would be to capture video with high speed camera. Since live view is changing with 60fps rate and there can be a visible transition between frames one would need a camera faster than 120fps to make sure that a single frame is captured without transition to next frame.

Because only few frames in focusing sequence would be more or less sharp these moments are hard to capture. I don't have such camera.

General logic says that vibration reduces quality of image (signal) that CDAF algorithm analyzes, and you can feel the vibration. Then it's easy to see why the algorithm needs more samples to produce good results on lower quality input.
Whether this quality impact is visible to human eye is another matter.

Further, have you examined the impact of hand-shake in the same situation (14x zoom AF)

There is no need to do that.

and how that impact compares in magnitude to any vibration from the focus motor (with the 20 or any other lens)? If so, what did that tell you?

Exposure time for AF is unlikely to be lower than 1/125s. With 40mm equiv. lens one would need to have serious tremor in order to consistently produce fuzzy images because of camera shake.

AF motor of 20mm lens, on the other hand, can generate whole range of frequencies starting from 200Hz (period close to probable low-light AF exposure time) and that would directly affect optical elements.

The lens element shake has an order of magnitude more impact on image quality than camera shake. For example, 8 degrees lens tilt would rotate focus plane by 90 degrees.

This is just a theory, of course. One possible explanation of long-term observation that 20mm F1.7 lens hunts more often than other lenses in the similar conditions.

PS. I thought these questions were rhetorical but you kept reminding about them in later posts, so here are the answers.

Because of that 20mm lens may require more AF iterations, and it's more likely to start hunting than other lenses in the same conditions.

This isn't happening in good light, but in low light exposure time during autofocus becomes longer and if it's around 1/125-1/250s the quality of AF samples is very likely to be affected by low-frequency vibration (around 200Hz or so).

You know very well about shutter shock. You can think of this as focus motor shock. You can feel vibration when 20mm is focusing, and camera is taking images when doing it.

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photo perzon
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This is the m4/3 forum, and sharp is sharp
In reply to Pixnat2, 4 months ago

Pixnat2 wrote:

photo perzon wrote:

No way. The 20mm is painfully sharp. Amazing for pets. The 17mm to me is a soft lens. Fast AF but fuzzy.

Mine isn't that soft/fuzzy.

E-M5 + 17mm @ f/5.6, converted in LR 5

Maybe you had a lemon?

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The 20mm may not be as fast.  But it is quirurgically sharp.  The 17mm is faster AF but Compared to the 20mm it is nowhere as sharp.

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Anders W
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Re: 17/1.8 is significantly faster than the 45/1.8
In reply to NZ Scott, 4 months ago

NZ Scott wrote:

Anders W wrote:

"Are you claiming that the 17/1.8 is noticeably faster than other modern lenses with similar AF design like the 12/2 and the 45/1.8 included in my test? If so, on what basis do you make that claim?"

Nobody seems to have answered this.

In my experience, the 17/1.8 autofocuses significantly faster than the 45/1.8 under real-world shooting conditions.

I've taken around 5000 photos with the 45/1.8 and 10,000 with the 17/1.8, often switching between the two lenses several times a day.

The difference is especially noticeable in situations that require big changes in focusing distance (ie. from near to far or from far to near) - e.g., when shooting street.

The 45 is occasionally slow enough to miss shots.

See my previous reply to your and Hen3ry's discussion about this earlier on:

http://www.dpreview.com/forums/post/53591384

In short: What you see is what would normally be expected in view of the different FLs and the way you are likely to use them since the focus lens group of the 45 usually has to move more than that of the 17 or 12 (which you noted were both faster in your experience). If you keep the amount of travel the focus lens group has to do constant (as I did in my testing with the 12 and 45), you are likely to see the difference disappear.

