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Forum: Pentax SLR Lens Discussion 11-13-2010, 06:40 AM  
Problems about DA 21mm focusing at infinity
Posted By LihongHao
Replies: 27
Views: 11,919
Wo, I am too anxious to check if the adjustment works, as the marks on the focusing ring does not mean too much for me, so I adjust a little more.
I have no split image focusing screen, and to shoot the moon I must get out of my room, it was too dark there to do some adjust.

I think, after loosen the screws, turn the focusing ring to infinite, then hold the focusing ring, then use the AF to focus on a distant thing, then tighten the screws, that should be a easy and effective way.

Thank you again.

These two photos show the focusing now work well, although the maks on focusing ring doesn't match.



the 100% crop of another.
Forum: Pentax SLR Lens Discussion 11-12-2010, 09:14 AM  
Problems about DA 21mm focusing at infinity
Posted By LihongHao
Replies: 27
Views: 11,919
Wlachan, you are very right, that's what I just found.



As show in this sketch, the blue part is the AF driver, and the purple one is the focusing ring with distance marks, they are fixed together by the black screws.
To adjust the distance marks, the screws holes on the focusing ring is made as pierced arc, so when the screws loosen, the two part will move a little bit and then can't focusing infinite.
But why infinite? I guess when the AF driver push the lens move toward infinite, there will be a sudden stop when the focusing ring hit the stop block, again and agin, the lens may be rush a little over the infinite, but the focusing ring can't go over the block, then problem come.

And, there are some photo I took when disassembling it.

This is the lens before disassembling.

Front cover Removed, they are sticked there by double side adhesive tape. The three screws there is used to fix the lens cover.


remove all the cover, then showed the three screws fixed the focusing ring, and the arc.
Its not necessary to withdraw the screw to adjust , loosen them is enough


the two part are connected only by the three screws, as they together turn and stop so often, I think loosen is inescapable.


the AF driver part.


After adjusting, I go out to find a distant thing, in midnight, moon is best.
with aperture wide open, 100% crop.
well, it seems all right, the only problem is that even moon is not at infinite marks, it's between the 1.3 and infinite. I have adjusted too much, but there will be no 'ka' noise and collision of focusing ring and the block any more.
I will test the lens more tomorrow.


Thank you all.
Forum: Pentax SLR Lens Discussion 11-11-2010, 06:49 PM  
Problems about DA 21mm focusing at infinity
Posted By LihongHao
Replies: 27
Views: 11,919
Thank you very much for your advice.
Maybe my unskilled English make you feel bad, sorry.

This lens is out of warranty, sent it to a pro will cost me a lot, although much cheaper than make it broken.
The guy fixed his said it's easy and safe (maybe for a pro), so I want to have a try.
I will never think about disassemble a zoom lens, but a prime lens will be easier, worth a try, I think.
Forum: Pentax SLR Lens Discussion 11-11-2010, 08:45 AM  
Problems about DA 21mm focusing at infinity
Posted By LihongHao
Replies: 27
Views: 11,919
I think the autofocus adjustment is used to adjust focusing errors, in my situation, the autofocus is good, but the lens can't reach the suitable point.
point.
Forum: Pentax SLR Lens Discussion 11-11-2010, 08:41 AM  
Problems about DA 21mm focusing at infinity
Posted By LihongHao
Replies: 27
Views: 11,919
Thank you
I have used this lens for three years, and I am sure I did not hold the focusing ring and there is something wrong.
Envn I set the focusing mode to MF, and screw the ring to infinity mark, there is no 'beep' and the shutter not released. For things not so far away, everything is OK, so I can still use it for some 'street shoot'.
Forum: Pentax SLR Lens Discussion 11-11-2010, 07:23 AM  
Problems about DA 21mm focusing at infinity
Posted By LihongHao
Replies: 27
Views: 11,919
光辉岁月四十年(内容已改为 DA21修复记) - 无忌论坛
This is the page I found, it's in Chinese, but the picture there can show something. This guy got a DA21 which has the same problem as mine, and he fixed it by disassembly and adjust. I want to do the same thing, and have removed the cover of the lens, but the three screw there is so small that I have not got the compatible screwdriver. I will buy a smaller one (1.5mm cross patten) and carry on tomorrow.
Forum: Travel, Events, and Groups 11-11-2010, 12:20 AM  
Any Pentaxians in Shanghai?
Posted By LihongHao
Replies: 3
Views: 2,155
I am in shanghai, just registered and can't send message yet.
Maybe we can go out for some shoot together.
Forum: Pentax SLR Lens Discussion 11-10-2010, 08:37 PM  
Problems about DA 21mm focusing at infinity
Posted By LihongHao
Replies: 27
Views: 11,919
I have a DA 21mm which has been used for 3 years. Recently, it can't focus on the infinity. When I focusing on things 50 meters away or further, the lens stop at the infinity mark, but the AF indication was flickering and the shutter didn’t release. I have search on the Google and someone said the reason is that the lens inside move a bit front as lens sways, it can be fixed by adjusting the locator ring, that's sounded believable,.
Does anyone here have the same problem? How do you solve it?
Thank you.
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