Busting the Lens dictates Focus Speed Myth

Started Mar 22, 2013 | Discussions
Sovern
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Busting the Lens dictates Focus Speed Myth
Mar 22, 2013

Why is that I hear so much on this forum and other forums that more expensive lenses especially primes AF faster than cheaper lenses and the kit lens a long with other cheap but more than capable lenses are such a bad lens for AF speed?

I have one of Canon's fastest focusing lenses (Canon 85 1.8 USM) and the kit lens and they both AF at the speed speed no manner the lighting conditions.

I have also had the Tamon 17-50 2.8 and 50 1.8 in the past and have never felt a difference in AF speed between any of these lenses they all lock on focus very fast.

Is this "This lens has faster AF" a myth sort of like how people claim that their $2,000 prime is "sharper" than a $350 primes or zoom (myth in my opinion)?

From what I have read the AF focusing system built on the camera determines the AF speed and not the lens itself (besides cycling between MFD and infinity being a minor difference obviously).

Whats your take on it?

Personally I'm not convinced.

I believe from my own personal experience that the body determines AF speed as my 40D AF's faster than my xsi but all of my lenses AF just as fast/precisely no manner the lighting conditions from my own experience using them myself.

Canon EOS 40D
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Gearóid Ó Laoi, Garry Lee
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Re: Busting the Lens dictates Focus Speed Myth
In reply to Sovern, Mar 22, 2013

I haven't really assessed it except to say that I've never noticed much of a difference UNLESS I fitted a tele-convertor.

Nobody ever says this, except me, but living in Ireland exposes a photographer to a lot of overcast skies. These produce a difficulty for auto-focussing in that there is a reduction in light plus a reduction in contrast. This affect autofocus a lot. If you're shooting in such conditions, try not to have the sky as a background if AF is important.

The best light for AF is what photographers used to call cloudy bright.

AF is an ornery critter. I have a few systems but one is a NEX-7. I bought the 50 f1.8. This has snail-like autofocus in continuous mode which is totally useless for action, BUT if you turn on face recognition in single mode it's fast and fantastically accurate. This makes this combo fab for portraiture..

Not only that but the face frame will move around to follow the face. Huge advantage for portraiture..

That's straying from the point, but interesting..

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Adrian Tung
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Re: Busting the Lens dictates Focus Speed Myth
In reply to Sovern, Mar 22, 2013

It's not the price of the lens that dictates the AF speed, but the AF mechanism.

Try using the 85L, 50L or 180L one day.

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irm
irm
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Re: Busting the Lens dictates Focus Speed Myth
In reply to Sovern, Mar 22, 2013

In simple terms there are two things that affect the focus speed and this from my experience

1/. type of focus drive

2/. camera type - same  lens on a 10D is way slower than on a 1D going back a few years. The higher quality cameras appear to have better drivers.

My experience is 10D, 40D and then the 7D. I have discussed focus speed of the 50 1.4 with a pro and said his was blindingly fast where as on the 10D it was very slow.

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Sovern
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Re: Busting the Lens dictates Focus Speed Myth
In reply to Adrian Tung, Mar 22, 2013

Adrian Tung wrote:

It's not the price of the lens that dictates the AF speed, but the AF mechanism.

Try using the 85L, 50L or 180L one day.

The 85L supposedly AF's noticeably slower than my 85 1.8 according to the lens "gurus". But I don't believe it.

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Sovern
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Re: Busting the Lens dictates Focus Speed Myth
In reply to irm, Mar 22, 2013

I can agree with that. I think it comes down primarily to the camera body and it's AF mechanisms  Some cameras have dedicated processors just for AF which I imagine will speed it up even more.

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Mike K
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Re: Busting the Lens dictates Focus Speed Myth
In reply to Sovern, Mar 23, 2013

Sovern wrote:

Some cameras have dedicated processors just for AF which I imagine will speed it up even more.

The dedicated processors may speed up AF a tad, but the real reason for that feature is for better tracking in AI Servo.  There the processor tries to calculate where the subject is heading and thus anticipates the focus distance.  This is a feature addressing the needs of the professional sports shooter.

