I (fully) dismounted my FA 28-70/4 !! Part I

Started Jul 17, 2006 | Discussions
AstroShooter Contributing Member • Posts: 504
I (fully) dismounted my FA 28-70/4 !! Part I
2

Hello.

I'm really occupied with my three childs and have no time to post, but I try to read the forum as much as I can.

Two moths ago I bought a FA 28-70/4. I did some test shots and I discovered some strange exposure errors. A more detailed exam revealed the problem: the sutter blades didn't close correctly because they were dirty (with some kind of grease).

The lens had no warranty (bought in ebay) and also the repairing could cost more than a new lens so... why not? I dediced to dismount it totally and clean the blades myself.

I took a pic before dismounting every piece to know how to put it again in the same position. I can say that the operation was a success, because I could dismount the lens, clean the blades, mount it again... and now it's working.

Unfortunately I'm not happy with the image quality of this lens. I'm sure the quality problems aren't due to the dismounting because I took some pics before and they have the same problem: softness or maybe front/back focus. The kit lens is performing better than this lens.

Anyway, here you are. I will post the pics showing you the whole process. I'm sorry about the lack of detail of some pics. I took the pics with a white background, and the len is black. Also I used the built-in flahs so there is a lot of reflections in many pics.

I'd like to write a long and detailed explanation with every pic, but I have no time and the time was passing, so I'll put it in order and I think you have pics enought to repeat the process yourself.

The tools: a small screwdriver, wife's tweezers, magnetic surface (to put the small screws above), lens cleaner.

Dismounting the front:

Remove the rubber ring and two small screws. Now you can turn the focus piece to the right and extract it.

You can see the inner glass (that moves with the zoom ring) and the shutter blades

Remove three small screws and a thin metal ring

Now remove four screws more and you'll can remove the inner glass. Now the blades are exposed. Yes, they are dirty!

Now let's go to the back side...

-- hide signature --

Javier.

OP AstroShooter Contributing Member • Posts: 504
Re: I (fully) dismounted my FA 28-70/4 !! Part II

This is the back side.

Remove four screws and take the back cover with care: there is a lot of springs and small contacts.

This inner piece is necessary fot the zoom to work. Try to understand how the mechanics works before remove any piece. The whole apperture mechanics are here!

Now you can remove the apperture ring and the zoom ring. Take care! There is a small little bal over there that you can lost easily! Apperture ring is in the left side in the following pic. Zoom ring is in the rigth side.

More detailed view. Note the grey piece like a "Y". We need to unscrew two screws to remove this piece and get the inner tube with the blades.

"Y" piece dismounted.

The inner tube is out. But this is not the end...

Inner tube: rear part. We need to remove three pieces that are part of the zoom mechanics.

Removed!

Now we can extract the blades for cleaning...

Cleaning the blades...

Mounting again: this is a HARD WORK! Just look at my rudimentary tools

It will continue...

-- hide signature --

Javier.

OP AstroShooter Contributing Member • Posts: 504
I (fully) dismounted my FA 28-70/4 !! Part III

This is a view of the lens fully dismounted.

Another view

The whole process took me two nigths but I think it can be repeated in about two or three hours.

Advice: don't try it with your favourite lens and don't try it if you have some heart illness

The lens is at present mounted and working...

Regards,

-- hide signature --

Javier.

ghk Regular Member • Posts: 399
Nice job!

I'm glad mine's ok.

-- hide signature --

Gerard

BiscuitMonster Senior Member • Posts: 1,021
Re: I (fully) dismounted my FA 28-70/4 !! Part III

You are a brave man! I wouldn't mind taking anything apart, but putting it together again so it works... (and there are no left over parts...) well, that's another story

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Enrico L Regular Member • Posts: 492
Re: I (fully) dismounted my FA 28-70/4 !! Part I

Hi,

Now be honest Javier...how many times did you sit on the floor looking for that one part that had fallen down?

Thank god for gravity!

Nice job, mine is still working fine (no focus problems as you mentioned) I do hope it stays that way. I repaired once a M42 Lens I am still hoping that it was the first and last time I did that....

-- hide signature --
Mousehill Veteran Member • Posts: 7,539
Re: I (fully) dismounted my FA 28-70/4 !! Part III

WoW Javier,

I'm impressed by your skill here! It's nothing for me though, I one dismantled the engine of my scooter and when I was finished it would only run backwards

Cheers,
Mike
--
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Best of Gallery at http://www.culinair.com
Macro photo gallery at http://www.macro-photo.eu

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Enrico L Regular Member • Posts: 492
Re: I (fully) dismounted my FA 28-70/4 !! Part III

Sure it was not a DAF?

I seemed to remember a Dutch tv program racing backwards you could have tried to participate

-- hide signature --
OP AstroShooter Contributing Member • Posts: 504
Re: I (fully) dismounted my FA 28-70/4 !! Part I

Enrico L wrote:

Hi,

Now be honest Javier...how many times did you sit on the floor
looking for that one part that had fallen down?

Ufff... I can't remember :-). The small ball that is part of the apperture mechanics were lost more than one time. I recovered it after sweeping the floor (I was lucky). Also a small gold spring that is part of the KAF contacts (mass) was lost, but I built a replacement with a thin copper cable... also a lot of screws were lost on the floor or into some piece more than a time (but I recover all of them) and also...

Thank god for gravity!

Nice job, mine is still working fine (no focus problems as you
mentioned) I do hope it stays that way. I repaired once a M42 Lens
I am still hoping that it was the first and last time I did
that....

