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Author Topic: Is focus tuning much of an issue with DSLR's?  (Read 1376 times)

Eric Brody

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Is focus tuning much of an issue with DSLR's?
« on: June 18, 2017, 04:07:14 PM »

I am curious how much of an issue focus tuning is to DSLR photographers. I have given up my DSLR for a mirrorless system but still wonder about this.

One of the major differences between DSLR's and mirrorless cameras is the potential need to focus tune the lenses with the DSLR. In fact there's a cottage industry of tools to do this, e.g. Lensalign. I dislike uncertainty and one of the things I really like about mirrorless is that it really is wysiwyg, at least in terms of focus (I'm ignoring other aspects of the great EVF-OVF debate).

I just did a workshop in which the overwhelming majority of photographers were using Nikon D810's and their images (sadly mostly projected rather than prints) were quite striking in their sharpness, and overall excellence. I did not think of this question until my return, I should have asked them and still may as I have their emails.

I'd appreciate hearing of others' experience.

Thanks.

Eric
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Chris Kern

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Re: Is focus tuning much of an issue with DSLR's?
« Reply #1 on: June 18, 2017, 08:27:06 PM »

I am curious how much of an issue focus tuning is to DSLR photographers. I have given up my DSLR for a mirrorless system but still wonder about this. . . .

I'd appreciate hearing of others' experience.

My experience with my D800E is that it is useful with some lenses but unnecessary with others.  But that experience is with a single body and a single copy of each of several lenses, which is not a good basis for generalizing.

Somebody like Roger Cicala of LensRentals is in a better position to offer a summary judgment because he has access to multiple samples of the same lens and multiple camera bodies.  This goes back quite a while, but here's what he said in a 2012 essay:

Quote
[A] copy of the 50mm f/1.2 was backfocusing badly on [one particular Canon body]. We did a quick microfocus adjustment (12 points) and reshot the lens with the results below.  [Image omitted.]

Here is a superb example of what microfocus adjustment accomplishes. After adjustment phase detection AF is now very accurate, although there still is going to be shot-to-shot variation. For the two or three of you who like to scream, ďI donít want to us microfocus adjustment! The lens should be perfect out of the box!ď, we went ahead and put the same lens on a different body with no microadjustment.  [Image omitted.]

On camera No. 2 the same lens autofocuses accurately. The other 50mm f/1.2 lenses we tested all autofocused accurately on the first camera. The lens is perfect, just not with the first camera. The first camera is fine with all the other lenses we tested. Sometimes a given lens thatís fine doesnít match up with a given camera thatís fine. So it goes.

The conclusion is pretty obvious: If you want to shoot wide aperture prime lenses and you donít want to use microfocus adjustment, you just refuse to cope with reality. . . .

We did several runs with 50mm f/1.2 lenses and found similar results all the way through. Standard deviations for sets using LiveView AF were 11 to 20, while phase detection ran from 20 to 35. These results are similar to what we saw with the 50mm f/1.4.

Conclusions . . .

    Microfocus adjustment pulls good phase-detection AF results up to a par with LiveView, but it doesnít eliminate the small amount of shot-to-shot variation that phase-detection AF has.

My take from this, which happens to be consistent with my own limited experience, is that it's worth investing the time to see if focus-tuning makes a difference with your particular samples of bodies and lenses.

BernardLanguillier

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Re: Is focus tuning much of an issue with DSLR's?
« Reply #2 on: June 19, 2017, 06:45:13 AM »

The recent Nikon bodies (D500/D5) automate this process and I am sure that the D810 replacement will have this capability too.

This being said it is easy to do manually also.

Cheers,
Bernard
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kers

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Re: Is focus tuning much of an issue with DSLR's?
« Reply #3 on: June 19, 2017, 06:45:36 AM »

I have fine tuned al my lenses on the d810 body and yes it is necessary and it takes time, but after that you nail focus even at f1.4.
I understand future Nikon cameras will have a system like in the d5 were there is an automated proces to do it.
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hogloff

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Re: Is focus tuning much of an issue with DSLR's?
« Reply #4 on: June 19, 2017, 08:18:48 AM »

Biggest issues with MFA is at what distance do you adjust as that affects the adjustments and for zooms, at what focal lengths do you adjust.

Needing to fine tune focus reveals the biggest issue with DSLR's...what you see in the viewfinder is not what the sensor sees. I remember needing to shim my focus screens to enable me to somewhat accurately manually focus.

