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02-08-2015, 02:27 PM   #1
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Helping with disassembling Pentax M 75-150 F4

Hi Guys!
I have a Pentax M 75-150mm f4 zoom lens with quite noticable fungus stain under the front lens element. I am curious how to disassamble this lens, I have repaired different kind of manual lenses so far but in this case I cannot find any way to go. There is no trace of any hidden movement or trick not to mention obvious screws close to its front part. Only screws can be seen on the mount. Maybe the whole lens should be disassembled to get to the front part?

I would really appreciate to have some clever hint or photos how to start repairing this lens!
Thanks in advance!

02-09-2015, 06:13 AM   #2
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Have a look at this article.
I don't see that lens in the database, but you may learn a lot looking at other examples.

To get at the front of the lens, you'll first need to remove the nameplate ring. Try using a rubber glove
and a plastic cap, (rear lens cap, spray paint cap, etc, whatever fits), to get remove the ring. Below
the ring you will see additional screws that will allow you to get to the front elements.
02-10-2015, 01:06 AM - 1 Like   #3
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That is the trick usually I know.
But not this time, that is why I am a bit clueless.
There is no front namering at all.
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02-10-2015, 02:37 AM   #4
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QuoteOriginally posted by udobam Quote
That is the trick usually I know.
But not this time, that is why I am a bit clueless.
There is no front namering at all.
On my M 80-200, which is a similar design, the narrow matt black ring on top of the front element has lens spanner notches and I think that I got in that way. Also look under the stick-on rubber grip band on the sliding bit. I remember that there was a way of moving that part (grub screws ?) towards the mount end so that the retractable hood could be 'over retracted', if you see what I mean ...

A very cunning design, these two lenses ...

02-10-2015, 04:52 AM   #5
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If you are in the US you could always send the lens to Eric for a CLA.
02-10-2015, 05:15 AM   #6
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QuoteOriginally posted by Not a Number Quote
If you are in the US you could always send the lens to Eric for a CLA.
He appears to be in Hungary. It might be worth contacting Asahi Photo in London - beware he's very good but a bit slow on e-mails, a phone call might be better.

This member might remember how to get in
02-10-2015, 11:05 AM   #7
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I vaguely remember some advice on taking this lens apart but can't find it. On the M135/3.5, you can loosen the rubber focus ring grip by sliding a plastic knife under it and moving it around to break the glue bond. Then slide the rubber down to see if there are slots hidden underneath. Pull the hood out. Move the ring until those slots expose some screws on the inner barrel. Remove the screws and you can pull the hood assembly off. Then you can probably see how the rest of the lens comes apart.
05-04-2015, 01:39 PM   #8
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If anybody is still interested in the answer.

The most important thing is not to try to disassemble the lens from the front. The rubber focus grip needs to be removed, and screws that guide the barrel slide must be removed to remove the front element with a barrel. It is very important that the barrel comes back exactly in the same position as it came off, otherwise it will be stuck zoomed in or out (focusing thread can be screwed in in multiple positions, 6 maybe). You need to be careful not to remove any of the grease from the focusing thread, otherwise it must be re-lubricated.

The whole job does not require a lot of skill, just the right tools (I use Wiha precision screwdrivers, ROR oil remover and Pec-Pads for the lenses). I also advise rubber gloves if they don't make you clumsy.

I hope this helps.

02-24-2017, 02:51 AM   #9
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Hi all

I guess I'm digging up an old thread but any help on this one would be highly appreciated. So I got a near mint copy of the 75-150 on ebay except for a very small amount of fungus on the inner side of the front element. Now, while this doesn't seem to affect the image quality in any way I would still like to get rid of the speck of fungus lest it should grow or spread to the other elements of the lens or maybe even infect the camera I was looking for tutorials online on how to disassemble this lens but didn't find much. So as I gather from @Audi 5 cyl's reply, there is no way to remove just the front element with this lens. Is that right? The only way is to remove the focus grip and then the barrel? How easy or hard is it to remove the grip? Will it spoil the exterior of the lens? My lens is externally in very good condition and so I don't want to ruin its look.

Thanks in anticipation
02-24-2017, 05:46 AM   #10
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I know this is not the answer wanted, but every time I have tried to disassemble a lens or camera, I have ended up sending it in for repairs or throwing it away, mostly the latter. There are people who are far more adept than I am, but the only reason I would take a working lens with an average price of $50 apart would be out of curiosity. If the fungus keeps you from taking a good photo or you just want to see how it works then go for it, but if the concern is whether fungus will grow, I'd just look closely at the photos of the numerous replacements offered online.
02-25-2017, 12:48 PM   #11
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QuoteOriginally posted by GeneV Quote
I know this is not the answer wanted, but every time I have tried to disassemble a lens or camera, I have ended up sending it in for repairs or throwing it away, mostly the latter. There are people who are far more adept than I am, but the only reason I would take a working lens with an average price of $50 apart would be out of curiosity. If the fungus keeps you from taking a good photo or you just want to see how it works then go for it, but if the concern is whether fungus will grow, I'd just look closely at the photos of the numerous replacements offered online.
I understand what you are trying to say. I also feel that there is no wisdom in taking a fully working lens apart just because of a little fungus esp if that's not affecting the images. I guess I should rather look at ways to kill the fungus or stop them from making it spread. I saw a simple copper coin trick on youtube. I don't know how effective that is but I'm ready to give it a shot.

In passing I should mention that I am encouraged to take a lens apart stemming from my past success. I have had a 100% success rate although I must admit that I never took any lens *fully* apart; only a few components.
02-26-2017, 07:44 PM   #12
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chances are from my experience is that you can turn or spin off the lens hood and then spin off the front lens group. Good luck
02-11-2019, 03:12 AM   #13
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1. Remove "rubber-focus-grip": Tt is glued onto a round plastic part, which has to be losened next: (do not touch any of those tiny screws which look like Philips but are JIS!)

2. Find 3 x tiny slotted screws and unscrew, this will allow that you can now easely turn this round plastic part so you have access to

3. Find 2 x slotted screws (with some white plastic underneath their heads!). They sit in those two long slots and hold the barrel itself

4. Now you can "unscrew" the barrel clockwise (try to somehow mark how the barrel is located before unscrewing it, because it has indeed 6 different possibilities to screw it back in!)

When I had the barrel off, I could clearly see the fungus on the inner element which sits closest to the front element. It was easy to clear the fungus of (I used clean alcohol and then wiped it thoroughly with "Pec Pads" (non abrasive wipes). But then I found more fungus deeper down. I could even remove the second element easely but the fungus sat deeper.
I was not interested to "dig deeper", was not worth it.
So it took me several turns to finally


5. get the barrel into the right position. Lots of patience needed. (and I would not know how to mark it, it was trial and error, took me 20 minutes!)
6. screw those 2 slotted screws back into position
7. align the round plastic part so it is in its proper position and then
8. fix it with those 3 x tiny slotted screws.

I was using the post by "Audi 5 cyl" as a guideline, the first part was clear, i.e. to remove the rubber, but then it was too vague for me because there are more tiny JIS screws which I took off first, it was unnecessary.


It is really important to find those 3 tiny slotted screws and those 2 larger slotted screws which sit in this long groove.

After all it was worth for learning, but not much more.

Yet, it is a nice lens! But full manual and a pump-zoom, i.e. it can pump dust into your DSLR and right towards the sensor.
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