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MAC
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Re: Busting the Lens dictates Focus Speed Myth
In reply to Sovern, Mar 23, 2013

Sovern wrote:

Adrian Tung wrote:

It's not the price of the lens that dictates the AF speed, but the AF mechanism.

Try using the 85L, 50L or 180L one day.

The 85L supposedly AF's noticeably slower than my 85 1.8 according to the lens "gurus". But I don't believe it.

The L is slower.  But it can track people fine in AIServo.

Lens speed comes into play in action photography and AI Servo.  That is where the 70-200 F2.8's for sports  shine.

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Freneticburn
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Re: Busting the Lens dictates Focus Speed Myth
In reply to Sovern, Mar 23, 2013

You also have to take into account other factors like the design of the lens, the weight of the elements, etc.  Some lenses go through their distance range with a 90 degree twist while others take 180 degrees or more.  Usually your fast lenses, like 1.2 or 1.4, have the longer twist to fine tune focus better.

I think the lens most certainly determines AF speed but it goes further than if its just USM or not.

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Keith Z Leonard
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Re: Busting the Lens dictates Focus Speed Myth
In reply to Sovern, Mar 23, 2013

Well, having used both, the difference is significant.  I think you are correct that most of the lenses I've used are all just quick, but the 85L is NOT fast, it's actually crazy slow.  I also notice a difference between my 100-400 and my 70-200.  If you think about it, it makes sense that they would be different speeds.  How far the focus ring travels has a lot to do with it, my Sigma 17-50 moves a VERY SMALL amount from closest to infinity focus, put the same motor in a lens that has a lot more focus ring travel and it will be slower.

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meland
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Re: Busting the Lens dictates Focus Speed Myth
In reply to Sovern, Mar 23, 2013

Sovern wrote:

Why is that I hear so much on this forum and other forums that more expensive lenses especially primes AF faster than cheaper lenses and the kit lens a long with other cheap but more than capable lenses are such a bad lens for AF speed?

I have one of Canon's fastest focusing lenses (Canon 85 1.8 USM) and the kit lens and they both AF at the speed speed no manner the lighting conditions.

I have also had the Tamon 17-50 2.8 and 50 1.8 in the past and have never felt a difference in AF speed between any of these lenses they all lock on focus very fast.

Is this "This lens has faster AF" a myth sort of like how people claim that their $2,000 prime is "sharper" than a $350 primes or zoom (myth in my opinion)?

From what I have read the AF focusing system built on the camera determines the AF speed and not the lens itself (besides cycling between MFD and infinity being a minor difference obviously).

Whats your take on it?

Personally I'm not convinced.

I believe from my own personal experience that the body determines AF speed as my 40D AF's faster than my xsi but all of my lenses AF just as fast/precisely no manner the lighting conditions from my own experience using them myself.

There are various factors that affect AF speed in a DSLR using phase detection:

  1. The focal length of the lens - long focus lenses generally focus slower than wide angles (see 5)
  2. The maximum aperture of the lens - a wider maximum aperture will let more light through for the AF system to do it's measurement. However a wider aperture also means that the depth of focus is narrower and this often means that precise focus takes longer to achieve.
  3. The type of AF motor used in the lens - you get what you pay for. The latest USMs are usually faster than cheaper micro motors.
  4. The mass of the lens elements that have to be moved for AF - this is the main reason why the 85mm f/1.2L is not as quick as the 85mm f/1.8 for example.
  5. The distance the lens elements have to be moved for any given focus point change. A lens like a 100mm macro can have several rotations of the focus ring to go from its closest focus distance to infinity. Focus limiters can help keep the focussing within a prescribed range and thus speed things up.
  6. When the lens / AF system was designed - later designs are often faster.
  7. The AF processor in the camera - later designs are often faster.
  8. The AF sensors themselves - later design are often more sensitive.

In many cases it can be hard to tell the difference between AF speeds under 'normal' conditions. The fact is that AF speeds are pretty quick and for users it's not easy to measure AF speeds accurately in any case.

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bhollis
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Re: Busting the Lens dictates Focus Speed Myth
In reply to Sovern, Mar 23, 2013

Sovern wrote:

Why is that I hear so much on this forum and other forums that more expensive lenses especially primes AF faster than cheaper lenses and the kit lens a long with other cheap but more than capable lenses are such a bad lens for AF speed?

