What matters more for autofocus, the lens or the body

[Guest]

This is just for knowledge .

I was just reading an article the sigma 85mm f1.4 art vs canon 85mm f1.2 for fun an i came across a part where it said that sigma was much better at autofocus than the canon.

I always thought it was the camera body that mattered for autofocus .

Like canon's 70D-80D are famous for their dual pixel autofocus , but I'd never heard of a lens affecting the autofocus performance.

Coming to the main question here, how much does a lens contribute to the autofocus ?

[79wjd]

The camera has the auto focus system, but not all cameras have an auto focus motor. So depending on the specific camera and your perspective, both can be more important. 

[Electronics Wizardy]

well the autofocus motor can only move so fast, so often cheap lenses focus faster as there lighter.

 

dual pixel is only for video and live view.

 

For normal stills, the 1d and 7d ii 5d iv have very good auto focus, with the 80d next, with everything else being worse.

[Electronics Wizardy]

1 minute ago, djdwosk97 said:

The camera has the auto focus system, but not all cameras have an auto focus motor. So depending on the specific camera and your perspective, both can be more important. 

almost no modern cameras have a autofocus motor, its in the lens.

[Guest]

2 minutes ago, djdwosk97 said:

The camera has the auto focus system, but not all cameras have an auto focus motor. So depending on the specific camera and your perspective, both can be more important. 

OK so lets keep the body a constant , say I have a canon 80d what will be the difference in autofocus between a sigma 18-35 f1.8 and a canon 24mm f2.8 STM lens , especially during video?

[79wjd]

2 minutes ago, Electronics Wizardy said:

almost no modern cameras have a autofocus motor, its in the lens.

The D7500 does, and I would assume a lot of Nikon's current DSLRs still do.

[m0k]

higher quality lenses can compliment a good autofocus system 

 

ex. my nifty 50 (50mm f1.8) is a dirt cheap POS lens is made of plastic and only a few lens elements. its autofocus is always misfiring on me

[Guest]

Just now, djdwosk97 said:

The D7500 does, and I would assume a lot of Nikons current DSLRs still do.

Out of curiosity , D7500 has an autofocus motor and so does the new nikon lenses like 50mm f1.8 G lens , then which of them actually gets used , the one in the camera or the one in the lens?

[johnt]

 

5 minutes ago, Electronics Wizardy said:

almost no modern cameras have a autofocus motor, its in the lens.

All mid tier and higher end Nikon cameras have built-in autofocus motors to maintain compatibility with older lenses.

[79wjd]

4 minutes ago, SarthakDhonchak said:

Out of curiosity , D7500 has an autofocus motor and so does the new nikon lenses like 50mm f1.8 G lens , then which of them actually gets used , the one in the camera or the one in the lens?

I think the one in the camera. 

[johnt]

1 minute ago, SarthakDhonchak said:

Out of curiosity , D7500 has an autofocus motor and so does the new nikon lenses like 50mm f1.8 G lens , then which of them actually gets used , the one in the camera or the one in the lens?

The camera's built-in motor is for older lenses. The lens's built-in motor will get used if it has one over the cameras. Nikon's G lenses all have built-in motors. Nikon's D lenses do not.

[Guest]

Thanks Everyone

[AkiraDaarkst]

34 minutes ago, SarthakDhonchak said:

This is just for knowledge .

I was just reading an article the sigma 85mm f1.4 art vs canon 85mm f1.2 for fun an i came across a part where it said that sigma was much better at autofocus than the canon.

I always thought it was the camera body that mattered for autofocus .

Like canon's 70D-80D are famous for their dual pixel autofocus , but I'd never heard of a lens affecting the autofocus performance.

Coming to the main question here, how much does a lens contribute to the autofocus ?

Neither and both are equally important.  What's more important is for the AF system to be properly calibrated.  It doesn't really matter if the AF motor is inside the lens or the body, as long as there is one.  What matters is that the AF system is properly tuned so that it can turn the motor precisely and detect when the scene is accurately in focus.  Even expensive lenses can have AF inaccuracy issues and that's why a lot of cameras tend to have AF fine tuning options somewhere in the menu.  (Or if there isn't an AF fine tuning option in the menu, then at least some mechanical system for fine tuning AF but this is something amateurs should not mess around with.)