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Anders W
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Re: I feel misled: Panasonic 20mm f1.7 II AF is SO SLOW!
In reply to micksh6, 4 months ago

micksh6 wrote:

Anders W wrote:

micksh6 wrote:

Anders W wrote:

micksh6 wrote:

Why do you feel mislead? Of course it's slow and it has been shown here long time ago. You just needed to look at the right tests:
http://www.dpreview.com/forums/post/52045407
http://www.dpreview.com/forums/post/52049352

A "controlled" test can also show that 20mm focuses much slower than other lenses and hunts more often too. It's not needed to refocus from close-up to infinity in order to see that. These tests show refocusing between about 5 and 7-8 feet.

Those tests are not controlled. They are biased in ways and for reasons spelled out in the thread to which you link. That's why they are not the right tests.

I didn't start this thread stating that 20mm is slow, so you might as well tell OP that he is biased and the lens is actually fast.

Don't worry. I already told him what the facts are a couple of times, latest here:

http://www.dpreview.com/forums/post/53583615

Whether you like my tests or not they showed exactly what OP is seing now. Your tests, on the other hand, showed that 20mm is as fast as other lenses.

My tests show exactly that yes, but only under the specific conditions I spelled out in the post where I originally reported my test results as well as in posts where I refer to them, latest in the post I link to above. As you you should be well aware by now, I have no trouble recognizing that the AF of the 20 is slower than that of other lenses under several other conditions. As you can see, this too is clearly pointed out in the post I link to.

The problem with your tests is that they don't show much at all due to unrobust test conditions that make the outcome very sensitive to minor variations along with a failure to control these variations sufficiently well.

BTW, a year ago I replied to your post with test results which you linked today: "the claim that 20mm focuses as fast as other fast primes is just plain wrong and it can mislead people". http://www.dpreview.com/forums/post/51100467

Perhaps, this is why OP feels misled now.

So you erected a straw-man. The unconditional claim made in the passage of yours that you quote is not and was not my claim. What I am, and have been, claiming is summarized in the post I link to above.

I think a curved focus target attributes to slow AF with this lens.

Any lens will have greater difficulty focusing on a curved than a non-curved surface since for the former there is no single point where the entire surface contained within the focus box can be in perfect focus. But on what grounds would the 20 have greater difficulty focusing on a curved surface than other lenses of similar FL?

This is what tests show.

No. For reasons already spelled out above, your tests do not show that and I don't know of any other ones that do either.

Explanation of test results can be a different topic.

One way of putting test results into question is to ask questions about them.

Some time ago I suggested that it might be because of noisy focus motor. Noise is caused by vibration. Vibration also leads to blurred images, and it's much harder for camera to find peak contrast on blurred images. Peak contrast of curved surface is already is harder to determine than of flat surface. And if some contrast samples are impaired by blur this can make AF fail, or it can lead to slow AF.

Have you ever tried focusing the 20 in 14x zoom AF using a remote and watching the screen as you focus? Did you compare with another lens? If so, what did that tell you?

Yes, I did. It told me that I'm not a superhuman. I can't see difference in blurrines on sequential live view frames because the frames are rapidly changing with 60fps frequency. Can you estimate blurriness of individual frames in fast-paced movie sequence? No? Why did you ask this question, then? (you don't have to answer, otherwise this will never stop)

I asked the question because, like you, I see no obvious sign of jitter in spite of the high magnification. So the amplitude of any movement caused by the focus motor must be very low and the impact therefore much smaller than that of handshake (for reasons further detailed below).

One way to see that would be to capture video with high speed camera. Since live view is changing with 60fps rate and there can be a visible transition between frames one would need a camera faster than 120fps to make sure that a single frame is captured without transition to next frame.

Because only few frames in focusing sequence would be more or less sharp these moments are hard to capture. I don't have such camera.

General logic says that vibration reduces quality of image (signal) that CDAF algorithm analyzes, and you can feel the vibration. Then it's easy to see why the algorithm needs more samples to produce good results on lower quality input.
Whether this quality impact is visible to human eye is another matter.