I have one of Canon's fastest focusing lenses (Canon 85 1.8 USM) and the kit lens and they both AF at the speed speed no manner the lighting conditions.

I have also had the Tamon 17-50 2.8 and 50 1.8 in the past and have never felt a difference in AF speed between any of these lenses they all lock on focus very fast.

Is this "This lens has faster AF" a myth sort of like how people claim that their $2,000 prime is "sharper" than a $350 primes or zoom (myth in my opinion)?

From what I have read the AF focusing system built on the camera determines the AF speed and not the lens itself (besides cycling between MFD and infinity being a minor difference obviously).

Whats your take on it?

Personally I'm not convinced.

I believe from my own personal experience that the body determines AF speed as my 40D AF's faster than my xsi but all of my lenses AF just as fast/precisely no manner the lighting conditions from my own experience using them myself.

Based on everything I've read, it's pretty clear that the camera body is a factor in focusing speed. But if your supposition is that all lenses focus at the same speed on a given body, you're wrong.

Differences in focusing speed among various lenses is well documented. It's up to you whether you want to believe it. Although you may not notice the differences, that doesn't mean that they don't exist. Personally, I find the difference in focusing speed between my 24-70 f/2.8L II and 100-400L quite apparent. Similarly, the change in focusing speed when I put a 1.4x TC on my 70-200 f/4L IS is very noticeable.

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tonyjr
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Re: Busting the Lens dictates Focus Speed Myth
In reply to bhollis, Mar 23, 2013

It is also little things like IS , condition of battery . For second shot - wether pop up flash is used and you are using burst mode . YES , I know the focus is supposed to be locked in burst bot it drifts when pop-up is used .

I have the 18-55 , 18-55 IS and the 17-55 . The 17-55 is the fastest [ especially in low light ] , then the 18-55 IS and then the 18-55 . The 7D focuses faster than the XTI - period .

There is a big difference between the AF speeds of the  180 , 70-200 , 135-400 and the 70-300

If you think there is no difference , try the new 40 mm 2.8 and the older 35 2.8 in low light  . If you see no difference - canon will probably pay big bucks for your camera .

Granted , some of the new lenses have different coatings that could slow down focusing and better focusing could take longer but I have found older lenses do better in manual anyway .

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Matt
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In reply to Sovern, Mar 23, 2013

I notice a big difference between Ring USM L lens AF and the AF of shitty lenses ...

AF speed depends on the AF motor in the lens and the amount of lenses it has to move over how much of a distance. Here is where primes may have an advantage...

For reasons that arent too clear to me, the body also affects lens speed. That said, if your body is the limiting factor then that may be why you dont see a difference

Sovern wrote:

Why is that I hear so much on this forum and other forums that more expensive lenses especially primes AF faster than cheaper lenses and the kit lens a long with other cheap but more than capable lenses are such a bad lens for AF speed?

I have one of Canon's fastest focusing lenses (Canon 85 1.8 USM) and the kit lens and they both AF at the speed speed no manner the lighting conditions.

I have also had the Tamon 17-50 2.8 and 50 1.8 in the past and have never felt a difference in AF speed between any of these lenses they all lock on focus very fast.

Is this "This lens has faster AF" a myth sort of like how people claim that their $2,000 prime is "sharper" than a $350 primes or zoom (myth in my opinion)?

From what I have read the AF focusing system built on the camera determines the AF speed and not the lens itself (besides cycling between MFD and infinity being a minor difference obviously).

Whats your take on it?

Personally I'm not convinced.

I believe from my own personal experience that the body determines AF speed as my 40D AF's faster than my xsi but all of my lenses AF just as fast/precisely no manner the lighting conditions from my own experience using them myself.

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Limburger
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Re: Busting the Lens dictates Focus Speed Myth
In reply to Sovern, Mar 23, 2013

Sovern wrote:

Why is that I hear so much on this forum and other forums that more expensive lenses especially primes AF faster than cheaper lenses and the kit lens a long with other cheap but more than capable lenses are such a bad lens for AF speed?

