The cropped lens I'd like to see tested on K1...

User Error wrote:

JNR wrote:

User Error wrote:

The image circle is actually so small that this lens is the perfect example for a combination where the x1.4 TC is not enough to reenlarge a x1.5 crop factor. Even using the DA TC this lens does not cover FF.

You're working on an assumption that the teleconverter magnification is directly related to expanding the image circle - when in fact there is not a direct cause and effect. The elements within the TC bend the image light rays to determine the magnification, while the diameter of the optics is a big part of the key to defining image circle. Looking at it another way, the Pentax DA TC essentially does not take in the full width of a DA image on the front end, and thereby does not expand the circle provided by the lens by 1.4x on the back end.

Pentax has been quite clear that a great many lenses will not widen the image circle to FF because the DA TC was not designed to cover the FF image circle.

#1

Yes there is a direct relationship. "crop" means cutting away. TCs do simply magnify the image by the given factor. That is how they work and have to work.

#2

The DA x1,4 TC does not show hard vignetting on a DA* 300/4 on FF.

The DA x1,4 TC does not show hard vignetting on a A50/1,2 on FF

The DA x1,4 TC does widen the image circle of a 8-16mm at 8mm to cover full FF (ghastly image quality outside center though).

It only shows vignetting where the image circle on APSC is already at the limit, like DA 16-85.

That is all I need to know.

You may have you theory-based opinion, but I rather go for experience.

Except that what I have stated, you are verifying with what you have stated in your observations (experience) such as regarding the DA 16-85. The differences between the 8-16 and the 16-85 are related to the distance from lens rear element and the front of the TC and how the light is projected; each situation is different. All of which proves that the magnification of the TC is only one element in determining the final image circle result.

It also would be good to consider what Pentax has indicated about compatibility. While you and others have contrary hopes, we'll just have to see who is right. My opinion on this one also goes toward the Pentax findings.