Further, have you examined the impact of hand-shake in the same situation (14x zoom AF)

There is no need to do that.

and how that impact compares in magnitude to any vibration from the focus motor (with the 20 or any other lens)? If so, what did that tell you?

Exposure time for AF is unlikely to be lower than 1/125s.

I am pretty sure that it is slower than that most of the time unless you run the EVF/LCD in high refresh. Normal screen refresh for the E-M5 is 60 Hz (1/60 s rolling shutter) and it probably drops to 30 Hz (1/30 s) when the light is sufficiently low. But the exposure time for each frame is of little importance for the AF signal for reasons spelled out below.

With 40mm equiv. lens one would need to have serious tremor in order to consistently produce fuzzy images because of camera shake.

As I have told you in earlier discussions about this, the point of importance with regard to the AF signal is how things compare between different frames. What the AF system is trying to determine is whether contrast is increasing or not from one frame to another. This depends not only on whether focus is actually improving or not but also on the extent to which you manage to keep the content within the AF frame constant. Of course, your handshake has a far greater impact on variations in that content than anything the focus motor might do.

AF motor of 20mm lens, on the other hand, can generate whole range of frequencies starting from 200Hz (period close to probable low-light AF exposure time) and that would directly affect optical elements.

The lens element shake has an order of magnitude more impact on image quality than camera shake. For example, 8 degrees lens tilt would rotate focus plane by 90 degrees.

This is just a theory, of course. One possible explanation of long-term observation that 20mm F1.7 lens hunts more often than other lenses in the similar conditions.

PS. I thought these questions were rhetorical but you kept reminding about them in later posts, so here are the answers.

Appreciate that you answered them. Now you also know why I asked them.

Because of that 20mm lens may require more AF iterations, and it's more likely to start hunting than other lenses in the same conditions.

This isn't happening in good light, but in low light exposure time during autofocus becomes longer and if it's around 1/125-1/250s the quality of AF samples is very likely to be affected by low-frequency vibration (around 200Hz or so).

You know very well about shutter shock. You can think of this as focus motor shock. You can feel vibration when 20mm is focusing, and camera is taking images when doing it.

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micksh6
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Re: 17/1.8 is significantly faster than the 45/1.8
In reply to Anders W, 4 months ago

Anders W wrote:

NZ Scott wrote:

Anders W wrote:

"Are you claiming that the 17/1.8 is noticeably faster than other modern lenses with similar AF design like the 12/2 and the 45/1.8 included in my test? If so, on what basis do you make that claim?"

Nobody seems to have answered this.

In my experience, the 17/1.8 autofocuses significantly faster than the 45/1.8 under real-world shooting conditions.

I've taken around 5000 photos with the 45/1.8 and 10,000 with the 17/1.8, often switching between the two lenses several times a day.

The difference is especially noticeable in situations that require big changes in focusing distance (ie. from near to far or from far to near) - e.g., when shooting street.

The 45 is occasionally slow enough to miss shots.

See my previous reply to your and Hen3ry's discussion about this earlier on:

http://www.dpreview.com/forums/post/53591384

In short: What you see is what would normally be expected in view of the different FLs and the way you are likely to use them since the focus lens group of the 45 usually has to move more than that of the 17 or 12 (which you noted were both faster in your experience). If you keep the amount of travel the focus lens group has to do constant (as I did in my testing with the 12 and 45), you are likely to see the difference disappear.

That doesn't explain why both 45mm F1.8 and 25mm F1.4 generally focus faster than 20mm F1.7, does it?

This test was conducted when magnifications for two different targets were the same for different FLs. According to your logic lens focusing elements would have to travel the same distance. Still, the results are different for different lenses.

There is something with Oly 45mm that makes its focusing element travel longer when refocusing to closer target under some conditions. In most other cases Oly 45mm is really fast, although 17mm F1.8 is faster.
Without knowing more details a correct answer would be - it all depends on lens design.

And answering your earlier question - why I didn't measure AF time when refocusing at the same target - because this rarely should be done in real life. I can lock focus if I need to.

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