Pentax K-7 + Tamron 18-250 Problem

StealthNet · 01-06-2010, 03:00 PM

Greetings,

I recently bought a Pentax K-7, a Tamron 18-250 and grip. My idea was to replace my old K10D, used with the default Pentax 18-55 and a Sigma 28-200 (that came from my old MZ-7 days). As soon as the K-7 arrived, I sold the k10d.

To be honest, pics are ok, and I think that overall IQ is nice for the price range and for the fact that this glass covers from 18 to 250mm.

But I´m having a strange and annoying problem: autofocus. If I let it autofocus, no matter if I´m in low light or sunlight, stopped down or not, 18mm images are always blurry and out of focus. It gets gradually better up to 65 to 70mm, where the problem seems to disappear.

Not that the glass isn´t sharp if I manually focus it, the problem is AF: it always "thinks" that the subject is closer than it actually is, while in th 18mm to 65 / 70mm range. Tried spot focusing, stopping down etc. Tried a tripod. Same results. Turning SR off improved results just a bit, tho.

I also tried fine tuning AF from the K-7 menus: tried up to +10 and -10. No deal.
Fact is, if I autofocus, it is clear, just by using the distance guide printed in the lens body, that something is wrong.

I was wondering if anyone came across the same behavior. I´m about to return the tamron and get a Sigma 18-250. I don´t have a Pentax body around to make more tests but I don´t know for sure if the problem is with the glass or body.

Any ideas, thoughts, suggestions ?

opiedog · 01-06-2010, 08:00 PM

did you upgrade to the latest firmware?

give that a shot first.

StealthNet · 01-06-2010, 08:18 PM

Unfortunately, yes (1.02).

Alfisti · 01-06-2010, 08:23 PM

You're screwed, you have a zoom that is AFing differently at differnet focal lengths.

Worst case scenario I am afraid.

Danny Delcambre · 01-06-2010, 08:25 PM

Huh I thought 1.01

Danny Delcambre · 01-06-2010, 08:26 PM

Huh I thought 1.01. For what 1.02??

StealthNet · 01-06-2010, 08:34 PM

Alfisti: it seems to be the case. I think I´ll get a Sigma with the new glasses planned (a 10-20 and a 31 prime).

Danny Delcambre: Software Downloads : Support & Service : PENTAX

Thanks for the opinions... !

Marc Sabatella · 01-08-2010, 01:02 AM

Can you post samples with EXIF?

netuser · 04-13-2010, 04:22 AM

There is a new firmware for k7

Class A · 04-13-2010, 05:22 AM

Originally posted by StealthNet

I´m about to return the tamron and get a Sigma 18-250.

It seems like you got a defect copy and should have it replaced. Why do you want to change brands at the same time?

It is the first time I read someone describing such behaviour for a lens. The Tamron 18-250 should not do that. I've got that lens and AF works fine at all focal lengths.

bymy141 · 04-13-2010, 11:39 AM

What you can do is correct the AF of your K-7 for this lens at 18mm.
Have a look at http://focustestchart.com/focus21.pdf and your K-7 manual for finding the correct option in the menu and then see what the effects are at the long end of the lens.

- Bert

01-06-2010, 03:00 PM	#1
StealthNet New Member Join Date: Nov 2009 Posts: 4	Pentax K-7 + Tamron 18-250 Problem Greetings, I recently bought a Pentax K-7, a Tamron 18-250 and grip. My idea was to replace my old K10D, used with the default Pentax 18-55 and a Sigma 28-200 (that came from my old MZ-7 days). As soon as the K-7 arrived, I sold the k10d. To be honest, pics are ok, and I think that overall IQ is nice for the price range and for the fact that this glass covers from 18 to 250mm. But I´m having a strange and annoying problem: autofocus. If I let it autofocus, no matter if I´m in low light or sunlight, stopped down or not, 18mm images are always blurry and out of focus. It gets gradually better up to 65 to 70mm, where the problem seems to disappear. Not that the glass isn´t sharp if I manually focus it, the problem is AF: it always "thinks" that the subject is closer than it actually is, while in th 18mm to 65 / 70mm range. Tried spot focusing, stopping down etc. Tried a tripod. Same results. Turning SR off improved results just a bit, tho. I also tried fine tuning AF from the K-7 menus: tried up to +10 and -10. No deal. Fact is, if I autofocus, it is clear, just by using the distance guide printed in the lens body, that something is wrong. I was wondering if anyone came across the same behavior. I´m about to return the tamron and get a Sigma 18-250. I don´t have a Pentax body around to make more tests but I don´t know for sure if the problem is with the glass or body. Any ideas, thoughts, suggestions ?

