DotTune: Video Tutorial for AF tuning without photographs

Started Feb 18, 2013 | Discussions
WIMorrison
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Re: Read Me: Major discovery for reducing confirmed range
In reply to Horshack, Mar 17, 2013

Horshack,

you post about leaving the AF enabled on the body and the lens confuses me and I wonder if I can ask a simple clarification point?

my view is that I leave AF enabled then when I press the button shouter or AF on) then the lens motor will activate moving the focus negating the objective of changing the focus using the micro-adjust to move the focus to the same place as the live view focus.

can you please explain what you are suggesting? I trmethods dot tune today on sigma 50-500mm at 500 with f6.3 today and got 4 different midpoints, -8, -2, 6, and 15. Clearly something is wrong as neither  the camera or target moved during the tests. I tested at 15m which is the range that I will be using the lens at.

hopefully you will be able to help me

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Horshack
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Re: Read Me: Major discovery for reducing confirmed range
In reply to WIMorrison, Mar 17, 2013

WIMorrison wrote:

Horshack,

you post about leaving the AF enabled on the body and the lens confuses me and I wonder if I can ask a simple clarification point?

my view is that I leave AF enabled then when I press the button shouter or AF on) then the lens motor will activate moving the focus negating the objective of changing the focus using the micro-adjust to move the focus to the same place as the live view focus.

can you please explain what you are suggesting? I trmethods dot tune today on sigma 50-500mm at 500 with f6.3 today and got 4 different midpoints, -8, -2, 6, and 15. Clearly something is wrong as neither the camera or target moved during the tests. I tested at 15m which is the range that I will be using the lens at.

hopefully you will be able to help me

You must configure the camera for back-button focusing ("AF-ON only") so that a half-press of the shutter wont reacquire focus while you're DotTunning.

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WIMorrison
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Re: Read Me: Major discovery for reducing confirmed range
In reply to Horshack, Mar 17, 2013

Thank you, I didn't realise that the shutter button still 'activates' the range finder without mac using AFS to take place

will try micro focusing the lens in daylight, I am sure that this will fix my issue and give me consistent micro focus

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Robin Casady
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Re: An additional comment
In reply to michaeladawson, Mar 17, 2013

michaeladawson wrote:

The dot range for a manual focus lens is way too wide to be able to get anything sharp on a repeatable basis. You can look at the focus scale on the lens barrel at each end of the dot range. It's way too wide. You can take a picture at each end of the dot range as well. You will get blurry photos. The dot range is almost useless for manual focusing if you like sharp photos.

It would be much better if the dot range for manual focus lenses was kept small. It would be far quicker and easier to focus with a narrow dot range than it would be with a wide range where you have to go back and forth many times to be confident that you are in the middle of the dot range.

What would be really nice would be a scale similar to the exposure scale so you can see the degree that it is out-of-focus, not just the direction. That way the center point could have a very narrow range, but you would know how close you are when not on center.

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Starred
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Re: DotTune: Video Tutorial for AF tuning without photographs
In reply to Horshack, Apr 1, 2013

Is it possible that there is significant difference in accuracy of the focuspoints at diffent focal lenghts? I used dottune to fine tune my 35/1.4 at a little under 2 meters. If I shoot something at 2meters, focus seems fine. However, when shooting somthing at 4 or more meters, the focus seems to be far off?

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Per Baekgaard
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Re: DotTune: Video Tutorial for AF tuning without photographs
In reply to Starred, Apr 1, 2013

Starred wrote:

Is it possible that there is significant difference in accuracy of the focuspoints at diffent focal lenghts?

Not sure if the accuracy as such changes, but the optimal micro focus adjustment may vary with distance (and zoom setting) for any given lens.

The "general" recommendation is often to adjust at 50x the length of your lens, so a 50mm should be tested at 50mm x 50 = 2500 mm = 2.5 m.

However, if you often use a particular lens at a certain distance, you may want to use that distance instead. This might be particular relevant for macro lenses, for instance.

For zoom lenses, the "general" recommendation might be to use the longest focal length as the basis for your adjustment, since the depth-of-field is smallest here and any errors are usually better tolerated at the shorter end of the zoom range.

Again, however, if you shoot more often at a particular range, you might want to use that range when you calibrate your lens.

Thus the "best" adjustment is typically a compromise, and you might have to find a balanced setting that averages over your most typical cases, in order to minimize the errors "on average".

Not much is perfect in this world

- Per.

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djsphynx
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Re: DotTune: Video Tutorial for AF tuning without photographs
In reply to Horshack, Apr 2, 2013

Horshack wrote:

I've just posted a video tutorial of the DotTune AF fine tuning method. Here's the link:

DotTune Video Tutorial (YouTube)

And here is a link to the original DotTune thread.

