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07-10-2012, 09:07 PM - 1 Like   #1
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what's in the lens? How can I clean/fix it? F 35-70

Hi

Just received the lens. Purchased on ebay with SF1 at low price, so I didn't bother to return it when I saw this in the lens.

What are these in the lens? Oil drops? How did oil drops get in there? Separation? They are not typically the separation I have seen.

If it is not separation, is it possible to clean it? The glass is in very good condition otherwise. The worst situation is I ended up some parts that I cannot put them back anymore.

Any suggestion? Has anyone seen step-by-step instructions for disassemble and cleaning?

Thank you!

Graham

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07-10-2012, 09:27 PM   #2
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Looks like separation, although I have only seen it start around the edges so this is different to what I have seen before. So probably not worth pulling apart to fix. But;

I have recently disassembled an F 70-210 to fix a jammed zoom, (turns out it was stuffed without a replacement part) but the F zooms are tricky little buggers to put back together there are about 3 internal barrels for the zoom/focusing which are a pain to get all aligned up again when putting it back together. Plus a couple of rather delecate electrical contacts. I haven't been bother writing a How to for it but my database of lens disassemblies might be of use:

https://www.pentaxforums.com/forums/maintenance-repair-articles/179884-pentax...-database.html
07-10-2012, 09:54 PM   #3
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Thank you, Scott.
I thought they must be separation, because I can not image where did the oil drops came from, and picture #1 really looks just like separation on other lenses I have seen. But I am afraid these white spots are caused by the liquid interface between the clear liquid and glass. When you look from front, they really look like clean clear liquid drops! See through the lens these small drops are actually small convex, and I can clearly see everything behind them. Picture #2 also shows the light pass through these drops is aggregated on the ring behind the drops. I have never seen separations like this before.

Your database is very helpful. I happened to have a A 50 1.7 has aperture ring stuck problem. I will try to fix it when I have time, following your instruction. Very helpful! Thanks!
07-10-2012, 09:57 PM   #4
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Do you think should I go from front or rear end if I want to give it a try? Could it be a little easier if I can reach that element from front? I can not tell which element though.

07-10-2012, 10:25 PM   #5
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There's no glued glass in the front element. I can certainly rule out separation. The front element is fairly easy to open. See the grooves? That's the front element. It's a group of three lenses. It's not very tight. On my copy, I just used my finger nails to twist anti-clockwise it and it comes loose. Once you get it out, you can further separate the front element group, but this time you'll need a caliper. There's no alignment whatsoever, so there's nothing to worry about.



Don't bother how the spots get there. Just clean them up and you'll be fine. A word of caution though, be wary of smudge and dust. The glass is coated, so it's very easy to smudge, even with isopropyl achohol.
07-10-2012, 11:33 PM   #6
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QuoteOriginally posted by grahame Quote
Your database is very helpful. I happened to have a A 50 1.7 has aperture ring stuck problem. I will try to fix it when I have time, following your instruction. Very helpful! Thanks!
Not my instructions; Just links to other peoples work.

It looks to be in the 2nd group from the front element so through the front is how you get at it. Although from memory I believe that to get the internal elements (atleast with the 70-210) you had to take the back off to undo the screws holding the zoom barrel and focusing barrel inside. This involved de-coupling the aperture lever (and removing the aperture ring) which can be a little bit fiddly, PS there is a ball bearing under the aperture ring that WILL vanish onto the floor if you are not VERY careful. From there you could get access to the internal elements. I don't have the photos on me at the moment so I could be wrong on that one.
But please remember, pulling a lens to bits is not always a good idea, especially if it is something that can't be (easily) fixed. So in the case of lens separation unless you plan on doing a re-setting of the cement which requires special equiptment to line the elements up correctly I think the lens will be better off left as is. By opening up a lens you can expose the internals to dust, and you will be fighting an up-hill battle trying to get rid of.
07-11-2012, 08:17 AM   #7
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Thank you all!

I will try to clean it, since go front the front sounds easier than the bid surgery from rear end. The caliper should be delivered this afternoon.
What's your suggestions in cleaning the coated glass? I used to ware latex gloves and use 100% ethanol, but have never worked on a internal glass with coating.

Scott, I will not go too deep. hopefully I don't have to go deep. I know I am not that type of person that can handle that. But right now, because the spots are clear drops and can bend the light, the pictures from the lens look bad.

If I realize the lens is not cleanable from easy disassembly, I will probably find a professional guy to do the cleaning when I go back to China. Service is cheaper there.
07-11-2012, 04:08 PM   #8
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Is it worth fixing or cleaning? Depending on how much you value your time, spending two hours on a $50 lens may not be worth the effort.

07-11-2012, 04:22 PM   #9
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The only F I'd taken to bits was the 28-80. Probably quite different design to this one. Disassembly was quite easy except for splitting up of the front group. I wouldn't worry too much about damaging the coating, it is quite tough.

Why don't you just get another one, they come up on eBay all the time ?
07-11-2012, 05:53 PM - 1 Like   #10
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grahame, have you managed to open up the lens? I could open up the front element group of mine with no difficulty.

By the way, when you take apart the front element, you will find it is a group of glass in one assembly. To open up the package, hold it at the side and insert the caliper in same slots you use to loosen it from the mount. You can remove the front most glass. Once the front glass is off, turn it upside down and tap a little and the middle piece will come off. However, if the stain is on the rear side of the front piece, or on front side of the middle piece, do not take it off. You'll introduce dust when assembling back.

To clean, a cotton bud with some alcohol followed by a buff with lens tissue is pretty sufficient.

The front element of this lens is very easy to deal with. You certainly do not need to bring it to China.
07-11-2012, 08:21 PM   #11
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Weijen,

Yes, I just got some minuets and opened the lens, as you suggested. I am lucky, the stain was on the outside of very rear end of first group assembly. So I don't have to remove anything after I take out the whole assembly, just wiped with Ethanol, dry it a little bit and put them back.Took me less than 5 min.

Thank you for your help and encouraging. This is my first time opening an auto focus zoom lens, although this is not any more difficult than any MF prim lens.

The lens is cheap and easy to find, but I just hate to through any lens away before trying to save it. Particularly this one. I love the size and zoom range, and think it might be a very good lens on K01, which I will probably get one soon or maybe wait for k02. I have seen quite a few of 35-7 lenses, but all of them have a lot of dust inside. Now this one is much cleaner.

Thank you all!
07-11-2012, 11:32 PM   #12
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Good to hear that! Mine was infested with fungus but I got it cleaned. It's a very nice lens.
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