Carefull: 70D AF Problems!

Started Dec 13, 2013 | Discussions
n0tinus3 Junior Member • Posts: 27
Carefull: 70D AF Problems!

Hi all,

it seems like not many people pay attention to a problem i think many 70Ds have. The center AF sensor is buggy when working with big appertures like f1.4 - 2.5 and long distances. Liveview AF is great though.

To proove my point I shot 21 shots with Canon 50mm f1.8 with same Settings (1/200, iso 200, f2.5).

First column is Center AF Sensor
Second column is Top AF Sensor
Third is 450D with same Glas and Settings.

I sorted the pictures: On the top you see the manual focused referrence and then the shots sorted from "ugly" to "well focused". I think you see the Problem. In german communities there're more and more people noticing this problem!

Even dpreview had this problem, but didn't point it out correctly.

eos 70D center AF issue

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Lanidrac Veteran Member • Posts: 8,069
Re: Carefull: 70D AF Problems!

n0tinus3 wrote:

Hi all,

it seems like not many people pay attention to a problem i think many 70Ds have. The center AF sensor is buggy when working with big appertures like f1.4 - 2.5 and long distances. Liveview AF is great though.

To proove my point I shot 21 shots with Canon 50mm f1.8 with same Settings (1/200, iso 200, f2.5).

First column is Center AF Sensor
Second column is Top AF Sensor
Third is 450D with same Glas and Settings.

I sorted the pictures: On the top you see the manual focused referrence and then the shots sorted from "ugly" to "well focused". I think you see the Problem. In german communities there're more and more people noticing this problem!

Even dpreview had this problem, but didn't point it out correctly.

eos 70D center AF issue

Have you tested this situation with another lens on both cameras? How about f/8?

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DVT80111 Veteran Member • Posts: 3,763
Cheapo lens, surprise?
1

The 50/F1.8 Focus inaccuracy problem is a well known.  There is no close-loop feedback for optical AF.

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WilbaW
WilbaW Forum Pro • Posts: 11,599
Re: Cheapo lens, surprise?
4

DVT80111 wrote:

The 50/F1.8 Focus inaccuracy problem is a well known.

True. It seems to be due to spherical aberration making it hard for the AF sensors to determine when the subject is in focus.

There is no close-loop feedback for optical AF.

False. All AF processes are closed-loop control systems. You can prove it for yourself with these tests.

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OP n0tinus3 Junior Member • Posts: 27
Re: Cheapo lens, surprise?

DVT80111 wrote:

The 50/F1.8 Focus inaccuracy problem is a well known. There is no close-loop feedback for optical AF.

Yes, but then the statistics of ugly shots would be always the same, doesn't matter which camera or sensor. Agreed?

Have you tested this situation with another lens on both cameras? How about f/8?

Me not, because i don't habe any other lenses with such big apperture, but several other users have. With f/8 there is no problem because DOF is too big too see the error even if the focus is false.

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R2D2 Forum Pro • Posts: 22,303
Re: Cheapo lens, surprise?
2

DVT80111 wrote:

The 50/F1.8 Focus inaccuracy problem is a well known.

Right.  The 50mm f/1.8 is the last lens that I'd expect consistent AF from.

The drive control just isn't up to the task.

R2

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R2D2 Forum Pro • Posts: 22,303
Re: Cheapo lens, surprise?
2

n0tinus3 wrote:

Yes, but then the statistics of ugly shots would be always the same, doesn't matter which camera or sensor. Agreed?

Then just MFA the lens.  Or exchange it.

My 70D focuses incredibly well with large apertures.

R2

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OP n0tinus3 Junior Member • Posts: 27
Re: Cheapo lens, surprise?

R2D2 wrote:

DVT80111 wrote:

The 50/F1.8 Focus inaccuracy problem is a well known.

Right. The 50mm f/1.8 is the last lens that I'd expect consistent AF from.

The drive control just isn't up to the task.

R2

If  I use manual focus through viewfinder camera gives me a signal that the focus is alright, but the image is crap!

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WilbaW
WilbaW Forum Pro • Posts: 11,599
Re: Cheapo lens, surprise?
1

R2D2 wrote:

DVT80111 wrote:

The 50/F1.8 Focus inaccuracy problem is a well known.

Right. The 50mm f/1.8 is the last lens that I'd expect consistent AF from.

It's very consistent, the problem is it gets focussed in two places.

The drive control just isn't up to the task.

That's a myth, the drive control exceeds requirements. All evidence suggests it's an optical problem.

