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04-01-2019, 12:51 PM   #1
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Disassembling front element/group from Pentax-A 1:4 70-210mm

Hi,

I own a sample of this lens, which was highly praised back then in the 80's. I intend to use it on FF (analog and digital), but there is some fungus! It seems to on the back of the front element. I expect there must be some way to remove (unscrew?) the front from the barrel, so the front element comes of. There are no slits for a spanner to be used.
So, anybody has some advice as to how to disassemble the front of this lens?

Responses much appreciated!

Regards,

Wim

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Last edited by huge10; 04-01-2019 at 01:34 PM. Reason: Typos in title and body of text.
04-01-2019, 02:25 PM   #2
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I've moved your thread to the correct section (was in the articles section).

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04-02-2019, 02:22 AM   #3
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Hi Wim,

First, you'll need to unscrew the filter thread ring. That will allow you to lift off the sliding hood. Then you'll have access to the front element group.

Alas, that's much easier to say than do!

Out of curiosity, I just tried it tonight. The filter ring piece on my lens was well and truly stuck. It took repeated applications of heat and a lot of effort to get it to turn. (I also tried solvent, but I don't think the ring was glued.)

A filter wrench may have made it easier for me, but I don't own one. Instead, I resorted to a jar lid opener. After the lens was heated, I set the jar opener on the floor and then pushed the lens onto it and twisted.

With the filter ring and hood off, the front elements group unscrewed with light effort.








The plastic piece around the lower half of the group just snaps on. There are notches to allow use of a tool to pry it off. The retaining ring at the top unscrewed easily after I applied some solvent to soften the glue.

And then . . . nothing. I couldn't get any of the elements free from the cluster. Heat, solvent and rubber gloves weren't enough to get them loose. Again, filter wrenches may have helped here.





The green arrow is pointing to a ring which, I believe, should unscrew to free the lower element - and perhaps also allow access to the rear of the front element? But, I couldn't get it loose.

So, that's as far as I could go. And by the way, if you get the front elements out and remove the front retaining ring, be sure to glue it back in place when you're done. If the ring isn't fastened securely, it might be difficult to remove the front group from the barrel in the future.


Tim
04-02-2019, 02:41 AM   #4
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Hi Tim,

This is of great help! I imagined that fliter ring should go off, but didn't dare to force it.Now I will!
I will post results of my effort to get to the fungus. I hope is is just under the top lens group.

Thanks a lot Tim!

Regards,

Wim

04-02-2019, 09:19 AM   #5
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You're welcome, Wim.

I'm always curious to know how my lenses are put together, so I had to give it a try.
I certainly hope your lens isn't as stubborn as mine!
04-04-2019, 01:43 PM   #6
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QuoteOriginally posted by .a.t. Quote
Hi Wim,

First, you'll need to unscrew the filter thread ring. That will allow you to lift off the sliding hood. Then you'll have access to the front element group.

Alas, that's much easier to say than do!

Out of curiosity, I just tried it tonight. The filter ring piece on my lens was well and truly stuck. It took repeated applications of heat and a lot of effort to get it to turn. (I also tried solvent, but I don't think the ring was glued.)

A filter wrench may have made it easier for me, but I don't own one. Instead, I resorted to a jar lid opener. After the lens was heated, I set the jar opener on the floor and then pushed the lens onto it and twisted.

With the filter ring and hood off, the front elements group unscrewed with light effort.








The plastic piece around the lower half of the group just snaps on. There are notches to allow use of a tool to pry it off. The retaining ring at the top unscrewed easily after I applied some solvent to soften the glue.

And then . . . nothing. I couldn't get any of the elements free from the cluster. Heat, solvent and rubber gloves weren't enough to get them loose. Again, filter wrenches may have helped here.





The green arrow is pointing to a ring which, I believe, should unscrew to free the lower element - and perhaps also allow access to the rear of the front element? But, I couldn't get it loose.

So, that's as far as I could go. And by the way, if you get the front elements out and remove the front retaining ring, be sure to glue it back in place when you're done. If the ring isn't fastened securely, it might be difficult to remove the front group from the barrel in the future.


Tim
Hi Tim,

Not succesfull yet in unscrewing the filter ring. How did you apply heat? I am a little hesitating because of the risk of overheating.

Regards,

Wim
04-04-2019, 02:41 PM   #7
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this may be a little late but you might want to look at this thread:

Cross-head screws - a caution: - PentaxForums.com
04-04-2019, 04:44 PM   #8
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QuoteOriginally posted by huge10 Quote
Hi Tim,

Not succesfull yet in unscrewing the filter ring. How did you apply heat? I am a little hesitating because of the risk of overheating.

Regards,

Wim


Wim,

Yes, I understand your caution regarding heat. I should probably be more careful about giving lens advice. I'm merely a "hack" who's learned from reading internet posts and by trying and failing many times.

That said... I use a small, 1500 watt space heater to loosen joints on my lenses. A hair dryer would be more precise (and safer?), but I don't own one.
So what temperature is safe, yet still effective? I really don't know. Just checking now, my heater warms up to at least 105C - that's the highest my baking thermometer will read!

Honestly, I suppose I'm reckless when it comes to heating lenses. I just crank up the heater to full blast and set my lenses in front of it for a couple minutes. That method almost always works for me. And I haven't (yet) had any trouble with grease melting / vaporizing or any other obvious lens damage.

And I should also say I'm talking about metal lenses. I've never tried to heat a plastic lens.

My A 70-210 is in parts / junk condition so I wasn't concerned about being gentle with it. I heated it for several minutes, several times and used significant force when twisting. And maybe the filter ring was glued and the solvent I applied did help? I put several drops of MEK around the outside of the filter ring. Acetone and isopropyl alcohol will also dissolve glue. But, of course, YMMV and please be careful with strong solvents!

04-04-2019, 05:39 PM   #9
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Stay with alcohol for Pentax Lens, no Mek for this Lens
04-29-2019, 01:34 PM   #10
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I did use alcohol, but I still could not get enough grip on the ring which holds the lens hood. Then screwed in a filter ring (with glass removed and clamped that filter ring. By clamping it there was enough deformation of the filter ring to clamp the ring to be removed. Yes, lens hood removed. I can unscrew the top ring to remove the front lens element, but the front lens grpoup didn't want to ove.

The story continues!

Wim
04-29-2019, 03:56 PM   #11
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Use Zippo TO clean the elements. At your own risk of coarse. But seriously use it np
04-29-2019, 05:53 PM   #12
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QuoteOriginally posted by huge10 Quote
I did use alcohol, but I still could not get enough grip on the ring which holds the lens hood. Then screwed in a filter ring (with glass removed and clamped that filter ring. By clamping it there was enough deformation of the filter ring to clamp the ring to be removed. Yes, lens hood removed. I can unscrew the top ring to remove the front lens element, but the front lens grpoup didn't want to ove.

The story continues!

Wim
IF you cant use the Lens then proceed, other wise just use it. I was read the other mans post regarding using heat, be careful you could end up with lens Separation if you melt the Balsam glue which is why you shouldnt use acetone or MEK OR IF SO SPARINGLY. Having said that if you have nothing to lose dunk it in alcohol and wait ten mins or so and try it, but only if you have nothing to lose. Best to leave it alone and use it the way it is.Truth be told you wont see ANY DIFFERENCE TRUST ME.
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