K3 and tamron 70-200

5teve · 07-18-2016, 06:58 PM

Hi Guys

I posted a thread a good while ago about the K3 and my Tamron 70-200 having issues focusing in Live view at distance. I don't use live view much but it effects video too.

the subject is quite badly out of focus and I have done some more investigation into this.

What I have found is that there is about a 1/4 turn backlash on the lens screw drive - when using normal phase detect the hunting seems to cope with this although may explain the slight oof images i get sometimes - when using live view / video the slow contrast detection seems to rack all the way back and then in again and then stop - but always stops out of focus. If i have the lens focus on MF (is engage the MF ring on the lens) and give it a very slight twist - it brings it back in focus properly. I think the very short throw this lens has is causing the issue when combined with the backlash.

Has anyone got a 70-200 they can check with this please - and also check the backlash on the screw thread - i just used a small flat screw driver and observed how much of a turn there was with no resistance.

Thanks in advance

Steve

Adam · 07-18-2016, 07:12 PM

I don't have the 70-200mm any more, but mine worked fine in live view with the K-30. Sounds like a defect to me.

Or it could be an incompatibility with the K-3's more powerful/violent AF motor.

**kiwi_jono** · 07-18-2016, 07:56 PM

My tammy doesn't focus in LV on my K-5 at all. It just never finds focus lock. However with viewfinder and PD it focuses well (relatively quick and accurate) - although it is most accurate 100 - 200mm with slight back focus as 70mm.
I know of at least 2 others that have the same problem with LV - in fact there are few in the user reviews for this lens.

My screw drive has about 1/8 of a turn play in it, so sounds like probably less than yours. Not that it helps mine focus in LV.

Anyway it does stop me using it, as I mostly use the viewfinder and can always use MF if I'm in LV anyway.

5teve · 07-19-2016, 01:06 AM

Thanks Adam and Kiwi

Be interesting to hear from more users - it sounds like the backlash combined with the very fast focus throw of the 70-200 is what causes it. From a bit more testing I am figuring that the following happens

Focus is initiate > Finds focal point but carries on driving focus all the way back > once stop is reached it focused back to its first found point - due to the backlash the point of focus is actually another 1/4 turn of the screw in this direction therefore the focus is out. Manually nudging it with the focus ring on the lens takes up the slack and brings it back into focus.

It looks like either the tamron is not compatible (and as its still being sold probably still isnt), I have excessive wear in the gearbox (there are only 3 gears) or the drive shaft / mechanism or the focus algorithm in the camera is wrong for this lens - its also very slow to focus compared to the one pentax lens i have! - PDAF seems fast and also throws the focus back and forth a lot while getting the focus right - which probably takes up the backlash enough.

If anyone else can chime in with their findings i'd greatly appreciate it. It looks like I may be saving up for some non screw drive lens's which leaves me with Pentax ($$) or second hand sigma - which are hit and miss in the 70-200 range

Steve

Last edited by 5teve; 07-19-2016 at 01:18 AM.

07-18-2016, 06:58 PM	#1
5teve Senior Member Join Date: Mar 2009 Location: Perth - Australia Photos: Albums Posts: 226	K3 and tamron 70-200 Hi Guys I posted a thread a good while ago about the K3 and my Tamron 70-200 having issues focusing in Live view at distance. I don't use live view much but it effects video too. the subject is quite badly out of focus and I have done some more investigation into this. What I have found is that there is about a 1/4 turn backlash on the lens screw drive - when using normal phase detect the hunting seems to cope with this although may explain the slight oof images i get sometimes - when using live view / video the slow contrast detection seems to rack all the way back and then in again and then stop - but always stops out of focus. If i have the lens focus on MF (is engage the MF ring on the lens) and give it a very slight twist - it brings it back in focus properly. I think the very short throw this lens has is causing the issue when combined with the backlash. Has anyone got a 70-200 they can check with this please - and also check the backlash on the screw thread - i just used a small flat screw driver and observed how much of a turn there was with no resistance. Thanks in advance Steve

07-18-2016, 07:12 PM	#2
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,594	I don't have the 70-200mm any more, but mine worked fine in live view with the K-30. Sounds like a defect to me. Or it could be an incompatibility with the K-3's more powerful/violent AF motor. Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

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07-18-2016, 07:56 PM	#3
kiwi_jono Loyal Site Supporter Join Date: Dec 2009 Location: Christchurch, New Zealand Photos: Gallery \| Albums Posts: 2,437	My tammy doesn't focus in LV on my K-5 at all. It just never finds focus lock. However with viewfinder and PD it focuses well (relatively quick and accurate) - although it is most accurate 100 - 200mm with slight back focus as 70mm. I know of at least 2 others that have the same problem with LV - in fact there are few in the user reviews for this lens. My screw drive has about 1/8 of a turn play in it, so sounds like probably less than yours. Not that it helps mine focus in LV. Anyway it does stop me using it, as I mostly use the viewfinder and can always use MF if I'm in LV anyway.

07-19-2016, 01:06 AM	#4
5teve Senior Member Join Date: Mar 2009 Location: Perth - Australia Photos: Albums Posts: 226 Original Poster	Thanks Adam and Kiwi Be interesting to hear from more users - it sounds like the backlash combined with the very fast focus throw of the 70-200 is what causes it. From a bit more testing I am figuring that the following happens Focus is initiate > Finds focal point but carries on driving focus all the way back > once stop is reached it focused back to its first found point - due to the backlash the point of focus is actually another 1/4 turn of the screw in this direction therefore the focus is out. Manually nudging it with the focus ring on the lens takes up the slack and brings it back into focus. It looks like either the tamron is not compatible (and as its still being sold probably still isnt), I have excessive wear in the gearbox (there are only 3 gears) or the drive shaft / mechanism or the focus algorithm in the camera is wrong for this lens - its also very slow to focus compared to the one pentax lens i have! - PDAF seems fast and also throws the focus back and forth a lot while getting the focus right - which probably takes up the backlash enough. If anyone else can chime in with their findings i'd greatly appreciate it. It looks like I may be saving up for some non screw drive lens's which leaves me with Pentax ($$) or second hand sigma - which are hit and miss in the 70-200 range Steve Last edited by 5teve; 07-19-2016 at 01:18 AM.

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