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02-13-2012, 03:53 AM   #1
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Cleaning a Cosinon 50/1.7 ... some advice please

Bonjour,

I picked up a long while ago a NMC Cosinon 50mm f1.7 that has really oily blades ... one can actually see a liquid on the blades.

Did not pay a lot here and the lens works relatively well, but it could be better ... plus there's maybe some "droplettes" on the interior glass elements, especially the rear element.

Any advice on a cleaning (I've scanned over some info) from your personal experience(s): how hard is this, any good PF and/or websites useful, what materials for this type of intervention (zippo fuild?)?

I have already dissamebled the front elements a Tamron Adaptall-2 in order to remove a chunk of debris, but have never attacked an oily apperature, but eager for a low-cost and low-risk experience.

Thanks in advance (merci d'avance) for any insights! Allez, J Frog


Last edited by Jean Poitiers; 02-13-2012 at 05:51 AM.
02-21-2012, 02:33 PM   #2
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Hi,
I don't know if this is the same lens, but I just cleaned a Cosinon Auto MC F=1.7 f=50mm. Getting to the front side of the aperture Blades was pretty easy. When you focus the lens as close as possible there will appear a grub screw set in the lens barrel towards the front end of the lens. When you loosen this a bit you can just twist off the front part of the barrel and simply take out the front element and a thin brass ring afterwards. Caution: the front element is not fixed by anything else but the front part of the barrel so don't let it fall out. Voilą the front side of the aperture blades.
Fortunately the aperture in my lens needed only cleaning from the front side for the time being as I have no idea how to remove the rear element - maybe someone else can shed some light onto this. I screwed off the ring around the rear element but wasn't able to remove the rear lens.
If the oil is only on the innermost lens of the rear element maybe you can clean it away from the inside with the aperture wide open. As for cleaning material I used lighter fluid and q-tips - just be very careful with the aperture blades - they are damaged easily.
03-04-2012, 01:20 PM   #3
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Merci

QuoteOriginally posted by McMac Quote
Hi,
I don't know if this is the same lens, but I just cleaned a Cosinon Auto MC F=1.7 f=50mm. Getting to the front side of the aperture Blades was pretty easy. When you focus the lens as close as possible there will appear a grub screw set in the lens barrel towards the front end of the lens. When you loosen this a bit you can just twist off the front part of the barrel and simply take out the front element and a thin brass ring afterwards. Caution: the front element is not fixed by anything else but the front part of the barrel so don't let it fall out. Voilą the front side of the aperture blades.
Fortunately the aperture in my lens needed only cleaning from the front side for the time being as I have no idea how to remove the rear element - maybe someone else can shed some light onto this. I screwed off the ring around the rear element but wasn't able to remove the rear lens.
If the oil is only on the innermost lens of the rear element maybe you can clean it away from the inside with the aperture wide open. As for cleaning material I used lighter fluid and q-tips - just be very careful with the aperture blades - they are damaged easily.
Bonjour McMac,

Thanks for your message. My lens reads "COSINA - NMC COSINON - 50MM 1:1.7", but they are probably not too far apart nor different since I have the grub screw that you described. I'd noticed it before, but wanted some advice so as not to blindly attack this cleaning ... As for th rear element, looks like I'll have to unscrew the 4 mount screws, plus 4 more screws on the rear barrel body (?)

Still trying to hunt up some more info here. I'll let you know how it finally ends up ... merci encore, J Frog
03-05-2012, 08:22 AM - 1 Like   #4
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Hi John,

I can tell you how far I got on the mount side of the lens. After loosening the four screws that fix the mount to the rest of the lens barrel you can take off the mount part including the aperture lever without problems. Also there will be a black ring coming loose and falling out which is coupled by a slot to the aperture ring. This is the aperture simulator which is used by the camera on pre-A lenses to determine which aperture is set. On my lens it took some fiddling on reassembly to get that properly into place but it is not too hard. This is the part where I did not succeed any further. At this point you have access to the rear element which is secured by a ring that sits around the rear lens. This ring was easily removed but to no avail - the lens did not leave is seating and I could not remove it. This was as close as I got to removing the rear lens assembly. At least I was successful in reassembling everything and the lens still works.

However I came across this link: Blendenlammellen reinigen Revuenon 55/1,2 - DSLR-Forum where someone fought with a lens that looks somewhat similar from the rear inside. The link is in german but maybe google translate is of some help there. I couldn't muster the necessary courage to use his instructions because he had to remove the focussing helicoid in order to remove the rear lens. It might even be possible to unscrew the entire rear lens from the lens barrel with some force from what I've understood but on my sample the rear lens wouldn't move a bit.

03-10-2012, 02:11 PM   #5
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Thanks again

Bonjour McMac,

Merci encore ... I'm going to attack this cleaning maybe next week if time allows. Thanks again for your advice!

Salut, John

PS - I'm going to ask my wife to help me with the link ... she speaks German, but she is also kind of fed up with my LBA ... delicate subject here!
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