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03-30-2016, 05:50 PM   #1
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Grooved tube inside rear mount on Pentax 300mm f/4 rattles, is this a problem?

So I've been trying to revamp my lens lineup and sold my Pentax 300mm f/4 prime lens on Ebay. Worked just fine before shipping it. The guy gets it, says that there's a rattling noise inside, but I can't quite understand his explanation due to his poor English. He attaches some photos but they're not very good either, still can't understand the problem. I thought he was saying there was something inside the glass rattling around. He says the lens works just fine, he just doesn't want it because of the rattling. We go to Ebay Resolution Center because I know for a fact this problem did not occur prior to shipment and he claims it was like that when it arrived. Ebay sides with him, so they reimburse him and he returns the lens to me.

So now I'm stuck with a potentially damaged lens that I may not be able to sell for the same amount anymore, and it could possibly degrade and not be useable for me either. Last thing I want to do is send it to Precision Repair and wait 3+ months for them to tell me either they can't fix it or that I have to pay several hundred more dollars to fix it. I'm pretty annoyed because the lens was freaking fine when I shipped it.

Anyway, currently I'm just trying to understand the scope of the problem, if there is one at all. I received the lens back in the mail today. Upon inspection, I can see what the problem (now) is. I'm not super familiar with the parts of lenses, so bear with me, but when you're looking into the rear mount of the lens, there's a tube just inside the mount (not inside the glass) that is grooved. It rattles around some when you move the lens, the grooved tube seems like it has become detached. That's basically it. It still attaches to the camera, it still takes pictures. Since I don't exactly know the function of this part, I can't really tell if this is a non-issue or if it's potentially an issue that's going to get worse over time and cause me (or someone else) real problems. Since many of you are much more knowledgeable than I on this subject, I thought I'd seek out your advice.

Thanks much. I'm attaching a pic to show you what part I'm referring to, it's the black grooved tube just inside the rear mount.

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03-30-2016, 06:00 PM   #2
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That baffle should be attached to the rear part of the lens. Up in your picture. I cannot tell from mine if it is just a friction fit or if it is glued in. If I had to guess I would say just friction fit.
03-30-2016, 06:14 PM   #3
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QuoteOriginally posted by jatrax Quote
That baffle should be attached to the rear part of the lens. Up in your picture. I cannot tell from mine if it is just a friction fit or if it is glued in. If I had to guess I would say just friction fit.
OK, thanks. So is the baffle in its current state a problem for the performance of the lens, or is it going to become a larger problem down the road? And how simple a repair is it to re-attach? Thanks so much.
03-30-2016, 06:28 PM   #4
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If it were my lens I would not let that rattle around on the rear element of the lens. Might not cause any problem, but I certainly would not chance it.

Performance wise, I assume the baffle is there to prevent stray light from hitting the sensor at the wrong angle. So it could cause some image quality issues. But since it is mostly still in place I doubt you could tell.

I would get it repaired. You might check with a local camera shop that has a repair tech. It isn't something that would require a special Pentax tech.

03-30-2016, 07:16 PM   #5
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If it's friction fit, all you would need to do is to line up the baffle around the rear element and push it down. I've had a few lenses with the same sort of baffle which friction fit around the rear element housing. Possibly, the baffle came off during transport to your former buyer.
03-30-2016, 07:22 PM   #6
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QuoteOriginally posted by excanonfd Quote
If it's friction fit, all you would need to do is to line up the baffle around the rear element and push it down.
Nope. You would have to pull up. It is attached to the rear mount not the element package. If I was adventurous I might fashion a couple of wire hooks and try slipping them under the baffle and pulling up. But considering how little clearance there is with that rear element I might not be that adventurous.
03-30-2016, 07:32 PM   #7
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QuoteOriginally posted by jatrax Quote
Nope. You would have to pull up. It is attached to the rear mount not the element package. If I was adventurous I might fashion a couple of wire hooks and try slipping them under the baffle and pulling up. But considering how little clearance there is with that rear element I might not be that adventurous.
Pardon me, the one I worked on was a Bushnell 400/6.3 in Nikon mount that I converted to K. OP might be able to get two fingers in the baffle, scissor the fingers to get a grip and pull the baffle into place.
03-30-2016, 07:33 PM   #8
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Good suggestions, thanks. Good to know it's something a local repair guy could possibly do for me, rather than ship it off to to Pentax repair shop. That's a huge difference in cost and time. I may try your suggestions first, with caution, and then if I can't make it work, will see if a local repair shop can do it for me.

03-30-2016, 07:45 PM   #9
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QuoteOriginally posted by excanonfd Quote
OP might be able to get two fingers in the baffle, scissor the fingers to get a grip and pull the baffle into place.
That might work. I would try that first, then the wire hooks. If I was adventurous.
03-31-2016, 06:39 AM   #10
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Why mess around with half measures? Just undo the four or five screws holding the mount on and press it back on with enough force to do the job properly. Just take care with the contacts and springs.
03-31-2016, 07:32 AM   #11
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Yes, I would definitely take it apart, rather than poke around that rear element with "hooks".

Two main issues come to mind for those who have never attempted such things. First, find good screwdrivers to precisely fit the mount screws. Dollar store ones often fit poorly and quickly strip.

Secondly, even for those experienced with lens repairs, those tiny springs that back up the electronic contacts are a real bear in Pentax lenses. You have to really pay attention to where they come from, and how many you're supposed to have.

On the plus side, when you've got that pesky loose baffle in hand, you can put a dab of adhesive on its edge before pushing it back into place, so it won't come loose again.
04-04-2016, 12:36 PM   #12
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QuoteOriginally posted by Ontarian50 Quote
.
On the plus side, when you've got that pesky loose baffle in hand, you can put a dab of adhesive on its edge before pushing it back into place, so it won't come loose again.
Suggest you use medium strength thread locking compound rather than adhesive because the latter might be a "problem" if the lens has to be taken apart for another repair later on.

PS: had the same problem with a Sigma 10-20 f4-5.6, and that's what I did!
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