Autofocus on C100: Anyone test?

[Steve Kimmel]

I searched but couldn't find much on this -- has anyone tested any of the STM lenses with autofocus on the C100? Also, anyone use it, with any lens, in a real-world setting? I'm curious how well it performs.

Thanks.

[Matt Davis]

I purchased the lens, tried it on the C100 and it has the following problems:

1) Very slow autofocus - 2-4 seconds to react and focus

2) Inaccurate autofocus - like most systems, it prefers to focus on the background*

3) The lens is as 'unparfocal' as I've seen - zooming will defocus so much you can't see what you're looking at

4) Iris is servo operated and tracks zoom - the lens iris is said to be between 3.5 and 5.6 depending on zoom setting. If it were the usual iris, you could set it at 5.6 and the image would not lighten as you zoomed out. This is NOT the case with this lens - the iris tracks the zoom.

Therefore, I strongly recommend that you pass on this lens for video use. It's a great 'walkabout' lens for a stills camera, but it's a huge steaming pile of 'liability' on a C100.


* If you want to know what a 'pro style' autofocus system can be like, the Sony FS700 with its 18-200 lens is an absolute joy in comparison - face track, 'tap to focus' (like Red), almost parfocal if you zoom with AF... I miss it. :)

[Steve Kimmel]

Thanks Matt. That's incredibly helpful!

[Mark Dobson]

Hi Matt,

I'm presuming that you are referring to using the C100 autofocus with the Canon EF-S 18-135mm f/3.5-5.6 STM IS lens?

Out of interest did you have 'Zoom Iris Correct' turned on? The reason I ask is that I use this lens with the C300 and have not encountered any of the damning faults you have found and can only assume that these occur as a result of the C100 autofocus functioning inefficiently.

With 'Zoom Iris Correct' turned on the aperture appears to remain constant between the zoomed and zoomed out range of the lens.

And again in manual mode, with autofocus turned off on the barrel, this lens has a very good parfocal capability, zoom in, set the focus, zoom out, the shots is in focus, zoom back in and the focus is still as sharp as a pin head.

I really cannot agree with your statement that ..... 'Therefore, I strongly recommend that you pass on this lens for video use. It's a great 'walkabout' lens for a stills camera, but it's a huge steaming pile of 'liability' on a C100'

I have been using this lens in demanding day and night situations with the C300 for a year now and whilst it is not in the same class as a 'L' lens, especially in the build department, it is a great lens for documentary situations where you just don't have the time to change lenses and need a good wide capability and also want to punch in to get good close ups and cutaways.

The nearest 'L' lens with a similar range is the Canon EF 24-105mm f/4 USM L IS.

Sounds like it would be a good idea to pass on the autofocus function on the C100 and turn off the autofocus switch on any lens you attach to the camera. From what you say the autofocus is very similar to that found on the Blackmagic Pocket Camera recently reviewed by Philip Bloom - not very good.

[Matt Davis]

Mark, you presume correctly.

I did this little video...

Canon 18-135 STM tests on C100 on Vimeo

It does take a few moments (!!!) to recognise the lens has been tweaked. The iris mode is odd.

I've not found a way of getting the autofocus to be any better. As I pointed out, perhaps I'm spoiled by the FS700 and E-mount lenses (and the phase detection AF of certain lenses).

As far as it's parfocalness (erm, you know what I mean), there is absolutely no way - NO WAY - that one would zoom in, focus and zoom out again. No way. We must be talking about different lenses. No. No way. Whatever you're refering to, please take a picture of it and post - it is NOT the lens I'm talking about. You're obviously passionate about the lens you refer to, I'm not going to shout you down about it, but if you zoom in, focus and zoom out, we must be talking about completely different lenses, and I'm interested in what you're talking about. The 18-135 STM does NOT do this. It's a cheap plastic lens, driven by servo motors under software control to achieve a remarkable price/performance ratio. You can't zoom with it, and you can't trust the iris in manual mode - check the video.

[Mark Dobson]

Hi Matt,

I've made a short video - not as comprehensive or detailed as yours but it demonstrates the parfocal ability of the lens and also the lack of variation in the iris appearing to change when zooming in or out.

