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09-27-2014, 07:38 AM   #1
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Focus adjustments - yes or no?

I've been reading a lot about forum users doing focus adjustments for their lenses.

But in a book I bought with my K-3, where a photographer explains all its functions, he strongly recommends to not touch this feature at all. Doesn't even explain how to do it but only writes about why not to do it. He argues, that the vast majority of cases out of focus happens due to wrong technique and not manufacturing error. And that one would need different settings for different focal lengths (with zooms) and distances anyways, so, in his mind, adjusting makes no sense at all.

So I am wondering if I should go through my lenses to verify they hit the spot on a focusing chart or if the author has a valid point and I shouldn't bother. Is doing focus adjustments a bit like pixel peeping, or is it actually founded? What's the chance, that a lens was actually delivered out of focus?

I'd appreciate your thoughts about this.

09-27-2014, 07:55 AM   #2
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Check if yours lenses focuses correctly, adjust when needed.
09-27-2014, 07:57 AM   #3
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If you have fast primes it is worth the time to tune the AF. But with consumer zooms most likely not.

The testing procedure needs to be precise and meticulous otherwise the margin of error in the test exceeds the potential error in the AF. A poorly done AF tuning can easily cause more harm than good.

In short, AF fine tuning is available for those situations where it is needed but is not something to casually mess around with. Most users will have no need for it especially on the k-3 which seems to be more accurate than the k-5 in my experience.
09-27-2014, 07:58 AM   #4
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I agree with him that most focusing problems originate from the photographer and not the lens or camera. And that playing with focus adjustement on an otherwise fine lens/camera will likely result in a worser situation. Simply put, focus adjustment is not a remedy for a faulty technique.

That said, in the other hand, there's nothing wrong to check if your lens/camera are okay. This is quite easy to do. You can do the "battery test" described on this webpage. If it everything looks fine, it's because you don't have front/vack focusing issues, or that they're not important enough for you to care about because they will not results in soft picture under normal conditions. If your lenses are fine with this test and you get focus problems, you then know that they are from you and not from your equipment.

09-27-2014, 08:16 AM   #5
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Don't worry about trying it out, it's just an adjustment.

Camera bodies and lenses are made within certain tolerances. Sometimes the tolerances are small, sometimes not. Tolerances are + and -.

If you get two negative or positive tolerances together then you might get poor AF. Positive on one and negative on the other might cancel each other out.

If you try AF fine adjustment and it goes wrong, as in oof gets worse, you just reset. No harm is done at all.
09-27-2014, 08:19 AM - 1 Like   #6
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Well, he is partly right. A lot of people complain that the camera or lens is not working correctly and then attempt these AF corrections, when in reality it is their technique. We see this often on these forums, when people upload sample photos it suddenly becomes clear it is handhshake blur, thin DoF, subject movement, diffraction or any of the many other reasons why a photo is not sharp where you want it to be. Getting a tack sharp,well-exposed photo is a skill.
That being said, it is true that some lenses and cameras might not be perfectly in tune with each other. If they are at opposite ends of factory tolerances, AF adjust might be needed. But this has to be done in a patient, methodological way, not just to vent some emotions. So I say only go for AF adjust if you have reason to suspect there is a problem, and read about it before attempting it. If you adjust wrongly, then even good technique won't help.

Good luck, may your photos be clear
09-27-2014, 08:29 AM   #7
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QuoteOriginally posted by Undot Quote
he strongly recommends to not touch this feature at all
Fire will likely rain down on me from many here, but I tend to agree. The detailed rational is a bit complex but the gist can be expressed by a conversation I had with Mike Knight, owner of Knight Camera and Repair here in Vancouver.

Me: Mike, how do you guys do AF calibration?

Mike: Oh, you mean fine adjust in the camera? (I nod). Jacob (an employee) does all those. He has a procedure where he shoots a resolution target with the camera on tripod.

Me: Does that work well?

Mike: I guess so, though he tells me that most of the time he is unable to improve on the factory calibration. AF, at best, is a bit imprecise and it is hard to pin down an exact adjustment. It is not intended for critical focus.

Me: Tell that to the folk on Pentax Forums!

Both: (Good long laugh)

The conversation continued with me sharing a comment from a Facebook photo group where a member was complaining that his high-end Canon would not consistently track the eyes of the waterfowl and shorebirds he favors as subjects (more good laughter). Mike suggests a higher shutter fps.


Steve
09-27-2014, 08:33 AM   #8
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I suppose the reason why he doesn't recommend you touch it is because it requires very precise testing and adjustments. I happen to regularly adjust my lenses - because many of them are faster than f/2.8, and precise AF is absolutely critical because I do a considerable amount of commercial photography.

