DA* 60-250mm f/4 on Z-1p

Images

Some of the "Wall" images didn't use a tripod, and all used a lenshood (because I forgot that the lenshood may contribute to vignetting because of the wider field of view). The "Target" images used a tripod and 2-second delay and no lenshood. No filters were used.

I used aperture priority and autofocus throughout.

Teleconverter Focal length Wall Target  
(None) 60 f/4 f/8 f/4 f/8  
(None) 85 f/4 f/8 f/4    
(None) 135 f/4 f/8 f/4 f/8  
(None) 200 f/4 f/8 f/4    
(None) 250 f/4 f/8 f/4 f/8  
1.4 (Kenko) 84 (60 on lens) f/5.6 (f/4 on camera)            f/5.6 (f/4 on camera) f/11 (f/8 on camera)  
1.4 (Kenko) 119 (85 on lens) f/5.6 (f/4 on camera)   f/5.6 (f/4 on camera)    
1.4 (Kenko) 189 (135 on lens) f/5.6 (f/4 on camera)   f/5.6 (f/4 on camera) f/11 (f/8 on camera)  
1.4 (Kenko) 280 (200 on lens) f/5.6 (f/4 on camera)   f/5.6 (f/4 on camera)    
1.4 (Kenko) 350 (250 on lens) f/5.6 (f/4 on camera)   f/5.6 (f/4 on camera) f/11 (f/8 on camera)  

Discussion

This is my most expensive Pentax lens, and by far my most used lens for all sorts of photography. Whether or not this lens is usable on any future Pentax camera may influence whether I buy that camera, and will certainly influence when I buy it and what I use it for.

This isn't an unqualified FF lens. But neither is it unusable on a 35mm camera. At 60mm on 35mm the corners are soft. At 250mm the corners are darker, but still usable. These improve on stopping down. In other words, similar to (although perhaps worse than) a typical kit lens used on an APS-C sensor. Perhaps that is a way to think about it - an expensive kit lens (unless you already own it, as I do) for an FF camera!

It appears that this is likely to be a useful lens on an FF camera when used with a 1.4 teleconverter. I am already looking forward to using it on an APS-C sensor as an 84-350mm f/5.6 lens if/when Pentax supply a 1.4x teleconverter. And I think it might be good as an FF lens in that combination.