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02-21-2013, 12:52 PM   #1
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Cosina Cosinon S 50mm f1.8 focusing, is that normal?

Hello!

So I have K30 and I have this nice old Cosina Cosinon S 50mm f1.8 lens.
And I faced a very interesting issue. When I want to focus and use OVF, the focus ring of the lens gets stuck if I reach the limit of the focus ring. And whatever I would do, it will not rotate anymore, it is stuck and I can;t modify the focus parameters, however if I turn on live view or put the mirror up, the focus ring gets freed up and I can bring it back to function. So when I am in live view, I can do focusing to both limits of the lens as much as I want, but if I use OVF, once the focus ring reach its end limit, it gets stuck. Is this normal behavior or is there something wrong with either the lens or the DSLR?

02-21-2013, 01:00 PM   #2
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QuoteOriginally posted by Danas_Anis Quote
Hello!

So I have K30 and I have this nice old Cosina Cosinon S 50mm f1.8 lens.
And I faced a very interesting issue. When I want to focus and use OVF, the focus ring of the lens gets stuck if I reach the limit of the focus ring. And whatever I would do, it will not rotate anymore, it is stuck and I can;t modify the focus parameters, however if I turn on live view or put the mirror up, the focus ring gets freed up and I can bring it back to function. So when I am in live view, I can do focusing to both limits of the lens as much as I want, but if I use OVF, once the focus ring reach its end limit, it gets stuck. Is this normal behavior or is there something wrong with either the lens or the DSLR?
I'd don't know, but before you proceed the first thing I'd find out is if the rear element is hitting the mirror or inside of the camera or something. When you say "limit" do you mean infinity? If so, I'd take it off the camera (focus away from infinity first) and see if the rear element juts out quite far at infinity. Could be something else, but first rule out the possibility of damaging your camera...
02-21-2013, 01:22 PM   #3
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the lens doesn;t have the infinity focusing if I understand the definition correctly, for example, olympus lenses I can rotate the focus ring as much as I want and it will never stop, it will just spin and spin as much a I want, this lens however has a limit, I can rotate it to to the certain spot clockwise and to the certain spot to the other side,

I will try your suggestion.
02-21-2013, 01:27 PM   #4
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apologies, just spotted the infinity marking, silly me, yes, if I push the focus to the nearest subject focus, then it stuck, if I push it to infinity, it is fine.

It doesn;t look like any rear element is getting out too much.

02-21-2013, 01:39 PM   #5
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It wouldn't be terribly unusual for a (broken) lens to get stuck on one end -- what worries me is that you say it doesn't do that in Live View mode, which sounds like it means it is getting mangled up with the camera body somehow when the mirror is down. Does the lens get stuck or have resistance at that end if you focus it OFF the body?
02-21-2013, 02:23 PM   #6
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So...does the lens do this when it is not mounted? I suspect so.


Steve
02-22-2013, 01:29 AM   #7
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QuoteOriginally posted by vonBaloney Quote
It wouldn't be terribly unusual for a (broken) lens to get stuck on one end -- what worries me is that you say it doesn't do that in Live View mode, which sounds like it means it is getting mangled up with the camera body somehow when the mirror is down. Does the lens get stuck or have resistance at that end if you focus it OFF the body?
No, it works fine when not mounted.
But there is one other thing I should tell then.

There was a case when it actually got completely stuck. Even not mounted it was like stuck, but I then disassembled the rear element to see what is going on as well as removed the exterior detail on the front and tightened the screws that were holding the focus ring, so the rear elements were disassembled for no reason. After putting it back together it all worked fine.

But later began to get stuck when focus ring reaches the opposite of the infinity, Don't know how that side is called, closest focus distance numbers?

The result is this, it works fine in Live View mode when mirror is up, it works fine when it is not mounted, it gets stuck if I want to use OVF. So the problem the mirror mechanism I guess.