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Sigma 18-250 or Pentax/Tamron 18-250?	mjbens01	Pentax SLR Lens Discussion	3	07-08-2010 09:10 PM
Pentax 18-250 always same as Tamron 18-250?	kitkat	Pentax SLR Lens Discussion	12	07-08-2010 08:30 AM
creep problem with pentax 18-250	dstar	Pentax SLR Lens Discussion	1	06-25-2010 01:17 PM
Pentax Problem with Flash and lens 18-250	spmarion	Pentax DSLR Discussion	3	03-22-2008 04:55 AM
New Pentax SMC 18-250 problem	mito	Pentax SLR Lens Discussion	13	01-22-2008 12:41 AM

01-06-2010, 08:00 PM	#2
opiedog Inactive Account Join Date: Jan 2008 Location: NC Posts: 787	did you upgrade to the latest firmware? give that a shot first.

01-06-2010, 08:18 PM	#3
StealthNet New Member Join Date: Nov 2009 Posts: 4 Original Poster	Unfortunately, yes (1.02).

01-06-2010, 08:23 PM	#4
Alfisti Veteran Member Join Date: Mar 2007 Location: Toronto (for now) Posts: 1,748	You're screwed, you have a zoom that is AFing differently at differnet focal lengths. Worst case scenario I am afraid.

01-06-2010, 08:25 PM	#5
Danny Delcambre Veteran Member Join Date: Oct 2008 Photos: Gallery \| Albums Posts: 550	Huh I thought 1.01

01-06-2010, 08:26 PM	#6
Danny Delcambre Veteran Member Join Date: Oct 2008 Photos: Gallery \| Albums Posts: 550	Huh I thought 1.01. For what 1.02??

01-06-2010, 08:34 PM	#7
StealthNet New Member Join Date: Nov 2009 Posts: 4 Original Poster	Alfisti: it seems to be the case. I think I´ll get a Sigma with the new glasses planned (a 10-20 and a 31 prime). Danny Delcambre: Software Downloads : Support & Service : PENTAX Thanks for the opinions... !

01-08-2010, 01:02 AM	#8
Marc Sabatella Veteran Member Join Date: Sep 2006 Location: Denver, CO Photos: Gallery Posts: 10,685	Can you post samples with EXIF?

04-13-2010, 04:22 AM	#9
netuser Veteran Member Join Date: Oct 2008 Location: Azores Islands, Portugal Photos: Gallery Posts: 2,236	There is a new firmware for k7

04-13-2010, 05:22 AM	#10
Class A Pentaxian Join Date: Aug 2008 Location: Wellington, New Zealand Posts: 11,251	Originally posted by StealthNet I´m about to return the tamron and get a Sigma 18-250. It seems like you got a defect copy and should have it replaced. Why do you want to change brands at the same time? It is the first time I read someone describing such behaviour for a lens. The Tamron 18-250 should not do that. I've got that lens and AF works fine at all focal lengths.

04-13-2010, 11:39 AM	#11
bymy141 Veteran Member Join Date: Aug 2007 Photos: Gallery Posts: 1,563	What you can do is correct the AF of your K-7 for this lens at 18mm. Have a look at http://focustestchart.com/focus21.pdf and your K-7 manual for finding the correct option in the menu and then see what the effects are at the long end of the lens. - Bert