Is this separation or fungus?

[Matus Kalisky]

Hello,

This is a view of the rear element on Pentax FA 33-55/4.5 - what is it? Is it separation or fungus? The owner says it is not on the outer surface.

thank you

[GPS]

A typical fungus - not fully developed yet. Could be cleaned without traces.

[Bob Salomon]

A typical fungus - not fully developed yet. Could be cleaned without traces.

And then it could have eaten into the glass a bit already. And spores could be developing without being visible yet.

[sun of sand]

I'll say completely cleanable
worst case 93%

[GPS]

And then it could have eaten into the glass a bit already. And spores could be developing without being visible yet.

Fungus that eats the glass must first cover a considerable area of it. Fungus in its hair stage can eat just that - hairlines. Spores are only visible in a microscope and at that stage they don't damage the glass. Once you get at the fungus, spores are the part of it that is the easiest to clean.

[David McNiven]

I see tool marks on the edges of the slots.
If I was considering buying the lens from a seller I didn't know I would think it wise to assume he had removed the cell and found the fungus still not accessible - I would value the lens accordingly.
Even if the glass isn't yet affected the coating may very well be.

[Matus Kalisky]

Thank you. The seller mentioned explicitly that he tried to remove the rear element but did not succeed.

BTW - how does one clean fungus from a lens? Any special chemistry / tools involved? I have the adjustable tool to mount the LF lenses onto lens boards, but I have no experience on this type of work.

I am waiting for a quote from official Pentax repair centre (I have sent them the photo) but I will only get it once the offer is ... ehm ... expired. I am still considering it ...

A tip for a good 3rd party service for this kind of problem in EU would be helpful too.

[GPS]

David will probably tell you better than me, but the "tool" you have is not enough if you don't have some experience too. There are too many hidden obstacles...
If the fungus did not start to eat the glass surface you don't need any special chemistry, just a cleaning tissue and a cleaning liquid. If the glass is eaten nothing helps to put it back though...;-)

[Ivan J. Eberle]

Yeah, those tool marks suggest either rough handling or some corrosion had gotten in there and made the threads tight. I'd steer completely clear unless the owner is practically giving it away. However, I did see on the Pentax Forums that someone had recently been able to order this rear element for the 33-55 still (took quite awhile, and maybe had to come from Pentax Japan?).

Also, though I've never used one myself, anecdotally have heard that the 33-55 may not be quite as stellar a lens as some of the other P645 line-up, though the zoom ratio is admitted interesting. It's rare enough to command a premium; hard to say if it has the performance to justify a high price.

To keep it in perspective, I found an optically perfect, reasonably clean manual focus SMC-A 35mm f/3.5 for under $300 awhile back. It is tack sharp, has no distortion. Mated to my 645N this rig soon became my favorite walking-around camera. More frequently these sell for $400-500 but there are much larger numbers of them in circulation.

[Matus Kalisky]

Thanks. The lens would come with a Pentax 645N body and the 45-90/4.5 zoom lens for 600 euro. If the lens was repairable under say 200 euro it would make sense to get it, have it repaired and sell it (I would probably sell the 45-90 too) should I not be happy with the performance.

In general pentax lenses do not pop up too often. the 35mm (MF or AF) if not easy to find either. But I am getting way too much off topic with this tiny format here ;)

[GPS]

...
In general pentax lenses do not pop up too often. the 35mm (MF or AF) if not easy to find either. But I am getting way too much off topic with this tiny format here ;)

Some LF lenses have even more tiny diameter than this one...;)

[Matus Kalisky]

Thank you. I have found out that even if a replacement of the rear element should be necessary it should not cost more that $150. But the question is - how high is the chance that also deeper sitting elements could be attacked by the fungus. That could turn the lens into paper weight (if the cleaning could not be done properly)

[GPS]

Thank you. I have found out that even if a replacement of the rear element should be necessary it should not cost more that $150. But the question is - how high is the chance that also deeper sitting elements could be attacked by the fungus. That could turn the lens into paper weight (if the cleaning could not be done properly)

You don't need to agonize over it. Once the lens change the climate that allowed the fungus to grow (the humidity) it dies calmly. Were the deeper sitting elements attacked, they too would already have their part of the fungus. If only you can open the lens and clean it it will serve you well.