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09-06-2017, 06:41 PM   #1
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Inaccurate autofocusing with HD PENTAX-D FA* 1 : 2.8 70-200mm lens on Pentax K1

Hi All, I have just upgraded to a K1 and 24-70 F2.8 plus 70-200 F 2.8. The 24-70 is 100% accurate every time but the 70-200 is very hit and miss. I use a tripod all the time and set my composition and focus in a fixed position all the time. I have tried all the focusing modes to no avail. I normally use spot focus then turn the camera to manual focus mode, mount on my tripod and fire with a cable release. The viewfinder confirms focus is correct but more often than not the result is out of focus. I have tried multiple times focusing on the same spot and most of the attempts are out of focus and then one will be absolutely pin sharp. Its driving me crazy, any help gratefully received !

09-06-2017, 06:51 PM   #2
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Any reason you're not using live view AF for such a use case? It's going to be more accurate regardless of your VF settings.

I'd also test the lens for front/back focus through the viewfinder:

Fixing Front and Back Focus - Introduction - In-Depth Articles

Lastly, keep in mind that the 70-200mm is big, heavy, and long, so the combination of weight plus shallower depth of field may be another factor (if you continue getting the same results with live view AF). Don't be afraid to post some samples illustrating the problem

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09-06-2017, 08:21 PM   #3
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I second Adam's comment that the AF needs to be tested properly and adjusted with the AF-FA menu if needed. This should be done for each individual lens you own.

I also concur that LV , zoomed 100% will give the most accurate focus.

Finally, you may be experiencing shutter shock rather than mis-focussing. What shutter speed are you using ? 1/30-1/200 range can be problematic. If this is the case use LV with ES to remove shutter shock.
09-07-2017, 12:32 AM   #4
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QuoteOriginally posted by pschlute Quote
Finally, you may be experiencing shutter shock rather than mis-focussing. What shutter speed are you using ? 1/30-1/200 range can be problematic. If this is the case use LV with ES to remove shutter shock.
I have experienced essentially no shutter shock with the DFA* 70-200, because of its weight I think. The much lighter DFA 28-105 does suffer from it though.

09-07-2017, 12:44 AM   #5
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QuoteOriginally posted by Paul the Sunman Quote
I have experienced essentially no shutter shock with the DFA* 70-200, because of its weight I think. The much lighter DFA 28-105 does suffer from it though.
Interesting. On a tripod with my K1 any long lens (DA* 60-250; DA* 300) exhibits shutter shock in the 30-200 range, but not noticeable at all with the D-FA 24-70.
09-07-2017, 01:14 AM   #6
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QuoteOriginally posted by pschlute Quote
Interesting. On a tripod with my K1 any long lens (DA* 60-250; DA* 300) exhibits shutter shock in the 30-200 range, but not noticeable at all with the D-FA 24-70.
DFA* 70-200: Sharp as a tack, hand held, 1/60 - 1/200.
09-07-2017, 02:17 AM   #7
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First, I don't think that a cable release automatically turns SR off - have you turned it off?
Second, I prefer to use back button AF, which disables the shutter release AF which you you probably also get with a cable release. I know you said you turned to manual AF, but this is another operation, and another possible source of error, so better maybe use back AF and leave the camera in AF

Then - relating to shutter shock (above) - use the 2sec timer where possible
09-07-2017, 02:42 AM - 1 Like   #8
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QuoteOriginally posted by ffking Quote
Then - relating to shutter shock (above) - use the 2sec timer where possible
It's shutter shock, not mirror shock. The timer doesn't help.

09-07-2017, 02:57 AM   #9
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QuoteOriginally posted by Paul the Sunman Quote
It's shutter shock, not mirror shock. The timer doesn't help.
never do an edit with a sudden thought

So - using the 2 sec timer might help reduce mirror shock, which might also be an issue
09-07-2017, 03:07 AM   #10
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I sometimes wonder about these postings describing a problem with this or that. 1 member post, no other activity. Yet another google hit about a supposed problem with some Pentax gear.
09-07-2017, 03:40 AM   #11
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QuoteOriginally posted by Paul the Sunman Quote
DFA* 70-200: Sharp as a tack, hand held, 1/60 - 1/200
I dont see shutter shock with any lens handheld. The combination of damping action of the hands and the SR feature eliminate it it...at least for me.

I was refering to tripod use only

---------- Post added 09-07-2017 at 11:48 AM ----------

QuoteOriginally posted by ffking Quote
never do an edit with a sudden thought

So - using the 2 sec timer might help reduce mirror shock, which might also be an issue
From extensive testing with longer lenses my experience is that the shock in the 1/30-1/200 range, on a tripod, with a long lens, is caused almost exclusively by the shutter. Mirror up does not help.

What does eliminate it is to use LV with ES.
09-07-2017, 09:09 PM   #12
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QuoteOriginally posted by pschlute Quote
I dont see shutter shock with any lens handheld. The combination of damping action of the hands and the SR feature eliminate it it...at least for me.

I was refering to tripod use only

---------- Post added 09-07-2017 at 11:48 AM ----------



From extensive testing with longer lenses my experience is that the shock in the 1/30-1/200 range, on a tripod, with a long lens, is caused almost exclusively by the shutter. Mirror up does not help.

What does eliminate it is to use LV with ES.
ES should be developed further... Very nice feature.
11-13-2017, 03:35 AM   #13
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Hi guys, I am now using LV spot focusing and the lens is 100% accurate every time, Happy Days !
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