Pentax M 200 1:4 strange form on back lens

Jome · 10-10-2016, 09:05 AM

Hello,

I just bought a Pentax M 200 1:4 and everything was working good except when I was stopping down at 4.0. And then I discover this:

what is it? Fungus or worse? Please help.

Kind Regards.

Jome

Last edited by Jome; 12-06-2016 at 09:02 AM. Reason: Typo

**gofour3** · 10-10-2016, 09:30 AM

Looks like separation of the lens elements?

Phil.

**marcusBMG** · 10-10-2016, 09:38 AM

Interesting. Tedril like form prompts to say fungus. Distribution around the edge of the rear doublet suggests separation. I would try to remove the doublet and have a closer look....

http://www.wiratama.net/camera/pentax-m-2004-repair

pics show the rear group just needs a lens spanner to unscrew it, the pics don't really tell me if that's possible to do without initial disassembly of the mount etc.
I would expect fungus to clean off ok. Separation is not fixable (realistically), it is possible that a dip of the cemented doublet in boiling water might remelt the balsamic cement and render it clear.

CarlosU · 10-10-2016, 09:44 AM

I've seen this before and I am almost sure it is cement degradation between two elements of a group.

Jome · 10-10-2016, 10:07 AM

Thank you for your answers,
Do you all mean that it is the "glue" between the lenses in the group? Any (easy) cure?
Boiling as suggested by Marcus isn't risky for the lenses (breack / limestone)?

**marcusBMG** · 10-10-2016, 10:40 AM

More info:

http://www.skgrimes.com/library/old-news/old-lenses-can-be-restored-by-re-cementing

Markus Keinath - Lens Separation Repair

Jome · 10-10-2016, 11:27 AM

Originally posted by marcusBMG

More info:

http://www.skgrimes.com/library/old-news/old-lenses-can-be-restored-by-re-cementing

Markus Keinath - Lens Separation Repair

WOW! Thanks for the links, I am not sure that the full operation is worth it (I am prone to Murphy's law) as I paid 70 $ for the lens.
It is still usable at 5.6 on APSC. Perhaps, I will create a "Frankenlens" if I can get another M 200 with a back lens group in good shape.
Thanks again.
Jome

**marcusBMG** · 10-10-2016, 11:40 AM

Best of British luck

**niceshot** · 10-10-2016, 11:43 AM

leave it be, it shouldn't affect your images

Jome · 10-11-2016, 02:07 AM

I have also a SMC-A 70-210 1:4 that will do for f 4.0 needs. It is simply heavier than the M 200.
Again thanks a lot to all of you for identifying the illness of the lens.
Kind regards.
Jome

10-10-2016, 09:05 AM	#1
Jome Pentaxian Join Date: Aug 2016 Photos: Albums Posts: 784	Pentax M 200 1:4 strange form on back lens Hello, I just bought a Pentax M 200 1:4 and everything was working good except when I was stopping down at 4.0. And then I discover this: what is it? Fungus or worse? Please help. Kind Regards. Jome Last edited by Jome; 12-06-2016 at 09:02 AM. Reason: Typo

10-10-2016, 09:38 AM	#3
marcusBMG Site Supporter Join Date: Nov 2012 Location: North Wales Photos: Gallery \| Albums Posts: 2,868	Interesting. Tedril like form prompts to say fungus. Distribution around the edge of the rear doublet suggests separation. I would try to remove the doublet and have a closer look.... http://www.wiratama.net/camera/pentax-m-2004-repair pics show the rear group just needs a lens spanner to unscrew it, the pics don't really tell me if that's possible to do without initial disassembly of the mount etc. I would expect fungus to clean off ok. Separation is not fixable (realistically), it is possible that a dip of the cemented doublet in boiling water might remelt the balsamic cement and render it clear. Last edited by marcusBMG; 10-10-2016 at 09:53 AM.

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10-10-2016, 09:30 AM	#2
gofour3 Site Supporter Join Date: Oct 2008 Location: Vancouver, Canada Posts: 8,090	Looks like separation of the lens elements? Phil.

10-10-2016, 09:44 AM	#4
CarlosU Senior Member Join Date: Nov 2012 Location: Caracas Photos: Albums Posts: 107	I've seen this before and I am almost sure it is cement degradation between two elements of a group.

10-10-2016, 10:07 AM	#5
Jome Pentaxian Join Date: Aug 2016 Photos: Albums Posts: 784 Original Poster	Thank you for your answers, Do you all mean that it is the "glue" between the lenses in the group? Any (easy) cure? Boiling as suggested by Marcus isn't risky for the lenses (breack / limestone)?

10-10-2016, 10:40 AM	#6
marcusBMG Site Supporter Join Date: Nov 2012 Location: North Wales Photos: Gallery \| Albums Posts: 2,868	More info: http://www.skgrimes.com/library/old-news/old-lenses-can-be-restored-by-re-cementing Markus Keinath - Lens Separation Repair

10-10-2016, 11:27 AM	#7
Jome Pentaxian Join Date: Aug 2016 Photos: Albums Posts: 784 Original Poster	Originally posted by marcusBMG More info: http://www.skgrimes.com/library/old-news/old-lenses-can-be-restored-by-re-cementing Markus Keinath - Lens Separation Repair WOW! Thanks for the links, I am not sure that the full operation is worth it (I am prone to Murphy's law) as I paid 70 $ for the lens. It is still usable at 5.6 on APSC. Perhaps, I will create a "Frankenlens" if I can get another M 200 with a back lens group in good shape. Thanks again. Jome

10-10-2016, 11:40 AM	#8
marcusBMG Site Supporter Join Date: Nov 2012 Location: North Wales Photos: Gallery \| Albums Posts: 2,868	Best of British luck

10-10-2016, 11:43 AM	#9
niceshot Site Supporter Join Date: Mar 2014 Location: NY Photos: Gallery Posts: 1,564	leave it be, it shouldn't affect your images

10-11-2016, 02:07 AM	#10
Jome Pentaxian Join Date: Aug 2016 Photos: Albums Posts: 784 Original Poster	I have also a SMC-A 70-210 1:4 that will do for f 4.0 needs. It is simply heavier than the M 200. Again thanks a lot to all of you for identifying the illness of the lens. Kind regards. Jome

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