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AF fine tune, why?
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Apr 22, 2019 10:24:34   #
Jerry G Loc: Waterford, Michigan and Florida
 
Fifty years ago I was a Navy photographer and pursued photography as a hobby for several years afterward. The only thing auto on any of my cameras was auto aperture, focus and exposure were manual. Now that I'm retired I purchased a new digital camera a couple years ago and quickly found photography has changed and I am still learning.
There have been many discussions here about the need to fine tune some lenses, some people saying every lens needs it and others saying almost no lens needs it. It seems some lenses tend to back focus and need to be tuned. I'm sure I am missing something in my understanding of how AF works so I hope someone can explain it or point me to a resource. My problem in understanding this is that if the camera, either through phase detection or contrast, controls focus, why does the camera not know the lens is not in focus?

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Apr 22, 2019 10:35:03   #
SpyderJan Loc: New Smyrna Beach. FL
 
Jerry, neither the camera nor the lens knows what part of the subject is your focal point. It will focus on something. Usually OEM lenses will not need to be calibrated, but you are more likely to find that lens from a manufacturer other than the camera maker could need attention. Here is a link to an article describing an easy method to test your lens's autofocus.
https://www.bettertravelphotos.com/blog/item/testing-the-accuracy-of-your-dsrl-camera-s-autofocus

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Apr 22, 2019 10:36:10   #
Tex-s
 
Jerry G wrote:
Fifty years ago I was a Navy photographer and pursued photography as a hobby for several years after ward. The only thing auto on any of my cameras was auto aperture, focus and exposure were manual. Now that I'm retired I purchased a new digital camera a couple years ago and quickly found photography has changed and I am still learning.
There have been many discussions here about the need to fine tune some lenses, some people saying every lens needs it and others saying almost no lens needs it. It seems some lenses tend to back focus and need to be tuned. I'm sure I am missing something in my understanding of how AF works so I hope someone can explain it or point me to a resource. My problem in understanding this is that if the camera either through phase detection or contrast controls focus, why does the camera not know the lens is not in focus?
Fifty years ago I was a Navy photographer and purs... (show quote)


I have not researched the technicalities of how each system can be fooled into front or back focusing errors, but I do have a single experience to relay.

In my only bout of fine tuning, I had an older lens that apparently responded too slowly for the on-board sensor to accurately 'stop' the focus drive motor once focus was detected. When searching from infinity forward, the lens would end up front focusing, and when searching from near focus outward, would back focus. Because I had zero budget for a new telephoto lens at the time, I settled on adjusting the lens for the near focus hunting outward (back-focus) error, and simply set the lens to near focus before each shot and was happy with the result, so long as I shot at f/8 or higher. Not optimal for impromptu wildlife shots, and not usable in low light without a tripod, but workable in general, and I got to spend my sparse cash on travel and camping.

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Apr 22, 2019 10:40:10   #
BebuLamar
 
Jerry G wrote:
Fifty years ago I was a Navy photographer and pursued photography as a hobby for several years afterward. The only thing auto on any of my cameras was auto aperture, focus and exposure were manual. Now that I'm retired I purchased a new digital camera a couple years ago and quickly found photography has changed and I am still learning.
There have been many discussions here about the need to fine tune some lenses, some people saying every lens needs it and others saying almost no lens needs it. It seems some lenses tend to back focus and need to be tuned. I'm sure I am missing something in my understanding of how AF works so I hope someone can explain it or point me to a resource. My problem in understanding this is that if the camera, either through phase detection or contrast, controls focus, why does the camera not know the lens is not in focus?
Fifty years ago I was a Navy photographer and purs... (show quote)


I don't claim to know exactly why but this is my thinking. AF fine tuning is not needed with cameras that use contrast detection. On early cameras with phase detect AF the camera would move the lens until focus is achieved and thus doesn't need AF fine tune because the camera does know when focus is achieved. This method is slow and could cause hunting. The phase detect sensor not only can know when the image is in focus but it also know how much out of focus it is and how much to move the lens to bring the image in focus. Using this method the camera simply command the lens to move the amount needed to achieve focus. However, the lens may not move the exact amount needed and thus the need for AF fine tune.