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WilbaW
WilbaW Forum Pro • Posts: 11,599
Re: Cheapo lens, surprise?
1

n0tinus3 wrote:

If I use manual focus through viewfinder camera gives me a signal that the focus is alright, but the image is crap!

If you have a means of fine position control, like a macro slide you can wind with delicate control, you can try The Beep Test. Set up the camera with the centre AF point, f/2.8, 50/1.8 in MF, close to in-focus on a subject near MFD.

Trigger AF (hold a half-press or AF-ON) and move towards focus. The camera will beep when it sees the subject in focus. Get a feel for exactly where that is, and take a shot. Approach from the other side of in-focus and compare the shots. Compare with shots taken in AF from gross front and rear-focus (you might have to take a few to get examples of both focus positions).

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Y Hafting
Y Hafting Contributing Member • Posts: 787
Re: Carefull: 70D AF Problems!
2

n0tinus3 wrote:

Hi all,

it seems like not many people pay attention to a problem i think many 70Ds have. The center AF sensor is buggy when working with big appertures like f1.4 - 2.5 and long distances. Liveview AF is great though.

To proove my point I shot 21 shots with Canon 50mm f1.8 with same Settings (1/200, iso 200, f2.5).

First column is Center AF Sensor
Second column is Top AF Sensor
Third is 450D with same Glas and Settings.

I sorted the pictures: On the top you see the manual focused referrence and then the shots sorted from "ugly" to "well focused". I think you see the Problem. In german communities there're more and more people noticing this problem!

Even dpreview had this problem, but didn't point it out correctly.

eos 70D center AF issue

The 70D focus points work down to f2.8. When you open wider, the correct focus changes particularly in the outer part of the frame, thus you will be able to focus better manually. This is quite visible at the dpreview test of the 50mm 1.8:

http://www.dpreview.com/lensreviews/canon_50_1p8_ii_c16/3

I'm not saying that there can't be an issue with your 70D, but if you are going to test focus accuracy of your camera, you should open as much as your focus point sees, no more.

BTW the site hosting your image offers the users scam based popup ads. Id suggest using dpreview for hosting your forum-post images to avoid this.

-Yngve

R2D2 Forum Pro • Posts: 22,303
Re: Cheapo lens, surprise?
2

WilbaW wrote:

R2D2 wrote:

DVT80111 wrote:

The 50/F1.8 Focus inaccuracy problem is a well known.

Right. The 50mm f/1.8 is the last lens that I'd expect consistent AF from.

It's very consistent, the problem is it gets focussed in two places.

Right.  1. Bad, and 2. Worse.  LOL.

My most recent copy was all over the place, and by varying amounts.  Just set yours on a tripod in a good testing environment and shoot off a bunch of shots.  You'll soon see where it gained its reputation.

The drive control just isn't up to the task.

That's a myth, the drive control exceeds requirements. All evidence suggests it's an optical problem.

BS. There are other lenses with the same optical formula (or with even worse spherical aberration) that focus much better than this one.  Just do the tests.

IMHO if the OP requires (much) better AF at a low cost, then they should consider the 40 STM (if they can live without the extra stop).  It's been a simply outstanding performer on my 70D.

R2

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WilbaW
WilbaW Forum Pro • Posts: 11,599
Re: Cheapo lens, surprise?

R2D2 wrote:

WilbaW wrote:

R2D2 wrote:

DVT80111 wrote:

The 50/F1.8 Focus inaccuracy problem is a well known.

Right. The 50mm f/1.8 is the last lens that I'd expect consistent AF from.

It's very consistent, the problem is it gets focussed in two places.

Right. 1. Bad, and 2. Worse. LOL.

Depends on calibration. My calibrated 50/1.8 is 1. perfect all the time, and 2. always in the same place outside the f/2.8 DOF near MFD, but you never know which one you're going to get. With the 450D I could get 1. "every" time by pre-focussing behind the subject, but that doesn't work with the 60D.

My most recent copy was all over the place, and by varying amounts. Just set yours on a tripod in a good testing environment and shoot off a bunch of shots. You'll soon see where it gained its reputation.

Here we go again - you're going to keep implying I've never tested one, no matter how many times I tell you I have and provide intimate details of its performance from first-hand experience, right? 

The drive control just isn't up to the task.

That's a myth, the drive control exceeds requirements. All evidence suggests it's an optical problem.

BS. There are other lenses with the same optical formula (or with even worse spherical aberration) that focus much better than this one. Just do the tests.

Try to find the smallest step (in mm of camera-to-subject distance) the drive control can take near MFD. Hint - use CD AF.

IMHO if the OP requires (much) better AF at a low cost, then they should consider the 40 STM (if they can live without the extra stop). It's been a simply outstanding performer on my 70D.