 

Sigma makes a USB lens mount dock (specific for each type of lens mount they utilize) that lets you calibrate and fine tune the focusing of their Art, Sports and Contemporary line of lenses.

 

And if you want to know how to calibrate a lens, read this article;

https://photographylife.com/how-to-calibrate-lenses/

[AkiraDaarkst]

23 minutes ago, mok said:

higher quality lenses can compliment a good autofocus system 

 

ex. my nifty 50 (50mm f1.8) is a dirt cheap POS lens is made of plastic and only a few lens elements. its autofocus is always misfiring on me

That's because the focus system is badly calibrated, likely from the beginning at the factory. It has nothing to do with being cheap or expensive.

[johnt]

This is a tricky question to answer. Auto focus systems are a function of the camera and the lens. The camera knows when the image is in focus and some cameras are marginally faster than others. The motor inside lens can only control how fast the focus ring moves, but it cannot improve the camera's accuracy. If the accuracy of the camera's system is not very good, it may trigger the lens to continue sweeping until the camera can confirm it's in focus. So in some regard, the accuracy of the camera's system can govern the total auto focus speed.

 

The conclusions from the article you read is rather misleading for many reasons. The Sigma is significantly newer than the Canon so it was probably designed with a faster motor. The Canon f/1.2 is a beast with heavier elements. Auto focus systems generally focus wide open and then close down the aperture blades for the shutter actuation. Meaning f/1.2 is probably not as easy for the camera's auto focus system to determine accuracy as f/1.4. It's a third of a stop different, but everything at f/1.2 is cream. 

[Guest]

4 minutes ago, AkiraDaarkst said:

Neither and both are equally important.  What's more important is for the AF system to be properly calibrated.  It doesn't really matter if the AF motor is inside the lens or the body, as long as there is one.  What matters is that the AF system is properly tuned so that it can turn the motor precisely and detect when the scene is accurately in focus.  Even expensive lenses can have AF inaccuracy issues and that's why a lot of cameras tend to have AF fine tuning options somewhere in the menu.  (Or if there isn't an AF fine tuning option in the menu, then at least some mechanical system for fine tuning AF but this is something amateurs should not mess around with.)

So, if a person doesn't have multiple copies of the same lens lying with him , how does one know that a lens is not properly calibrated ?

[AkiraDaarkst]

1 minute ago, SarthakDhonchak said:

So, if a person doesn't have multiple copies of the same lens lying with him , how does one know that a lens is not properly calibrated ?

Use a focus test chart or system.  Refresh the page and re-read my first comment.

[Guest]

1 minute ago, AkiraDaarkst said:

Use a focus test chart or system.  Refresh the page and re-read my first comment.

Thanks

[Guest]

5 minutes ago, JohnT said:

This is a tricky question to answer. Auto focus systems are a function of the camera and the lens. The camera knows when the image is in focus and some cameras are marginally faster than others. The motor inside lens can only control how fast the focus ring moves, but it cannot improve the camera's accuracy. If the accuracy of the camera's system is not very good, it may trigger the lens to continue sweeping until the camera can confirm it's in focus. So in some regard, the accuracy of the camera's system can govern the total auto focus speed.

 

The conclusions from the article you read is rather misleading for many reasons. The Sigma is significantly newer than the Canon so it was probably designed with a faster motor. The Canon f/1.2 is a beast with heavier elements. Auto focus systems generally focus wide open and then close down the aperture blades for the shutter actuation. Meaning f/1.2 is probably not as easy for the camera's auto focus system to determine accuracy as f/1.4. It's a third of a stop different, but everything at f/1.2 is cream. 

Maybe , but i personally don't find it misleading. Yes the canon may be old and with heavier elements leading to slower autofocus.

But Sigma is faster at autofocus for whatever reasons is a fact and it is in noway misleading.

[AkiraDaarkst]

39 minutes ago, SarthakDhonchak said:

Out of curiosity , D7500 has an autofocus motor and so does the new nikon lenses like 50mm f1.8 G lens , then which of them actually gets used , the one in the camera or the one in the lens?