I have one of Canon's fastest focusing lenses (Canon 85 1.8 USM) and the kit lens and they both AF at the speed speed no manner the lighting conditions.

I have also had the Tamon 17-50 2.8 and 50 1.8 in the past and have never felt a difference in AF speed between any of these lenses they all lock on focus very fast.

Is this "This lens has faster AF" a myth sort of like how people claim that their $2,000 prime is "sharper" than a $350 primes or zoom (myth in my opinion)?

From what I have read the AF focusing system built on the camera determines the AF speed and not the lens itself (besides cycling between MFD and infinity being a minor difference obviously).

Whats your take on it?

My 50mm 1.8 mkII is slow and my 15-85 is much faster, so in this comparison the lens is decisive.

Personally I'm not convinced.

It's a combination of body and lens.

I believe from my own personal experience that the body determines AF speed as my 40D AF's faster than my xsi but all of my lenses AF just as fast/precisely no manner the lighting conditions from my own experience using them myself.

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brian1366
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Re: Busting the Lens dictates Focus Speed Myth
In reply to Sovern, Mar 23, 2013

Having owned the a number of canon lenses from the 50mm f/1.8 II to the 15-85mm I can say there is a big difference in AF speed on a T2i or T3i. In bright light most focus just fine. The 50mm might take 1 second to focus where a ring USM lens is seemingly instant, probably 100-200mS. But you don't notice is much there because anything under a second is reasonably fast for most shots.

Where you notice the difference is in low light shooting where the camera's AF needs to hunt around a bit to get a focus lock. This is where that slow 50mm f/1.8 is REALLY SLOW as it makes a couple passes back in forth. Yes the ring USM lens is slower than it was in bright light but much faster than the 50mm.

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wildwilly
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Focus locked in burst???
In reply to tonyjr, Mar 23, 2013

"Focus is locked in burst"?

According to my 7D manual p86, in AI Servo mode, focus is continuous while the shutter button is held down.

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Tinu_ch
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In reply to Sovern, Mar 24, 2013

With stationary subjects focus speed rarely is an issue. AF speed is critical for tracking moving subjects especially with long lenses. That's where ring-type USM takes the lead.

Tinu

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Steve Balcombe
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Re: Busting the Lens dictates Focus Speed Myth
In reply to meland, Mar 25, 2013

meland wrote:

3 The type of AF motor used in the lens - you get what you pay for. The latest USMs are usually faster than cheaper micro motors.
...
5 The distance the lens elements have to be moved for any given focus point change. A lens like a 100mm macro can have several rotations of the focus ring to go from its closest focus distance to infinity. Focus limiters can help keep the focussing within a prescribed range and thus speed things up.

One complicating factor is that lower-cost lenses are designed as such from the ground up - you don't just take a high quality lens and stick a cheaper motor in it. So while they will typically have micromotor AF which is inherently slow, they will also be designed with a very short travel so they can get from (say) 5m to infinity in just a few degrees of rotation - which takes a fraction of a second.

But TANSTAAFL and the penalty is less accurate AF (but often perfectly acceptable in an f/4-5.6 lens) and much less satisfactory MF.

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Schwany
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In reply to Sovern, Mar 25, 2013

Sovern wrote:

Why is that I hear so much on this forum and other forums that more expensive lenses especially primes AF faster than cheaper lenses and the kit lens a long with other cheap but more than capable lenses are such a bad lens for AF speed?

Is this "This lens has faster AF" a myth sort of like how people claim that their $2,000 prime is "sharper" than a $350 primes or zoom (myth in my opinion)?

Whats your take on it?

You need to try a larger sampling of lenses, and get in some experience photographing fast moving subjects. I agree that bodies do make a difference in focus speed, but there are certainly faster focusing lenses than others. Canon even makes a point of it in their product literature for the big Whites.

Personally I'm not convinced.

I believe from my own personal experience that the body determines AF speed as my 40D AF's faster than my xsi but all of my lenses AF just as fast/precisely no manner the lighting conditions from my own experience using them myself.

My personal experience differs from yours. I've used and own many lenses. They are not all the same in sharpness nor focus speed. All of them would work equally well for cats though.

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