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FA50 disassembly and infinity focus adjustment

Being unable to find a manual on the disassembly of these popular lenses, I had to find the method by trial and error. By the way, my experience can be useful for the community  The lens described is the FA50/1.7, FA50/1.4 must be identical, or very similar.

Of course, you perform the actions described below on your own risk

It is recommended to have a set of quality screwdrivers.

0. Infinity focus adjustment. If you just want to adjust infinity focus (like me), you don’t need to disassemble the lens!

0a. Set the focus to the MFD, so that the moving lens housing is all the way out. There are three screws around this moving part (one of them shown with an arrow), unscrew them.

Take the decorative lens housing off.

0b. Set the focus to infinity. There are three screws inside the focusing ring that are holding it, shown by arrows on the picture below. Loosen them. Be attentive: the screws in the deep, closer ones hold the front lens group, don’t touch them!

0c. Hold one of the screws with tweezers or something similar and turn the inner ring counter clockwise. When the infinity focus is obtained (check on the camera), carefully set the outer focusing ring on the infinity mark (to the limit) and fasten the screws.

0d. Install the decorative lens housing back.

Lens disassembly.

1. Unscrew the five screws shown by arrows and remove the bayonet mount. Hold it while removing, because there are spring loaded contacts inside. In my case they did not actually jump out, but who knows…

2. Here are the contacts and springs, don’t lose them.

3. Remove the aperture ring, A-position lock button will fall out of it. The little ball bearing that goes with the inside bumpy bit might also fall out.

4. Remove the round part that transfers the set aperture stop to the aperture blades and camera lever.

5. Remove the plastic contact group housing, it is held by one screw.

6. Remove the screws, shown by arrows.

7. Unscrew the screws shown by arrows (1). Be careful with the ball, that clicks aperture stops (2).

8. Unscrew the screw (1). After that you can take the lens assembly with the helicoid and electronics out of the external barrel. While doing this, the AF drive shaft (2) may fall out. Take care of the flex PCB with the contacts (see previous pictures).

9. So, the lens assembly is out. Remove the aperture lever (1). You’ll need to detach the spring (2).

10. Very important notice: remove the contact brush (shown by arrow) before removing the focusing ring, otherwise you can bend or brake the contacts.

11. Take the decorative lens housing off (if you have not done it yet). Set the focus to the MFD, so that the moving lens housing is all the way out. There are three screws around this moving part (one of them shown with an arrow), unscrew them.

12. Unscrew three screws shown by arrows and remove the focusing ring.

13. Clean the contact tracks with solvent, just in case.

14. In order to take the lens assembly out of the helicoid, set the focus to MFD and unscrew four screws that hold the guiding parts. Pay attention to the place, where each of them belongs to, they are different.

15. After that you can take the lens assembly out. It is recommended to mark alignment of parts, otherwise you will need to assemble them by trial and error 

And that’s all. I didn’t need to disassemble further, because cleaning and lubrication do not require this.

Assemble the lens in reverse order.

Originally posted by gflauti Wich solvent did you use to clean contacts? Ethanol (was available), but I prefer isopropanol, it is much more efficient and convenient.

09-04-2012, 05:14 PM   #10
Chaos_RealmVeteran Member
Join Date: Feb 2011Location: Melbourne, AustraliaPhotos: Gallery | AlbumsPosts: 1,251
I have added your article to the little database I have going: 
https://www.pentaxforums.com/forums/maintenance-repair-articles/179884-pentax…ml#post1878155

Read more at: https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/197889-fa50-disassembly-infinity-focus-adjustment.html#ixzz5uCa1au9Y