From my perspective, one of the biggest advantages of mirrorless systems is focus accuracy.
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kers

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Re: Is focus tuning much of an issue with DSLR's?
« Reply #5 on: June 19, 2017, 08:50:24 AM »

I remember a spokesmen of Nikon saying that with focus on the sensor, some pixels have to interpolated making the image less exact.

robably a more theoretical issue, but for some kind of photography important.
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BernardLanguillier

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Re: Is focus tuning much of an issue with DSLR's?
« Reply #6 on: June 19, 2017, 10:32:17 AM »

I remember a spokesmen of Nikon saying that with focus on the sensor, some pixels have to interpolated making the image less exact.

robably a more theoretical issue, but for some kind of photography important.

The banding reported by some a7/a9 users seems to confirm that this can be an issue in some cases.

Cheers,
Bernard
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scyth

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Re: Is focus tuning much of an issue with DSLR's?
« Reply #7 on: June 19, 2017, 11:04:38 AM »

I have fine tuned al my lenses on the d810 body and yes it is necessary and it takes time, but after that you nail focus even at f1.4.

even Nikon marketing does not dare to claim that AF points have precision better than f2.8 DOF  ;D , but users are always (as opposite to a possibility of random event happen) nailing it @ 1.4 with fully automatic focusing... indeed 2x2 can be > 5 with a skilled hand...
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Eric Brody

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Re: Is focus tuning much of an issue with DSLR's?
« Reply #8 on: June 19, 2017, 11:36:44 AM »

I posed this question to Lloyd Chambers, whose opinions I respect. He tests many autofocus lenses for his blog. He responded by saying he tests only with magnified live view. Check out his answer at his blog, diglloyd.com. I'm not about to go back to a DSLR but am impressed that a new generation of cameras has automated the process.
Thanks for all the responses. Keep 'em coming.
 
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hogloff

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Re: Is focus tuning much of an issue with DSLR's?
« Reply #9 on: June 19, 2017, 11:46:36 AM »

I posed this question to Lloyd Chambers, whose opinions I respect. He tests many autofocus lenses for his blog. He responded by saying he tests only with magnified live view. Check out his answer at his blog, diglloyd.com. I'm not about to go back to a DSLR but am impressed that a new generation of cameras has automated the process.
Thanks for all the responses. Keep 'em coming.

Yep, landscape shooters have traditionally used the rear LCD for critical focus. Nuff said about auto focus...if it can't be relied upon for critical focus.

Personally I found micro focus adjustments a kludge as the values change depending on the focal distance you are trying to focus on and in the case of zooms, the focal length. I've spend enough time micro focus adjusting to know both the distance and the focal length affect the micro focus adjustment values so you have to choose what focal length and distance to be optimal at and let the rest become not so optimal.

I now shoot mirrorless and I get nearly 100% of my images tack sharp using AF...whereas with my DSLR equipment it's much less than that.
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davidgp

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Re: Is focus tuning much of an issue with DSLR's?
« Reply #10 on: June 19, 2017, 05:10:16 PM »

The banding reported by some a7/a9 users seems to confirm that this can be an issue in some cases.

Cheers,
Bernard

The number of AF pixels, even on the A9 that has 699 pixels it is too small comparing to the number of megapixels. I don't have the camera and I'm not paying Digilloyd site anymore, so I can not check, but after reading all the reviews around there, like one at dpreview, I think the issue it is not that big, but of course, it will depend in each person and their preferences.

Saying that, Canon dual pixel af solves that problem. It does not have the issue of using some blue and red pixels for AF losing information in them, it makes all pixels in the sensor AF pixels, so probably it is the best in sensor technology (every review you read everybody mentions how good dual pixel AF it is to focus video). Curiously, Canon it is not trying seriously the mirrorless market. When they do it is maybe a bit late... Sony it is already publishing patents quite similar to Canon Dual Pixel AF.

razrblck

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Re: Is focus tuning much of an issue with DSLR's?
« Reply #11 on: June 21, 2017, 06:32:24 AM »

I had to adjust three of my lenses on my D7000 (also had to change slightly the D7000 alignment as it was always a bit off, probably the result of age and handling as it was more accurate when new), and now I can definitely nail focus at f/1.4 all the time. Took me just a few minutes.

Not all cameras will have to be adjusted, but there might be some variation. If you never shoot wide open with fast lenses you may never notice it, but if your works depends on this it is worth doing.
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E.J. Peiker

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Re: Is focus tuning much of an issue with DSLR's?
« Reply #12 on: June 21, 2017, 09:50:24 AM »

Having run a business that does this for people, I have probably done more lens/camera focus tuning than 99.99% of the photographers on the planet.  The answer to your question is "it depends".

