Help calibrating lens (80x400) using D850

jeff5150

Hello all,
I could use some help. I noticed my 80x400 nikkor isn't as sharp as I'd like. I purchased a spyderlenscall kit and have set it up precisely to their instructions for parallel, distance for 400mm, level, etc. When I take a picture at default, I can see it is about 1/2 inch back focusing based on the scale. I tried adjusting the AF fine tune, but, it doesn't seem to make a difference. So, I took an image at +20 and -20, they seem to be the same - not sure that is possible if AF fine tune is actually working as it should, albeit, I'm not sure. I posted the images to flickr and hoping someone with experience calibrating can help.
Thanks in advance,
Jeff
https://flickr.com/gp/jeffmiller_photography/PEb4b7

Pistnbroke

Contary to popular belief some lenses are better set one stop down when using the AF fine tune . The picture is not sharp enough wide open and looks the same at + and - 20.

Looking at your posted shots the left one looks spot on the right is out .
You should be looking when the numbers around zeero go fury .eg are the 3s equally unsharp? or do the 2 and 5 look equally unsharp?

Personally when setting a 400mm lens I would be using a target about 60 yards away.
I photograph a house number down the street and can tell instantly if its in perfect focus by checking the clarity of the screw heads.. Initially I go from +20 --20 in 5s and then hone in on the perfect setting. If you are doing this in JPEG have you got the sharpness at +9. If not you have fury vision anyway.
I also suggest you check it after a little use ,say 500 pics as the focus often moves . My wifes new 100-400 Tamron has gone from +6 to +4 .

JUST NOTICED YOU SAID DEFAULT..no no that's for lenses not on your fine tune list .
you want AF fine tune ON then move the fine tune slider and press ok. Forget Default, should be left at zero. When you done your testing and return to the menu it should still show the setting you inputted.

Pistnbroke

Just written this all up and it disappeared ..so here we go again.
I notice you said default ..NO No that's for lenses not on your AF fine tune list .Leave that at zero. Fine tune ON and adjust the Saved Value fine tune slider and press OK. leave the default at zero.
Notes,
Some lenses are better to adjust at 1 stop down ..not sharp at wide open ,everything looks fuzzy.
If doing this in JPEG you need sharpness set at +9 or everything is in fuzzy vision
For a 400mm I use a target at 60 yards ..The house number down the street , I go from -20 to + 20 in 5s and hone in on the sharpest . The screw heads are a good guide.
Use a flash over the lens ..that triangular shadow on the scale is not helping you judge.
When you have it adjusted then check after about 500 shots (if its a new lens) as they tend to run in ..my wifes 100-400 tamron has gone from +6 to +4 in that time.

Now lets press post and see if it goes to internet heaven.

jeff5150

Hey Pstnbroke, thanks for the reply.
You are right, it is the Saved value I was changing. Though, I'll admit, I tried changing both. I also tried deleting the save and restarting. I have added studio lights as well, I'm still not able to change the backfocus.
Agree that lenses are not sharp wide open, I typically shoot no lower than 7.1. However, sharpness and where the focus is are two different things. The most focused sport should be on the 0, even if it is not as sharp as a couple stops down.
Also, with the distance, the guide and other youtube videos save I should be at 400mm x ~5-10 which is about 78 inches to 157 inches...I'm at 100 inches away from the Spyderlenscal. I'll try and find something outside like you suggested, just pointing out that I did what this kit said to do.
That said, after adding in more light and resetting all values, I'm still struggling to change the backfocus. Perhaps the lens needs service - it is less than a year old and maybe a few thousand shots taken.


Oh, also, I learned the D850 has an auto fine tune option. I did that and it said 0 was where it needed to be, redid the test, it is still backfocusing. ARG!

Pistnbroke

The fine focus adjust is a function of the camera not the lens . its " moving" the focus module at the bottom of the light box to match the focus to the sensor plane.
If you take a shot at +20 and another at -20 they to some extent must be different and not in focus ..100inches is totally stupid. You probably have focus breathing at that distance . I built a giant focus unit out of a 6 ft length of 4x2 leaning against my fence at 30 deg with a ruler down it . there is no way you can adjust a 400mm inside your house ...

BVS

Just curious, but what kind of values does the Auto AF-Fine Tune function give you?

Steve Perry made a good video on how to use it here:
https://backcountrygallery.com/get-nikons-auto-af-fine-tune-system/

jeff5150

That video is great! Let me redo my test and conduct the 12 shot method at an appropriate distance. I'll get back to you soon. thanks again.

spraynpray

Good post @BVS.

Pistnbroke

I would be interested to know what you find Jeff. From what I read the auto focus adjust system is not very good..any sort of averaging is not going to work as I find if its + or - 1 out it makes a big difference with a 400mm lens.

LatoshaStr

BVS said:

Just curious, but what kind of values does the Auto AF-Fine Tune function give you?

Steve Perry made a good video on how to use it here:
https://backcountrygallery.com/get-nikons-auto-af-fine-tune-system/

That video helped a lot! Thanks @Steve

Pistnbroke

I have e mailed the OP to ask what he found … but I can only say that any ;process that involves averaging is floored as there is only one correct number for 400mm.