Why does my Mamiya Sekor C Macro 140mm 4.5 have f/3.8?

holggger · Nov 5, 2017

Well, if think the title says it all!
This has been confusing me for a long time so yesterday I decided to do some internet research but couldn't come up with anything: Why does my Mamiya Sekor C Macro 140mm f/4.5 lens have a maximum aperture setting of f/3.8? Always thought the aperture number in the lens name indicates its widest aperture setting...

Of course I don't mind but it just seems very strange. Anyone?

Theo Sulphate · Nov 5, 2017

Here is my 140mm C Macro lens:

Are you saying your aperture ring shows f/3.8? Or are you saying that although f/4.5 is the widest marked, the ring turns beyond it?

On my lens f/4.5 is the widest marked on the ring and the aperture ring cannot be turned further to make it wider.

AgX · Nov 5, 2017

I understood the OP that the lens designation says 4.5. On the front ring.

What would mean two strange things: the lens being different and a mismatch concerning the front ring.

Theo Sulphate · Nov 5, 2017

AgX said:
I understood the OP that the lens designation says 4.5. On the front ring.

Indeed it does. It's both on the front ring and aperture ring. I do not see f/3.8 anywhere, nor can I coax the lens wider than f/4.5 -- I'm curious to see a photo of the OP's lens.

holggger · Nov 5, 2017

Whoa, now this is very strange indeed. Here are images of my lens, front ring and aperture ring:

sepiareverb · Nov 5, 2017

Looks like a simple mistake in engraving.

TheFlyingCamera · Nov 5, 2017

sepiareverb said:
Looks like a simple mistake in engraving.

Or perhaps in the past the lens was serviced and someone swapped in the aperture control ring from a 90mm or 127mm f3.8. Or maybe someone at the factory the day it was assembled had too much sake at lunch.

holggger · Nov 5, 2017

Huh, how strange! But it makes sense now that I've seen your "normal" lenses… Sake at lunch it is.

I'm happy that at least the other values seem to be correct!

AgX · Nov 5, 2017

Have you verified the step from 5.6 to 3.8?
That to exclude the erroneously engraving, which I find harder to believe than two versions and a mismatched front ring.

Theo Sulphate · Nov 5, 2017

More likely than Sake at lunch is an "expedient repair" sometime during the life of the lens.

Theo "expediency is the last refuge of scoundrels" S.

holggger · Nov 5, 2017

AgX said:
Have you verified the step from 5.6 to 3.8?
That to exclude the erroneously engraving, which I find harder to believe than two versions and a mismatched front ring.

Verify how? Mechanically it all works like a charm. I haven't checked if aperture actually is at 5.6 when I set it to 5.6, but it can't be (much) off or I would've noticed—been using this lens a lot these days.

If there are other Mamiya lenses that open up to f/3.8 and have an aperture ring exactly like this then I agree that wrong engraving is very unlikely. So is that this would've slipped factory QC.

"Repair" sounds plausible, and if that was the case I have to say they did an excellent job, because the lens is in great condition and mechanically flawless.

holggger · Nov 5, 2017

P.S: Nor would I have noticed the difference between 3.8 and 4.5 I think, especially since I haven't been using this lens at the widest aperture all that much.

AgX · Nov 5, 2017

Such step would be about 1 stop. If your lens still had 4.8 it only would be 1/2 stop. Such would be easy to meter in stopped down mode.

MattKing · Nov 5, 2017

The real issue with this being the result of a repair (which i expect it was) arises because if they got the ring switched, did they do anything else incorrectly? For that reason, I would check whether the aperture is performing properly.
Careful visual review plus an exposure test with an accurate meter and slide film should do the trick.

holggger · Nov 6, 2017

MattKing said:
The real issue with this being the result of a repair (which i expect it was) arises because if they got the ring switched, did they do anything else incorrectly? For that reason, I would check whether the aperture is performing properly.
Careful visual review plus an exposure test with an accurate meter and slide film should do the trick.

Did a test by measuring exposure directly TTL instead of exposing film.
Assuming f/5.6 is f/5.6 the widest setting is f/4.5, the click inbetween f/5.0 and all the other clicks on the aperture ring as indicated on the ring itself… so I guess it really is just a wrong aperture ring on there, for whichever strange reason (repair maybe being the one most likely, but why would anyone exchange the aperture ring, which I bet is the last part being damaged of all the parts in this lens).

Questor84 · Nov 6, 2017

The aperture ring looks just like an aperture ring on my 90mm Sekor C 3.8 lens. Rings switched at repair or factory assembly.

AgX · Nov 6, 2017

That is the most plausible explanation: it only involves one instead of two variations.

Gerald C Koch · Nov 6, 2017

It is fairly common to design a lens which physically has a larger aperture than is attainable. I have a Schneider enlarging lens which is actually an f/2.8 but because of an internal stop cannot be opened any larger than f/4. This is done to reduce aberrations that would normally occur if the lens was used full open. This is not the case for lenses designed to be used full open such as the Noktons where light gathering takes presidence over resolution. These lenses are designed to be used full open and not usually stopped down. However I am stumped as to why the full open aperture is indicated if it cannot be attained. Perhaps that lower stop is intended for use when focusing and not for picture taking.

Theo Sulphate · Nov 6, 2017

Gerald C Koch said:
... Perhaps that lower stop is intended for use when focusing and not for picture taking.

No. It's a botched repair. As the comparison photo of my lens shows, my ring shows f/4.5 as does every other 140/4.5 coming out of the factory.

Gerald C Koch · Nov 6, 2017

Theo Sulphate said:
No. It's a botched repair. As the comparison photo of my lens shows, my ring shows f/4.5 as does every other 140/4.5 coming out of the factory.

Can you open the aperture to f3.8? If you can't the the botched repair theory is probably correct. If not then ...

Theo Sulphate · Nov 6, 2017

Gerald C Koch said:
Can you open the aperture to f3.8? If you can't the the botched repair theory is probably correct. If not then ...

The OP did a test; I don't have the lens with me at work, so cannot test.

Anecdotally, except for the OP's lens, every single 140/4.5 I've seen in person (maybe three) and on the internet (dozens) have a ring that shows f/4.5 as the widest aperture, which is consistent with the front decal and the official designation of the lens.

Additionally, there's the Z version manual (see photo, page 7):

https://www.manualslib.com/manual/1187512/Mamiya-Sekor-Macro-Z-140-Mm-F-4-5.html

Soeren · Nov 8, 2017

I find it pretty straightforward. An amateur or small shop repair using available parts from, or maybe even sacrificing, a 127mm to keep the macro lens working.

holggger · Dec 5, 2017

Gerald C Koch said:
Can you open the aperture to f3.8? If you can't the the botched repair theory is probably correct. If not then ...

Sorry for the late reply! No, I cannot physically open the aperture any more than the max. which says 3.8 on the ring but measures 4.5 on the meter. Either someone messed up when repairing it, or someone thought they could sell it for more money when the aperture goes wider

Why does my Mamiya Sekor C Macro 140mm 4.5 have f/3.8?

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