AF Fine tune & Manual Focus

[toohuge]

All, - I hope this is the correct section - if not sorry!

I am pulling my hair out over trying to fine tune a prime lens I just picked up. - certainly not a good exercise if you have any form of OCD! It's a Canon 85 1.8 and at a certain distance, I thought I had it dialed in correctly for the camera. However, my shots at wide apertures (f1.8 F2 etc) show a slight miscalculation of the AF system.

My limited understand is as follows:

1) Af fine tune sets the lens for that specific distance and it is possible that the lens will front / back focus at different distances

2) For critic focus applications, it is better to use manual focus to ensure correct focal point

My plan of action:

I usually shoot sport, so AF fine tune the lens at circa. 50x focal distance and leave it at that - (for when I am shooting indoor sports) and for anything else, shooting at wide apertures, use manual focus to nail for focus.

Is this correct? Do you guys use manual focus a lot on your wide aperture shots?

Hoping to put my mind at rest

Thanks

Chris

 

[Box Brownie]

Hmmm!

On the Reikan site, the makers of FoCal lens calibration software they say for the 85mm lens that:-

The recommended minimum target distance is 3.4m (approx 11 foot 1 inches).

HTH?

 

[toohuge]

Thanks Box Brownie.

I will try that distance later today.... but I am trying to get to the bottom of the physics - as the distance is always changing - I wont be carrying a ruler around with me! Does AF performance (front / back) alter with distance - I think it does.

Chris

 

[Box Brownie]

Thanks Box Brownie.

I will try that distance later today.... but I am trying to get to the bottom of the physics - as the distance is always changing - I wont be carrying a ruler around with me! Does AF performance (front / back) alter with distance - I think it does.

Chris

I have always been under the impression, especially with prime lens, that unless there is a fault in either the lens of the AF of the body that it will be in focus whatever the distance.

But do please bear in mind that depending on how close you are to the subject the DoF will vary and this will be more pronounced the wider the aperture such f1.8 e.g. closer in the subject it will be razor thin................but further out the DoF will be bigger. This is important because, even though you have focus (confirmation) should you move only slightly or the subject moves slightly there could/will be a loss of 'critical focus'.

Edit ~ I just re-read your OP and note Indoor Sport................so likely rapidly moving subjects with low light (wide open @ f1.8). Not an ideal situation for 100% pin sharp focus depending (and bearing in mind 85mm not that long a lens) how far away you are from the action. Oh, and what Canon body are you using what what AF settings to capture the action?

Can you post some examples pictures to show us exactly what you are getting???

 

[toohuge]

2I4Q0100 by Chris Reynolds, on Flickr

image url: https://photos.app.goo.gl/NUgIYAzjwYpGzcCm2

edit - can't work out how to embed an image on this forum!

The problem isn't absolute focus - it is more to do with focus accuracy. To me, the pine cone is not in good focus. However, if you look at the left side of the cone, away from the camera, things sharpen up.

The pine needles behind the cone appear to be sharper and in focus too.

Camera is a 1DMkiii with single shot AF.

What are your thoughts?

 

[GreenNinja67]

I'd suggest using a proper "target" specifically for this purpose if you want it accurate.

A pine cone in a tree may move in the breeze, especially at wide apertures.

 

[toohuge]

I'd suggest using a proper "target" specifically for this purpose if you want it accurate.

A pine cone in a tree may move in the breeze, especially at wide apertures.

Thanks GreenNinja67 - I used a target to calibrate the AF. However it was at a different distance (circa 2.5m iirc) in comparison with this subject, approx. 6 ft from the camera.

Should the AF shift (front/back) alter a lot with distance?

When I left the house, I thought my AF adjustment was completed, but in the image above it shows that either a) I performed it incorrectly (stranger things have happened ) or b) I could be chasing my tail trying to dial in the AF at very wide apertures because it'll never be 100% unless the exact same distance as when the calibration was done.

Chris

 

[Box Brownie]

As

Thanks GreenNinja67 - I used a target to calibrate the AF. However it was at a different distance (circa 2.5m iirc) in comparison with this subject, approx. 6 ft from the camera.

Should the AF shift (front/back) alter a lot with distance?

When I left the house, I thought my AF adjustment was completed, but in the image above it shows that either a) I performed it incorrectly (stranger things have happened ) or b) I could be chasing my tail trying to dial in the AF at very wide apertures because it'll never be 100% unless the exact same distance as when the calibration was done.