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Apr 22, 2019 10:40:14   #
Haydon
 
Jerry G wrote:
Fifty years ago I was a Navy photographer and pursued photography as a hobby for several years afterward. The only thing auto on any of my cameras was auto aperture, focus and exposure were manual. Now that I'm retired I purchased a new digital camera a couple years ago and quickly found photography has changed and I am still learning.
There have been many discussions here about the need to fine tune some lenses, some people saying every lens needs it and others saying almost no lens needs it. It seems some lenses tend to back focus and need to be tuned. I'm sure I am missing something in my understanding of how AF works so I hope someone can explain it or point me to a resource. My problem in understanding this is that if the camera, either through phase detection or contrast, controls focus, why does the camera not know the lens is not in focus?
Fifty years ago I was a Navy photographer and purs... (show quote)


Mirrorless have the AF on sensor so no adjustments in AF are necessary. With DSLR's because of tolerance variations with both lenses and camera bodies it's possible to have either front or back focusing occur. Lower end camera bodies do not necessarily have AF tuning. That feature is generally left to the more expensive cameras. With third party lenses such as Sigma, these concerns are resolved with their "dock" although at one time, *don't know if they still provide this service*, you could send in both your camera and body for this adjustment.

If AF does concern you with a lens/body, it's best to check the manual to find if AF tuning is available with your camera body.

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Apr 22, 2019 10:58:16   #
Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)
 
SpyderJan wrote:
Jerry, neither the camera nor the lens knows what part of the subject is your focal point. It will focus on something. Usually OEM lenses will not need to be calibrated, but you are more likely to find that lens from a manufacturer other than the camera maker could need attention. Here is a link to an article describing an easy method to test your lens's autofocus.
https://www.bettertravelphotos.com/blog/item/testing-the-accuracy-of-your-dsrl-camera-s-autofocus


OEM lenses are just as susceptible to focus errors as third party lenses. But just because a lens seems "off" doesn't mean it's a lens problem. It can be a communication error between a specific body and lens(es), or a misalignment of AF sensors, or some other electro/mechanical issue.

In any case, in-camera focus calibration or tuning only adjusts the specific body - not the lens, and it only adjusts DSLR cameras and how lenses interact with the lens(es) and only in Phase Detect AF mode (PDAF).

The problem with in-camera adjustment is that the adjustment is linear and it offsets all AF performance. Lenses - OEM or Third Party - are not often linear in their AF behavior. They can be perfect at 20 ft, back focusing at 5 ft, and front focus at 100 ft. When you correct at 5 ft you will make the focus at 100 ft worse and vice versa.

The best solution is to ensure that your camera is focusing "to spec" so that when you have a lens that appears to have an issue, you can isolate the issue in the lens. This is even more important when you have multiple bodies. I routinely have 2-4 bodies that I use on a regular basis. If my cameras were not focusing accurately, it would be impractical to adjust every body for every lens. Much easier to make sure everything is performing within spec - problem solved.

BTW, the tools available to technicians are more comprehensive and do not merely offset all focus behavior. And they can also open a lens or access the lens' firmware and adjust the focus behavior at multiple distances and focal lengths - similar to the tool now being provided by Sigma and Tamron for sine of their newer lenses.

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Apr 23, 2019 05:42:04   #
Architect1776 Loc: In my mind
 
Jerry G wrote:
Fifty years ago I was a Navy photographer and pursued photography as a hobby for several years afterward. The only thing auto on any of my cameras was auto aperture, focus and exposure were manual. Now that I'm retired I purchased a new digital camera a couple years ago and quickly found photography has changed and I am still learning.
There have been many discussions here about the need to fine tune some lenses, some people saying every lens needs it and others saying almost no lens needs it. It seems some lenses tend to back focus and need to be tuned. I'm sure I am missing something in my understanding of how AF works so I hope someone can explain it or point me to a resource. My problem in understanding this is that if the camera, either through phase detection or contrast, controls focus, why does the camera not know the lens is not in focus?
Fifty years ago I was a Navy photographer and purs... (show quote)


I have numerous Canon lenses and experimented with that.
They are perfect as issued.
Found it a waste of time but educational.
Once I get a mirrorless RF mount camera that game will be unneccessary.
Go ahead and check for your education but thus far I have not found any Canon lens I have owned needed it.

