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11-28-2018, 03:04 PM   #1
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Please help. Disassembly Problem to Pentax A 28mm f2.8

Hi everyone, this is my first post and I ask you to apologize if it is not the right section to post it, and even more I apologize for my bad English. I write to ask if anyone has the assembly scheme of an old pentax A 28mm f2.8. sn.5332597 I'm trying to open to remove a mold. the problems I have at this moment are two: on the front I can not remove the front cover ring, while the back I managed to open and clean it, but in my absence my niece "played" with the removed lenses and now I have the doubt of having mounted them by reversing the position of the faces. I'm sure the order of arrangement is correct but I'm afraid of having inverted the inner face with the external one, and in the absence of the assembly scheme I do not know how to do it. I have already searched on the page dedicated to the lens here on the website, but unfortunately it is not present. Can someone help me? also someone has any idea why I can not unscrew the front? thank you in advance. Dani

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11-28-2018, 03:22 PM   #2
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Welcome to PentaxForums!

Our Disassembly Database doesn't look like it has this lens in it:
Pentax Lens Disassembly Database - PentaxForums.com
11-28-2018, 04:03 PM   #3
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Is this what you're looking for? http://kmp.pentaxians.eu/wp-content/uploads/bojidar/lenses/primes/_optics/28f2.8-ii.gif
11-28-2018, 04:39 PM   #4
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QuoteOriginally posted by Sider Quote
but in my absence my niece "played" with the removed lenses
No treats for naughty niece for a week !

11-28-2018, 06:48 PM   #5
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I have a set of these:
https://www.amazon.com/Japan-Vacuum-Camera-Opener-Repair/dp/B0013HFYKK/ref=s...ords=lens+tool
You should be able to remove the front ring with one of them.
11-28-2018, 08:51 PM   #6
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The lens elements are shown in the M 28mm f2.8 page, your A should have the same configuration.
11-28-2018, 09:13 PM   #7
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I know I've taken apart the front of that lens, but can't remember how. The plastic beveled trim ring often has two thin rectangular slots 180 degrees apart. You might try to slip something in there to get the ring to turn. The plastic rings are more forgiving of dirty or damaged filter threads but it helps to have the threads in good shape. Some A series lenses don't come apart the same way an M counterpart would, so it's possible that the trim ring isn't the first step. Focus to the minimum distance so the front barrel protrudes as much as possible and look for small screws in the side of the barrel.
11-29-2018, 06:38 AM - 1 Like   #8
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QuoteOriginally posted by Cipher Quote
The lens elements are shown in the M 28mm f2.8 page, your A should have the same configuration.
The lens diagram shown for the M 28/2.8 is from the older version, which is not similar to that of the A 28/2.8. The diagram for the A 28/2.8 is shown here: http://kmp.pentaxians.eu/wp-content/uploads/bojidar/lenses/primes/_optics/28f2.8-ii.gif



11-30-2018, 09:29 AM   #9
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QuoteOriginally posted by FozzFoster Quote
Welcome to PentaxForums!

Our Disassembly Database doesn't look like it has this lens in it:
Pentax Lens Disassembly Database - PentaxForums.com
Yes FozzFoster, unfortunately there is not. I had already consulted the db and I saw that it was absent. It seems however that I found the exact scheme on an Australian site. I hope it is reliable
11-30-2018, 09:33 AM - 1 Like   #10
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QuoteOriginally posted by deus ursus Quote
yes, this is it. I had already found it on an Australian site .. now I just hope it is the right scheme, even if I have some doubt. The shell enclosing the lenses has a sign that makes it clear exactly until the point of the thread was screwed, but respecting this scheme the metal "plug" does not screw to the same point. Very strange
11-30-2018, 09:35 AM - 1 Like   #11
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QuoteOriginally posted by pschlute Quote
No treats for naughty niece for a week !

neither to her nor to her uncle. I was very nervous when I wrote this post and I could not sleep. As a result, since I could not finish cleaning on the 28th, I started to disassemble the M 55 1.7, and at 4:00 AM, it is not the right time to do these things.
11-30-2018, 09:38 AM   #12
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QuoteOriginally posted by blumoon722 Quote
Thanks blumoon722. I have to check if they are available in Italy, because in addition to the biblical times to get them from the states, I should still consider shipping costs. I'm trying with anything I have available, but it seems literally soldered

---------- Post added 11-30-18 at 09:42 AM ----------

QuoteOriginally posted by Cipher Quote
The lens elements are shown in the M 28mm f2.8 page, your A should have the same configuration.
Thanks blumoon722. I have to check if they are available in Italy, because in addition to the biblical times to get them from the states, I should still consider shipping costs. I'm trying with anything I have available, but it seems literally soldered

---------- Post added 11-30-18 at 09:45 AM ----------

QuoteOriginally posted by Just1MoreDave Quote
I know I've taken apart the front of that lens, but can't remember how. The plastic beveled trim ring often has two thin rectangular slots 180 degrees apart. You might try to slip something in there to get the ring to turn. The plastic rings are more forgiving of dirty or damaged filter threads but it helps to have the threads in good shape. Some A series lenses don't come apart the same way an M counterpart would, so it's possible that the trim ring isn't the first step. Focus to the minimum distance so the front barrel protrudes as much as possible and look for small screws in the side of the barrel.
I confirm that this has no opening at the sides, it is visible screws at maximum extension. It is practically impossible that it should be done from behind, so the only possible problem is that it has been soldered or maybe some old owner has glued it
11-30-2018, 10:44 AM   #13
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you may want to review this thread:

Cross-head screws - a caution:

" Those screws that look like Phillips 00 and 000 in Japanese cameras and lenses? They aren't. They're JIS cross-heads and life's a lot simpler using JIS screw driver bits on 'em.

Whether you do this only once and run into trouble, or intend to do it often, it's worth your sanity to do it with the correct JIS tools so you don't risk stripping a screw head. T-shirts should be available for those that have been there, done that!

Sooner or later, you'll be sorry if you don't use the JIS bits since the Phillips bits make great roto-rooters in JIS screw heads because they don't fit all the way into the cross slots as you can see here: . . . "


Read more at: Cross-head screws - a caution: - PentaxForums.com
11-30-2018, 11:46 AM   #14
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QuoteOriginally posted by Sider Quote
yes, this is it.
Glad to be of help. ☺
12-03-2018, 05:56 PM - 1 Like   #15
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ok friends,
when you understand that with the good you can not get anything, move on to the bad. Here are the photos of the lens opening, after making two holes in the plastic ring, opening it with a watchmaker's tool, lens cleaning and reassembly.
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