Just a quick note to say how fine a lens the Hasselblad XCD 135mm f/2.8 lens is on the Hasselblad X2D Mark II. Yes, it very heavy, very bulky, and expensive too, yet it produces IMO incredible photos.
Here is the original and an enlargement of a photo of a female Bullfrog in one of the endless marshes of northern Michigan where I live. It also comes with a 1.7x teleconverter that is as fine an add-on as I know but still takes its little piece of IQ and light, so I seldom use it. I had and sold this lens but lived to regret it and saved and bought it back.
With the XD 135 lens, I can’t see much difference (or enough to worry about) between the lens with and without the 1.7x TC. I am certain there is a difference, just not one that makes a difference. Oh yes, I will shoot without the TC most of the time, when I can. Yet, if I need a little extra closeness, I am confident that the TC does not sacrifice much of the image quality.
However, it does make the whole operation more clumsy to have the TC and the mount ring. If I can get away with handhold that is better, but without a tripod I have to go to AUTO ISO or auto something to compensate for my own shakiness and that does cost me image quality.
Here is another photo WITH the 1.7TC and I don't see much loss in quality.
With TC's (in general), the degradation comes from them "spreading the light" (to achieve the magnification).
As the angular (trig) dispersion moves farther from the central axis, the "spread" becomes greater. Hence, when the subject / focal plane is on / closer to central axis (Zone A) ... it retains the least amount of degradation from the TC ... Zones B / C progressively more so.
