K-x and Tamron 28-75 issue?

K57XR · 07-01-2011, 09:26 AM

I recently tested a Tamron 28-75 f2.8. When I mount it on the K-x (firmware: 1.01) and gave it whirl, I immediately noticed a few issues.

1) I couldn’t get an accurate AF wide open at f2.8. It is coming completely OOF. Manual focusing seems to be ok and actually produced good results.

2) The exif data only shows two focal lengths. Shots from 28mm up to ~45mm the exif shows 35mm throughout. From ~50mm to 75mm exif shows 55mm all the way.

3) Exposure at f2.8 seem to be darker than f3.5-f4 ….same exact setting and shooting conditions.

4) May not be an issue but worth mentioning, RAW file isn’t showing the lens model…..I honestly do not know if it should or not but I was under the impression it did for this lens.

I did about 30 or so test shots; indoors/outdoors, low light, daylight, etc. and got the same results.

Has anyone with a K-x (fw 1.01) had an issue with Tamron 28-75 f2.8, perhaps compatibility issue? Or is lens repair in order?

Cheers!

K57XR · 07-01-2011, 11:10 AM

I just realized I should've put this in the troubleshooting forum...

Ole · 07-01-2011, 12:21 PM

Moved!

rawr · 07-03-2011, 05:12 PM

Sounds like a lens contact issue (solution: clean the contacts on camera and lens).

I have the Tamron 17-50 and it reports itself OK in the EXIF under the Maker Notes and the general EXIF sections, so I expect the 28-75 would too.

Metering is also always a bit under-exposed on my 17-55 but note that (theoretically) Pentax bodies like the K-x do not support full Matrix AE metering on non-Pentax brand lenses, and default to Center weighed average metering mode when third-party lenses are used. That may explain some of your metering issues, and it is certainly something to be aware of as it can make a real difference for a lot of scenes that matrix AE can handle well but center weighed averaging may not.

Note that the reporting of EXIF data values will sometimes depend on what EXIF reader you use, how up to date it is, how intelligently it can decode the EXIF codes etc.

K57XR · 07-04-2011, 06:52 AM

Originally posted by rawr

Sounds like a lens contact issue (solution: clean the contacts on camera and lens).

I returned the lens back to the owner but I believe he did try to clean the contacts and still had the same incorrect focal length issue on his K100D. I suspect there maybe something else going on.

Originally posted by rawr

Metering is also always a bit under-exposed on my 17-55 but note that (theoretically) Pentax bodies like the K-x do not support full Matrix AE metering on non-Pentax brand lenses, and default to Center weighed average metering mode when third-party lenses are used.

I actually wasn’t aware of that as all except one of my lenses are Pentax. Although I do shoot Center weighted most of the time

Originally posted by rawr

Note that the reporting of EXIF data values will sometimes depend on what EXIF reader you use, how up to date it is, how intelligently it can decode the EXIF codes etc.

Agreed, the lens info do show up on Photo Me but not on PDCU4.

Thanks for your help, rawr! Cheers!

mysticcowboy · 07-04-2011, 10:48 PM

My Tamron 17-50 focuses perfectly, but the company has a bad reputation for sending too high a percentage of front or back focusing lenses. Though the only off lens I have that's off now now is a Pentax FA 100mm macro, which does back focus a bit. First thing I do with a new lens is test it against a focusing distance chart.

K57XR · 07-05-2011, 11:17 AM

Originally posted by mysticcowboy

My Tamron 17-50 focuses perfectly, but the company has a bad reputation for sending too high a percentage of front or back focusing lenses. Though the only off lens I have that's off now now is a Pentax FA 100mm macro, which does back focus a bit. First thing I do with a new lens is test it against a focusing distance chart.

Thanks for the input. I am still looking at the Tammy 28-75 preferably good used as the new ones are a little outside of budget. Though Tamron is currently having a rebate. Either way, I will surely test rigorously whatever I end up with while still within return policy.

mysticcowboy · 07-05-2011, 09:27 PM

Originally posted by K57XR

Thanks for the input. I am still looking at the Tammy 28-75 preferably good used as the new ones are a little outside of budget. Though Tamron is currently having a rebate. Either way, I will surely test rigorously whatever I end up with while still within return policy.

Good plan.

