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Disassembling the rear group of a Porst 55mm 1.4 - Tomioka?
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PostPosted: Tue Jan 04, 2022 11:12 am    Post subject: Disassembling the rear group of a Porst 55mm 1.4 - Tomioka? Reply with quote
Hallo all,

I can't find a way to open the rear group from a Porst 55mm 1.4, the flat rear lens type, which is generally known as a Tomioka lens.

There is a cylindrical ring that covers most of it, leaving outside just the thread to attach it to the barrel.

This ring has two notches that were used to extract the group: however it looks glued to the body (the white substance is the fruit of a reaction with isopropyl cleaner).

I don't know how to go on, is it possible that this ring may be threaded inside, the thread being reverse?

I'm afraid I couldn't go further than this, however there is some active fungus inside so I must try to open it.

Any help would be appreciated




https://www.flickr.com/photos/194732689@N07/51799055579/in/dateposted-public/

https://www.flickr.com/photos/194732689@N07/51798684351/in/dateposted-public/

https://www.flickr.com/photos/194732689@N07/51799055609/in/dateposted-public/


PostPosted: Tue Jan 04, 2022 12:10 pm    Post subject: Reply with quote
Looks like a burnished edge to me.

After mounting the lens, a protruding lip is either pressed or rolled over the edge of the lens to retain it, which is called a burnished mounting.

There is no non-destructive way to remove this; the lip needs to be carefully ground/cut away. Re-mounting would be by means of an adhesive.

Judging from the images I would say your lens may have both a glued as well as burnished mounting. One complication there is that the solvents used to soften/dissolve the glue (e.g. acetone, MEK, methylene chloride, possibly xylene etc.) have a tendency to also affect any lens cement used between doublets.

It can be done, but it may be more trouble than it is worth.

An example of a couple of burnished mounts below, but the spring is unlikely to be present.



PostPosted: Tue Jan 04, 2022 12:22 pm    Post subject: Reply with quote
RokkorDoctor wrote:
Looks like a burnished edge to me.

After mounting the lens, a protruding lip is either pressed or rolled over the edge of the lens to retain it, which is called a burnished mounting.

There is no non-destructive way to remove this; the lip needs to be carefully ground/cut away. Re-mounting would be by means of an adhesive.

Judging from the images I would say your lens may have both a glued as well as burnished mounting. One complication there is that the solvents used to soften/dissolve the glue (e.g. acetone, MEK, methylene chloride, possibly xylene etc.) have a tendency to also affect any lens cement used between doublets.

It can be done, but it may be more trouble than it is worth.

An example of a burnished mount below, but the spring is unlikely to be present.



Thank you very much, it is a good explaantion. I agree on the hassle thing ... maybe some long exposure under ultraviolet light could do something, even if many here have reported failures in this sense.

I could obtain some results in summer, under a heat wave, leaving a Tair 300 with some fungus and an horrible mold smell under the scorching sun for hours.

Front lens was aimed at the sun.

The lens lost its smell and the inenr fog was gone. Not sure it was real fungus, though.

From your diagramas I understand that disassembling this group would do some harm.


PostPosted: Tue Jan 04, 2022 12:58 pm    Post subject: Reply with quote
Attempting to kill the fungus (with UV or otherwise) may be a bit of a pointless exercise. The air (and any lens) is already full of mould spores. Even if you completely disassemble and sterilise the lens, by the time you are done with re-mounting the elements, the lens will be full of mould spores again.

Key to preventing fungus from growing (and stopping growing fungus from spreading) is to keep the relative humidity low and don't provide a food source. Below 65-70% RH fungal spores don't germinate, below 50-55% RH existing growing mould goes dormant. Keeping your lenses as free as possible from dust reduces the food source. The occasional exposure to UV light does help.

Any actual damage done to the lens results from the acid most moulds produce, this may affect coatings and in severe cases etches the glass, so this should ideally be removed.

Signs of light fungus in a lens means the relative humidity got too high (>70%) for several days at least. Extensive fungus indicates that apart from sustained high humidity levels there is also an excessive amount of dust and/or organic oil contamination in/on the lens for it to feed on.


PostPosted: Tue Jan 04, 2022 1:37 pm    Post subject: Reply with quote
RokkorDoctor wrote:
Attempting to kill the fungus (with UV or otherwise) may be a bit of a pointless exercise. The air (and any lens) is already full of mould spores. Even if you completely disassemble and sterilise the lens, by the time you are done with re-mounting the elements, the lens will be full of mould spores again.

Key to preventing fungus from growing (and stopping growing fungus from spreading) is to keep the relative humidity low and don't provide a food source. Below 65-70% RH fungal spores don't germinate, below 50-55% RH existing growing mould goes dormant. Keeping your lenses as free as possible from dust reduces the food source. The occasional exposure to UV light does help.

Any actual damage done to the lens results from the acid most moulds produce, this may affect coatings and in severe cases etches the glass, so this should ideally be removed.

Signs of light fungus in a lens means the relative humidity got too high (>70%) for several days at least. Extensive fungus indicates that apart from sustained high humidity levels there is also an excessive amount of dust and/or organic oil contamination in/on the lens for it to feed on.


The lens came from a humid environment, so I cleaned it all and i let it in a very hot and dry environment for some hours (a ventilated oven at circa 50 celsius).

the flat surface of the lens had been badly etched by fungi, there were spiders and thin grooves, which could be seen with a strong lens.
I manage to fix it with cerium oxide polishing,frst tests showed me that now this lens provides a clear image.

the fungi I see are at the extreme edge, they do not interfere with image formation but they seem to be thick and dense.

I'm doing this lens just for fun and passion, I already have an identical exaktar in good shape for actual use.
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