2 x 5d3s and 1 7D2 all front focusing - is it a Canon DoF choice?

I'm new here but have now read a lot of threads and decided to yesterday, take 1/2 a day, and methodically go lens by lens, camera by camera and do a Dot-Tune, mico-focus, of each lens on each camera to see what I got.

First of all, mathematically I understand and get that there is a slightly larger area of critical focus behind the spot focused area than in front of the 'zeroed' spot so before I give the details of what I found, it would seem to me that Canon has chosen to set up their cameras with this 'mathematical fact' and all that I discovered is just the fact that Canon did this as oppose to 'equalizing' this PLANE of focus evenly (Forward and Aft). I did also find that a few lens lay outside this and always were in the same direction.


So, I have:
- two 5D3s
- a new 7D2
- L Primes (35 F1.4, 50 F1.2, 85 F1.2, 100 F2.8 macro, 135 F2, 200 F2.8)
- L zoomes (24-70 II, 70-200 II F2.8, 70-200 II F4.0)


I came across the Dot Tune Auto Focus Micro Adjustment method and decided to see if I could do it (it is easy) because I haven't been happy with all my lenses and I just wanted to know if they were good or not.

(The video I watched before I started)
https://www.youtube.co​m/watch?v=7zE50jCUPhM&​hd=1


I did a Google Search for Auto Focus Charts and printed off 2 identical charts that I put at two different spots to check initially if they would both give the same results as I wanted to make sure different lighting wasn't a factor - they were both the same after a few checks so I then set up 2 stations with taped off marks on the floor using (50 x Focal Length) as the distances to perform the Micro Focus Adjustments on for each lens.

Before I get to my findings, I want to say that every single lens fell within the area of critical focus - i.e. they were technically all 'sharp'. I did very quickly find that every single lens was NOT in the MIDDLE point of the plane of focus (it was forward of center - this has to be a Canon choice) but I did find a few, as I suspected, that while within the zone of being classified as Sharp, were on the very very edge of this plane (again all in the same biassed direction - FORWARD) so my final adjustment has put a smile on my face (like a fresh sharpening on a hockey skate or a fresh stringing on a tennis racket).

The second punch line I want to give is that if you shoot at F1.2 (as I do) on your 50L or 85L, trust me when I say this, do what I have done and test these lens, but also, when you get your results, think very carefully what they are saying, and what from a DoF perspective (forward and Aft) that you want and need for your photography (this is very important).

So, since not everyone is going to be familiar with this method, you are basically pushing your Micro adjustments both (Closer and Farther) until the camera can no longer achieve Focus Lock. This information then tells you your Zone of critical focus both in front of and behind your chosen spot focus target - you can then adjust each lens, to your desire, to have your desired DoF plane RANGE around your Spot Focus for each lens - the Math guy in me loves this approach as I think of it as a Normal Distribution around a Mean with a certain Standard Deviation. I was also interesting to see the differences between lenses and cameras, for my own education, what this range was (usually between 17 on the low-end and 24 on the high-end of Micro Adjustment increments is the RANGE of Critical Focus at 50 x Focal Length).

So, here is what I got (+3 means +3 micro adjustments were needed to center the range)

5D #1
- 35 F1.4 +3
- 50 F1.2 +3
- 85 F1.2 +9
- 100 F2.8 +7
- 135 F2 +10
- 200 F2.8 +8
- 24-70 F2.8 +4
- 70-200 F4 +4
- 70-200 F2.8 +8

5D #2
- 35 F1.4 +5
- 50 F1.2 +5
- 85 F1.2 +9
- 100 F2.8 +9
- 135 F2 +11
- 200 F2.8 +10
- 24-70 F2.8 +4
- 70-200 F4 +4
- 70-200 F2.8 +8

7D2
- 35 F1.4 +4
- 50 F1.2 +4
- 85 F1.2 +8
- 100 F2.8 +10
- 135 F2 +6
- 200 F2.8 +7
- 24-70 F2.8 +4
- 70-200 F4 +4
- 70-200 F2.8 +8


What does the above data say?

