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Rexagon 28mm repair/cleaning
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PostPosted: Thu Jan 07, 2016 4:21 pm    Post subject: Rexagon 28mm repair/cleaning Reply with quote
Hello,
I just got a Rexagon 28mm f2.8 lens rather cheap (USD 27 = €25 cheap? or not?)
This one, the one with th egreen stripe
http://m42lens.com/m42-lens-database/577-rexagon-auto-mc-28mm-f-2-8-16

On first sight it looks OK, .. on second sight it does not ..

Is there a lens diagram that be found somewhere ? Apparently this is a "Prinz-Rexagon" built lens ?
Intense internet readings seem to suggest that Porst is a similar/same build ? also a number of other "suggestions" are made but ... ?

Any info/advice on disassembling this thing? just for the fun of it ... !
TIA !

First sight .. and second ...






PostPosted: Thu Jan 07, 2016 10:48 pm    Post subject: Reply with quote
Gosh. Sorry to see something like that.

My only Rexagon is their 23mm f3.5, for which I paid circa 10 bucks. I've never had it apart.

Are you unable to return the lens? It appears to me you paid top price for a lens in great condition . . and as things turned out it wasn't. Rolling Eyes

I once bought a lens which appeared superficially to be in wonderful condition. Upon receipt, the lens scarcely passed light, so badly was it in need of cleaning from one end to the other. When I brought the problem to the seller's attention, he refunded my payment and told me to keep the lens. I believe that lens will clean up OK. But a great deal of work will be involved, and there will be some risk to the lens upon disassembly because it is glued together.


PostPosted: Fri Jan 08, 2016 11:00 pm    Post subject: Reply with quote
guardian wrote:
Gosh. Sorry to see something like that.

My only Rexagon is their 23mm f3.5, for which I paid circa 10 bucks. I've never had it apart.

Are you unable to return the lens? It appears to me you paid top price for a lens in great condition . . and as things turned out it wasn't. Rolling Eyes

I once bought a lens which appeared superficially to be in wonderful condition. Upon receipt, the lens scarcely passed light, so badly was it in need of cleaning from one end to the other. When I brought the problem to the seller's attention, he refunded my payment and told me to keep the lens. I believe that lens will clean up OK. But a great deal of work will be involved, and there will be some risk to the lens upon disassembly because it is glued together.


Thank you for your answer.

I bought this lens based on a review in this very forum Wink Unfortunately I cannot drive 300Km to go and have a look at the goods Wink

So, I decided to keep the lens and give it a try to repair it. As I'm retired, it seems like a good occupational therapy to fill the winter months! Laughing Unfortunately I cannot find a lens diagram nor a tutorial on how to access the front optics. I partially removed the back end lenses and there was a lot of oil in there. Now I wonder if someone went "lubricating the thing ! Laughing
I have found possible further "relationship" with "Rexatar" and other similar low end lenses ... maybe I paid way too much for a piece of windows glass ?? LOVL !


PostPosted: Fri Jan 08, 2016 11:21 pm    Post subject: Reply with quote
Rigel wrote:
guardian wrote:
Gosh. Sorry to see something like that.

My only Rexagon is their 23mm f3.5, for which I paid circa 10 bucks. I've never had it apart.

Are you unable to return the lens? It appears to me you paid top price for a lens in great condition . . and as things turned out it wasn't. Rolling Eyes

I once bought a lens which appeared superficially to be in wonderful condition. Upon receipt, the lens scarcely passed light, so badly was it in need of cleaning from one end to the other. When I brought the problem to the seller's attention, he refunded my payment and told me to keep the lens. I believe that lens will clean up OK. But a great deal of work will be involved, and there will be some risk to the lens upon disassembly because it is glued together.


Thank you for your answer.

I bought this lens based on a review in this very forum Wink Unfortunately I cannot drive 300Km to go and have a look at the goods Wink

So, I decided to keep the lens and give it a try to repair it. As I'm retired, it seems like a good occupational therapy to fill the winter months! Laughing Unfortunately I cannot find a lens diagram nor a tutorial on how to access the front optics. I partially removed the back end lenses and there was a lot of oil in there. Now I wonder if someone went "lubricating the thing ! Laughing
I have found possible further "relationship" with "Rexatar" and other similar low end lenses ... maybe I paid way too much for a piece of windows glass ?? LOVL !


Understood.

Your finding of oil is good because, once exposed, it is easily cleaned away.

If there are no spanner slots in the name ring, disassembly might be accomplished simply by unscrewing things, beginning with the front-most portion of the lens. Holding the lens body in one hand, use your other hand gently to apply torque to the protruding filter thread ring, on the outside of course, not to the threads themselves.

If there are spanner slots, or opposed holes, in the name ring, then the name ring simply unscrews through use of the appropriate tool. Even if slots and holes both are absent, it is still possible the name ring unscrews. However, you would need some sort of friction tool, one of the correct diameter, to accomplish this. While such tools are sold on eBay, they also sometimes can be jury rigged. But it is very important with a jury rigged tool not to scratch the first lens element while attempting to unscrew the name ring.

Some Japanese lenses are glued together, so do not apply too much torque with any tool or it will slip and damage the lens. If your lens is glued you will need first to soften the glue using a solvent, e.g., acetone, before any disassembly can be undertaken.

