When I use AF-S instead of AF-C, it's just by mistake. I'm no tripod, I also move, so the AF better keeps on moving, too. I just set an AF-ON button and use this instead of the "normal" shutter button half pressed. It's remarkably quiet, when there's no movement. The only hunting I know in AF-C is the one of the Fuji mirrorless - and I'm very curious about the Kaizen-Firmware update which will be out tomorrow.
Quote:Interesting stuff.
I am strugging with a Tamron 17-50 has well (non-VC). It has a tendency to severely front-focus at times. We're talking static shots where I point the lens at infinity, I have only the center AF point activated, yet focus is somewhere near close-focusing distance. The next shot could be spot on.
Since it's an intermittent problem (50% of shots or more) this is not something for AFMA, which fixes lack of accuracy rather than lack of precision. It irks me that in each case I get focus confirmation.
Focus in live-view works flawlessly, as does focus on my old 400D (and 300D before that, now sold).
I just had an idea. What if I started using AI servo instead of one-shot, even for static shots. It should hunt when AF goes awry. I'd lose focus-recompose unless I use back-button focus. I'll have to give this a try later today.
I had the Tamron 17-50 F2.8 non VC in the Pentax mount. It took me a while to realize why the lens front focused.
After having calibrated it, when shooting fully open the lens was accurate, and from F2.8 it was accurate all FLs and all apertures up to F5 ....as soon as you stopped down to F5.6 or more it front focused........something in the AF algorithms within the lens created this problem, the focus ring would turn about 2mm more front focused, than when F5 was selected on the camera or higher.
I posted here about it asking for anybody to try this test.....no response.....maybe nobody here had the lens.
I also posted my results on DPreview Pentax forum, and Bingo, five or six people ran the test and found the same result!
Many suggested including Klaus that maybe it was there to counteract RSAs, which would seem reasonable..........but it wasn't that......it was a flaw in the programming maybe confined to the K mount, I never looked further at other mounts.
Once I found the problem I rarely stopped down to more than F5 and all shots were in focus.
It was the "sneakiest fault" though, so anyone having front focusing issues with the lens should try the test......check whether the front focus is confined to apertures smaller than F5.
This is of course PDAF though the viewfinder!
Quote: I had the Tamron 17-50 F2.8 non VC in the Pentax mount. It took me a while to realize why the lens front focused.
After having calibrated it, when shooting fully open the lens was accurate, and from F2.8 it was accurate all FLs and all apertures up to F5 ....as soon as you stopped down to F5.6 or more it front focused........something in the AF algorithms within the lens created this problem, the focus ring would turn about 2mm more front focused, than when F5 was selected on the camera or higher.
I posted here about it asking for anybody to try this test.....no response.....maybe nobody here had the lens.
I also posted my results on DPreview Pentax forum, and Bingo, five or six people ran the test and found the same result!
Many suggested including Klaus that maybe it was there to counteract RSAs, which would seem reasonable..........but it wasn't that......it was a flaw in the programming maybe confined to the K mount, I never looked further at other mounts.
Once I found the problem I rarely stopped down to more than F5 and all shots were in focus.
It was the "sneakiest fault" though, so anyone having front focusing issues with the lens should try the test......check whether the front focus is confined to apertures smaller than F5.
This is of course PDAF though the viewfinder!
Thanks for the suggestion! The problem exists at f/2.8.
If I look through the lens, point to infinity, and repeatedly half-press the shutter button, the lens will refocus at seemingly random spots, beeping every time for autofocus confirmation. I've gotten used to keeping a finger on the focus ring and sensing whether it turns to the right, towards infinity.
12-02-2017, 08:16 AM
(This post was last modified: 12-02-2017, 08:17 AM by aleras.)
Quote:2. Some lenses can do inaccurate, or "crude" AF steps when the camera is going through its AF algorithms. They basically mess up what the camera accurately says about where focus should be reached. Your Tamron 17-50mm is an example of such a lens. The Tamron service center has tried to lessen the inaccuracy of the steps the lens makes, to make it step more in line with what the camera body tells it to do. The Canon 35mm f2 and 70-200mm f4 L do not make such inaccurate steps, and hence produced better focus results without the need of "calibration".