Chris

As Terry says, if it was even remotely breezy it was quite likely the pine cone moved between you locking focus and pressing the shutter. Exactly the sort of movement I mentioned.

In regard to manually doing MFA (micro focus adjustment) show us the target and explain how you did it. No one can second guess you.

 

[toohuge]

As

As Terry says, if it was even remotely breezy it was quite likely the pine cone moved between you locking focus and pressing the shutter. Exactly the sort of movement I mentioned.

In regard to manually doing MFA (micro focus adjustment) show us the target and explain how you did it. No one can second guess you.

Thanks Box Brownie.

I'm going to redo the af adjustment later today, using the dot tune focus method and I'll take some shots and report back.

The other method I did was with a chart at an angle and judged it by eye to where the focus point was.

Can lenses front/back focus at different distances? - I suppose that's the real question that'll put my mind at rest!

Chris

 

[Box Brownie]

Thanks Box Brownie.

I'm going to redo the af adjustment later today, using the dot tune focus method and I'll take some shots and report back.

The other method I did was with a chart at an angle and judged it by eye to where the focus point was.

Can lenses front/back focus at different distances? - I suppose that's the real question that'll put my mind at rest!

Chris

I am not familiar with The Dot Tune Method but have read of it.

In the past I have checked focus using a printed measurement chart that I downloaded (cannot recall now which website) the chart needs to be at 45 degrees and the camera positioned properly.

AFAIK distance does not affect back or front focusing, it either mis-focuses or not.......I can only imagine such happening if there was an issue with either the lens and/or camera.

 

[toohuge]

I am not familiar with The Dot Tune Method but have read of it.

AFAIK distance does not affect back or front focusing.........I can only imagine such happening if there was an issue with either the lens and/or camera.

Thanks BoxBrownie.

That is my concern... I am still under the returns period for this lens so I want to make sure it's good before sending back.

I have both charts, one for dot focusing and one for traditional af tuning. I'd be interested to see how the two compare.

Chris

 

[Box Brownie]

I hope you can resolve this to your satisfaction but please keep in mind that working with such a fast wide open @ f1.8 does need a good discipline of camera technique to make sure you control DoF

The 85mm f1.8 is by reviews a superb lens, including used in portraiture. But I have seen examples of portraits where when shot wide open at short subject distances the eyes are in focus but the nose and ears are soft.......that is how narrow the DoF can be!

 

[toohuge]

I hope you can resolve this to your satisfaction but please keep in mind that working with such a fast wide open @ f1.8 does need a good discipline of camera technique to make sure you control DoF

The 85mm f1.8 is by reviews a superb lens, including used in portraiture. But I have seen examples of portraits where when shot wide open at short subject distances the eyes are in focus but the nose and ears are soft.......that is how narrow the DoF can be!

Thanks BoxBrownie.

Yes - the shallow depth of field does take some getting used too! I am confident it is my abilities over the lens itself - I find that once you go down the route of af micro adjustment then it's a never ending OCD nightmare! I'll try recalibrating tonight and see how I go. I think I am there now - but we'll see.

I'll report back here.

Chris

 

[Furtim]

Thanks BoxBrownie.

Yes - the shallow depth of field does take some getting used too! I am confident it is my abilities over the lens itself - I find that once you go down the route of af micro adjustment then it's a never ending OCD nightmare! I'll try recalibrating tonight and see how I go. I think I am there now - but we'll see.

I'll report back here.

Chris

Mirrorless is a good cure for lens micro adjustment OCD
Been there, done that!!!

 

[HoppyUK]

Thanks Box Brownie.

I'm going to redo the af adjustment later today, using the dot tune focus method and I'll take some shots and report back.

The other method I did was with a chart at an angle and judged it by eye to where the focus point was.

Can lenses front/back focus at different distances? - I suppose that's the real question that'll put my mind at rest!

Chris

When a lens is properly adjusted, it should focus accurately at all distances. Unfortunately, they often don't, which is why it's important to use a 'typical' shooting distance when testing, given that any errors will likely show up when you're furthest from the calibration distance. A common problem is to have the target too close, because it's easier to see what's going on that way, but then you run a greater risk of it being out at normal distances. Another danger is using a slanted target, because you can never be exactly certain what the AF has picked up on and they have some sensitivity outside the little box in the viewfinder.