1) There is pretty clearly a choice by canon, that from a Depth of Field perspective, they chose to place more Depth of Field behind the Center Point of Focus because every single lens, on all three cameras, had to be moved Rearward by +3 to +4 to center the spot focus point between the front and rear points of critical focus

2) I also found it interesting that the 3 lens that appeared to need outsized Rearward adjustments to center the spot focus point were the 85 1.2, the 100 2.8 Macro and the 70-200 2.8. Again, after some thought about shooting style and why they might have done this (if it is deliberate) is that these 3 lens are probably the 3 that are used to construct Out Of Focus / critical planes of focus / close-ups and thus it appears they chose to deliberately have more of the sharp focus behind the spot focus point and maybe not to 'waste' critical focus area in front of the point (seems reasonable)


I now have my data for each lens and camera and I'm glad to have it. My 2 5Ds seem very close (maybe 1-2 micro adjustment points apart), the 7D2 seems to fall exactly in the middle of the 5Ds and all my lenses were technically sharp.


What did I decide to do with this information?
- it is all stored per lens in each camera so they will automatically 'center' the spot focus area within the plane
- but, since it is very easy to go into the menu and disable the correction, it is easy to do for lens such as the 85, 100, 70-200 if I want to move each of these lens spot focus point to the very front of the focal plane
- for the 85 at 1.2, this is the lens that I noticed the most, along with the 50 but on the 85 there is huge difference, the lens is now sharper as before it was on the absolute edge of being in focus / not in focus and you could tell with your eye that it could be sharper - and now - WOW - it is way f'ing sharper - VERY happy about this

The other interesting fact that I found, and I haven't completely come to grips with its meaning, is that on the 7D2 versus the 5D3s, it can either be statistical noise (don't think so), but for the 135 F2 and 200 F2.8, both required less adjustment at the 50 x Focal Length distant point to center the spot focus point within the focal plane that the 5D3s did - I wonder if this is an issue of higher pixel density being and allowing finer focus on the 7D versus the 5D


Hope some of this information is useful.


Paul

Interesting results, and I've noticed the same trend with my lenses on my 650D (slightly front focussed) and then 70D where I can tweak it.

If it is indeed a concious decision I wonder if another contributor could be to allow some forgiveness with the faster lenses out of the box, for those who focus & recompose on the centre point?

Something I've not yet tested but might be interesting, is to determine if this behaviour changes with focus mode - ie does it do the same thing in AI Servo.

Just a coincidence. I have lenses that need negative MFA.

What were the light conditions when you performed the test?
Most Canons shift focus based on the temperature of the light. Often there are even 5 units of difference between MFA results when shooting under different lights (e.g. outdoor cloudy vs. indoor tungsten.)

gabebalazs wrote in post #17283844
What were the light conditions when you performed the test?
Most Canons shift focus based on the temperature of the light. Often there are even 5 units of difference between MFA results when shooting under different lights (e.g. outdoor cloudy vs. indoor tungsten.)

Too cold here for outdoor test, it was a combo of indoor tungsten light with some window light - test was done with AWB

As a math / stats guy by training, I find it comforting that most of my lenses were 'out of spec' by a similar amount (= consistent therefore the 'outliers' are obvious). Thus, whether or not the test was accurate, as long as it was equally wrong on all lenses consistently, it highlighted those that needed adjusting (85, 100, 70-200). And while it is absolutely possible that canon did not do this on purpose, the large number of tests that i did on all my lens would lead me to strongly believe that this is deliberate - i.e. there is designed in more critical in-focus behind the spot focus point than if front (makes sense to me).

But if that is true, which I'm pretty certain it is, then it is useful information as it allows you to dial in your DoF for different lenses depending on what you want.

Examples
- you do certain F1.2 shots at a wedding (eye lash shot), I would likely switch off my adjustment to return the lens to its as delivered from the factory setting that had the spot focus point at the very front of the critical in-focus plane from my now significantly adjusted center position (nice to have a quick menu click to adjust on/off)
- you take pictures of birds with significantly different sized beaks (would be very useful to know where your len's center is in the range of critical focus (front, middle, back)

Thanks for the reply about the colour of the light affecting things - I will repeat the test outside when things warm back up for outdoor wedding season next year.


