Calibrating Autofocus on Sigma 150-600 Contemporary

Rather than make my other query overly complicated, I'll ask separately...
Sigma 150-600 C on a Nikon D500.

This combination spends the vast majority of it's time at 400mm or longer (90% probably at 600mm). And the focus distance is RARELY closer than 30-40 feet. Not 100% of the time, but things shot at 10 - 30 feet seem sharp and not a problem.

So, if I need to calibrate anything (I have hundreds of disastrous images from an earlier shoot when the bif are very visibly out of focus even when the focus point is right on the bird), I'd say 400 and 600mm at the ~45 feet and infinity distances. I don't see a way to shift the focus distances in the calibration so I presume my choices are 9.2, ~20, ~45 and infinity feet.

First question is HOW do you tell if there is likely a front or back focus issue? I can put a long-ish chart out, mark it where I want to focus, put the camera on the tripod and all that. Focus on the spot and voila... Except even at 600mm and f/6.3 the DOF is at least 6 inches, and I can't see any significant loss of sharpness for at least a foot in either direction... And even then it's so subjective I'm reluctant to shift the focus...

And HOW do people actually do this? For example - 600mm ~45 feet f/6.3. Let's say I want to shoot a series of images from +20 to -5 in 5 step increments. So I'd have to pull the lens off the tripod and body, put it in the dock, go to the calibration, set it at +20, put it all back together and take a picture. Then repeat at +15, +10 +5 0 -5 -10 -15 -20... I figure with my luck it would take a huge amount of time and I'd probably drop the lens at least once! Is this brute force method what people use to do the calibration?

And HOW do you do it at infinity? I'm not sure where this lens hits infinity, but how far do I have to be from the chart (or whatever subject I use) to get a reliable "infinity" test? Again, even at 6.3, at 100 feet the dof is at least 2 FEET, and at 150 feet it's over FOUR feet... How do you even make a guess that there's a problem?

My normal testing for long lenses is simple, i place an obvious target like a fag packet on tarmac or short grass, at 600mm focused on the target you will see if its front or back focused easily, only today i dumped all my test shots from yesterday or i cou;d have shown you how obvious it is.
Long lenses i only do at the long end and i gave up on the D500 auto fine tune, i got too many different results.

GracieAllen... You spent $2800+ between that camera and lens... Spend $90 and get Focal and calibrate it correctly.

https://www.bhphotovideo.com/c/prod...f988X8NOdunA0dQq61kSrFd9HExVDGTsaArAHEALw_wcB

Does Focal replace the multiple distance/focal length calibrations done in the Sigma dock, getting rid of the need to shoot images at the different calibration focal lengths and distances? How does it do that? Am I correct that Sigma had some valid reason to provide the ability to do up to 16 individual microfocus calibrations, or is it just a marketing thing?

In any case, given that at the moment I DON'T have Focal, can someone who's done the calibration with the Sigma dock provide their process? Or confirm that I'm correct about having to go back and forth between dock and tripod multiple times for each focal length and distance?

Focal does a series of adjustments using Nikon's Fine-tune adjustments... It tethers to your computer, it has a couple of calculators that analyze the Target for distance and exposure... From that point forward, it does its own analysis without you trying to determine whether it's front or back focusing... and creates a series of data points that your camera's fine tune setting needs to be for a specific focal length... After you've tested a particular lens at different focal lengths, and IF there's a difference in Fine tune adjustment, you can either elect to use an average of that data, or if it's significant enough, you might want to consider that when shooting at those lengths...

Focal certainly eliminates trying to determine small visual differences between dozens of images...

I don't have a clue what Sigma's dock/adjustment does...

Thanks Fred. Sounds like it's automating the camera's microfocus adjustment. The dock is adjusting the lens' firmware so it's a different, and I suspect lengthier process...

