[maxxxx]

I just got a Samyang 10. It works fine but the camera display shows 1.4 when then actual aperture value is 2.8. Is this normal for this lens? Does anybody here have a Samyang 10mm and can check if it shows the same behavior?

[severalsnakes]

You'll probably want to clean your contacts, first. Might not be a permanent fix, though. I have a lens (not the Rokinon 10/2.8) with an auto-aperture setting that reads wrong and it becomes a real headache when it vacillates back and forth between a true indicator and a false one. (I just use manual aperture on that lens.)

[stevebrot]

Is this normal for this lens?

No, it is not normal, assuming you are using a Pentax dSLR. The maximum aperture detection is passive and is based on the pattern of contacts on the lens mount. A f/1.4 lens has a different pattern of contacts having continuity than a f/2.8 lens. The pattern for f/1.4 is one off from that of a f/2.8 lens (100*00 vs. 000*00) (100*01 vs 000*01). It appears the camera is detecting continuity on contact R1 (furthest towards bottom) where none should exist.

You may want to clean the contacts on both body and lens and see if that helps. Also check to make sure the lens is fully mounted.


Steve

---------- Post added 11-13-14 at 08:55 PM ----------

BTW...If you have an ohm meter you can test continuity between base and contacts on the lens. There is no harm in doing so. My mistake...it is the body that can be tested this way.


Steve

[maxxxx]

You'll probably want to clean your contacts, first. Might not be a permanent fix, though. I have a lens (not the Rokinon 10/2.8) with an auto-aperture setting that reads wrong and it becomes a real headache when it vacillates back and forth between a true indicator and a false one. (I just use manual aperture on that lens.)

I have cleaned the contacts but no change. It also always works and doesn't go back and forth.

I guess I should return it.

[severalsnakes]

I have cleaned the contacts but no change. It also always works and doesn't go back and forth.

I guess I should return it.

Very strange. Test it out in a controlled environment... On my malfunctioning lens, it told me f/3.5 was f/1.7... I made myself a little chart to figure out exactly where it was at, because that's physically impossible. The lens physically stopped down to f/22, but the equivalent when the circuitry was jacked was something like f/11 or f/13... In any case, the lens works fine used manually, and I'm pretty sure all the Rokinons have manual apertures. It would probably be worth it for you to return it for one that functions properly, but there's nothing "non-functional" about a lens with a working manual aperture diaphragm. It's your call, obviously. (Personally, I prefer to adjust the aperture manually.)

[stevebrot]

If your camera works properly with other lenses, I would contact your dealer for a replacement lens. It is quite likely that the aperture diaphragm is fully functional, but the contacts on the lens base are not. I suspect that the wrong mount (say from a f/1.4 lens) was attached to your lens, either that or the contact itself is poorly positioned such that the ball on the body shorts across.


Steve

---------- Post added 11-13-14 at 11:06 PM ----------

On my malfunctioning lens, it told me f/3.5 was f/1.7...

Here is a link to Dimitrov's K-mount Page where there is a chart showing the contact patterns:

Features and Operation of the Ka Mount

As with the OP's lens, yours differs by the value for one contact. A f/1.7 lens has the mapping 101*11 while a f/3.5 lens has the mapping 001*11. A missing insulator or misalignment could cause the issue.


Steve

[Adam]

It could be a bad lens, perhaps. It definitely should report the correct aperture.

Adam
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[vonBaloney]

Yeah, most likely a contact problem, so you should probably exchange it.

However, I'd want to rule the body out also -- do you have other A lenses? Preferably with a 2.8 aperture? (I think DA lenses read these things differently because they have a chip in them.) If you have access to another Pentax body, check the Samyang on it also.

[maxxxx]

Yeah, most likely a contact problem, so you should probably exchange it.

However, I'd want to rule the body out also -- do you have other A lenses? Preferably with a 2.8 aperture? (I think DA lenses read these things differently because they have a chip in them.) If you have access to another Pentax body, check the Samyang on it also.

I don't have access to another Pentax body but none of my other lenses show this problem.
Considering that quality control is not exactly Samyang's strong suit (see reports of misaligned focus rings) a problem with a contact seems most likely.
I guess the lens goes back. Which is a bummer because it works really well besides the aperture problem.