If you are a Nikon user - most definitely!  It is very rare for a Nikon lens and Nikon body to be perfectly optimized at a zero setting and the probability of any third party lens requiring a zero offset is zero!  Some combinations are especially bad like the Nikon 500mm f/4G VR (not the newer E lens) with any Nikon 1.4x TC - there is a 40% probability that the amount of tuning required falls outside of the tunable range.  This is based on over 400 calibrations of that combination.

If you are a Canon user - if you are using the latest lenses with the latest bodies - basically 1Dx/5D3 or later and the generation 2 and 3 lenses, more often than not there is little to be gained as offsets are typicall within 1 or 2 points of zero or at zero.  But put an older lens or a third party lens on or use an older teleconverter or body then you are in the same boat as Nikon - everything needs some amount of adjustment.  The Canon 300mm f/2.8 lenses prior to the IS models are especially bad needing, in general 15 points or so of adjustment. There is no Canon combination that I have run across that can not be calibrated within the tuning window - if you have such a combo, there is something physically wrong, likely with the lens.

It is also important to note that there are many variables which can shift the optimum tuning point including ambient temperature and the light source being used.  I do all of my tunings with a full spectrum light source but if you only use your gear in a studio with LED panels than I would do the calibration that way as there is likely a slight shift.

Another thing to note is that Nikon, in their latest bodies, builds in an auto focus tuning feature - it does not work very well and is all over the place.  take 10 different samples and you will likely get 10 different answers , some wildly different from others.  If you are going to do it this way, take many readings and throw out the obvious outliers and then average the rest.

One other thing, after reading the f/1.4 comment right above my post - if you calibrate a fast prime like an f/1.4 lens at f/1.4, it is likely to be off at smaller apertures.  Fast primes tend to have significant focus shift as you stop down.  For a landscape photographer using fast primes I recommend doing the cal at f/2.8, for portrait photographers at the aperture they are most likely to use.  As an example, the very popular Sigma 35mm f/1.4 Art will have an offset value that is 5 points different at f/2.8 than it will at f/1.4.
« Last Edit: June 21, 2017, 10:03:41 AM by E.J. Peiker »
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Chris Kern

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Re: Is focus tuning much of an issue with DSLR's?
« Reply #13 on: June 21, 2017, 07:54:46 PM »

Having run a business that does this for people, I have probably done more lens/camera focus tuning than 99.99% of the photographers on the planet.

Very interesting post.  Any possibility of a follow-up describing your focus-tuning tools and technique (assuming that's not proprietary information, of course. . . . )?

scyth

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Re: Is focus tuning much of an issue with DSLR's?
« Reply #14 on: June 22, 2017, 08:22:20 AM »

Sony it is already publishing patents quite similar to Canon Dual Pixel AF.


Sony does manufacture actual sensors with such AF... already... and so does Samsung... albeit for cell phones.

http://techinsights.com/about-techinsights/overview/blog/survey-of-enabling-technologies-in-successful-consumer-digital-imaging-products/
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scyth

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Re: Is focus tuning much of an issue with DSLR's?
« Reply #15 on: June 22, 2017, 08:27:05 AM »

As an example, the very popular Sigma 35mm f/1.4 Art will have an offset value that is 5 points different at f/2.8 than it will at f/1.4.

and camera / lens combo might have the different adjustments for different focus points across the frame and for zoom lenses across the zoom (between wide and tele ends) and for focus distances too...
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davidgp

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Re: Is focus tuning much of an issue with DSLR's?
« Reply #16 on: June 22, 2017, 08:39:38 AM »


Sony does manufacture actual sensors with such AF... already... and so does Samsung... albeit for cell phones.

http://techinsights.com/about-techinsights/overview/blog/survey-of-enabling-technologies-in-successful-consumer-digital-imaging-products/

Yes, I saw that article the other day, after I did that post... I wasn't unaware they were already doing it for iPhone 7 and Samsung phones. It will be a matter of time for them to release a camera with bigger sensor that also uses it (like the stacked or bsi sensor technologies, they tested first in the small phone sensors (you get better yields just for being the sensor smaller, better to try new things and when the manufactoring process is well tested to scale it to bigger sensors), I wouldn't be surprise if next RX100/RX10 cameras come with this technology).
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