Note: link to video updated by moderator per the O/P's request

Pretty neat stuff, thanks for the information! I have just one question: does it matter which focus point is used, or should the test be repeated for a certain number of points then everything averaged out?

Thanks again

Rob

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Horshack
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Re: DotTune: Video Tutorial for AF tuning without photographs
In reply to djsphynx, Apr 2, 2013

djsphynx wrote:

Pretty neat stuff, thanks for the information! I have just one question: does it matter which focus point is used, or should the test be repeated for a certain number of points then everything averaged out?

Thanks again

Rob

Typically the center point is used since camera bodies don't support per-AF point tune values but you can use the method on other AF points to see if there's a tune difference between AF points. Keep in mind that some lenses have strong field curvature and for those a tune delta is expected, like the 28G f/1.8.

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entlassen
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Different ranges when I change ISO
In reply to Horshack, Apr 12, 2013

I watched the video and performed the DotTune procedure using a D800 with 50mm f/1.4.  The tests were done wide open on a USAF test chart, with the camera 9 ft away from the wall.  Wireless remote shutter, sturdy tripod, non-fluorescent lighting, camera parallel to the target.

With ISO at 100, I'm getting a valid range from 6 to 11.  My midpoint would be 8.5.
With ISO at 200, I'm getting a valid range from 10 to 15.  My midpoint would be 12.5.

I did multiple tests at each ISO value to make sure to get rid of any outliers.  All tests were done in the same 1 hour time window with no environmental changes.

Any idea what might be causing me to get such a difference in values just by changing the ISO?

Any insight would be appreciated.

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NBMZ
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Do you have AF lock set?
In reply to Kaj E, Apr 12, 2013
I am quite sure I had the camera set to AF-S. Can't double check now because the camera and lens is at Nikon Melville despite servicing one and a half weeks ago. By the way what is the default for live view AF-S or AF-F in live view (the manual does not seem to tell).? Nikon reset them to default when they had the camera, I had to do all my own settings once I got it back

Your explanation sound logical for my issue. But I remember checking everything before doing the tests, That does however not mean that it's absolute.

If you do a lot of "focus and recompose", disable any custom functions(CF) you may have setup for the AE/AF lock and  AF-ON button.

It messed me right up when testing on a D4...and would not let me AF using the liveview using a friend's camera.  He programmed the AFON button to be a AF-LOCK button, and it totally messed up focusing using liveview...

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vitamins
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Re: Using global-default AF Tune as +/- 20 workaround
In reply to Horshack, Jul 16, 2013

I tried this with my D800 and several different nikon lenes (50mm 1.8G, 20mm 2.8D, 105 2.8 Macro and the 24-85) No matter what value I put in the AF Fine tune - ranging from +20 to -20 it wont focus right with either of the lenses when I'm using the viewfinder. It focuses perfectly when I use the live view the best I got was with the 50mm 1.8G but not that too not in focus like the live view. Is this a D800 body problem? What can I do in this situation?

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Horshack
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Re: Using global-default AF Tune as +/- 20 workaround
In reply to vitamins, Jul 16, 2013

vitamins wrote:

I tried this with my D800 and several different nikon lenes (50mm 1.8G, 20mm 2.8D, 105 2.8 Macro and the 24-85) No matter what value I put in the AF Fine tune - ranging from +20 to -20 it wont focus right with either of the lenses when I'm using the viewfinder. It focuses perfectly when I use the live view the best I got was with the 50mm 1.8G but not that too not in focus like the live view. Is this a D800 body problem? What can I do in this situation?

Are you saying that no AF tune value between -20 through +20 produces acceptable focus results on any of your lenses? If so which end focuses better, +20 or -20? Also have you tried using the default tune value vs the lens-specific values, which provides a greater tuning range.

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Horshack
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New recommended AF target
In reply to Horshack, 10 months ago

FYI: After considerable testing I've created new AF target based on a cross-hatch of variable width lines. This new target produces much consistent results compared to the focus chart I used in the video. You can download the new target here.

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Stevequad
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Re: New recommended AF target
In reply to Horshack, 10 months ago

It worked for me. Thanks.

Steve

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AndyW17
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Re: New recommended AF target
In reply to Stevequad, 10 months ago

I have 24-70 and 70-200 zooms for my d600. No primes.  Is there a preferred way to do this calibration with a zoom lens?  Sorry if this was covered in the thread, but I didn't see it.

Thanks.

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Leonard Shepherd
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Re: With regret - why do so many ignore Nikon's guidance?
In reply to Horshack, 10 months ago

With regret - why do so many ignore Nikon's guidance?