The biggest thing I got out of this was that I know the specs on each lens and each camera and it confirmed that I thought certain lens could be a little better. The great thing is that 3 of my favourite lenses (85, 100, 70-200) are now all sharper and I know why - and I loved them even before I did this - especially the 100 and 70-200.

In my experience too, tungsten required up to +6 points (from memory) difference compared to daylight MA. There were other reports about this phenomenon as well.

With regard to front DOF vs. rear DOF, you may want to download VWDOF, an extremely informative calculator (also for background blur) and check for your specific cases.

http://toothwalker.org​/optics/vwdof.html

Can you link us to the AF Target you ended up using? Just curious to see.

the results are weird. I did not see such a trend when I did my 5D3 and 1D4 in a similar mass tweeking afternoon

Not even close to enough data to come to your conclusion.

For example, I have one lens that need -15 and the rest are pretty spot on, so if did the same as you and assumed all canon's hundreds of millions of lenses and cameras are all the same as mine, then it show the opposite result to what you got.

I tried the dot tune method and I wasn't happy with it. Looking for the little green dot when I used my 5d3 and 70-200 f2.8II it went off between +3 all the way up to +19. Either I did something drastically wrong or it just wasn't a good system for me.

wallstreetoneil wrote in post #17283497
First of all, mathematically I understand and get that there is a slightly larger area of critical focus behind the spot focused area than in front of the 'zeroed' spot so before I give the details of what I found, it would seem to me that Canon has chosen to set up their cameras with this 'mathematical fact' and all that I discovered is just the fact that Canon did this as oppose to 'equalizing' this PLANE of focus evenly (Forward and Aft). I did also find that a few lens lay outside this and always were in the same direction.
Paul

Although you've made the statement that you "understand and get" that there is space in front of your focus point and behind your focus point that will be in focus, you have expressed concern that it isn't "even". That, in itself, demonstrates that you don't "understand and get" DOF calculations.

wallstreetoneil wrote in post #17283497
The second punch line I want to give is that if you shoot at F1.2 (as I do) on your 50L or 85L, trust me when I say this, do what I have done and test these lens, but also, when you get your results, think very carefully what they are saying, and what from a DoF perspective (forward and Aft) that you want and need for your photography (this is very important).
Paul

This is something that those that have used manual focus lenses and focusing screens designed for manual focus lenses should already know. It's not unusual to focus a subject while holding the dof preview button to ensure the portion of your image you want in focus will be in focus when the image is captured.

wallstreetoneil wrote in post #17283497
1) There is pretty clearly a choice by canon, that from a Depth of Field perspective, they chose to place more Depth of Field behind the Center Point of Focus because every single lens, on all three cameras, had to be moved Rearward by +3 to +4 to center the spot focus point between the front and rear points of critical focus

Paul

Again, The smaller focus distance in front of the focus point compared to the larger distance in focus behind the focus point is not a variable. It is controlled by a number of constants designed into the lens. The one we are allowed to change on a prime lens is the aperture. On a zoom lens we get to change the aperture and the focal length.

Ideally, when you move your focus point using MA adjust, you should be putting it where it is supposed to be by design, not where you think it should be.., at least if you want the lens to function as designed.

It's possible I misread your diatribe, but I'm not thinking so a the moment.

I have to admit to being a bit baffled and concerned about all you folks having these AF issues. With the exception of a 50D I used to have (which would only focus with a 400 f2.8 and nothing else!) I have had zero issues with any film or digital Canon SLR on any Canon (+1 Tamron) lens that I have ever owned.
Am I doing something wrong?

johnf3f wrote in post #17284361
I have to admit to being a bit baffled and concerned about all you folks having these AF issues. With the exception of a 50D I used to have (which would only focus with a 400 f2.8 and nothing else!) I have had zero issues with any film or digital Canon SLR on any Canon (+1 Tamron) lens that I have ever owned.
Am I doing something wrong?

