Slightly sluggish aperture on 45mm f/2.8 AiP

[FGAng]

I have some questions, but first the background.

Yesterday I succumbed by my NAS and bought a silver 45mm f/2.8 AiP.  The pricing was 200 EUR, and as seller hadn't use the lens for the past few months, he checked it and found out the aperture was sluggish, in his words, beyond f/8.  With that known issue, I got him to sell it to me at 150 EUR.  Prices equivalent from Singapore dollars.

Sure enough I tested it there was some sluggishness in the aperture, and initial shooting at f/16 yielded about 1.3 stops of overexposure.  Brought it home, exercised the diaphragm, and this morning I tested the aperture to close down "correctly" at f/11, and at f/16 the value was about between 2/3 and 1 stop out (closing to 1 stop).  Unscientific test, using the lens on a Df and shooting a scene outside my window, cycling through the apertures from f/2.8 through f/16.  Significant vignette at f/2.8, improving by f/4, gone by f/5.6.  Consistent histogram from f/5.6 through f/11, and at f/16 to shifted to the right, determined to be between 2/3 and 1 stop by shooting at f/8 and using exposure compensation and watching the histogram.  Weather condition remained relatively constant - overcast, which is good, as there would be little change of lighting.

My question:
- could this issue be due to storage of lens at its widest aperture, hence putting the spring at tension in storage?
- subjectively, if I now store the lens at the minimum aperture, and exercise the lens (use the lens) regularly, would I be able to get the aperture back to (or close to its original performance specification?

I have tested and am satisfied that up to f/11 there is no problem.  And should be able to work around the f/16 issue if needed (like shoot manual exposure with lens stopped down).

Thanks.

[Erik Lund]

My answer:

- No.

- No.

There must be either some oil or grease in the aperture somewhere, bad return spring or the aperture leaver is bent out of shape.

So, lens not on the camera, feel with your the tip of your finger how the operation feels like when operating the leaver at smallest aperture, compare it to other lenses.

Shoot a couple of images close up of the aperture blades and the leaver.

[richardHaw]

yes, oily aperture definitely.

i flick the lever in rapid succession and you should see some inconsistencies.

look at the front or back side, see if there is shiny or dark marks on the blade.

[Bjørn Rørslett]

Lubrication  seeping onto the aperture blades is a troublesome matter unless the lens is properly and professionally cleaned to get rid of it. I sincerely doubt whether the lens being used or not has much influence once the damage has been inflicted.

Unless repaired, one can never really trust the lens in operation. Sometimes it might work well, sometimes the aperture seizes up and you get gross overexposure. The 55/2.8 Micro-Nikkor was infamous for this issue and my first copy was cleaned twice before I gave it up and just dumped it into the waste bin. A second copy bought many moons later is just fine, though.

I have had several copies of the 45/2.8 Ai-P without any aperture issue, thus apparently this problem is not applicable to the whole production run. My current black 45P has perfect aperture functionality.

[FGAng]

Thanks to Erick, Rick and Bjorn for your replies.

Some photos to see if some diagnosis can be arrived at:

First the lever






The the blades.

From rear


From front


Thank you once again.  I am resisting the urge to dismantle the lens... trying to be not OCD (disassembler).

[Erik Lund]

Leaver and blades look pristine.

Could be the return spring or,,, the camera

What are those specs around the edge of the blades?

[FGAng]

Thanks Erick, the specs are simply dust at the front baffle - nearly 1:1 on a D300, so greatly magnified (nearly 1.5:1).

Unlikely to be camera, since the situation was detected by the seller using a different body, confirmed to be so with my Df.

I did what Rick told me, last night, and today, and the aperture appear to return more snappy than when it first arrived.  My thoughts are that it is likely the spring (that's what I felt from the beginning anyway), since the blades look pristine and clean to me as well.

Maybe I will need to cannibalize from a piece of junk in Rick's pile to replace the spring... .

[Bjørn Rørslett]

Agree with Erik. No signs of oil seepage in the lens or any issue with the aperture stop-down lever. Thus one has to look elsewhere. A badly tensioned return spring should be detectable if you set the aperture on the lens to the smallest value (lens off camera), push the stop-down lever to open the aperture, then release it; the blades should stop down immediately without any delay. Do this repeatedly to check that stopping down is consistent. If the aperture responds sluggish on occasion, the return spring is the major candidate. I doubt there is true oil leakage when the actual leaves are this pristine (ref. your photo).