If the lens has a focus motor inside, there's no mechanism on the lens mount for the camera body's focus motor to do anything to the lens.  The lenses with built in focus motors have a recessed notch on the lens mount instead of a screw for the in-body motor to turn.

 

Lens with screw for in-body AF motor to focus the lens.  Lenses with AF motors will not have that screw.

 

EDIT: my mistake, lenses with in-lens AF motors will not have a notch.  The AF motor pin in the camera body is spring loaded and will get pushed back into the body when lenses with in-lens focus motors are mounted.

 

43 minutes ago, Electronics Wizardy said:

almost no modern cameras have a autofocus motor, its in the lens.

Apart from the two lower tier of Nikon cameras (i.e. Nikon D3#00 and D5#00 series), all Nikon camera bodies above them should have in-body AF motors.

[AkiraDaarkst]

49 minutes ago, Electronics Wizardy said:

well the autofocus motor can only move so fast, so often cheap lenses focus faster as there lighter.

AF speed is also dependent on the type of motor used.  Old Nikon lenses (non-G) have slower motors than newer lenses which uses ultrasonic motors or better.

13 minutes ago, SarthakDhonchak said:

Maybe , but i personally don't find it misleading. Yes the canon may be old and with heavier elements leading to slower autofocus.

But Sigma is faster at autofocus for whatever reasons is a fact and it is in noway misleading.

 

[AkiraDaarkst]

49 minutes ago, SarthakDhonchak said:

OK so lets keep the body a constant , say I have a canon 80d what will be the difference in autofocus between a sigma 18-35 f1.8 and a canon 24mm f2.8 STM lens , especially during video?

This answer will depend on the AF system the camera uses and can be spot on or have a lot of focus hunting issues.  As for the differences between the two lenses, depending on the type of motor used the AF during video could either be silent or noisy (something that an in-body mic or mic placed close to the lens will pick up), and AF tracking/performance can either be smooth or jittery.

 

Another issue regarding AF during video is how the AF system works. Does it give priority to elements that are closer to the middle of the frame even if they are far away or to whatever element is closest to the camera even if they are located in the far corner of the frame.  AF systems are not intelligent or telepathic.  They have no clue what you are trying to focus on.  You could be trying to film a scene where your main talent is positioned off center in the frame but the AF system thinks the tree located far in the distance is what it should be focusing on because it's right in the middle of the viewfinder or you are trying to keep focus on the person standing in the middle of the viewfinder frame but a bird flies into the shot from the side.

[johnt]

40 minutes ago, SarthakDhonchak said:

Maybe , but i personally don't find it misleading. Yes the canon may be old and with heavier elements leading to slower autofocus.

But Sigma is faster at autofocus for whatever reasons is a fact and it is in noway misleading.

Well now I'm a little confused. Your original post you wrote the article said the Sigma had "better" auto focus. Now you're saying "faster." I was listing the reasons why I thought the Sigma would be considered "better" at auto focusing, and lens speed could be one of them.

 

Basically between the two lenses on the same camera body, the only difference can be speed since they both have a built-in motor, and the accuracy of the focus is determined by the same sensor in the camera. So how can a lens have "better" auto focus than another on the same camera? Did they just mean faster?

[Guest]

8 hours ago, JohnT said:

Well now I'm a little confused. Your original post you wrote the article said the Sigma had "better" auto focus. Now you're saying "faster." I was listing the reasons why I thought the Sigma would be considered "better" at auto focusing, and lens speed could be one of them.

 

Basically between the two lenses on the same camera body, the only difference can be speed since they both have a built-in motor, and the accuracy of the focus is determined by the same sensor in the camera. So how can a lens have "better" auto focus than another on the same camera? Did they just mean faster?

Well , I apologize, you're right. 

Faster and better are two different things and I got confused and took them both as the same.

I rechecked and it says faster , not better.

[johnt]

8 hours ago, SarthakDhonchak said:

Well , I apologize, you're right. 

Faster and better are two different things and I got confused and took them both as the same.

I rechecked and it says faster , not better.

No worries! I was trying to figure out what's going on. Sometimes I'm crazy.

 

For sure then. The article is not misleading. Sigma's auto focus is expected to be faster... that's definitely not reflected in the price though