Tamron 17-50mm f2.8 - between a rock and a hard place

I have used a Tamron 17-50mm f2.8 with a K30 without issue for about a year, but only after having the Tamron lens recalibrated, under warranty, by Intro2020 so that it would focus properly on the K30. This involved a change in the firmware board, as firmware updates cannot be uploaded to the lens for the Pentax version. I have just bought a K70 and the Tamron now front focusses substantially. At f/2.8, it still does, even with the AF fine adjustment set at -10, though it is obviously better than if it is set at zero.

There is a possibility that the Tamron could be recalibrated to focus properly with the K70, but there is a real possibility that it would no longer focus accurately on the K30 which I had intended to keep as a spare. I have a number of possible solutions for this ........

* Have the Tamron lens recalibrated again for the K70, but risk it becoming unusable on the K30
* Buy a new normal zoom for the K70, such as the Pentax 16-85mm f/3.5-5.6
* Losing the K70 could be a solution too, but I would be reluctant to do that.

Do any of you have any sudden bursts of inspiration that might offer me a simple solution to this? Has anyone used both a Tamron 17-50mm and a Pentax 16-85mm om the same camera? Has anyone got any thoughts about how good the (much slower) Pentax lens would be on a K70?

Andrew

I use a Sigma 17-50 f2.8 on the k5lls without a problem. Could you part-ex your Tamron for a lens to use on both your bodies

I've a feeling that the fine adjustment system only really works properly with actual Pentax lenses unless the exif acurately recognises the lens. Often non Pentax lenses just show as something like 'Sigma or Tamron lens' which can cover multiple versions or describes the wrong lens completely. So is the lens properly recognised for what it is in the exif?

I have that problem. My Sigma 17-70 always shows up as Tamron or Sigma.

Possibly, but I doubt that I would be offered much for it. In any case, buying another lens to use on the K30 could be opening just a different can of worms. Why do that when the Tamrom works so well on it. I s'pose that one option could be to buy a second Tamron and have that calibrated to match the K70.

Ponder .........

Andrew

On reading DNGs into Lightroom, it does recognise the Tamron correctly from the EXIF.

ANdrew

This page on RiceHigh's blog may explain some of the anomalies of fine focussing.
The comments suggest that Pentax only support Pentax lenses with an identifiable lens ID for the Pentax F series AF lenses or later and do not test Pentax cameras with 3rd parties lenses.

Also of note is that the focus point can shift in low light and with wide aperture ( >f2.8 ) lenses.

Just pulled the trigger on a Pentax 16-85mm for the K70 - so problem solved (hopefully).

Andrew

Great lens - now my preferred zoom for normal APS-C work.

Just regarding the focus adjustments again, the focus point for a zoom can vary slightly over its range, so get it right at one end and it will be out at the other. I've had no issues with my 16-85 (so far!)