A good target is something like the Spyder LensCal, but it's very easy to create something just as good with a box of cornflakes on the kitchen worktop, with a ruler propped up against one side. Set the camera up square to the box, on a tripod, and focus on some bold graphics just to one side of the ruler. In that way, there is no danger of the AF point picking up on anything else and you can easily see on the ruler exactly where the point of sharpest focus actually is.
http://www.datacolor.com/photography-design/product-overview/spyderlenscal/

Experience on these forums suggests that most AF problems are user error - either because the lens actually hasn't been accurately calibrated, or something else has influenced a problem image. In the case of the pine cone, it could be one of several common issues, bearing in mind there's less than a couple of cms depth-of-field to play with. Such as, the subject moved after focusing, the camera moved a few mms after focusing, they both moved, or the AF point wasn't exactly in position when focus was set.

 

[sk66]

When you understand that the AF system is comparing multiple images for position (phase) and that these images are TINY, you will understand that the AF sensor has it's limits (it's kind of amazing to me that it works at all). And then when you realize that the lens' AF system contains moving parts (often gear driven) you will realize that there is a required element of play/slop to it... all of this results in a required "AF tolerance." I.e. you will likely find more consistent results if AF is always initiated from one extreme/direction of travel (i.e. MFD) and with a better/more defined subject. The AF system cannot see really small details in a scene (how small varies by camera/system) because the images it is using are so small... small details are in focus due to their association with larger details the system can see/resolve.

The DOF of the lens aperture has no effect on the DOF/sharpness of the images used by the PDAF module (unless smaller than the aperture of the AF system, ~ f/32 equiv)... but it does make it easier to determine the depth of the point of focus in the resulting image.

Additionally, the MF system also has it's own aperture, which is somewhere around f/2-f/2.8... so if the lens aperture is larger than that, you cannot see the difference in the viewfinder. Plus the image in the viewfinder is probably smaller than the image on the sensor, which makes it even harder to judge point of focus/DOF.

If you refine the focus for one distance (fine tune) you may very well additionally compromise other focus distances... Because of all of this, IMO most people are better off leaving it alone unless there is a significant/consistent issue in one particular situation that is very important.

 

[toohuge]

Thank you gents...

I tried to calibrate the lens last night - my eyes must be terrible

I used the dot tune method and ended up at +5 - I confirmed this with an angled chart

I initially had the lens set at +5, as if the lens was back focusing. I went out with the tripod and shot this:

+5 by Chris Reynolds, on Flickr

I focused on the 'Professional' sign on the silver bike and as you can see, the blue bicycle behind is in focus. Especially the crank and the silver writing.

I then went the opposite way for compensation to bring the focus back in line, this was the best I could come up with at that length (-6):
-6-3 by Chris Reynolds, on Flickr

I then tried moving further back, still focusing on the 'Professional' sign, again at -6:

-6-5 by Chris Reynolds, on Flickr

Finally - I moved a lot further back and things got a little interesting....

At no compensation:
0-8 by Chris Reynolds, on Flickr


At -4:
-4-8 by Chris Reynolds, on Flickr

At -6 (Starts to go here):

-6-8 by Chris Reynolds, on Flickr

At -10:

-10-8 by Chris Reynolds, on Flickr

So there we have it.... still none the wiser I think -5 would be a good compromise ... what do you guys think?

At -5:

-5-8 by Chris Reynolds, on Flickr

 

[toohuge]

Well... I got fed up trying different, non-conclusive tests...

So I used the dot tune method and a ruler to confirm....

At a distance, dot tune gave a recommend +11, at a closer distance, this still looked to be ok, but I tried dot tune again and it recommend at +1! Yikes! But I took some test shots and it looks like +11 is where I need to be, given about 1/3 in front of the subject is sharp and approx 2/3 behind is too.

Images below:

At -11:

+11 by Chris Reynolds, on Flickr

Closer at +1:
-1--1 by Chris Reynolds, on Flickr

Closer at -11:
+11-1 by Chris Reynolds, on Flickr

It looks like I can put this subject to rest now! Thanks for all your help! Time to go out shooting....

Many lessons learnt! Hopefully I am all good to go now!

Chris

 

[SsSsSsSsSnake]

Well... I got fed up trying different, non-conclusive tests...

So I used the dot tune method and a ruler to confirm....

At a distance, dot tune gave a recommend +11, at a closer distance, this still looked to be ok, but I tried dot tune again and it recommend at +1! Yikes! But I took some test shots and it looks like +11 is where I need to be, given about 1/3 in front of the subject is sharp and approx 2/3 behind is too.