The final check is with the camera. First, set up the camera to use aperture ring on lens to control the aperture, then stop down the lens to f/22. Find a bright subject, mount camera on a tripod and put the camera to the fastest possible frame rate in continuous release mode (you might use jpgs for this as they are just test dummies). Fire away, then make an overview of the jpgs to see they are evenly exposed. If they OK, do a second series in which you change to make aperture selection on camera instead, then dial in f/22 and repeat. If the jpgs now are unevenly exposed (and the first series is OK), the problem is the stop-down lever in the camera.

Obviously, if the first series as described above produces uneven exposures, the lens needs to be serviced. Replacing a worn tension spring should be a quick and easy fix with any camera repair shop worthy of the description.

.... - nearly 1:1 on a D300, so greatly magnified (nearly 1.5:1)....

An assumption often made, but still entirely wrong. Magnification is a scaling property, thus the format does not change the ratio number at all. Life-size 1:1 is the same on any format. What changes is the field of coverage. It can go from encompassing a match head on a CX camera to a full facial portrait on 8x10". What does not change is the exposure compensation required and the depth of field as both are influenced by the actual magnification.

[FGAng]

Thank Bjorn.  This morning I ran 2 series of test on my Df, 10 and 11 frames, at CH.  Hand held, shooting out of the window of my flat.

First series, 1st shot


6th shot


10th shot


Not sure if it is a little hard to see on the screen, there is some over exposure on the first 3 or so shots, then the exposure was more even, but not very even.

Similar results from the second series.

I am actually quite inclined to leave it as it is, at least for now, until such time I find a reason to open up this lens and replace the spring from a cannibalized lens...

Thanks Bjorn.

[FGAng]

Thank Bjorn, I understand the math that 1:1 is 1:1 is 1:1 whatever the format.  What I was saying is that at 1:1 I get a 50% larger image ... on screen or on print.. .  But, you are correct.

[Bjørn Rørslett]

50% wider coverage (at 1:1) is different from 1.5X magnification.

This stuff was so obvious back in the old days when we shot with different film-based formats. For example, on my 6x9 cm camera I might need a panoramic coverage so just put the 6x12 or 6x17 back on it whilst keeping the lens (if it had adequate cover, but most had since I regularly used 4x5" lenses on the smaller camera). One didn't need refocusing, altering exposure, or anything, but just got a broader view. Of course details on film kept their exact same size as I had just extended the format not altered magnification.

These days most of this is downed in the tsunami of "equivalence" and "crop factor" nonsense. Nobody cares because they have read the 'truth' - on the internet.

Rant mode off.

[Erik Lund]

I fail to see any difference in those three exposures at all,,,

[FGAng]

Thanks Erick.  That confirms my inclination, of not meddling with the lens and live within the minor issue.

There is a difference - when seeing the histogram - the first one is further to the right, and shot at 5.5 fps, the lighting should not be the issue... but remember these are all f/16 shooting in rapid burst.

And when I shot from f/2.8 cycling through to f/16, change is pronounce between f/11 and f/16.  Anyway the problem has decreased after I shot it repeatedly for 50 or so shots. 

This was the first f/16 shot after leaving the seller's place, clearly over exposed, due to the sluggish aperture blades closing.:


And thanks for all your help.  I am quite sure the spring has a little problem.  One day I will open it up and replace the spring with a cannibalized spring and try again!

[David H. Hartman]

There is a ball race in manual focus lenses that must remain dry, unlubricated. The stop down lever in the lens runs on this ball race. The lever must run very fast to stop down to minimum aperture and to keep up with a motor drive. I wonder if those ball bearings could have a tiny bit of oil on them that separated from the grease. That's probably unlikely. I don't see lube contamination of the aperture blades. It could be just starting.

I'll bet there is something impeding the aperture stop down lever in the lens just a bit.

If the camera is set manual exposure and there is no change in the exposure settings is the problem still seen? If so I'd have the lens serviced.

Dave

[Erik Lund]

...
This was the first f/16 shot after leaving the seller's place, clearly over exposed, due to the sluggish aperture blades closing.:
..

IMHO this is not very serious,,,  Shot though a car window,,, ?