---------- Post added 11-14-14 at 06:35 AM ----------

Very strange. Test it out in a controlled environment... On my malfunctioning lens, it told me f/3.5 was f/1.7... I made myself a little chart to figure out exactly where it was at, because that's physically impossible. The lens physically stopped down to f/22, but the equivalent when the circuitry was jacked was something like f/11 or f/13... In any case, the lens works fine used manually, and I'm pretty sure all the Rokinons have manual apertures. It would probably be worth it for you to return it for one that functions properly, but there's nothing "non-functional" about a lens with a working manual aperture diaphragm. It's your call, obviously. (Personally, I prefer to adjust the aperture manually.)

The lens seems to work fine and I personally could live with this problem but I am concerned about selling it at some point. The value would be reduced most likely.

[vonBaloney]

I don't have access to another Pentax body but none of my other lenses show this problem.

But manual A lenses communicate differently (passively) than most modern lenses (I think), so the problem might not appear with other lenses you have (if the problem is the body, not the lens), that's what I was getting at.

Considering that quality control is not exactly Samyang's strong suit (see reports of misaligned focus rings) a problem with a contact seems most likely.
I guess the lens goes back. Which is a bummer because it works really well besides the aperture problem.

Yes, you should definitely exchange it. (I had to swap the Samyang 14/2.8 three times to get a good [optical] copy.) If replacement acts the same way, suspect the body...

[maxxxx]

But manual A lenses communicate differently (passively) than most modern lenses (I think), so the problem might not appear with other lenses you have (if the problem is the body, not the lens), that's what I was getting at.

Yes, you should definitely exchange it. (I had to swap the Samyang 14/2.8 three times to get a good [optical] copy.) If replacement acts the same way, suspect the body...

I have a Rikenon 28 2.8 and SMC 50 1.7. I'll try those tonight.

[stevebrot]

But manual A lenses communicate differently (passively) than most modern lenses (I think)

It is always passive for all manual focus lenses with A contacts.* The acid test is what you suggested...mounting a different manual focus lens with f/2.8 maximum aperture.

I have a Rikenon 28 2.8 and SMC 50 1.7. I'll try those tonight.

The Rikenon will not be helpful (no A contacts). The 50/1.7 will likewise not be helpful even if it is Pentax-A because it does not have an insulator at the R1 position.


Steve

* The data contact found on AF lenses potentially transmits a wealth of information back to the body and may override the passive system under some conditions.

[maxxxx]

It is always passive for all manual focus lenses with A contacts.* The acid test is what you suggested...mounting a different manual focus lens with f/2.8 maximum aperture.



The Rikenon will not be helpful (no A contacts). The 50/1.7 will likewise not be helpful even if it is Pentax-A because it does not have an insulator at the R1 position.


Steve

* The data contact found on AF lenses potentially transmits a wealth of information back to the body and may override the passive system under some conditions.

Steve, *if* the camera had a problem in what other way could that manifest? I also have DA 35 and 12-24 and Sigma 70-200 and 150-500. They all work great.

[vonBaloney]

Another manual focus lens with A contacts with a max aperture of 2.8 is what you want ideally because it should be the same as the Samyang. But I'd try any manual A lens you can get your hands on just to see if those are correct for they should be. Totally manual lenses (like the Rikenon) won't tell you anything because they won't read the aperture (they will just say "F--")...

[stevebrot]

Steve, *if* the camera had a problem in what other way could that manifest?

The R1 contact on the body would always show continuity regardless of lens mounted. This is hard to test directly.

I also have DA 35 and 12-24 and Sigma 70-200 and 150-500. They all work great.

AF lenses have the option to communicate maximum aperture through the data contact. Whether they do depends on the lens. Please take a look at the link I supplied above. It has a table that shows the switch logic for the contacts. The difference between f/1.4 and f/2.8 is whether the circuit for the first contact (R1) is open. Insulate at that point and the body detects f/2.8. Remove the insulation or short across to the mount face and the body detects f/1.4.


Steve

---------- Post added 11-14-14 at 08:06 PM ----------

Try slipping a piece of paper between lens and body at the low point of the mount where the lens has a round plastic insulator at the contact point. If the LCD reads correctly as f/2.8, the fault is with the lens. Slip the paper out and confirm a change to f/1.4.


Steve