It's a pity that, after making this effort to clean the blades, my copy isn't working fine

Regards,

-- hide signature --

Javier.

Jim King
Jim King Veteran Member • Posts: 8,541
Better you than me!

My FA28-70/4 showed similar symptoms, but not being as bold as you, I sent it in to Pentax for service nd they charged me about $70 for replacing the entire iris mechanism and doing a C/L/A. It works fine now - I fear that had I attempted the repair, it would still be in pieces on my workbench...

BTW, I agree that this lens does not perform especially well on digital. That's a bit puzzling considering how well it was rated by the PDML crowd on film, but so it goes...
--
Jim King - Retired Colormonger - Suburban Detroit, Michigan, USA; GMT -4h (EDT)

* * * * *
A fanatic is one who can't change his mind and won't change the subject.

  • Sir Winston Churchill

* * * * *
The difference between genius and stupidity is that genius has its limits.

  • Albert Einstein

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D TONG Senior Member • Posts: 2,559
Re: I (fully) dismounted my FA 28-70/4 !! Part I

AstroShooter wrote:

Enrico L wrote:

Hi,

Now be honest Javier...how many times did you sit on the floor
looking for that one part that had fallen down?

Ufff... I can't remember :-). The small ball that is part of the
apperture mechanics were lost more than one time. I recovered it
after sweeping the floor (I was lucky). Also a small gold spring
that is part of the KAF contacts (mass) was lost, but I built a
replacement with a thin copper cable... also a lot of screws were
lost on the floor or into some piece more than a time (but I
recover all of them) and also...

Thank god for gravity!

Nice job, mine is still working fine (no focus problems as you
mentioned) I do hope it stays that way. I repaired once a M42 Lens
I am still hoping that it was the first and last time I did
that....

It's a pity that, after making this effort to clean the blades, my
copy isn't working fine

Regards,

My gosh. That reminds me of my replacement of a G1 surface mount fuse . After that I have 5 screws more than I could put bakc. It worked and it was the most gratifying moment I had during that 5 yrs .

Job well done and I have saved the images just in case later on I have the need to repair or remove some grease my lens.

Daniel, Toronto
http://www.pbase.com/danieltong

Jay Taylor Contributing Member • Posts: 881
Re: I (fully) dismounted my FA 28-70/4 !! Part I

Javier,

Thanks for the illustrating your process. Do you know how to fix the element separtion problem so many of these lenses seem to develop? Mine doesn't have the problem (yet) but I have a 100mm Macro that is still in pieces on my bench because I can't fiqure out how to fully seperate the rear lens element. I tried hot water soaking and isopropyl alchohol. Any other ideas?

Thanks,
JayT
--

OP AstroShooter Contributing Member • Posts: 504
Re: I (fully) dismounted my FA 28-70/4 !! Part I

Jay Taylor wrote:

Javier,
Thanks for the illustrating your process. Do you know how to fix
the element separtion problem so many of these lenses seem to
develop? Mine doesn't have the problem (yet) but I have a 100mm
Macro that is still in pieces on my bench because I can't fiqure
out how to fully seperate the rear lens element. I tried hot water
soaking and isopropyl alchohol. Any other ideas?

I'm sorry Jay, but I'm afraid I couldn't give you any advice. I need to see the problem you are describing to know how to solve it. At present, this is only the second lens I have dismounted so still I have not too much experience doing this kind of work, and I'm afraid that your fixed focal macro lens is too different from my FA :(. Could you tell me where (pic number) is the element you are refering to?

Regards,

-- hide signature --

Javier.

CurtisR Regular Member • Posts: 263
Thanks for posting!

Highly entertaining, and nice clear photos. Very gracious for taking the time, and I really enjoyed the walkthrough.

alfredo77 Forum Member • Posts: 55
Re: Better you than me!

I too was a little disappointed in the 28-70 after it did well on film. Many pictures show CA and overall I don't have the sharpness I like. However, I deemed it unreliable as I have also been able to take some good ones (for MY standards, of course):

-- hide signature --

Ciao!

alf.

vjacesslav
vjacesslav Junior Member • Posts: 37
Re: I (fully) dismounted my FA 28-70/4 !! Part III
1

Excellent work, I did it same one hour ago. It is really easy and it took only 90 minutes.

Unfortunately the lens element is impossible to repair. "The glue" in last optical element is too old and it is impossible to repair it :/

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Joseph Tainter Forum Pro • Posts: 10,676
Re: I (fully) dismounted my FA 28-70/4 !! Part III
1

Wow!

Joe

Manituwa Regular Member • Posts: 433
Re: I (fully) dismounted my FA 28-70/4 !! Part III
1

Excellent work!  Thanks for sharing.

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R A Roberts

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KentG Veteran Member • Posts: 4,575
Re: I (fully) dismounted my FA 28-70/4 !! Part III
1

Nice job of disassembly for sure. Even if it is an old thread. Actually the cement is optical grade Canadian Balsum. You can actually buy that stuff. Before taking the elements apart you need to mark the lens alignment, then clean all the "cement" off and re-glue it. The actual process is not as simple as that because you need to know how much to use and how to make sure you don't get any air bubbles in it.

Kent Gittings

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sleepwalker400 Senior Member • Posts: 1,849
Re: I (fully) dismounted my FA 28-70/4 !! Part III
1

can you even get the balsum glue any more, I  thought it comes in a form of a brick and that you need to mix with certain chemicals.

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