In the last image you can see the problem with the Tamron 90 SP BBAR lens , ( Sensor Refection )
I was able to minimise it with the use of a 36mm Macro tube , unfortunately it rears its ugly blue dot every now and again spoiling what could have been a nice photo ...

I think this lens needs to be relegated to curiosity , rather than a serious working tool ...
I will try it on the K20D and see what happens ...

Sharing Pictures !
Not fishing for answer's

[bobpur]

Get a 1.4 tele adapter and problem gone, no blue dot and no image loss.

[old4570]

Get a 1.4 tele adapter and problem gone, no blue dot and no image loss.

Did try a 2x Tele macro converter and still there ...

On the k20D its almost gone , but it was late in the afternoon and the bees were not there any more ...
+ It needs a little effort to set up .. ( The settings )

SP 90 BBAR + 36mm Macro tube ( On K20D ) , you can hardly tell .. Im going to try the Ricoh 2x Tele Macro adapter and see what happens ..
I have a Tamron 2x Macro adapter for the BBAR , that was showing ...
I have a few others to try ..

[bobpur]

The problem happens with any lens that has a flat rear element, it acts like a mirror and you get a reflection of the
sensor that's why it is a purple color. Have a look at the sensor, same color.
Happens more stopped down or strong lighting ( Flash ).
The tele adapters have a slightly curved element so it helps
My reveunon 55 1.4 has the same problem if I go lower than f5.6 at times. The Tam 90mm is an excellent lens
you just have to work around the limitations, or spend $1000.!