Pentax FA28/2.8 disassembly

I've recently acquired an FA28/2.8 and it has traces of fungus around the edges of the front element.

I've dismantled and cleaned a range of pentax lenses before, but all K and M models. I assumed that the FA would be equally staightforward, but it seems not!

I have removed the front optical block, but can find no way of dismantling it to remove the elements. Is this one of the models where the elements are permanently bonded/machined into the housing?

Any advice would be agratefully received, thanks.

I have heard that more recent lenses rely heavily on precise torque settings and/or bonded elements, as opposed to the "little more than finger tight and it'll work" approach seen in the K and M series.

Given the value of a clean FA 28mm it may be worth investigating professional attention for the lens?

It is quire likely that the part to which you refer cannot be disassembled any further. I don't have personal experience of that particulaar lens, but I had a DA16-45mm which I bought knowing that the front element was quite badly damaged.

I tried removing the front group, and enquired of Pentax about a replacement and was told that the whole lens was essentially scrap as they would not sell an element by itself.

Each group of lenses that makes up an element is generally glued into an assembly which essentially cannot be seperated into its component part.

If the fungus you describe is indeed fungus, rather than some other issue like delamination, and it is ocurring between an element assembly, you'd best try and get a refund if possible.

Thanks for the advice - I'm pretty sure it is fungus, however it is not bad and does not seem to affect the performance. Hopefully with a dose of UV (assuming we get some more summer before autumn) and careful storage, it will not get any worse and I will continue using it.

With regard to a refund, unfortunately the fungus was disclosed when I bought it (and it was priced accordingly), so it's one to chalk up to experience.

Ref the lack of strong sun in the UK, I heard a rather bizarre story recently about someone renting a sunbed for three hours and cranking it up to max to get rid of fungus on two lenses he's bought, and apparently it worked....might be worth a try

Graham , not much help, but FYI

According to 'Boz' http://www.bdimitrov.de/kmp/lenses/primes/wide-angle/index.html the 'FA' is optically different to earlier F , A and M series, which do allow access to the front element.

Looking at the schematic diagram, it does seem that it should be possible to separate the front element. It might be worth calling Johnsons http://www.johnsons-photopia.co.uk/ to discuss the proble. I have found the guys in thier technical department most helpful. Ask for an official Pentax PDF for the lens and hopefully that should help you on the way.

Regards - Steve

Hi Graham, I have the FA 28/2.8, it is a different design to all other 28mm Pentax lenses and IMHO the equal best optically the other being the K 28/3.5. Well worth spending a little to have it serviced. All my lens service/repairs have been handled by Michael Spencer, factory trained 47 years experience, if it can be cleaned then he's your man!
Very friendly and helpful, ring him for a chat and advice 01246 250767
cleaning a lens usually costs approx £25 including return postage Special Delivery, never had a problem

http://www.camerarepairs-r-us.co.uk/

Regards,

John

Thanks John, I'll give him a try.