Hi,

I calibrate my D850 withthe Sigma 150-600 C, with a combination of the green dot method and making test pics.
At 150, 250, 400 and 600 mm. At distances of 2.8, 6, 15 meter and infinity.
16 test situations, each test situation I calibrate in the camera with AF Fine Tune.
I write down these correction numbers.
At the end, I set the AF fine tune in the camera at 0 and through the USB dock, I set the 16 correction numbers in the lens.
In this way (this is a old screen print with my former D750):

Quite time consuming but if you want your AF as perfect as possible...
I think it will work a bit in the same way if you want to use Reikan Focal software.
Maybe a bit faster, but you still have to do 16 tests.

In this way I also have a Tamron 24-70 F2.8 G2...
Able to fine tune in the lens at 12 places...

The camera's fine tune is only one setting for the entire lens, right? Sigma's dock allows you to fine tune for various distances AND at various zooms, is that correct?

I have a Sigma prime 135 Art, but thought the dock was a waste of time after I bought it. It doesn't zoom, so I just used the camera's AF adjustment.

But maybe I should give the dock another try to set different tunes for different distances???

Hi Blade Canyon,

you're absolutely right, various distances and various zooms.
For a prime lens it "only" will do various distances.
More perfection for a perfect lens...

I did some testing the other evening. Using the dock, I set up a target at 48 feet and shot images at 400mm at +20 +15 +10 +5 = -5 -10 -15 -20. Then did the same thing at 600 mm....... Then found a fairly detailed subject that was DEFINITELY at infinity and did the same thing at 600mm.

I finally decided if the lens was off at either focal length, it's not enough for me to see an OBVIOUS problem. I'll have to try again on a really bright day 'cause it was somewhat overcast, which I think makes it more difficult to see small imperfections...

One thing I DID find was that the 150-600 jumps WAY past infinity VERY quickly. It looks like anytime it can't find a subject it likes, it goes way past infinity... I haven't tried it, but I had a thought about that - if you took one of the custom settings and went into focus range and move the furthest back ONE notch so in theory the lens would NEVER QUITE get to infinity, would that keep it from doing anything stupid when it loses the subject against a bland sky...

Hi, I just happened across your post on using the Sigma USB dock to adjust AF points on the Sigma 150-600 with a Nikon D850/D750.

I have been doing the same thing, noting the AF adjustment values from the Nikon AF Fine Tune, to avoid taking the lens on and off the camera umpteen times.

However I was advised (in another post) to DOUBLE the Nikon values when putting them into the Sigma adjustment table.

Are you getting good results with a straight copy of the values?

David Eagle said:

Hi, I just happened across your post on using the Sigma USB dock to adjust AF points on the Sigma 150-600 with a Nikon D850/D750.

I have been doing the same thing, noting the AF adjustment values from the Nikon AF Fine Tune, to avoid taking the lens on and off the camera umpteen times.

However I was advised (in another post) to DOUBLE the Nikon values when putting them into the Sigma adjustment table.

Are you getting good results with a straight copy of the values?

Click to expand...

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@GracieAllen[/FONT]

Yes, if I recall correctly the values I got from the Nikon microAF were doubled. But, the whole thing with using the dock was laborious enough that I finally quite worrying about any focal length other than 600mm. I set those values and so far all the shorter focal lengths have been fine since they have more DOF than 600. I did the lens on both the D500 and d850 and did them all with the 1.4X on the lens on both bodies. Works pretty well and things are perceptibly sharper at 600. And shorter.

Never mind. My post came off as snide, which is the way I meant it. But never mind.

Ad B said:

Hi,

I calibrate my D850 withthe Sigma 150-600 C, with a combination of the green dot method and making test pics.
At 150, 250, 400 and 600 mm. At distances of 2.8, 6, 15 meter and infinity.

Click to expand...

How many meters was your infinity test? What type of focus target did you use at this distance?

cmalra said:

How many meters was your infinity test? What type of focus target did you use at this distance?

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