# Question on USM speed on M/M3 with L lenses



## xps (Feb 14, 2015)

Does anybody know, if the speed of an USM powered lens, used on an EosM/M3 shows an delayed reaction when focussing?
I do not mean the AF speed od the camera. A member of our local photoclub has this problem, when he uses one of his L lenses with the adapter on the Eos-M. The original 55-200mm lens works much faster. The camera focusses and about a second later, you can hear and see the reaction of the lens. This phenomenon does not appear with his 55-200mm.

I just ask, because I am a little bit willed to buy the M3, if it has an good IQ.


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## crashpc (Feb 14, 2015)

Nope. My USM primes focus immediately on my M.


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## Luds34 (Mar 2, 2015)

xps said:


> Does anybody know, if the speed of an USM powered lens, used on an EosM/M3 shows an delayed reaction when focussing?
> I do not mean the AF speed od the camera. A member of our local photoclub has this problem, when he uses one of his L lenses with the adapter on the Eos-M. The original 55-200mm lens works much faster. The camera focusses and about a second later, you can hear and see the reaction of the lens. This phenomenon does not appear with his 55-200mm.
> 
> I just ask, because I am a little bit willed to buy the M3, if it has an good IQ.



I have a couple of the original Ms. The few USM primes I have used seem to operate at full speed. Granted the focus ability of the M makes the overall experience slower. However, I have a 70-200 and that focus motor runs sloooow. I don't know why, but take it for what it is.


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## MickDK (Mar 3, 2015)

I think it is because the body needs to power the autofocus motor. The "big whites" was designed to be used with larger DSLRs having larger batteries and (I assume) better power circuitry. 

If my theory is correct the M/M3 should generally focus much faster with small primes and slowest with big zooms


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## mangobutter (Mar 3, 2015)

All my Ls work perfectly on my M. I love the M and would easily pay full original retail for it. Too many people doubting and nitpicking it. If you need absolute speed, use an SLR. Period. For what it is, the M is brilliant.


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## Rocky (Mar 3, 2015)

xps said:


> Does anybody know, if the speed of an USM powered lens, used on an EosM/M3 shows an delayed reaction when focussing?
> I do not mean the AF speed od the camera. A member of our local photoclub has this problem, when he uses one of his L lenses with the adapter on the Eos-M. The original 55-200mm lens works much faster. The camera focusses and about a second later, you can hear and see the reaction of the lens. This phenomenon does not appear with his 55-200mm.
> 
> I just ask, because I am a little bit willed to buy the M3, if it has an good IQ.


Ask your friend to test the AF speed with a fully charged battery and then with an almost empty battery. The result will tell you if the slowness is due to the M itself or a small battery.


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## Mt Spokane Photography (Mar 3, 2015)

The EOS M Cameras use contrast detection for autofocus. Contrast detect works by moving focusing elements inside the lens back and forth to determine the best focus based on image contrast.

Large lenses have heavier and more complex glass focusing groups than the smaller and lighter weight consumer lenses. They also use more powerful motors to move those elements. All of this tends to slow down contrast detect autofocus for lenses with large and heavy glass elements.

This is one reason behind the patent for a EOS-M camera to lens adapter recently posted on CR. The adapter has a small light weight lens element that can move very fast and then send the correct focus information to the attached lens, which then moves straight to the in focus position. The processes decreases time for autofocus. It may never actually happen, but the write up in the patent gives a good insight into the reasons for slow autofocus of the big "L" lenses when used with a contrast detect AF system.

I won't buy a "M" until they add phase detect AF or another technology that is equivalent.


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## Luds34 (Mar 5, 2015)

Mt Spokane Photography said:


> The EOS M Cameras use contrast detection for autofocus. Contrast detect works by moving focusing elements inside the lens back and forth to determine the best focus based on image contrast.



That is not true. The M uses a hybrid system. It seems to work by using on sensor, dedicated phase detection points to get the lens most of the way there and the contrast detection fine tunes it and really locks it in. It's the same sensor in the T4i. I've used the T2i (100% contrast) and the T4i side by side in live view to see the difference. We're talking about a magnitude difference in performance.

From Canon via The Digital Picture:

"The EOS M APS-C sensor features a new Hybrid AF System with a total of 31 AF points which uses the central pixels of the sensor to enable continuous AF when shooting in Live View Mode or when recording EOS Movies. The Hybrid AF system uses a combination of both phase detection and contrast AF to ensure quick and accurate auto focus."


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## Tinky (Mar 5, 2015)

switch off continuous AF in menu
use the bin button to localise the focus mode
forget ai servo set to one shot (not a camera for action, even with fw2)

Enjoy for what it is. A very compact EOS with some caveats.


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## Luds34 (Mar 5, 2015)

Tinky said:


> switch off continuous AF in menu
> use the bin button to localise the focus mode
> forget ai servo set to one shot (not a camera for action, even with fw2)
> 
> Enjoy for what it is. A very compact EOS with some caveats.



+1

Don't forget magic lantern for focus peaking. With BBF I can often pre-focus and the nice little red dots really help me see where my plane of focus is, especially shooting fast aperture or video. 

Speaking of video, I use a little flash bracket, an external mic, and the 18-55 (for IS). The bracket allows two hand holding to be really steady. The external mic guarantees no lens sounds, the IS gives extra stable video. This thing is a nice little home video maker. To your point above, must have continuous focus off as it just hunts too much.


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