Back focus and AF Fine Tune question

mjeffries · Oct 26, 2015

For years I've been frustrated with back focus issues on my 80-200 f2.8 AF-D lens. As I hold a black belt in procrastination, I've only just now attempted to use AF Fine Tune within the camera (D700, D750) to correct the issue.

At 200mm f2.8, I have the D750 AF Fine Tune set to -20 and the end result isn't bad. I came up with my own DIY calibration setup so I won't call it perfect by any means, but definitely an improvement.

When testing it at 80mm f2.8, still using the -20 AF Fine Tune, I now win the gold medal at the front focus olympics.

Am I correct in stating that there is no way to program the AF Fine Tune to only make adjustments to certain focal lengths? That I'm stuck with the adjustment (in this case -20) across the full range of the 80-200mm?

If that is the case I'll just leave the adjustment at -20 and try to remember to manual focus at shorter focal lengths. With this lens 200mm is where I spend most of my time so I might as well leave the AF Fine Tune adjustment so that the lens can properly focus at 200mm.

I just want to make sure I'm not overlooking any obvious solutions. Your time and input is greatly appreciated.

Braineack · Oct 26, 2015

Buy a lens with a dock that allows fine focusing at different focal lengths.

ie. Sigma.

runnah · Oct 26, 2015

Canon allows for fine tuning at both ends...just saying.

Nikon only allows for one range. Normally tho if you adjust at the long end it should be close enough.

astroNikon · Oct 26, 2015

It might just be a problem with that particular lens.
My 80-200/2.8 AF-D is just fine at 80, 200 and in between.
You may want to check with Nikon if they would service the lens for the issue.

JacaRanda · Oct 26, 2015

I say if you are almost always at the 200mm end, go with that.
Here a AF method I will play with next.

And here is a test chart that I will also use next. http://bobatkins.com/photography/technical/lens_testing/reschart2015(9).zip

runnah · Oct 26, 2015

I bit the bullet and bought one of the the real testers. So far I haven't taken it out of the box but it does make the process much easier as it had a much finer adjustment scale.

Braineack · Oct 26, 2015

runnah said:
Canon allows for fine tuning at both ends...just saying.

Crap like this annoys me in the year 2015. This would take a programer about 5 minutes to add to the firmware of any camera.

runnah · Oct 26, 2015

Braineack said:
runnah said:

Canon allows for fine tuning at both ends...just saying.

Click to expand...

Crap like this annoys me in the year 2015. This would take a programer about 5 minutes to add to the firmware of any camera.

Yup! But hey don't fret, at least Nikon has a built in intervalometer.

But crap like that is why I run magic lantern. It's shocking how many feature could be added with a few lines of code.

Braineack · Oct 26, 2015

it's not shocking at all.

it's 2015 and you still cant choose to shoot longer than 30sec without having to hold the "bulb" squeezed.

runnah · Oct 26, 2015

Braineack said:
it's not shocking at all.

it's 2015 and you still cant choose to shoot longer than 30sec without having to hold the "bulb" squeezed.

Well they want you to buy the $40 timer, or in Nikon's case give you a reason to buy the next 3xxx or 5xxx model.

Mr.Photo · Oct 26, 2015

mjeffries said:
For years I've been frustrated with back focus issues on my 80-200 f2.8 AF-D lens. As I hold a black belt in procrastination, I've only just now attempted to use AF Fine Tune within the camera (D700, D750) to correct the issue.

At 200mm f2.8, I have the D750 AF Fine Tune set to -20 and the end result isn't bad. I came up with my own DIY calibration setup so I won't call it perfect by any means, but definitely an improvement.

When testing it at 80mm f2.8, still using the -20 AF Fine Tune, I now win the gold medal at the front focus olympics.

Am I correct in stating that there is no way to program the AF Fine Tune to only make adjustments to certain focal lengths? That I'm stuck with the adjustment (in this case -20) across the full range of the 80-200mm?

If that is the case I'll just leave the adjustment at -20 and try to remember to manual focus at shorter focal lengths. With this lens 200mm is where I spend most of my time so I might as well leave the AF Fine Tune adjustment so that the lens can properly focus at 200mm.

I just want to make sure I'm not overlooking any obvious solutions. Your time and input is greatly appreciated.

View attachment 110456 View attachment 110457

What you are experiencing is an inherent aspect of the 80-200 2.8. I have the older one touch zoom (push pull) version and when I attempted to adjust the AF fine tune on it I got the exact same results as you. Nikon actually mentions this in the user manual of my D7000. I still don't know what causes the issue to occur, but what I do know (at least on my lens) when the issue can occur. It appears to be a distance issue of some sort as I will explain below.

With my AF fine tune set to zero my lens is tack sharp at all apertures between 80mm to approximately 150mm. Beyond 150mm (especially when shooting wide open) if the subject distance is between the lenses minimum focus distance to about 9' from the lens it will appear to back focus terribly. If the subject is outside that distance the lens is then extremely sharp. Again this only seems to occur on my lens between 150-200mm and is most noticeable when shooting wide open as the depth of field is extremely narrow at that distance and focal length.

When using AF Fine Tune (as you discovered) it then makes things good on one end, but worse on the other. It comes down to how close you shoot to your subject and at what focal length that will determine how you will want to adjust your fine tuning. I kept mine at zero and just be aware that I don't want to shoot subjects closer than about 9'. This is pretty easy to do as the minimum focus distance on the lens is close to 6' anyways.