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Apr 23, 2019 06:35:59   #
billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont
 
Jerry G wrote:
Fifty years ago I was a Navy photographer and pursued photography as a hobby for several years afterward. The only thing auto on any of my cameras was auto aperture, focus and exposure were manual. Now that I'm retired I purchased a new digital camera a couple years ago and quickly found photography has changed and I am still learning.
There have been many discussions here about the need to fine tune some lenses, some people saying every lens needs it and others saying almost no lens needs it. It seems some lenses tend to back focus and need to be tuned. I'm sure I am missing something in my understanding of how AF works so I hope someone can explain it or point me to a resource. My problem in understanding this is that if the camera, either through phase detection or contrast, controls focus, why does the camera not know the lens is not in focus?
Fifty years ago I was a Navy photographer and purs... (show quote)


Relax, I own over 20 AF lenses and enlarge to 20X30 for show prints. Never had to fine tune one of them. If you own a 300, 400, 500, or 600 and shoot wide open at 2.8 or F4 and you want to make sure the lens focuses accuracy WIDE OPEN, take you camera and lens to a Nikon facility and THEY will do it for you. Otherwise I would not bother, many here however will disagree with me.
Nikon does not recommend fine tuning your own lenses. I wonder why?

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Apr 23, 2019 06:59:10   #
Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)
 
billnikon wrote:
Relax, I own over 20 AF lenses and enlarge to 20X30 for show prints. Never had to fine tune one of them. If you own a 300, 400, 500, or 600 and shoot wide open at 2.8 or F4 and you want to make sure the lens focuses accuracy WIDE OPEN, take you camera and lens to a Nikon facility and THEY will do it for you. Otherwise I would not bother, many here however will disagree with me.
Nikon does not recommend fine tuning your own lenses. I wonder why?


That has been my experience as well. BTW, Canon has similar language in their literature, manuals and on line. AF Fine Tune is a temporary and/or creative solution( deliberate defocus).

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Apr 23, 2019 08:36:07   #
Jerry G Loc: Waterford, Michigan and Florida
 
Gene51 wrote:
That has been my experience as well. BTW, Canon has similar language in their literature, manuals and on line. AF Fine Tune is a temporary and/or creative solution( deliberate defocus).


Are you saying if you need to fine tune an oem lens you really need to have the camera adjusted?

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Apr 23, 2019 08:48:46   #
camerapapi Loc: Miami, Fl.
 
In the first place, I am a Nikon user and I only use Nikon made lenses. In my more than 50 years photographing I NEVER had any problems focusing a lens, manual or AF.
That statement applies to old and new AF lenses.

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Apr 23, 2019 09:02:28   #
muphoto
 
camerapapi wrote:
In the first place, I am a Nikon user and I only use Nikon made lenses. In my more than 50 years photographing I NEVER had any problems focusing a lens, manual or AF.
That statement applies to old and new AF lenses.


I too am a long time Nikon user. Bought my first Nikon F body, used, in 1972 when I was a student at Marshall University. I used that Nikon during my student days and well at the almost 2 years at a small newspaper. Then in 1979 I landed the job as the university photographer at Marshall and I am still there.
I have used, among others, Nikon F2, F3, F4 and F5. We went digital in 2001 and I have progressed from the D1 to now using the D5. Over those many years I have had, and still do,many Nikon lenses. Never had a focus problem with any of them.

