# AF speed 40/2.8 vs 85/1.8 on EOS M



## yakman (Sep 8, 2014)

I already own the 40/2.8 and considering 85/1.8 as a kid portrait lens.

I'm curious on the AF speed on M of 85/1.8 compared to 40/2.8


Btw, I got 70D + Sigma 50/1.4. But I carry M out more often than 70D for casual shots.

Thanks


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## Maximilian (Sep 8, 2014)

*Re: AF speed 40/2.8 vs 85/1.8*



yakman said:


> I already own the 40/2.8 and considering 85/1.8 as a kid portrait lens.
> 
> I'm curious on the AF speed on M of 85/1.8 compared to 40/2.8
> 
> ...


I own both 40/2.8 and 85/1.8.
Although haven't compared them directly, I would say the USM of the 85/1.8 is definitely and noticeablely faster.
But I will check this out as soon as possible.

Edit: I do not have an EOS M (missed this the first time reading), so I can only compare on EOS DSLR body. Sorry.


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## yakman (Sep 9, 2014)

*Re: AF speed 40/2.8 vs 85/1.8*

Thanks all the same.

I think EOS prefer lighter usm lens.
My heavy USM lens certainly not as fast as my light 40/2.8 STM
Hope 85/1.8 can beat the 40/2.8 STM, otherwise it can't be used as a kid lens..


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## Maximilian (Sep 10, 2014)

*Re: AF speed 40/2.8 vs 85/1.8*

Now I had the time to try it out in a quick and dirty test.
Sorry, it took me some time to find the time.

Test conditions:
EF 85/1.8 USM and EF 40/2.8 STM on 5D3 (sorry, no EOS M as already mentioned):
Focus from preset infinity and MFD at a target in about 1 m and 5 m distance. Low Indor light condition.
AF settings on standard and One Shot.
No precise time measurements. 

Result:
The 85/1.8 was about 2 to 3 times faster than the 40/2.8.
The 40/2.8 was much noisier (as expected). 


Hope that helps. Maybe you can got to a stroe and try it out with an EOS M.


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## DRR (Sep 11, 2014)

*Re: AF speed 40/2.8 vs 85/1.8*


A little surprised the 85/1.8 is quieter than the 40mm.... isn't the STM supposed to be a quiet motor?


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## Mt Spokane Photography (Sep 11, 2014)

*Re: AF speed 40/2.8 vs 85/1.8*

Lens testers typically do not measure AF speed, there are too many variables. Its one of those things that varies by camera and by the actual image being photographed, as well as light level and color.

A off camera fixture might be able to test one at varying apertures, voltages (1 series use a higher voltage) without the lighting and camera issues. 

However, the STM focus motor is almost certain to be slower than the USM focus motor in the 85mm f/1.8. Its main feature is usability for video.


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## rs (Sep 11, 2014)

*Re: AF speed 40/2.8 vs 85/1.8*



DRR said:


> A little surprised the 85/1.8 is quieter than the 40mm.... isn't the STM supposed to be a quiet motor?


STM lenses make a high pitch noise, almost similar to a loud version of baldy shielded processor noise leaking into amplifier circuitry. Nothing like the volume of micro motors of older cheap lenses. It's almost completely silent, and great for video work. USM motors are silent to all intents and purposes, although there is typically the noise of components other than the motor - the internals of the lens gliding over each other etc. And of course there's the fairly abrupt torque as the AF system start/stops to achieve its fast focus acquisition speed. This is no good when it comes to slow, smooth video AF requirements as the USM system will go through a constant start/stop sequence.

So - for video with DPAF, STM is significantly quieter and smoother (both for focus smoothness and torque/recoil you feel as you hold the lens), whereas USM is a little quieter and typically much faster for images.


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## Maximilian (Sep 12, 2014)

*Re: AF speed 40/2.8 vs 85/1.8*



DRR said:


> A little surprised the 85/1.8 is quieter than the 40mm.... isn't the STM supposed to be a quiet motor?


AFAIK the 40/2.8 is one of the STM lenses that is NOT silent. 
At least all samples I've seen (and heard) and all about I've read in the internet.

From these two - 85/1.8 and 40/2.8, maybe just my samples - I would only chose the 85 for video. 
The 40 is way to noisy. But I'm more into stills and therfore the shortfourty is a nice lens cap with very good optical performance and decent AF - for a lens cap  I really like it for light traveling and in the evening.


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## DRR (Sep 14, 2014)

*Re: AF speed 40/2.8 vs 85/1.8*

I would not characterize my 40mm as noisy, but I don't shoot much video so it's possible I haven't really paid attention.

I do have both a 50mm f/1.8 and a 35mm f/2 in the stable which are very noisy so perhaps my perceptions are skewed!


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## fwoodman (Sep 14, 2014)

*Re: AF speed 40/2.8 vs 85/1.8*

I own both. The 40mm AF is barely audible (not a motor sound like the 50mm f1.8 ) but can be quite slow especially for tracking my moving kid. The 85 f1.8 AF is really fast since it has USM and quieter. IQ the 40mm is quite good, definetly better than my 24-105, while the 85mm blows both them away.
I personally uses the 40mm more due to a more versatile focal length and lighter on my 5Dmk3.


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## albron00 (Sep 14, 2014)

*Re: AF speed 40/2.8 vs 85/1.8*


Hi,
I have both.
EF 85mm f/1.8 faster than EF 40mm f/2.8.


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## steliosk (Sep 14, 2014)

*Re: AF speed 40/2.8 vs 85/1.8*

i own both lenses too,

the STM motor is a pain in the ass if you want to focus manually through live view.
the USM feels better and is much more responsive.

As it comes to AF, the USM is faster too.

The STM is smooth and quiet on video mode but NOT faster than USM


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## yakman (Sep 16, 2014)

I got both lenses now.
Did a quick test yesterday, all figures below subjective..

On 70D, the 85/1.8 takes half the time or faster than the 40/2.8, every time.
On M, the 85/1.8 is takes around 2/3 the time, in some cases equal..


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## Maximilian (Sep 16, 2014)

yakman said:


> I got both lenses now.


Hi yakman! 

I hope you are pleased with the 85. I like it very much, although it has some CA. 
But for its price it's really a steal.


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## yakman (Sep 17, 2014)

Maximilian said:


> Hi yakman!
> 
> I hope you are pleased with the 85. I like it very much, although it has some CA.
> But for its price it's really a steal.



Absolutely. Thanks
I also just realized my lens group are ready for a upgrade to FF.
But I'll be patiently wait for another three to five years. Hope I can get a FF 70D by then.


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