AIS 28-85mm/3.5-4.5 focus shifts when zooming

[leonardo_cohen]

Hello All, Happy New Year.

 

I recently bought a Nikkor AIS 28-85mm lens, and something really

strange happens when zooming the lens: the focus shifts, and after

zooming, I have to refocus the lens.

 

Is this common with this lens? I never had an equivalent problem with

any Nikkor zoom before. What could be wrong with it?

 

Mind you, the focus shift is quite aggressive. I checked against

other lenses, and at the 85mm setting, the zoom's focus mark is where

it should be (for example, 3m for a subject 3m away). But after

zooming to 28mm, I have to refocus the lens to 1.2m! Same happens to

far away buildings, for instance, which focus at the infinity mark at

85mm, but at the 3m mark at 28mm...

 

Thanks!!

 

Leo

 

ps: and no, I did not move after zooming!!! Nor did the subject!!

[walt_donovan]

Sounds like the lens has gone "funny". Not ha-ha funny, just funny. I've never owned a lens that lost focus while zooming. Are there any dents in the lens barrel. Sounds like something has been jarred out of adjustment.

[alex_lofquist]

Some earlier zooms are not "parfocal". That is a compromise in the optical design along with other constraints in execution. The focus shift seems a bit more than should be expected, but as long as the images are sharp at all FL, and you always refocus after zooming, it many be of minor importance.

[YS2]

I have a similar issue with 24-85 f/3.5-4.5 AF-S and this was a brand new lens when I got it.

[al_tan]

I don't have the 28-85 AIS but my 35-105 AIS has this symptom as well.

 

That's also one of the reasons I'm selling it, though it doesn't affect the picture quality. Just that it irks me to have to refocus after zooming.

[leonardo_cohen]

I have the 35-105 as well, which is perfectly fine.

 

I don't know if something was knocked out of place internally, cosmetically the lens looks fine.

 

What annoys me the most is that far away subjects have to be focused at the 3m mark! And of course, I can't use the lens' minimum focusing distance anymore at 28mm, only at 85mm.

 

I am worried that if something IS out of place, even though the image might look sharp after refocused, it actually has more distortion that originally intended (since the formula for good glass, especially zooms, is a perfect balance of all the imperfection amongst the different elements...)

 

Thanks all!

 

Leo

[mi.x_join]

As a general rule, Nikkor MF lens don't have focus shift while zooming,but its consumer AF zoom do have its focus shifted while zooming.I presume your MF28-85/3.5-4.5 do have some problems.You may contact your local Nikkor dealer.As of MF35-105/3.5-4.5zoom, it's pull-push zooming,I wonder if you manually changed focus while zooming.

[john_stockdale2]

There was a thread around here a while ago in which the once proud owner of a VERY expensive Leica zoom was unhappy about such a focus shift. He was told that it is normal for that lens, and to refocus.

[Brian1664876441]

I noticed the same "problem" as well in my AF-Nikkor 28~85. When focussing at wide® angles and then zooming in, the focus was lost. My solution was to zoom-in, focus, and then zoom-back to compose. The increased DOF covered the shift. I could never convince myself that the focus really shifted when focussed wide/then zoomed. I attributed most of the effect from loss of DOF and the AF mechanism (or me, the human servo-motor) from gaining acceptable focus at wide angle which was unacceptable zoomed in. I traded the lens for a 10.5cm RF lens and solved the problem.