It's a pretty ugly exercise doing an active zoom on a Canon still lens and I've yet to put one in an edit but when the lens is left wide open at f3.5 - f5.6 there is very little 'hunting' at the beginning and end of the zoom. However when the iris is stepped down to f8 it all gets nasty. Absolutely unusable, however it resolves very quickly if all one is doing is re-framing.

So you might try an experiment with the lens left wide opened, not stopped down, and see how that affects both the parfocal issue and the autofocus.

lens test on Vimeo

[Matt Davis]

*Boggle*!

Your and my experiences differ by such a huge amount, I am left reeling.

Is this:

a) A case of a faulty lens?

b) A difference in control software on the C100?

TBH, when you mentioned Zoom Iris Correct, I had one of those 'Oh Feck' moments and rushed to my camera. Have I really missed this menu control? But it isn't there. I updated the C100's firmware specifically for this lens, and I can't find a 'Zoom Iris Correct' mode.

Virtual pint of beer to anyone who can steer me to it *ON THE C100*, but I've just scanned through and found nada. And again, I guess this explains our difference of experience. Also, as you're from UK too I can use an analogy from Dad's Army in that the focus and iris seem to react to changes in the same way that Corporal Jones did to parade duty. For the rest of the world - Penguins of Madagascar moment: "Well.... This sucks."

[Keith Anderson]

Under Menu>Camera Icon(1st One)scroll down to iris> Zoom-Iris Correct

[Mark Dobson]

[QUOTE=Matt Davis;1810613]*Boggle*!

Your and my experiences differ by such a huge amount, I am left reeling.

Is this:

a) A case of a faulty lens?

b) A difference in control software on the C100?


Hi Matt,

I would be really interested to know whether having 'Zoom Iris Correct' turned on in the C100 and keeping the iris wide open on the lens makes any difference to the autofocus and parfocal capability of the Canon EF-S 18-135mm f/3.5-5.6 STM IS lens.

I basically believe that the C100 and the C300 are inherently the same camera wearing different outfits with the same processor and core recording functions so I would imagine that the lenses would behave the same way on each camera.

I've just read a thread on nofilmschool.com

Paul on 06.29.13 @ 10:19PM
I’ve updated my C100 as well and tested with my 18-135 STM. What’s interesting is that it starts to auto focus very slowly, or even not at all after f8.0. However, t’s very fast and accurate at f3.5-5.6. The auto-iris feature is very impressive, with results mirroring a lens with a clickless aperture.

Be interesting if you have the time to test this out.

[Matt Davis]

Forehead slap moment - yes, I found Zoom Iris Control thingy. Lens iris works as expected in this mode.

Many thanks Mark and Keith - virtual beer to you! Cheers.

However, still not convinced by this lens, due to the autofocus. In fact, even more frustrated now that the iris thing is cured.

The big issue for me is 'waiting for the AF to kick in' in continuous AF, the horror of it losing the focus point when it has kicked in, and the inability to correct it or at least help it.

On my other camera - the Sony EX1-R - you can set it to AF and, if it's not getting a lock, you can manually 'help it' - the focus ring remains active, albeit in its endless spinning mode. If you sense the focus beginning to drift, you can 'hoik' it back. The FS700's kit lens is frightening in this respect, totally 'fly by wire' like the 18-135, but it's tamed by the 'push auto' function and the 'tap to focus' feature.

So, I'm at a loss with the 18-135: autofocus not fast enough to react, can do it better manually, but manual control of lens is a bit 'rubberised' in that the controls and the actuation motors have a healthy whack of latency.

My usual gear test is to spend half an hour trying to film my backyard chickens, and the 24-105 passed this test with flying colours. The 18-135 now has steady exposure (thanks again, erm, another virtual beer!) but we're back to the OPs point: does continuous AF work? For me, no - can't trust it when pressure's on, needs manual override.

But still a great lens for stills on a 550D! :o)

[Mark Dobson]

I presume your new tests were with the lens wide open.

It's definitely a disadvantage to not be able to manually over ride the autofocus. I've noticed that as soon as you flick the autofocus switch on the lens the focus ring is disabled.

And you are right to say it's a great lens for the 550D - can't wait to get one again!