Lens with broken aperture mechanism

Hi folks,

I've got a JCPenney brand 135 f/2.8 lens in Pentax K mount that I picked up in a bag full of stuff. It seems to be pretty nice, coated optics, integrated lens hood and obviously all metal. Sadly the aperture mechanism doesn't work - the lens is always wide open. There is evidence of a blunt force trauma on the lens barrel and it rattles when you shake it, so I'm assuming at some point the lens took a blow and that was that.

Question is what can I do with this lens? Obviously I can shoot it wide open all the time which is fun, but does anyone have experience repairing an issue like this? I'm not inclined to send it off, these lenses are a dime a dozen so it's not really worth the cost. But if you all have tips on ways I can either try to repair myself, or alternatives like harvesting the lens elements for other uses, I'm all ears.

It is very common for the apertures of SLR lenses to be stuck wide open. It occurs because oil migrates from the focus helical onto the leaves, making them stick due to surface-tension. The solution is to disassemble the lens enough to remove those oily blades, and then clean both them and the nearby surfaces. Given that the lens was damaged from a blow, I suggest using this lens to learn lens-repair, and assume that it will never work again.
You can often unscrew the front or rear group of elements as one sub-assembly, giving you access to the aperture. To remove the rear group, you will need to remove the lens mount first.

Mark Overton

You can access the aperture mechanism by removing the mount ring only. Be careful lifting the ring off as there may be a spring or spring loaded pin that will pop out. The screws holding the ring likely have a clear thread locker that is dissolved with Acetone/nail polish remover.

Not sure this is simply oil on the blades if impact damage + rattle when you shake it. This is a great opportunity to practice lens repair, you can't break something that is already broken and it's not a high value lens.

You could always make a couple of apertures out of lens caps. Drill a hole in one for, say, F8, in another one for F11.
I would recommend focusing before you attach one of those caps!

Is something broken or simply dislodged? Dislodged can also set something loose.

John Koehrer said:

Is something broken or simply dislodged? Dislodged can also set something loose.

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I am not sure. I need to open it up. As others have said, the lens is broken as it is so there's nothing to lose by opening it up.