[vonBaloney]

SMC Takumar 20mm f/4.5

Does anyone happen to know:

-- How to disassemble? Seems to be different from most Takumars.

-- The optical formula?

-- Does it have sealed elements? I'm guessing yes, cause I'm looking at one that seems to exhibit beginning of element separation, but could be I'm just seeing the edges of some internal elements that aren't supposed to be sealed -- I've seen similar with other vintage extreme wides -- several elements stacked on each other, each bigger than the one previous so you can see the edges of the smaller ones as sort of a bubble pattern. But on this lens the bubbles only go around part way which makes me think they are sealed and are just becoming visible as they become unsealed.

The last question is what is motivating the others -- I have one here I want to sell, but need to verify if these elements are coming apart. At the moment, performance is fine -- lens is sharp, etc. In fact, overall condition is practically like new, but if the elements are separating that's a problem.

[jatrax]

I think there is a print of the optical formula on the review page. I have a Takumar manual at home, I'll check to see if the 20mm is in it when I home from work.

[vonBaloney]

Hmmm...pretty complicated in there. That's how they get it so small, I guess.

A follow-up if anyone has this lens -- see any floating bubbles/edges in there? (Use a flashlight.) Going by the optical formula diagram, what I am seeing is probably the top edge of the third element. Doesn't seem like there is anything else for it to be glued to -- it would be nice if I could get in there and check it, or at least have it verified that there is no issue with the lens. I'm probably just being paranoid, but if I'm going to sell it I have to represent it properly.

[jatrax]

Just checked my manual and the 20mm is not listed not sure why. I have the S-M-C version and looking in from the front I can see a ring of what might be bubbles or maybe just glue around the outside edge of what might be the third element. Everything else is clear and this ring is at the extreme edge. Hope that helps.

[vonBaloney]

Just checked my manual and the 20mm is not listed not sure why. I have the S-M-C version and looking in from the front I can see a ring of what might be bubbles or maybe just glue around the outside edge of what might be the third element. Everything else is clear and this ring is at the extreme edge. Hope that helps.

Yeah, the unpolished edges of lenses are rough and glittery -- they show up as glittery bubbles, which is what I think what we are seeing here rather than glue separation. So sounds like it is normal.

Here is a photo of mine -- the bubbles are rather exaggerated under the lights on the bottom half. Is that what yours looks like?

[SyncGuy]

That, my friend, is confirmed lens element separation... :/

[vonBaloney]

That, my friend, is confirmed lens element separation... :/

Just going by appearance? Cause I've seen the exact same thing on another lens that was just element edges (confirmed by disassembly) -- that's what they look like, at least some of them. (Like the edge of a handheld magnifying glass -- it is a rough and glittery surface.) And if that optical diagram is correct, I don't think there is anything for it to separate from at the spot, so I'm leaning towards "not separation" at this point.

And like I said, the lights exaggerate it. Looking at the lens you can't really see it without a flashlight -- and it does go all the way around if you hold the light right -- you just can't see it all at one time. But separation may look like that as well...

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Last edited by vonBaloney; 05-24-2012 at 06:45 PM.

[jatrax]

Is that what yours looks like?

Yes, identical. I agree, I think it is the unpolished edge of the first element. But no way to be sure without opening it up.

[vonBaloney]

Yes, identical. I agree, I think it is the unpolished edge of the first element. But no way to be sure without opening it up.

Unless someone can definitely confirm that there is nothing to separate at that location, which seems to be the case...

[rhodopsin]

Just checked my manual and the 20mm is not listed not sure why. I have the S-M-C version and looking in from the front I can see a ring of what might be bubbles or maybe just glue around the outside edge of what might be the third element. Everything else is clear and this ring is at the extreme edge. Hope that helps.

Look with a magnifying glass -- depending on the how the lens is rotated, mine shows "Super-Multi-Coated" or "Super-Takumar" in tiny letters. There are multiple reflections of name ring lettering from multiple elements which looks like edge separation first glance.

I didn't just spoil a joke thread did I?

[Blue]

11 elements in 10 groups

[SyncGuy]

Just going by appearance? Cause I've seen the exact same thing on another lens that was just element edges (confirmed by disassembly) -- that's what they look like, at least some of them. (Like the edge of a handheld magnifying glass -- it is a rough and glittery surface.) And if that optical diagram is correct, I don't think there is anything for it to separate from at the spot, so I'm leaning towards "not separation" at this point.

And like I said, the lights exaggerate it. Looking at the lens you can't really see it without a flashlight -- and it does go all the way around if you hold the light right -- you just can't see it all at one time. But separation may look like that as well...

Yep! Just by looking.. Coz i had one recently and was informed that it indeed is the beginning of lens separation.

Try pretending that you wanna repair the lens and send your lens images to Zeiss repair center for a quote and opinion.

PS:That's what i did.. Quoted repair cost was USD$250-USD$350.. :/ So that's how i know..

[Blue]

There is only 1 group with more than one element and that appears to be the rear element.

[SyncGuy]

There is only 1 group with more than one element and that appears to be the rear element.

Hmm... That's true... Maybe it isnt lens separation after all! Since there isn't any to begin with.. Hahah! Well, I'd say just open it up man.... Since it's more of the front, it's really easy.. Just unscrew the front ''beauty'' ring..

[vonBaloney]

Yep! Just by looking.. Coz i had one recently and was informed that it indeed is the beginning of lens separation.

Try pretending that you wanna repair the lens and send your lens images to Zeiss repair center for a quote and opinion.

PS:That's what i did.. Quoted repair cost was USD$250-USD$350.. :/ So that's how i know..

Yeah, I asked a local repair guy about it last year, and he said it was element separation (which I had never even heard of at the time), although he wasn't familiar with this lens. But I now think he is wrong. People are wrong sometimes. Given the optical formula (which I hadn't seen before today -- I figured that there were elements of the same curvature grouped together), it doesn't seem that it is even possible for it to be separation because it wasn't sealed to begin with. I was resigned to the fact that it was separating, so I hadn't done anything about selling it, and then recently I took apart an 18mm Sigma where there were a bunch of unsealed elements stacked on each other and the edges of each element looked just this lens. Which got me to thinking it could look like that normally OR if it was coming unsealed. But since these elements are all separate (at the front, where the bubbles are) with opposing curvatures, and we've got another guy in this thread with an identical looking lens, I think we can put this to rest. Not separated because there is nothing to separate.

Maybe that is also the case with yours...