Using only your hands, though, you are less likely to damage the lens unless you are a very powerful person with great strength.

Incidentally, the oil you found is less likely to be from lubrication, and more likely is owing to exposure of your lens at some point to too much heat. The helical lubes used in these old lenses often as not contained volatile substances. With heating those substances are released, only to condense out on the lens elements, clouding them.


PostPosted: Sat Jan 09, 2016 12:48 am    Post subject: Reply with quote
That's exactly the same as a Hanimex lens I have in front of me right now. If you grip the focus ring and the front 'body' with the green ring, the front part unscrews complete - the name plate and the surround.
Under there you will see two sets of three small screws ( almost certainly JIS pattern screws ) I think the three nearest the front will release the front lens block, but I'm not certain and this lens is unmarked and I don't really want to take it apart.

If you possibly can, return it. They are cheap and plentiful lenses so ones in good condition are easy to find.


PostPosted: Sat Jan 09, 2016 3:02 pm    Post subject: Reply with quote
Unfortunately it was too late to produce a good answer yesterday, but I forgot to mention that I already had unscrewed the top ... the trick with the rubber glove Wink

I also expected to find 2 sets of 3 screws, as I have seen in so many youtube videos .. but there is only one set that seems to keep the helicoid focussing system in place ?
My unexperienced gut feeling says .. "go for the notched ring" ???
I don't think there may be such an agreement as "try before you buy" .. especially not after partly disassembling the package Laughing

as per picture ..


PostPosted: Sat Jan 09, 2016 3:57 pm    Post subject: Reply with quote
this may get me going ?? Wink

https://www.youtube.com/watch?v=jb-a_GhfyII


PostPosted: Sun Jan 10, 2016 9:46 pm    Post subject: Reply with quote
Ah HA! Seeing now in your most recent photo the spanner slots . . . good job.

Use those slots to unscrew the structure holding front lens element in place.

You will need a proper lens spanner, of course, unless you want to risk breaking a couple of fingernails. Wink

And as always, beware of glue!


PostPosted: Sun Jan 10, 2016 10:25 pm    Post subject: Reply with quote
Did cost me a lot of effort to unscrew that front element ... in the end the whole group came out in one piece and I did not scratch the lenses so far .. Now I have no clue on opening that block to get access to the inside ... I think that I'm going to use a tiny amount of high temp special vacuum lubricant onto the thread (used in ultra-centrifugation)
I was told that the "pattern" on the front lens could be "oily haze" ... Never heard of it .. Wink


PostPosted: Tue Jan 12, 2016 9:07 pm    Post subject: Reply with quote
FYI Managed to take the optics apart .. seems that it is all oil inside .. weird .. something very greasy indeed. It does not even go away with dish washing soap. I think I will try naphta (lighter fuel). 75% is more or less clean ! Wink


PostPosted: Tue Jan 12, 2016 10:03 pm    Post subject: Reply with quote
Good news, and lighter fuel is good stuff. I get though tins of the stuff. Wink


PostPosted: Wed Jan 13, 2016 12:00 am    Post subject: Reply with quote
Rigel wrote:
FYI Managed to take the optics apart .. seems that it is all oil inside .. weird .. something very greasy indeed. It does not even go away with dish washing soap. I think I will try naphta (lighter fuel). 75% is more or less clean ! Wink


I am happy for your success. The oil coating is not at all surprising . . it is commonplace in old lenses with fugitive "grease". If you are not able thoroughly to clean the non-glass portions of the lens, and to re-grease the helicoid of your lens, than resign yourself to keeping that lens cool for the duration of your ownership.

My many old lenses are currently in storage at a temperature just above zero degrees Celsius. At such temperature as that, oil release from the greases inside those old lenses is minimized. Also, fungus grows more slowly.


PostPosted: Wed Jan 13, 2016 11:04 am    Post subject: Reply with quote
I was wondering what sort of lubrication grease is used in lenses ? I am a bit reluctant to add more "lubricants" in this lens as everything moves quite swiftly at he moment Wink

I must have some high grade, ultra-centrifugation grease somewhere. Guess it should fit the bill ? no ?

BTW IMHO keeping lenses near 0°C is not the best idea. You'll be fighting condensation issues ad vitam aeternam ... and moisture => fungus ?


PostPosted: Wed Jan 13, 2016 1:44 pm    Post subject: Reply with quote
Rigel wrote:
I was wondering what sort of lubrication grease is used in lenses ? I am a bit reluctant to add more "lubricants" in this lens as everything moves quite swiftly at he moment Wink

I must have some high grade, ultra-centrifugation grease somewhere. Guess it should fit the bill ? no ?

BTW IMHO keeping lenses near 0°C is not the best idea. You'll be fighting condensation issues ad vitam aeternam ... and moisture => fungus ?


I neglected to mention each lens is inside a sealed baggie together with a large packet of silica gel. So each is cold . . and dry. And it is true a lens must first be brought up to room temperature before opening the baggie else condensation is the unwanted outcome.

As for grease, here is what I recommend:

Click here to see on Ebay

But to be honest most of my lenses still have the old oil-emitting grease. I only re-lube a lens if I have it apart anyway, owing to other reasons.
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