09-27-2014, 08:59 AM   #9
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QuoteOriginally posted by Undot Quote
Is doing focus adjustments a bit like pixel peeping, or is it actually founded? What's the chance, that a lens was actually delivered out of focus?
It is combination of pixel peeping and measurebation obsession. AF lenses are generally the passive partner in that they mainly follow the camera's instructions and (in the case of motor-in-lens) confirm when the action is done. That being said, it is possible to tune the lens workings to mesh better with a specific camera. Usually that requires the services of a good shop.* An alternative is to attempt a per lens fine tune in the camera settings. My experience has been that it is hard to derive a bias adjustment that works consistently and does so at all distances and (for zooms) focal lengths.

Sigma has a product called the USB Dock that works with its most recent "Global Vision" lens lines. This device attaches to the lens base in the manner of a rear cap and may be used to access and modify various firmware settings when attached to a personal computer. You would think that AF tuning would be a single adjustment. No way! You must adjust for four different distance ranges and (for zooms), several different focal lengths. Hmmm...in-camera fine adjust is only done at one distance and one focal length (your choice for both).


Steve

* I have no idea what they do, except maybe to adjust mechanical tolerances and confirm optical centering and element position/alignment. For motor-in-lens situations, it is possible to tweak the lens response for specific cases.
09-27-2014, 09:05 AM   #10
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QuoteOriginally posted by stevebrot Quote
You must adjust for four different distance ranges and (for zooms), several different focal lengths. Hmmm...in-camera fine adjust is only done at one distance and one focal length
I cover the use of the Sigma lens dock in my review of the 18-35mm f/1.8 ART Vs Pentax FA31mm f/1.8 Limited. While I do adjust the AF on my lenses, I have use testing methods and an optical testing bench that have very high tolerances, far beyond the reach of a casual photographer.
09-27-2014, 09:05 AM   #11
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QuoteOriginally posted by Digitalis Quote
I happen to regularly adjust my lenses - because many of them are faster than f/2.8
I respect your technical expertise and am curious as to how you make this work with truly fast glass. After all, even the best AF systems have no better focus sensitivity at f/1.4 than at f/2.8.* Do you do multiple measurements and average the results?

Edit: We posted simultaneously. I am reading your comment on the linked review thread suggest that it is very pertinent to the general topic of AF adjustment.


Steve

* The same ability to detect out-of-focus at f/2.8 as at 1.4. The result is less precision at f/1.4 than you would need to do a consistently accurate calibration.

Last edited by stevebrot; 09-27-2014 at 09:15 AM.
09-27-2014, 09:12 AM   #12
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QuoteOriginally posted by stevebrot Quote
Do you do multiple measurements and average the results?
yes, in the case of an AF lens I do ten AF tests from the minimum focus distance, and an additional ten from the infinity setting. This gives me a good set of data points to arrive at an optimal adjustment setting. With manual focus lenses I use a high precision laser rangefinder to check the distance scale - with horrendously fast lenses such as the Leica 50mm f/0.95 Noctilux-M the RF focusing system has to be carefully maintained to ensure accuracy. Thankfully the laser rangefinder helps me tune my RF cameras so I can avoid repeated ( and costly) servicing of my Leicas.
09-27-2014, 11:09 AM   #13
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I don't check focus chart anymore...

I used to check focus chart
Maybe I don't check because my K5 camera does well with any lens I have tried. I 'checked' a used K100 and it was fine... My K20 didn't ever seem right. But the K20 was never right on focus chart. (talking levels and math to get 45 degrees just right and daylight illumination and 8x10 glossies with notes on the back = wtf)

Now, I check by taking pictures of stuff and this is how I check K100 & K5.
If the point of focus looks to be where I intend it be, all is fine

I also believe the sensors are no more sensitive than f/2.8... but I have pretty good and consistent results with 77 at f/1.8-2 and minimum focus distance.
09-30-2014, 05:16 AM   #14
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Thank you for all this feedback. I suppose I was expecting more of a "that guy is a loon, here's what you do", but got plenty of good information instead.

I wasn't even thinking about cameras and lenses not just being "correct" but manufactured within tolerances, with the possibility of errors adding up or cancelling out. Always such an easy trap to think in right and wrong instead of all the shades in between.
So, I suppose checking my equipment, especially my primes, on a chart won't hurt. If only to get an idea about things. Well maintained optical test bench with use of laser rangefinder does sound a bit out of my league though - more of a scientific setup than the hack-it-at-home I had in mind. With a swiss army knife and some gum...
But then, I don't have quite that fast optics to worry about either.
09-30-2014, 06:13 AM   #15
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I checked my lenses with the travelling Lens Align this summer. Only one required any slight adjustment, and since it was a zoom I don't often use I didn't bother. All the other lenses worked as intended. It's a nice little system.
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