Nikon 24mm F2 Ai - decentering?

[dugrant153]

Hi folks,

Long time no post. I have a Nikon 24mm that I had been using up until recently when some of my results came out a little... fuzzy.

I usually shoot this lens wide open at F2 or stop down to F2.8.
At F2, the lens exhibits a blur effect on the left and right edges of the frame. Almost like the "instagram" circular blur (where only the center portion is in focus). This is great if it's what I want but ... it's not.

The thing is, at F2.8, most of the effect is gone except for the left side where a bit of the image turns to a blurry mess.

Image attached for reference. I'm thinking this isn't normal for this lens?

 

[illumiquest]

try shaking the lens and see if anything rattles? I've had lenses where element rings get loose over time and caused similar issues. Definitely doesn't look normal.

 

[nyoung]

You don't say old your lens is but in general, lenses can become internally misaligned with age and use.
(I think this is more of a problem with the wider angle lenses.)
Never could afford the 24/2 but I did have an old (about a 1980 model) 24/2.8 that made pictures about like your example.
A trip to the shop for a CLA and re-alignment on the Nikon collimating (SP) jig and the world was all in focus again.

 

[semi-ambivalent]

I have a 28mm f/2 AiS that rattles a lot when shaken laterally. That guy Rockwell says they're prone to a loosening of something in the moving CRC group. I think the 24 f/2 Ai has CRC too. Might be a similar issue. Looks like de-centering to me. Good luck and let us know how this turns out.

s-a

 

[dugrant153]

Thanks for the tips folks. I gave it a good shaking but it had no rattling. Glad to know its a problem with the lens!
Sounds like it needs a trip to the Nikon doctor... So will probably post it to them soon.

 

[Christiaan Phleger]

I wouldn't be too quick to send it off; I've had 3 copies of this lens and still have one, and they all basically look like that when its wide open at that distance. Its not this lens' forte, the mid to far range at wide open, where it shows lots of softening towards the edges. I would test it against a brick wall to see if the defocus is uneven, if it is even on both sides then the lens is fine.
At mid to close range wide open and at 2.8 with the subject at the center or near it the lens does very well. This is not a landscape lens. It's a low light mid to close range wide angle, where you need to get the shot. I'm not saying that it could actually be a de-centering but all the 24mm f/2 at wide open at that distance very much look like your image.

As for the CRC and rattle, all the 28f2's I have (2) and others that I've worked on have a bit of rattle due to the front CRC (as opposed to the 24 f2 and 2.8 with REAR CRC), the mechanism has a bit of play in it that does not shift the elements.

 

[Arvee]

Had a 28 f2.8 AIS that the CRC cell had worked its way so far out that the unit wouldn't focus properly. You might check to see if you can rotate the front cell in a clockwise direction. I pushed the lens against my palm and found I could rotate it back and forth. I rotated it back into position and tightened it and all was well.

 

[fstop]

Why are you shooting a wide wide open?

 

[Newt_on_Swings]

I also have this lens, and it is also a just slightly loose on the front barrel. I should take it apart one day and try to tighten it. I have not noticed any image degradation when using this lens though. This type of image did occur once on my Canon Demi S when I first got it, the lens was not tightly screwed down onto the body, It is supposed to be screwed in with 4 screws, and when I opened it up, only one was on, the two others were very loose. This allowed the lens to tilt a bit if pushed.

 

[Ian C]

I suggest checking the pressure plate to verify that it’s holding the film flat against the film registration rails.

If the right side of the pressure plate wasn’t holding properly, that could account for the blur on the left side of the image.

 

[Christiaan Phleger]

The CRC on this lens is done with the rear, in my experience with lenses with rear CRC is that its really quite durable and stable. The front element is the one that can be off, I've replaced the front element on a couple of 24mm f/2's and they all needed fine tuning to the torque of the retaining ring holding the element in order to get max sharpness.
If its still a right/left issue it could also be the mount, check to make sure all the mount screws are set and torqued properly. Your camera mount could also be out as well.

 

[dugrant153]

I just checked the back and all the screws seem be in tight. Nothing is rattling as far as I can tell. Fromt element and the lens tube seem to be on tight. When I shoot it with a Nikon D40, I don't see much issues at the edges like I have had on film.

However I did put on a very large lens hood and have also used a uv filter. Going to try without both and just a step up ring as a "hood". Seems like a long shot but will try it anyways.

 

[dugrant153]

Correction. On a D40 there is definite blurring only in the left side when wide open at F2. Stop down and it starts to go away. F2.8 it's still there. Again, left side only.

 

[Christiaan Phleger]

Yep, then it needs to be checked. The elements are set in an optical group together into the focussing barrel held in place by the front retaining ring which is where the filter and hoods are screwed into. If the lens has taken a knock to the front its possible that the barrel has come ever so slightly ajar enough to affect. If it were MY lens I'd be into right away. If you're handy with the screwdrivers I could talk you thru it.