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11-12-2015, 10:36 AM - 3 Likes   #1
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DIY 21 Lim Service

Hi, fellas.
There're several similar threads and posts about what's inside DA 21/3.2, but they are a bit unclear here and there and contain some errors. So I think it is worth to come up with mine. The background: I've finally come to a conclusion that I'm the 35mm-normal photographer (as you all know there're photographers who consider 50mm effective focal length to be the normal one and there're photographers, whose normal is around 35mm) and since Sigma isn't going to bring the 24/1.4 in the K-mount to the market, I've got no other choice, but to buy the DA 21 Limited. An order placed and in a week and a half later used - but as new! - lens is picked up.

I already own a copy of DA 15 Limited (bought brand new) and I do know what a Pentax Limited is about: https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/145797-da15...-infinity.html
I had to open it and grease it and to optically adjust it before it started to feel, look and perform like something worth the Limited badge. And since the DA 21 is well known for coming apart - SUDDENLY! - there was no question if I should service it or not, but rather if I should have it done today or yesterday. So, if yours is going past infinity or can't reach the infinity focus or wobbles like a junk in the pond or you just got a brand new copy and are afraid whether it is going to break in half or not - read on!

N.B.: from my experience of reading people dissecting lenses, many of them are mechanically impaired so I decided to explain almost every step in detail. If you know the stuff well and don't need the basics, then you'll learn all you need from the pictures.

1. Here're the essential tools required:
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Clockwise:
- a container to clean the screws;
- a thread-lock compound;
- a thread-lock remover (I prefer the acetone, but it stinks and you can easily damage the lens coatings, be careful);
- a tube of proper grease (main feature: must not vaporize giving you haze on the lens);
- precision screwdriver-set;
- a cotton-bud;
- a toothstick;
- tweezers;
- a clean A4 sheet of paper, A3 preferred.

2. Do not do anything on the rear-end. DA Limiteds are designed to be opened from the front. For a start you've got to remove the center decorative ring (or beauty ring as some say). See the next two photos on where to apply your 1.5mm flathead screwdriver and what to expect:
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3. Using a proper-sized screwdriver (Number 0 if you speak metric or JPS #something if you're from the XIX century) undo those three screws and remove the front plate assy. Beware, whenever you use too big or too small screwdriver, you will damage the screw head. See the 11- and 3-o'clock screws on the photo above (I started with a Number 00 screwdriver but changed it to the proper one right when I felt that it gonna eat those screwheads).

4. Ok, here's the main assy:
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The four center screws hold the optical unit while the three screws around hold the focus ring to the focus base-plate. Those three are the screws which all the oh-my-da21lim-just-fell-apart people are for.

Note lots of the thread-lock compound on the screwheads and around: THIS IS BAD, DO NOT DO THIS. Thread-lock should be applied to the screw's thread, not poured onto the screwhead! Get yourself some good automotive repair manual (better from '80s, the golden era) - I strongly recommend manuals from Robert Bentley Publishers - and learn how to deal the a threadlock.

5. If you lens assy is wobbling and feels like crap, read on. Otherwise, skip to #6.
You need to remove the four center screws. Rotate the focus ring into the infinite focus position. Using the cotton-bud apply the thread-lock remover onto the screwheads. Rub the cotton-bud on each screwhead until it's clean and your screwdriver firmly seats in it. Undo the screws. Remove the lens assy - but be careful no to lose the tilt-adjustment shims:
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Make a note on what opening each shim was applied to.

Put the screws into the can and pour the thread-remover so it covers the screws. Get the can closed (what a smell, ya?) and keep rubbing the cotton-bud wetted with the threadlock remover on the screw seats to remove the threadlock remains if there're any.

Check each and every helical screw and bushing. If a screw can be tightened up, remove it, have the screw's thread cleaned and de-greased, apply the threadlock to the screw's thread and re-seat the screw all the way in. If the lens assembly is still wobbling, then you've got a bad copy and the only way to have it tightened is either to replace the whole assy or to apply a small amount of grease to the roller races/tracks while rotating it clock- and anticlockwise. Be careful not to spoil the grease on the lens. Re-seat the lens assy back onto the focus ring plate (close the aperture diaphragm so aperture lever goes into the slot of the interim lever on the lens rear-end). Mind those tilt-adj shims! Use the toothstick to center the shims against each opening (or on each hole as uneducated people say).

