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M* / A* 300mm disassembly/cleaning guide
Posted By: RXrenesis8, 01-30-2012, 06:44 PM

(Posted as a request) . If anyone can take this a step further and elaborate on the rear elements I'd be grateful!

Also note: I am using made-up names for some of the parts (front element assembly?) Any corrections will be appended to the text of the post.



Step 1: focus the lens at 4 meters (< 14 feet).



Step 2: grip the lens by the aperture ring (or mount, or anything attached to the mount, ie: a camera) and the front protective cover and twist the front protective cover clockwise until it falls down and hangs loosely.



Step 3: grip the focus ring and the front element assembly and twist the front element assembly counter-clockwise until it disengages.



Step 4: remove the lens hood from the front protective cover and set aside.



Step 5: attach the front element assembly securely to the lens by turning it clockwise



Step 6: attach the front protective cover to the front element assembly by pressing it up and turning it counterclockwise.

(I could swear I took a picture of this...)


Step 7: continue turning the front protective cover counterclockwise until the front half of the lens disengages from the back half and set the back half aside.



Step 8: remove the front element assembly from the front protective cover by turning counter clockwise.



Step 9: twist the front element assembly apart by rotating the front element counter clockwise.






In this state of disassembly you can clean most of the lens surfaces and the aperture blades.

I think that's it for the easy stuff. Pretty sure the rest requires unscrewing tiny little screws on the mount but I haven't gone that far yet.

Last edited by RXrenesis8; 02-17-2012 at 10:54 AM.
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01-30-2012, 07:43 PM   #2
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although my A*300 does not need disassembling, bump for you.

stored this for future reference.
01-30-2012, 08:04 PM   #3
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Moving this to the articles section. Excellent resource!

Adam
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01-31-2012, 01:58 AM - 1 Like   #4
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I was that request!!

Thanks for taking the time to post such a detailed guide to dissasembly of this lens. The sliding hood on my otherwise perfect copy was quite loose, so I wanted to replace the felt slider inside it. There is no way I would have figured out how it came off, but now I know.

Many thanks for providing such a useful article, and in under 24 hours of my post to you! Guys like you make Pentaxforums the great resource it is!

02-17-2012, 10:54 AM   #5
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Another tip (worked out from helping another forum member disassemble his M* 300): If the elements are stuck: use a big rubber band around them for grip!
02-18-2012, 03:12 AM   #6
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Anyone know what the specification is for the felt like slider materials that are fitted between the inside the hood and the lens body, or where to get them? I want to replace these worn strips on my A*300 to stop the hood sliding under its own weight.

There is a 3/8ths inch wide grey flat strip of material attached to the inside rear end of the hood, and a thinner more rounded black velvet like material around the body near the front of the lens.

I'm in the UK but any ideas or sources of material are of interest.

Thanks for any help or advice!
02-18-2012, 04:41 AM   #7
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Ditto Ed. My glass is clean but the hood has a mind of its own. Great article! Thanks.

02-18-2012, 05:43 AM   #8
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I'll email or have a chat with pentax support to see if I can't find out. Mine flops around as well.
02-27-2018, 10:56 AM   #9
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Images are gone... would love to see this.
04-03-2020, 02:15 PM   #10
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Protective collear won't move!

How much force is needed to unscrew the collar in the first picture? I tried very hard, but I'm afraid to cause damage. Any tips on how to loose the threads? Is there threadlocker inside?
Any clues much appreciated!
04-04-2020, 05:35 AM   #11
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QuoteOriginally posted by huge10 Quote
How much force is needed to unscrew the collar in the first picture? I tried very hard, but I'm afraid to cause damage. Any tips on how to loose the threads? Is there threadlocker inside?
Any clues much appreciated!
... I have not yet succeeded in unscrewing the lens as described. The thing is stuck pretty damn tight.
08-21-2020, 07:31 AM   #12
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Does anyone know if this is the same lens hood disassembly as the A 28-135 of the same era?
03-24-2023, 09:04 AM   #13
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Can confirm the M* version of this ring disassembles the same way. Because of the way these lenses are assembled, you pretty much need to take out the 'front element assembly' before you can remove the screw ring holding the first lens in place. The two pieces of the front element assembly took a considerable amount of force but did come apart eventually.

I recently bought a M* with fungus for an extremely good price and I probably wouldn't have taken a chance on this lens if this guide didn't exist. Thanks!
03-25-2023, 09:35 AM   #14
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I reached the point where I have separated the front lens group. My goal is to reach the inner surface of the front element. Tried hard to turn the slotted retaining ring in the front of the lens as it seems to hold the glass. Not succesfull (yet). I'm wondering if I could reahc the inner surface of the front element in splitting the front lens groiup in two parts, i.e. does removing the back part of the front lens group reveal the surface of the front lens element?
If yess, any tips on unscrewing the halfs of the front lens group. Is there any glue on the threads? I tried acetone with no result. Any tips on getting a firm grip?

Thanks for responding!
03-25-2023, 08:57 PM   #15
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QuoteOriginally posted by huge10 Quote
I reached the point where I have separated the front lens group. My goal is to reach the inner surface of the front element. Tried hard to turn the slotted retaining ring in the front of the lens as it seems to hold the glass. Not succesfull (yet). I'm wondering if I could reahc the inner surface of the front element in splitting the front lens groiup in two parts, i.e. does removing the back part of the front lens group reveal the surface of the front lens element?
If yess, any tips on unscrewing the halfs of the front lens group. Is there any glue on the threads? I tried acetone with no result. Any tips on getting a firm grip?

Thanks for responding!
I had the same problem, it was extremely difficult to get that lens ring turning to the point that I was wondering if I had to remove something else first or if it was threaded in the other direction. I was starting to strip the two divots. I took a chance and put a spritz of lens cleaning solution in the thread and rotated the lens 360 degrees so that the solution ran along and into the whole ring. I was able to get it moving without much trouble a few minutes later. Definitely a risk because if it doesn't work you may just introduce moisture into that chamber without loosening the ring. As far as I can tell the lens cleaner I have is one of the alcohol free water and detergent types ("KuuZuse" brand on amazon, came in a kit).
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