I have no idea. I must be clueless when it comes to this too.

I have tried 3 methods and got 3 results. This is just an example using a 5D2 and 135L.

Lens Align - +15
This method from Creative Live https://www.youtube.co​m/watch?v=SpiJ9qX_-Ds - +3
Dot tune method - -2

johnf3f wrote in post #17284361
I have to admit to being a bit baffled and concerned about all you folks having these AF issues. With the exception of a 50D I used to have (which would only focus with a 400 f2.8 and nothing else!) I have had zero issues with any film or digital Canon SLR on any Canon (+1 Tamron) lens that I have ever owned.
Am I doing something wrong?

This thread isn't really about focus issues, it's about the tolerances that are necessarily built into any non-100% perfect system. Luckily, with current cameras we have the capability of adjusting for mismatches in tolerances. Sometimes you get lucky, as you note, and sometimes you don't.

the flying moose wrote in post #17284302
I tried the dot tune method and I wasn't happy with it. Looking for the little green dot when I used my 5d3 and 70-200 f2.8II it went off between +3 all the way up to +19. Either I did something drastically wrong or it just wasn't a good system for me.

That is exactly what happens and I glad it happened to you as well (and in the same direction) - and that is the point of this method. On almost all of my lens, from +1 to about 'about +15 to +17 (i.e. moving backwards) the camera will acknowledge critical focus, but when moving forward (-1, -2, ..., -7 to -8) is where the critical focus would stop. Thus the range (-6 to +16) is the range of the critical focus plane. So, you take that entire range (-6 to +16) which equals 22 micro focus adjustment increments then divide 22 by 2 to get the mid point of the critical focus range which equals 11 in this case. If you then wished to 'center' the spot focus point in the middle of the range, you would then do so by finding the middle point of this range as being -6 + 11 or equally +16 -11 both which equal +5. Therefore to center your lens, in the canon system you would enter +5 as the adjustment.

What I found amazing, is that every lens the range was in the same direction. And, as you pointed out on the 70-200, my 70-200 got al the way to +20 but only got to -4. This would imply a critical focus range of 24 micro adjustment units - half of which is 12 and thus on my 70-200 I 'centered' the lens by moving it 'rear-wards' by using a +8.

After thinking about what I said earlier, my numbers were correct (the pluses and minuses in the canon system) but I got the direction backwards that Canon seems to be putting on their lens - i.e on my 85, 100 and 70-200, and it would seem yours as well, they are consistently 'front' focusing them, not rear as I stated early - I apologize for getting this incorrect in my original post.

I just did a test to confirm this - this is the test I did. Exactly 12 feet from my couch I place a hockey stick standing up against the wall. The lettering on the stick facing me was 2 inches off the wall. Using my 70-200 at 2.8, @ 200 the DoF at 12 feet is 2.11 inches of which 1.05 is forward of center and 1.06 is rear of center. With the lens in as delivered from the factory setup (no micro adjustments), if I center spot focused on the wall that was 2 inches behind the stick, the lettering on the stick was almost in focus 'almost' - it was almost what I would say was acceptable. On my 70-200, I was able to get all the way to +20 on the micro adjustment and it would still achieve critical focus - but moving forward I was only able to get to -4. Thus my $2200 70-200, and it sounds like the other poster as well, had significant 'front focus' dialled in by the factory - in my case +8 rearward was the correction. When I re-set the lens to the +8 setting that the Dot Focus said was 'correct', and I focused on the wall 2 inches behind the stick, sure enough the lettering on the stick 2 inches forward of the stick was not in focus.

I stand by my results and it is pretty clear, but I did get it backwards and I apologize, that on ALL my Canon L lens, using the Dot Focus method, all of them were front focused it seems deliberately (but still in focus) by 'approximately' +4 micro focus adjustment units - and in my case the 70-200, 85 and 100 were front focused by +8.

If as another poster suggested that Tungsten lighting can be responsible for this I completely accept this but I will recheck this in daylight when I can.

