Stuck aperture on Nikon 300 4.5 ed if (no oil)

Hi I just got in the lens for parts. The lever that controlled the aperture was completely stuck (Its the lever the camera uses to stop down when taking a photo).

I removed the mount and moved the aperture lever back and forward till it moved. It feels dry but I'm not sure. Anyways, now The blades open perfectly when I set it wide open. They close down when I stop it down and manually move the lever, but they do not spring open as they should.

There is no oil on the blades. They look new. Everything on the lens looks great. Any idea on what is causing this? Thanks for your help folks.

Sometimes the tiniest drop imaginable of naphtha on the blades will help melt whatever is sticking. Work it a bunch. Let it dry out well before sealing it off.

 

NO OIL is good. More good lenses have been ruined by nasty lubricants than by anything else, I think.

Thanks for the tip. I will try it.

Holy cat crap! Just went to dab the blades with lighter fluid, heard a pop and they immediately began working perfectly. 85 bucks for a perfectly working, but ugly, lens!

Its possible the lever assembly has developed some grime deeper down in the barrel, causing higher friction/resistance in the re-open direction. Since it was completely stuck to begin with, and working it repeatedly loosened it up, working it some more may restore normal function. If not, the lens may need further disassembly to diagnose.

 

Some of these have diaphragm actuating levers that stretch three inches or more from mount slot to inner barrel (where the aperture is). The little tab that couples to the camera stop-down arm is part of curved bar that becomes much wider under the mount, and can rub against the inner barrel (esp if it or the focus helicoid gets very slightly deformed from impact). This system in the teles can be unexpectedly tricky to get working properly after doing something as simple as just removing and replacing the bayonet mount.

 

I'm sure trained Nikon repair techs have a procedure they follow to avoid this, but after my own seat of the pants service attempts and AI mods I've sometimes had to remove/replace the bayonet three or four times, with the lens set at various apertures, until everything synced up again. Its been awhile since I've worked on a Nikkor tele, but you kind of need three hands to mate everything correctly. I suspect this may be your issue: the lens stopping down easily but not reopening(or vice versa) is a common indicator the parts are not lined up exactly right. Really hard to explain, and it sounds crazy, but perhaps take a shot at removing and replacing the mount again (especially if the aperture ring was also removed at any point).

 

EDIT: cross posted this at the same time you reported solving the problem with naptha. Congrats on the bargain lens, then! Sometimes we get lucky like that. I'll leave my post here anyway since it may apply to someone else.

Edited July 17, 2019 by orsetto

Thanks and I'm glad your leaving it up. I could find no other posts explaining possible stuck blades not involving oil on the blades. I'm sure it will help someone.

Holy cat crap! Just went to dab the blades with lighter fluid, heard a pop and they immediately began working perfectly.

 

Not for nothing am I known as

"the Lord Naphtha, king of the petroleum wastes"