Images below:

At -11:
+11 by Chris Reynolds, on Flickr

Closer at +1:
-1--1 by Chris Reynolds, on Flickr

Closer at -11:
+11-1 by Chris Reynolds, on Flickr

It looks like I can put this subject to rest now! Thanks for all your help! Time to go out shooting....

Many lessons learnt! Hopefully I am all good to go now!

Chris

I feel your pain Chris,its what actually made me give up on DLSR's in the end. I can be OCD too and it can drive ya nuts just like a steering wheel down your trousers keep smiling

 

[sk66]

But I took some test shots and it looks like +11 is where I need to be, given about 1/3 in front of the subject is sharp and approx 2/3 behind is too.

Sorry to throw another wrench into the mix... the 1/3-2/3 DOF is only applicable when the subject distance is near the lens' HFD. At shorter distances it reaches 1-1, and at very long distance it reaches 1-9 or greater.

 

[toohuge]

Sorry to throw another wrench into the mix... the 1/3-2/3 DOF is only applicable when the subject distance is near the lens' HFD. At shorter distances it reaches 1-1, and at very long distance it reaches 1-9 or greater.

Thanks sk66.... All this expertise is very much appreciated!

It is another wrench - I just looked and it looks like some of the +1 shots have a ratio larger in favor in front of the lens which seems to be incorrect regardless of distance.... I am about to head out and give the lens a go at these new settings....

 

[Furtim]

Thanks sk66.... All this expertise is very much appreciated!

It is another wrench - I just looked and it looks like some of the +1 shots have a ratio larger in favor in front of the lens which seems to be incorrect regardless of distance.... I am about to head out and give the lens a go at these new settings....

My earlier comment was tongue in cheek but in all seriousness, If this is going to drive you nuts, really do consider mirrorless - they take the focus read directly in the sensor, so there's no need for any micro adjustments - it's always spot on (all things being equal).

 

[tijuana taxi]

Desist now, you are on the road to madness.

Even worse if you have even a hint of OCD, don't go down the route to lunacy that is monitor/printer calibration either.

Mirrorless cameras may have their faults, but all this fine tuning isn't one of them

 

[HoppyUK]

Thanks sk66.... All this expertise is very much appreciated!

It is another wrench - I just looked and it looks like some of the +1 shots have a ratio larger in favor in front of the lens which seems to be incorrect regardless of distance.... I am about to head out and give the lens a go at these new settings....

Steven is right, but you're getting very picky now with a lens that was introduced in 1992 when we weren't so critical. On the DoFMaster calculator, it gives the percentage DoF in front and behind. There is never more DoF in front, but it's around 50/50 at very close range, with DoF behind steadily increasing as distance increases. The third-in-front and two-thirds-behind rule works roughly for a lot of general photography http://www.dofmaster.com/dofjs.html

What is the consistency like? As in when you take multiple test shots without moving anything, and defocus the lens in different directions each time? That will tell you if you're just expecting too much. But don't be too obsessed - it will drive you mad trying to perfect something that was always designed and built with a tiny bit of tolerance. If it's within the acceptable DoF zone, the lens/camera are unlikely to be the weakest link in the chain

 

[sk66]

Thanks sk66.... All this expertise is very much appreciated!

It is another wrench - I just looked and it looks like some of the +1 shots have a ratio larger in favor in front of the lens which seems to be incorrect regardless of distance.... I am about to head out and give the lens a go at these new settings....

Part of the reason for mentioning it was to add to the list of reasons why this is somewhat futile/irrelevant...
Of the images posted here, at these sizes it makes near zero difference. For me to see a significant difference I need to open the full size images on flickr which an average viewer isn't going to do... and it's rather counterproductive to do. And even if I do open the full size images, as a viewer I probably don't care where the exact point of focus is... it's generally not that important for creative images.

It's kind of like obsessing over maximum sharpness or ISO noise... it's another technical aspect which has little to do with the (more important?) creative/artistic value of photography.

 

[toohuge]

Thank you guys. I have been out with the lens and things look better

It's the first time that it has really got on my nerves - and having read so much about AF systems and DOF etc, etc, now i use the AF in a more intelligent way I get better, more consistent results - no surprise there.

I think the reason i was working so hard to perfect this was the original pine cone shot - when I noticed the focus error - that's all I can see!

Still - thank you all very much for your help, understanding and patience! It is all very much appreciated.

Chris