Again, I apologize for getting it backwards but now it makes even more sense given my experience with my 85 shooting at 1.2 on bride's eyes / eye lashes - and that is, if I didn't get the spot focus on the actual eyeball and instead hit the eyelashes, at 1.2 the eyebal wouldn't be sharp as there was way too much 'critical' focus forward of 'my' 85 1.2 which needed a +8 to +10 'rearward adjustment on my 3 cameras.


Paul

wallstreetoneil wrote in post #17284551
That is exactly what happens and I glad it happened to you as well (and in the same direction) - and that is the point of this method. On almost all of my lens, from +1 to about 'about +15 to +17 (i.e. moving backwards) the camera will acknowledge critical focus, but when moving forward (-1, -2, ..., -7 to -8) is where the critical focus would stop. Thus the range (-6 to +16) is the range of the critical focus plane. So, you take that entire range (-6 to +16) which equals 22 micro focus adjustment increments then divide 22 by 2 to get the mid point of the critical focus range which equals 11 in this case. If you then wished to 'center' the spot focus point in the middle of the range, you would then do so by finding the middle point of this range as being -6 + 11 or equally +16 -11 both which equal +5. Therefore to center your lens, in the canon system you would enter +5 as the adjustment.

What I found amazing, is that ever lens the range was in the same direction. And, as you pointed out on the 70-200, my 70-200 got al the way to +20 but only got to -4. This would imply a critical focus range of 24 micro adjustment units - half of which is 12 and thus on my 70-200 I 'centered' the lens by moving it 'rear-wards' by using a +8.

After thinking about what I said earlier, my numbers were correct (the pluses and minuses in the canon system) but I got the direction backwards that Canon seems to be putting on their lens - i.e on my 85, 100 and 70-200, and it would seem yours as well, they are consistently 'front' focusing them, not rear as I stated early - I apologize for getting this incorrect in my original post.

I just did a test to confirm this - this is the test I did. Exactly 12 feet from my couch I place a hockey stick standing up against the wall. The lettering on the stick facing me was 2 inches off the wall. Using my 70-200 at 2.8, the DoF at 12 feet is 2.11 inches of which 1.05 is forward of center and 1.06 is rear of center. With the lens is as delivered from the factory setup (no micro adjustments), if I center spot focused on the wall that was 2 inches behind the stick, the lettering was almost in focus 'almost' - it was almost what I would say was acceptable. On my 70-200, I was able to get all the way to +20 on the micro adjustment and it would still achieve critical focus - but moving forward I was only able to get to -4. Thus my $2200 70-200, and it sounds like the other poster as well, had significant 'front focus' dialled in by the factory - in my case +8 rearward was the correction. When I re-set the lens to the +8 setting that the Dot Focus said was 'correct', and I focused on the wall 2 inches behind the stick, sure enough the lettering on the stick 2 inches forward of the stick was not in focus.

I stand by my results and it is pretty clear, but I did get it backwards and I apologize, that on ALL my Canon L lens, using the Dot Focus method, all of them were front focused it seems deliberately (but still in focus) by 'approximately' +4 micro focus adjustment units - and in my case the 70-200, 85 and 100 were front focused by +8.

If as another poster suggested that Tungsten lighting can be responsible for this I completely accept this but I will recheck this in daylight when I can.

Again, I apologize for getting it backwards but now it makes even more sense given my experience with my 85 shooting at 1.2 on bride's eyes / eye lashes - and that is, if I didn't get the spot focus on the actual eyeball and instead hit the eyelashes, at 1.2 the eyebal wouldn't be sharp as there was way too much 'critical' focus forward of 'my' 85 1.2 which needed a +8 to +10 'rearward adjustment on my 3 cameras.


Paul

I just put more effort into doing the dot tune method. According to the dot tune method all of my bodies and lenses are - except for one and that's the Sigma 50 on the 1D3. Almost all of them were in the -1 to -5 range with one -8.

I am testing:

5D3
5D2
1D3
24-70 f2.8II
Sigma 50 1.4
135L f2
70-200f2.8II