Yes, I don't recommend the 50/1.8 unless you're shoot at f/2.8 or tighter and you're using live AF or deep DOF, and even then I'd recommend spending the extra $50 for the 40/2.8.

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OP n0tinus3 Junior Member • Posts: 27
Re: Carefull: 70D AF Problems!

The 70D focus points work down to f2.8. When you open wider, the correct focus changes particularly in the outer part of the frame, thus you will be able to focus better manually.

Interesting thoughts. Nevertheless, i assumed the focus works always with widest apperture. And apperture becomes smaller only when the shot is done.

I did the MFA and have better Results now. What do you think, are these ok? Should I keep the cam? I've got not much time anymore to bring the cam back. And i tested so long and did a lot pixel peeping, that i have real paranoya now and don't know what's good and what is not. ^^

Please help.

as you can see Center AF is much better now. The Top one is... the same? But the right one sucks some how. Does it because of the lense?

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Dale Buhanan Veteran Member • Posts: 4,280
Re: Carefull: 70D AF Problems!
2

n0tinus3 wrote:

The 70D focus points work down to f2.8. When you open wider, the correct focus changes particularly in the outer part of the frame, thus you will be able to focus better manually.

Interesting thoughts. Nevertheless, i assumed the focus works always with widest apperture. And apperture becomes smaller only when the shot is done.

I did the MFA and have better Results now. What do you think, are these ok? Should I keep the cam? I've got not much time anymore to bring the cam back. And i tested so long and did a lot pixel peeping, that i have real paranoya now and don't know what's good and what is not. ^^

Please help.

as you can see Center AF is much better now. The Top one is... the same? But the right one sucks some how. Does it because of the lense?

Anything like that with a soft side pretty much has to be a lens issue unless the target was not totally perpendicular to the lens axis.  The camera body seems fine.  Best wishes.

edit:  Another thing that could cause this issue is shooting with a large aperture and the lens having some field curvature.  That will pretty much straighten itself out at longer distances and smaller apertures.

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kind regards
Dale

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bull detector New Member • Posts: 4
Re: Cheapo lens, surprise?

I was very keen on upgrade to the canon 70d. Well you just change my mind. Looking at canon 7d or nikon D7100. I have the canon 500d and it serve me well. I only have twoo lenses so if I want to make a change I must do it now! Think its time for me to move on!!!! Thanks

Pacific462
Pacific462 Regular Member • Posts: 122
Re: Cheapo lens, surprise?
1

Seriously, I would try the camera myself rather than jump to any conclusions based on the strength of a forum post.

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R2D2 Forum Pro • Posts: 22,303
Re: Cheapo lens, surprise?

bull detector wrote:

I was very keen on upgrade to the canon 70d. Well you just change my mind. Looking at canon 7d or nikon D7100. I have the canon 500d and it serve me well. I only have twoo lenses so if I want to make a change I must do it now! Think its time for me to move on!!!! Thanks

Don't be too hasty.  The 70D's autofocus runs rings around the other two cameras on your list.  Take it from those of us who have actually been using the camera day in and day out.

R2

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Jerry-astro
Jerry-astro Forum Pro • Posts: 16,600
Seriously? Really? LOL
1

bull detector wrote:

I was very keen on upgrade to the canon 70d. Well you just change my mind. Looking at canon 7d or nikon D7100. I have the canon 500d and it serve me well. I only have twoo lenses so if I want to make a change I must do it now! Think its time for me to move on!!!! Thanks

Are you serious?  You read one thread and make an important decision like that?  Geez, I hope you don't purchase automobiles and other expensive toys with the same level of research.  I might gently suggest that you look through a few other threads before jumping to conclusions.  There are hundreds of accounts here by photographers who shoot some really challenging subjects (e.g. birds) that love the 70D's AF, and in some cases decided to replace their 7Ds with one.  Given the differences in ergonomics, build quality, etc., that says something about how compelling the 70D really is.

If jumping to Nikon is what you had in mind anyway, go for it.  But doing so based on just this thread sounds more like a good excuse to do what you were planning anyway rather than any legitimate attempt to gather some facts.

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bill hansen Forum Pro • Posts: 10,025
Re: Carefull: 70D AF Problems!
1

If Live View AF is working well and focus through the viewfinder is not accurate, it's very likely that you need to microadjust your lens. It seems that you're using an aperture which has a very thin DOF to begin with, and then focusing on something relatively distant, which makes an even thinner DOF. That's a very severe test - not of the 70D camera it self, but of *your* particular camera-lens combination.

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