04-26-2012, 10:16 AM
Hi guys,
I have discovered a problem with the Tamron 17-50mm 2.8 which may concern anybody who owns that lens on Pentax mount(or other mount). I have already posted on DPreview and have had responses from others who have found the same problem after having checked. It would be interesting to see whether this affects other mounts.
Although I love this lens,every now and again on portraits the lens has front focused,so after receiving my K5 I was calibrating lenses and I noticed this;
First choose AF continuous and then choose a subject at 1 meter and select F2.8 half press the shutter button to focus and hold the button half pressed,then with the rear wheel select F4,the camera should not refocus,select F5,the camera still doesn't refocus, select F5.6 (always holding the shutter button half down) and suddenly the focus changes to front focus!! This explains why sometimes I have front focus shots at close distances and sometimes not, at less than F5 the focus is correct at F5.6 and above it front focuses more that the AF microadjust.This can be confirmed in Liveview!
I have telephoned Tamron who didn't have a pentax at the time and the guy said that he would have one at beginning of next week and would try it.
So far I have received results from just 6 tests of which 4 have shown the same problem so it's not an isolated case and could explain some of the AF criticisms leveled at this lens. It should be noted that this problem disappears into the depth of field at about 3 meters.
I would be grateful to anybody trying this test (on any mount)as described as this lens is one of the most common lenses sold. I don't know if the staff at PZ have a copy of the lens at the moment ,but it would certainly interesting to hear your findings. The test can be completed in 2 minutes and the results could be very revealing.
Grateful to anybody replying to this post.
Dave's clichés
I have discovered a problem with the Tamron 17-50mm 2.8 which may concern anybody who owns that lens on Pentax mount(or other mount). I have already posted on DPreview and have had responses from others who have found the same problem after having checked. It would be interesting to see whether this affects other mounts.
Although I love this lens,every now and again on portraits the lens has front focused,so after receiving my K5 I was calibrating lenses and I noticed this;
First choose AF continuous and then choose a subject at 1 meter and select F2.8 half press the shutter button to focus and hold the button half pressed,then with the rear wheel select F4,the camera should not refocus,select F5,the camera still doesn't refocus, select F5.6 (always holding the shutter button half down) and suddenly the focus changes to front focus!! This explains why sometimes I have front focus shots at close distances and sometimes not, at less than F5 the focus is correct at F5.6 and above it front focuses more that the AF microadjust.This can be confirmed in Liveview!
I have telephoned Tamron who didn't have a pentax at the time and the guy said that he would have one at beginning of next week and would try it.
So far I have received results from just 6 tests of which 4 have shown the same problem so it's not an isolated case and could explain some of the AF criticisms leveled at this lens. It should be noted that this problem disappears into the depth of field at about 3 meters.
I would be grateful to anybody trying this test (on any mount)as described as this lens is one of the most common lenses sold. I don't know if the staff at PZ have a copy of the lens at the moment ,but it would certainly interesting to hear your findings. The test can be completed in 2 minutes and the results could be very revealing.
Grateful to anybody replying to this post.
Dave's clichés