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Apr 23, 2019 09:38:24   #
dsmeltz Loc: Philadelphia
 
Jerry G wrote:
Fifty years ago I was a Navy photographer and pursued photography as a hobby for several years afterward. The only thing auto on any of my cameras was auto aperture, focus and exposure were manual. Now that I'm retired I purchased a new digital camera a couple years ago and quickly found photography has changed and I am still learning.
There have been many discussions here about the need to fine tune some lenses, some people saying every lens needs it and others saying almost no lens needs it. It seems some lenses tend to back focus and need to be tuned. I'm sure I am missing something in my understanding of how AF works so I hope someone can explain it or point me to a resource. My problem in understanding this is that if the camera, either through phase detection or contrast, controls focus, why does the camera not know the lens is not in focus?
Fifty years ago I was a Navy photographer and purs... (show quote)


Some of this has been covered:
DSLRs have a separate focusing sensor, which MAY be at the root of some AF issues,
Some lenses may just be off a bit and need adjusting either in camera or, if severe, by the manufacturer,
Computer programs exist (like Reikan FoCal) to assist in performing micro adjustments.
Some lenses (Sigma and Tamron) provide devices that allow you to do more complicated calibration at more points than what can be done in camera or by using calibration programs.

But, a little front or back focusing is not a problem if it is not important to the type of photography you do. If you shoot with a huge depth of field, you will probably never notice the difference. But if you are doing portraits at f/1.2 or even f/2.8 and trying to get the eye in focus, it could make a huge difference.

So the question is, are you unhappy with the AF performance of your camera and lens?

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Apr 23, 2019 11:47:48   #
Chief Rob
 
Jerry, Steve Perry's book "Secrets To The Nikon Autofocus System" has 46 pages dedicated to fine tuning Nikon's automatic focus system. Steve Perry is a Ugly Hedgehog member so you can google him or search UHH for more information. By the way the principle of fine tuning auto focus systems are more or less consistent. Respectfully, Chief Rob

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Apr 23, 2019 12:16:37   #
olemikey Loc: 6 mile creek, Spacecoast Florida
 
This is another feature that can be handy (handy, or unnecessary - you get to decide!!) if a lens and body (any lens/any body) has an issue with true focus at certain distances. It is not panacea, does not replace a lens technician calibrating a lens to proper parameters, or in tune with a particular body. Probably much more helpful with zoom lenses, since many have regions throughout their range that are sharper than others, at different distances, but could be useful with a prime (again, only if needed).

Since it is not a physical adjustment to the lens (focal plane in camera), and can be voided or changed anytime, it is probably more usefull to the technoGeek, or someone like me who buys used/broken/need rapair/need adjustment lenses and brings them back to life. That said, I have "played" with the feature in the house at short distances and found on several lenses I could make minor changes where I thought it necessary, that sharpened focus for a certain zoom range at a certain distance (haven't had the room or the inclination to do further long range testing). It is much easier than removing the lens mount and re-shiming for correct lens focal plane to camera flange/focal plane distance, and then testing, and re-shiming, etc. etc.

Although I'm not a factory trained lens technician (self taught technogeek) I have seen just as many lens anomalies with 1st party (camera manufacturers lenses) as I have with aftermarket, but since I did not buy them new, I don't know their true history, only what someone (seller) claims. And, most of the major camera manufacturers use third party lens makers on a sub-contract basis to manufacture lenses for them, to their specs, (which is why so many similar looking lenses also look very similar inside)!! Don't know if this is done with high dollar/top class primes (probably not, only the MFG. can answer that, if they would even entertain the question) but it sure is with the lower $$/class stuff.

When the manufacturers switched from metal everything in lenses and cameras, to Engineered Plastics, the world of "tolerance anomalies" also changed. Metal isn't perfect, tolerances can be affected by heat, for instance, but plastic is another beast altogether, it warps, compresses, de-compresses, stretches, and wears & breaks more easily (love those old metal lenses).

As dsmeltz stated, if you do not require tight focus or shoot with large DOF, no issue. If you have a lens that front/back focuses in a certain range, you can accomodate that issue with a minor adjustment..... Like a lot of things we discuss here, it's really up to you.

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