6. If you have a proper infinity focus on your DA 21/3.2 copy and if you trust in the Pentax way of applying the thread-lock, skip this section. Otherwise, remove those three outer screws using the technique from #5 (cotton-but wetted with threadlock remover to be rubbed on the screws and the plate... well, see above). No, you don't need to remove those two screws at 7-o'clock! No, you better do not do that! Clean the screws in the threadlock remover can as per #5 above. Clean the plate from the threadlock remains. If you inf focus setting is spot-on, apply the thread-lock compound on the screw threads and screw the fasteners in firmly. YES, FIRMLY. I came across some posts saying that those three screws should not be screwed in firmly or the focus ring does not rotate - this is false. It is the base-plate which handles the focus and the focus ring must be firmly secured to it.
If your inf focus setting is incorrect, you've got to rotate the focus base-plate to have it adjusted. Yes, it is the one underneath the focus ring which the focus ring is screwed on with those three screws. You don't need to remove the focus ring, just use tweezers or T5 screwdriver thru the focus ring openings to twist the focus base-plate clock- or anticlockwise. In a case you DID remove the focus ring or in a case of curiosity what it looks underneath, here's the fragile thing which your curiosity can damage:
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7. Assembly is the reverse of disassembly as they say.

8. Re-check the AF performance and complete the AF micro-adjustment if necessary.

Good luck with your 21 Limited copy!

Zig


Last edited by Siegfried; 12-01-2015 at 10:32 AM.
11-12-2015, 10:54 AM   #2
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wow this is awesome! I have had no problem with my DA 21mm so far (knock heavily on wood) but this is a tremendous resource to have just in case. Thank you for sharing it!
11-12-2015, 11:07 AM   #3
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Seventysixersfan,
my pleasure.

Just noticed that I forgot to have it mentioned (though it is obvious, but in a world where they say "CAUTION! HOT!!!11one" on the coffee cup it's worth pointing out): be careful with ANY thread-lock remover stuff because it can eat the lens coatings. No, you can't DIY coatings at home. No, I am not responsible for you coatings. Yes, it is easy not to damage your coatings if your hands are firm and steady. Just use a good pinch of common sense:


Zig

Last edited by Siegfried; 12-01-2015 at 10:24 AM.
11-12-2015, 06:28 PM   #4
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You will have fewer problems damaging screw heads if you use JIS (Japan Industrial Standard) cross point screw drivers. The Society of Photo Technologists sells them. You don't have to be a "member". They have an article explaining the difference.

11-12-2015, 10:09 PM   #5
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Pentaxus,
thanks for your input. Probably I was less correct than usual with my JIS remark. I've got to add JIS screwdriver-set into my inventory and try it and compare it with Philips when dealing with lens fasteners.

Thanks,
Zig
11-25-2015, 02:29 PM   #6
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Thanks for this. Considering doing my 21 due to not stopping at infinity, being wobbly etc. A couple of questions:

1. How do you fix the decorative ring back after removing it. I understand it's fixed with adhesive but supergluing it back sounds like a dubious plan.
2. Are there any steps that are of a "calibration" type ie. is it likely that the lens focusses incorrectly in some way due to bits being minutely misaligned. Seems step 6 and rotating the baseplate could be one.
12-01-2015, 10:18 AM   #7
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Dear house,

1) that very front (beauty/decorative) ring is indeed fixed with that very double-sided adhesive tape. This tape can handle several ring removals and re-installations without any noticeable adhesion performance decrease. Moreover, you can leave the ring off if you like the look of the lens without the ring;

2.1) to fix the lens wobbling you better start with tightening the lens assy (barrel) side screws which hold the plastic rollers. Don't apply too much force or you'll crush the plastic. If the wobbling is still there even after you have checked all those rollers, then the only way to get rid of it is to grease the helicoid - see my original post on the greasing tips and hints. It is a good idea to remove the roller screws (not all at once, but a screw by screw) and have them re-installed with a thread-lock after you practice with applying the proper torque when tightening those screws;
2.2) I don't fully understand your question re bits being minutely misaligned. Anyway, here's the infinity setting guide:
- having your DSLR on the tripod and set into the manual focus mode mount the lens dialed to infinity setting;
- take a picture, remove the SD card and download the photo onto PC (laptop, whatever);
- re-install the SD card, halfway undo those three screws which clasp the focus ring to the focus base-plate, and using a toothstick or such (e.g. an awl, a spoke, tweezers, a T5 screwdriver mentioned on the original post and so forth) rotate the baseplate two hole clockwise (or anti-clockwise), reposition and tighten the three screws to firmly mount the focus ring onto the focus base-plate;
- double-check your lens to be set to infinity, take a photo having DSLR in MF mode, remove the SD card and download the photo onto PC;
- compare the last photo with the previous ones zoomed to 100% resolution, repeat the steps above until you've got a perfect contrast/resolution;
- remove the three screws and have them re-installed using a thread-lock compound.
USB-tethering (lurk for PK Tether software) can be handy, though optional if you're ok with jogging with SD card.
After you have your infinity focus lens setting adjusted, check and complete the DSLR AF micro-adjustment.

Good luck,
Zig

Last edited by Siegfried; 12-01-2015 at 10:34 AM.
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