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11-06-2012, 04:01 PM   #1
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Lens looseness value

I have a Pentax M 50 f4 macro that has some play in it.
Is it fixable with out spending money on it?
I have not used it much, but it seems to work well...but then again I don't own another dedicated macro to compare
How much value does it loose on advantage in this condition?
I have not been able to get any information on a dedicated macro

Thanks

Randy

11-06-2012, 04:08 PM   #2
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I'm not sure how that particular one is made, but many Pentax M lenses have some screws just under the name ring that will loosen up over the decades and cause some play. It might be as easy as pulling the name ring off, removing some screws, putting some thread locker on them and re-installing them.
11-06-2012, 04:23 PM   #3
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There are a few guides on M 50mm lenses here: https://www.pentaxforums.com/forums/maintenance-repair-articles/179884-pentax...-database.html

Among other things. Generally speaking manual focus prime lenses are pretty simple, things get alot more complex in the zooms though.
11-06-2012, 05:22 PM   #4
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QuoteOriginally posted by slip Quote
...Pentax M 50 f4 macro that has some play in it.
Is the "play" in the extending barrel or the junction between the mount end and the further forward barrel?

The things that get loose first is the guides inside. The two halves of the barrels are locked in place by a pair of guides to keep them aligned and the helical portion is pressed within the two points and act on both barrels while itself remains stationary. Over time the tension of sliding within the channels loosens the guides... grease also thins as well and allows for "play". In some case the guides wear down from the dirt and lack of grease and must be replaced.

The possible other thing that gets loose is the cup portion of the lens that is towards the rear. Usually hidden under the aperture ring are a set of screws and sometimes the mounting and dis-mounting as well as twisting of the aperture can sometimes wear metal around the screw holes.

If only the focus barrel is loose, then... as Chaos_Realm mentioned... the lock screws have gotten loose or broke free from the thread lock. The disassembly usually involves removal of the shroud sleeve and gaining access to the focus barrel. Commonly the name ring is the place to go and sometimes it can be a set of screws under the rubber grip that allows the focus barrel to split, but don't pry it off first... try the name ring.

11-06-2012, 05:41 PM   #5
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It seems that the F stop ring has most if not all the play.

How do you take the name part off when it looks like this?
It's not a picture of mine but it is the same model


Thanks

Randy
11-06-2012, 05:46 PM   #6
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QuoteOriginally posted by slip Quote
...take the name part off when it looks like this?
First off... you have a pair of surgical gloves? Finger cots or rubber gloves to improve your grip.

Inspect the edge of the name plate to be sure it is a threaded in piece.

The name and the funnel part should be all one piece. With the extra grip on, you spin it off... however...

QuoteOriginally posted by slip Quote
It seems that the F stop ring has most if not all the play.
So that sounds like the rear portion is loose? This will require the removal of the mount - loose lever/armatures - aperture ring (watch out for the ball-bearing).
11-06-2012, 11:19 PM   #7
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You may visit the mflenses forum, repair threads, for more info and tools.

I never needed to open up pentax lenses, but many other. Some easy, but some took days.
Inner elements can be made by soft glasses and can be destroyed/leaving marks.
11-07-2012, 01:21 PM   #8
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Soft glass is not an issue unless the elements are being removed... in this case it is a question of which part of the lens is actually loose.

If this is a matter of a loose screw, then most of the time is is just a removal of shrouds and barrels.

IMPORTANT! If you are not comfortable dismantling of the lens, then it is best to leave it to a professional.

QuoteOriginally posted by slip Quote
It seems that the F stop ring has most if not all the play.
As to the steps outlined prior...if the lens is loose near the mount, the removal of the name plate and funnel end is not going to get you to the rear of the lens.

If the looseness is observable as movement and a gap showing from the mount and aperture ring and the scale ring and focus barrel, the place that needs looking at is the rear of the lens.


Last edited by MysteryOnion; 11-07-2012 at 01:28 PM.
11-07-2012, 10:38 PM   #9
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It's way easier to sell a problem-free lens. By the time you describe the issue, then protect yourself from the idiot who buys it without reading, I'd just fix it myself. My guess is, $30 since you don't exactly know what's wrong.

To fix yourself, it's probably worth buying some JIS screwdrivers like this, though all you actually need is the smallest one of the set. I have one of these and would be happy to take it apart more than this. Because it's a macro and extends a lot more than an ordinary lens, it's not quite the same as other M series. The first photo shows the mount and aperture ring removed (5 screws, take the mount off, then carefully slide the aperture ring off and look for the ball bearing):


Note that a lot of M series lenses have the ball bearing right under the orange diamond, but here it's offset to the side where the ivory locator bump thing is. The bearing on your lens should stick out like this. There's a flat spring-steel spring behind it, normally shoving the bearing out into teeth on the inside of the aperture ring. You can see a rivet for one end of the spring to the left of the bearing. If the bearing gets stuck in old grease or dirt, it won't be pushed out enough and the aperture ring will have a sloppy feel to it. Anyway, it's easy enough to check if you can get the mount screws off.

Here's the front just for completeness. As mentioned above, the whole "cone" unscrews. It has its own threads cut just inside the filter threads. Because it's got a large surface to grip and the threads are less likely to be dirty or bent, it should come off easy.



Inside, the lens is a bit weird, because of the macro thing. Another assembly quirk is some screws hidden under the rubber focus ring grio. I forget exactly what they do.
11-09-2012, 10:49 AM   #10
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this is great start. I will have to try this on the weekend

thanks a million!

randy
11-09-2012, 06:52 PM   #11
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QuoteOriginally posted by Just1MoreDave Quote
Anyway, it's easy enough to check if you can get the mount screws off.
And you need to be VERY careful else you will never see it again! I suggest putting down a tea towel so it won't bounce away.
11-10-2012, 08:10 AM   #12
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QuoteOriginally posted by Chaos_Realm Quote
And you need to be VERY careful else you will never see it again! I suggest putting down a tea towel so it won't bounce away.
Was thinking about one of those magnetic trays that you can get a an auto parts store?

Thanks

Randy
11-10-2012, 04:58 PM   #13
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QuoteOriginally posted by slip Quote
Was thinking about one of those magnetic trays that you can get a an auto parts store?

Thanks

Randy
yeah that might work. I ended up getting a tradies tool retriever super strong magnet - the ones they use to get tools they drop in wall cavities. But that was to find an already lost Bearing Worked a treat even though I found it in a spot I must have look about 10 times!
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