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Hope that sheds some light on how PD AF works, and why you have had trouble with that Tamron.
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Your Tamron will not behave the same on the M5 as it does on your 1000D. There are some lenses which will not focus well or at all with live view, because their AF implementation is just that horrible, but probably that Tamron is not one of those. But you just have to try that out and see. The work your Tamron has seen being done to it in service centers will not have a negative bearing on how it functions on an EOS M5, or another Canon APS-C DSLR, for that matter. Your Canon lenses will focus pretty accurately on an EOS M5 (or even a EOS M (the 1st EOS M camera).
Now that makes a heck lotta sense to me now after re-reading your comments again. After Tamron Service fixed a very obvious front-focus issue (they did confirm that to me verbally back then over the phone), they adjusted the lens a couple of times until the front-focus was basically gone. However, I still observe(d) (to this day) that sometimes the AF focal plane is just not where I expect it, sometimes slightly behind, sometimes slightly before. I always attributed this to some manufacturing/adjustment "tolerance ranges" between Canon, Tamron, EF lens mount specs, etc. - and eventually started to doubt my own photography skills and thought I'm getting older and can't keep the camera still and micro movements messed up my focus - until not so long ago I took a series of pictures using a tripod (I don't use a tripod often) where I observed that the AF was not spot on a lot of times.
The crude AF steps could explain this - it's sometimes just slight off - a big before or behind the focal plane. And I never observed this with my Canon lenses. By any chance, do you know if crude AF stepping is a general issue with Tamron? Or just certain lenses? And do you know if this is the same with Sigma, e.g. the Sigma 17-50 f/2.8? And could we safely assume Canon is generally not doing such crude things? 
Quote:Thanks for the suggestion! The problem exists at f/2.8.
I can basically confirm that as well - on my Tamron 17-50mm (VC version) it appears to randomly happen at any aperture.
(However, in general, I have to say the few times I used live view for focusing, my impression was the focus typically was more "spot on" than focusing through the mirror. Not sure how that fits into all of the above .... I could be wrong here though. )
The Sigma 17-50mm f2.8 appears (from accounts of users on forums) to be better regarding how it focusses. Lenses from 3rd party manufacturers (Sigma, Tamron) have gotten better the last few years, regarding focus accuracy (at lest on Canon). But some Sigma Art lenses appear to still have some issues (often the 35mm f1.4 Art from Sigma gets mentioned on forums regarding inconsistent focus).
Sigma might have addressed the issues (if there are some) with firmware update 1.03 (for the 35/1.4 on Nikon, released Mid 2016). My guess (!) is that a lot of users complaining about focus inaccuracies haven't the dock or the latest firmware on their lens.
Of course, a lens should be doing alright out of the box - but what to do with newer camera models? With different behavior regarding AF? Third party manufacturers have to develop the firmware of their lenses by reverse engineering - that can't be as good as the original firmware of camera manufacturers. Doesn't alter the fact that few genuine lenses are optically better than the Art or Sports series - I'm not so sure about contemporary, I don't have one.
But what good is "being better optically" for, if one sees that only sometimes, when the AF hits the spot? To be fair, I can't tell much about comparisons between genuine and 3rd party lenses. I exchanged 24/1.4, 50/1.4 and 24-85 (that's simply a no good for anything lens for me, distortions are at the unpleasant side of things) with Sigma Art. I'm hesitating to replace the 85/1.4 as the weight difference of the Sigma pendant is massive. But optically it's no question, the Sigma doesn't let the older Nikkor look good.
Anyway, to me the Nikkors were not that much more reliable in focusing wide open at certain distances to stay in a negative opinion about 3rd party glass. And once I was very much convinced, it's best to use genuine lenses.
I wanted a 35/1.4, the Sigma had AF and was half the price of the Nikkor. It got very good reviews so there was only a little risk - in case things would have gone bad, I'd had to replace it, but it's very often in my bag, sometimes with no partner lens.
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