Pentax DA 70mm Limited - Possible oily residue inside lens?

Started 4 months ago | Questions thread
resistingLBA Junior Member • Posts: 27
Re: Pentax DA 70mm Limited - Possible oily residue inside lens?

[the next steps, again with disclaimer]

I take no responsibility for whatever you do, or anyone who reads this does. Whatever happens, i am out of it. When this disclaimer/limitation cannot apply do to your local laws, or for whatever reason, including that you do not agree, do not even start, stop here and do not read the rest. By reading what follows you confirm you read and understood this part. You have been warned.

9. Three of the screws have that, three don't.


10. After you unscrewed and safely stored the screws, you can remove the front optical group. It is NOT screwed in place. Just turn slowly the lens to a side towards upside-down while continuously holding the front optical group, you will be able to pull it out gravitationally. Make sure you don't let it fall.


11. With both optical groups (back and front) out of the way, the diaphragm is accessible from both sides. There is no glass left. Most of what is there is metal, but if you have in mind some thermical treatment, keep in mind there is a PCB with some electronics as well somewhere there, so rather don't.


12. Cleaning the diaphragm - here I cannot really advise properly. As I've written before, I had to reopen the lens several times because whatever I did, the fix did not last, oil came back from somewhere. I can list all the ideas I've collected over the years:

First a warning: the diaphragm blades are a very delicate thing. Apply too much pressure and disaster will happen. Put something on their way, same end. Once out, you will never put them back. And they might break as well while trying.  Nothing will make them straight once you bend one.

a) [Maybe yes] Use cigarette lighter fluid on cotton stabs (Zippo something). When it evaporates it would leave no traces and hopefully would take some of the oil with it. Had success with that in other lenses. Damaged other lenses'diaphragm with it as well - one needs patience and to avoid applying in excess. Applying directly from a spray tends to freeze the blades thus they can glue to each other briefly. Applying force with the diaphragm lever at that moment is a very bad idea.

b) [Fairly safe but maybe ineffective] Just use cotton stabs to wipe/collect the oil and make a lengthy routine of carefully opening, closing the diaphragm, wipe some more, etc.

c) [might help] Heat the assembly with a hair dryer to make the oil more fluid

d) [Ineffective, ugly] At the end, use truly carbon pencil to apply some carbon on the blades by gently drawing on them some (random?) lines. In my experience, this looks terrible afterwards and does not seem to help.

I did b) and c) this time. (c) is my novelty.

13. The diaphragm is now fairly clean on both sides and "snappy" - once open and let free it closes instantly.



14. Mount back everything in reverse order. Air-blow any glass surface that will be inside the lens (later inaccessible) and examine the diaphragm with a magnifier for any cotton threads left before putting back the optical groups.

14. Done

I hope it helps. Sorry for splitting this long post, the editor has a bug thus at times it was not possible to continue in same post.

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