Is it really very dangerous to use this lens well in Live view mode only? that will not be a problem for me since the focus peaking is really a great feature so I guess I will be okay with using LCD with this lens. But the question is will it be safe to use in that manner when avoiding the problematic conditions (mirror down). ?
02-22-2013, 10:23 AM   #8
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QuoteOriginally posted by Danas_Anis Quote
No, it works fine when not mounted.
But there is one other thing I should tell then.

There was a case when it actually got completely stuck. Even not mounted it was like stuck, but I then disassembled the rear element to see what is going on as well as removed the exterior detail on the front and tightened the screws that were holding the focus ring, so the rear elements were disassembled for no reason. After putting it back together it all worked fine.

But later began to get stuck when focus ring reaches the opposite of the infinity, Don't know how that side is called, closest focus distance numbers?

The result is this, it works fine in Live View mode when mirror is up, it works fine when it is not mounted, it gets stuck if I want to use OVF. So the problem the mirror mechanism I guess.

Is it really very dangerous to use this lens well in Live view mode only? that will not be a problem for me since the focus peaking is really a great feature so I guess I will be okay with using LCD with this lens. But the question is will it be safe to use in that manner when avoiding the problematic conditions (mirror down). ?
If what you say is accurate, I wouldn't even mount it until you figure out what is going on. Something is rubbing up against something it should not be, and you'll be in danger of damaging the camera. Mirror up or down should make no difference to the lens -- it really makes no sense. Could it be something strange like you hold it differently based on OVF or Live View and it gets stuck when you put pressure at a particular angle or it gets caught on your sleeve?

02-22-2013, 12:35 PM   #9
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this problem first appeared when I was trying to shoot an object that was above me, so I held the camera front face up.
Now it only does this when I reach 1.75 ft. Well actually a little bit beyond it, but it is the limit after which the focus ring gets stuck.
02-22-2013, 12:43 PM   #10
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oh one more detail about this issue, if I set aperture in this range f4- f16 the focus ring gets stuck in general, f2.8, f1.8 makes it be smooth. Issue is not present in live view mode though.
02-22-2013, 12:59 PM   #11
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Well, obviously the lens is broken. Is your aperture actually working -- opening and closing?

Still can't figure the difference between OVF and Live View -- in either case it would be attempting to hold the aperture wide-open when mounted. This is a totally manual lens, but still a bayonet K-mount, right? Does it have an 'A' setting? (No, I think.) And so you should be using the camera in M mode, eh? And you should have aperture ring set to "permitted" and the green button set to "tv shift"? If you are not doing all that, maybe there is a difference I'm not thinking of...
02-23-2013, 01:45 AM   #12
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The aperture ring is working really fine and the aperture works as it should luckily Yes I have set aperture ring to permitted, well actually it says aperture ring enabled. The only thing I didn't have had set up is the green button. But there is no difference that I could see so far. And yes, I am using it in M mode. The lens also works in AV and TAV modes. No, this lens doesn;t have the "A" setting, you are right. The lens is bayonet K-mount, that is why I got it.

That is the same thing I am thinking, there should be no difference when on OVF and Live view. Especially when the lens focus ring gets stuck when the lens rear elements that moves move away from the camera, so basically it should not touch anything in the camera, but since I am not a technical guy, I don;t know many things on how such devices work. But from my point of view I jsut don;t see what could be causing such behavior.
02-25-2013, 09:09 AM   #13
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Hello!

So after some further investigation, I don;t know how much this could be related, but in the attached image you can see the rear of my lens.
Then there is this little thingie, don;t know how it is called, but if I move it to the right, it opens the aperture and when I try to manipulate focus ring, it get stuck at appertures ranging from f4 to f16, f2.8 and f1.8 are doing fine. So with this thingie on the right I get the same behavior as when the mirror is down. Does this indicate something?
Attached Images
 
02-25-2013, 11:44 AM   #14
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It indicates your lens is busted. Could be as simple as that lever (that's the aperture lever) being bent. Surely would need disassembly to repair.
02-26-2013, 02:30 AM   #15
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is it safe to be used on a camera? It still serves its function in live view mode.
than you very much for your time and advice!
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