I have been recently testing many of the lenses that I own and have noticed that some of the Auto Pentax Lenses such as the DA 18-55mm or DA 55-300mm or FA 50mm f`1.4 have variations in the color balance as the aperture is closed
. I don't know how it can happen but it has been consistent. The manual prime pentax lenses that I have don't display such behavior.
I have two Tamron lenses 28-75mm f2.8 and 17-50mm f2.8 that also have a different white balance overall (warmer colors), however, it doesn't change with changing the aperture.
Can someone please explain how this is so and if it is normal.