The suggested target is a symmetrical target .

Nikon say auto focus does not perform well with symmetrical targets, and also 5 other groups of target. My 14 experience using Nikon is, in general, the Nikon guidance is good.

The video starts by suggesting initial focus using Live View. Nikon explain in instruction books some subjects can confuse Live View and be OK with phase detect, and vice versa.

It would make much more sense to start with a target likely to be 100% reliable with phase detect and also good with Live View.

Then include instructions on focus distance for each focal length being tested to make sure the AF target remains a suitable size for likely 100% reliable phase detect AF.

Most complaining and posting links probably would not post if they looked at Nikon guidance first as almost all post examples using links where AF may not work well.

Llinks following Nikon's guidance seems close to nil, strongly indication in most cases the problem is not in front of the camera eyepiece.

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Leonard Shepherd
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If they are great images does what lens, body or technique was used matter more than the skill of the photographer?

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Humanoid
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Re: New recommended AF target
In reply to Horshack, 10 months ago

Horshack wrote:

FYI: After considerable testing I've created new AF target based on a cross-hatch of variable width lines. This new target produces much consistent results compared to the focus chart I used in the video. You can download the new target here.

I'm using the Focal test target and have had success recently, with my D800e and 600mm VR lens.

FocalPro calibrated the camera at -4 and Dot-Tune calibrated the camera at -4 or -5.  After shooting some real world  it looks like -5 is the sharper of the two.

As long as you can get a sharp LV image for setup and have a decent test target you should get excellent results using the Dot-Tune method.

Ray

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Horshack
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Re: New recommended AF target
In reply to AndyW17, 10 months ago

AndyW17 wrote:

I have 24-70 and 70-200 zooms for my d600. No primes. Is there a preferred way to do this calibration with a zoom lens? Sorry if this was covered in the thread, but I didn't see it.

Thanks.

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Andy

I would first tune at the various focal lengths of the zoom. Ideally they'll all tune within a few ticks of each other and you'll be done. However sometimes one end of the focal range will differ significantly from the other. For those cases you either have to average the two tune values (hopefully producing acceptable results for both) or pick a value closer to the one end you shoot at more often. Hopefully future Nikon bodies will implement dual-tune values for zooms like Canon did for the 5DM3/1DX/6D.

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RumpelHund
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Aperture is one of the influences to the calculation I'd say
In reply to entlassen, 10 months ago

If not the aperture might change, leading to a change in AF compensation necessary.

Not that the image coming onto the sensor changes (no aperture involved then), but the camera might know about the lens's characteristic on aperture-dependent focus shift?

From my experience the perfect AF-fine-tune has the following influences

- lens (obviously) and (for zooms) focal length
- aperture used (while only small numbers like 1.4..3.5 really show the problem)
- focus distance (closeup or infinity and quite  a bit of positions in between)
- light type (Kelvin basically, seen mostly as daylight vs. tungsten taking very different tuning)
- AF-illu used or not, especially if white or red pattern of strobe

So when I shot at landscape-daylight at infinity and move to my kid's indoor-tungsten-party closeup (portrait style) my 1.4/85 and my 1.4/24 really make me sick on the D800. The D700 was much more robust in this regard. Had a D4 on a Nikon workshop long before I had my D800 and found this there already, too.

So basically we have to find the perfect values for a 4-dimensional feature space. That's way too much, Nikon needs to adress that in the next generation. The 4s seems to have mostly AF enhancement from what I read of the pre-announcements, and I definitly think this makes sense.

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JCB123
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Re: DotTune: Video Tutorial for AF tuning without photographs
In reply to Robin Casady, 10 months ago

Robin Casady wrote:

Horshack wrote:

Robin Casady wrote:

Thanks Horshack.

How much does the range vary? Instead of moving increment by increment can you take a jump to speed up finding the other end of the range?

It depends on the lens. On my Sigma 35mm f/1.4 the range is very small, only 4 AF tune units. On my 50G f/1.4 it's 9 tune units. You can jump around at any increment you'd like when trying to locate the general are of the range.

Thanks. Just out of curiosity, any idea what characteristic of the lens determines the range?

That would be anything that affects DOF. So for a given distance the focal length and the max aperture. We test at 50 x FL so the distance increases with focal length. Depth of field reduces with reduced distance so FL & distance tend to cancel (but not exactly) We also test wide open, so lenses with a fast max aperture will have shallower DOF. The shallower the DOF the smaller the range.

Heres a link to a DOF calculater - http://www.cambridgeincolour.com/tutorials/dof-calculator.htm

Regards

John

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