07-01-2011, 09:26 AM	#1
K57XR Veteran Member Join Date: Feb 2011 Location: Colorado, USA Posts: 830	K-x and Tamron 28-75 issue? I recently tested a Tamron 28-75 f2.8. When I mount it on the K-x (firmware: 1.01) and gave it whirl, I immediately noticed a few issues. 1) I couldn’t get an accurate AF wide open at f2.8. It is coming completely OOF. Manual focusing seems to be ok and actually produced good results. 2) The exif data only shows two focal lengths. Shots from 28mm up to ~45mm the exif shows 35mm throughout. From ~50mm to 75mm exif shows 55mm all the way. 3) Exposure at f2.8 seem to be darker than f3.5-f4 ….same exact setting and shooting conditions. 4) May not be an issue but worth mentioning, RAW file isn’t showing the lens model…..I honestly do not know if it should or not but I was under the impression it did for this lens. I did about 30 or so test shots; indoors/outdoors, low light, daylight, etc. and got the same results. Has anyone with a K-x (fw 1.01) had an issue with Tamron 28-75 f2.8, perhaps compatibility issue? Or is lens repair in order? Cheers!

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07-01-2011, 11:10 AM	#2
K57XR Veteran Member Join Date: Feb 2011 Location: Colorado, USA Posts: 830 Original Poster	I just realized I should've put this in the troubleshooting forum...

07-01-2011, 12:21 PM	#3
Ole Administrator Join Date: Sep 2006 Location: Copenhagen, Denmark Photos: Gallery \| Albums Posts: 4,408	Moved!

07-03-2011, 05:12 PM	#4
rawr Veteran Member Join Date: Jun 2009 Posts: 11,913	Sounds like a lens contact issue (solution: clean the contacts on camera and lens). I have the Tamron 17-50 and it reports itself OK in the EXIF under the Maker Notes and the general EXIF sections, so I expect the 28-75 would too. Metering is also always a bit under-exposed on my 17-55 but note that (theoretically) Pentax bodies like the K-x do not support full Matrix AE metering on non-Pentax brand lenses, and default to Center weighed average metering mode when third-party lenses are used. That may explain some of your metering issues, and it is certainly something to be aware of as it can make a real difference for a lot of scenes that matrix AE can handle well but center weighed averaging may not. Note that the reporting of EXIF data values will sometimes depend on what EXIF reader you use, how up to date it is, how intelligently it can decode the EXIF codes etc.

07-04-2011, 06:52 AM	#5
K57XR Veteran Member Join Date: Feb 2011 Location: Colorado, USA Posts: 830 Original Poster	Originally posted by rawr Sounds like a lens contact issue (solution: clean the contacts on camera and lens). I returned the lens back to the owner but I believe he did try to clean the contacts and still had the same incorrect focal length issue on his K100D. I suspect there maybe something else going on. Originally posted by rawr Metering is also always a bit under-exposed on my 17-55 but note that (theoretically) Pentax bodies like the K-x do not support full Matrix AE metering on non-Pentax brand lenses, and default to Center weighed average metering mode when third-party lenses are used. I actually wasn’t aware of that as all except one of my lenses are Pentax. Although I do shoot Center weighted most of the time Originally posted by rawr Note that the reporting of EXIF data values will sometimes depend on what EXIF reader you use, how up to date it is, how intelligently it can decode the EXIF codes etc. Agreed, the lens info do show up on Photo Me but not on PDCU4. Thanks for your help, rawr! Cheers!

07-04-2011, 10:48 PM	#6
mysticcowboy Veteran Member Join Date: Apr 2009 Location: port townsend, wa Photos: Albums Posts: 968	My Tamron 17-50 focuses perfectly, but the company has a bad reputation for sending too high a percentage of front or back focusing lenses. Though the only off lens I have that's off now now is a Pentax FA 100mm macro, which does back focus a bit. First thing I do with a new lens is test it against a focusing distance chart.

07-05-2011, 11:17 AM	#7
K57XR Veteran Member Join Date: Feb 2011 Location: Colorado, USA Posts: 830 Original Poster	Originally posted by mysticcowboy My Tamron 17-50 focuses perfectly, but the company has a bad reputation for sending too high a percentage of front or back focusing lenses. Though the only off lens I have that's off now now is a Pentax FA 100mm macro, which does back focus a bit. First thing I do with a new lens is test it against a focusing distance chart. Thanks for the input. I am still looking at the Tammy 28-75 preferably good used as the new ones are a little outside of budget. Though Tamron is currently having a rebate. Either way, I will surely test rigorously whatever I end up with while still within return policy.

07-05-2011, 09:27 PM	#8
mysticcowboy Veteran Member Join Date: Apr 2009 Location: port townsend, wa Photos: Albums Posts: 968	Originally posted by K57XR Thanks for the input. I am still looking at the Tammy 28-75 preferably good used as the new ones are a little outside of budget. Though Tamron is currently having a rebate. Either way, I will surely test rigorously whatever I end up with while still within return policy. Good plan.

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