Originally posted by Kunzite Ouch. Another "equivalence" victim.
There is no "focal range in 35mm terms".
You don't change a lens' focal length/range by putting it on a camera or another. You don't make a lens' focal length disappear by removing it from a camera.
You don't change a lens' focal length/range by removing a baffle. You simply remove a restriction, in effect reducing the vignetting presumably well enough in this case to successfully use the 60-250 without crop, on the K-1.
If you're asking about the field of view, it will be unchanged after this operation.
I do realize that the optical or real focal length of a lens does not change when putting it on a different camera or when removing a baffle. However, as you obviously realize, a lens of a given focal length will not produce the same field of view when cast onto a different sized sensor, and the field of view is
frequently or even
typically expressed in terms of a proxy: in terms of a focal length on a FF sensor - hence "in 35mm terms". So an *optically* 18mm lens on an APS-C sensor camera will give a field of view roughly equivalent to an *optically* 28mm lens on a FF sensor, and so on. This is what I take to be meant and understood by saying something like "an 18mm lens on an APS-C camera is [equivalent to] a 28mm lens in FF/35mm terms". If interpreted pedantically, this would be incorrect, but, as with language generally, I take it that what really matters is whether we understand each other. So long as others understand this way of talking, there is no problem. What we care about and communicate concerns the field of view, but we communicate in terms of the focal lengths of lenses with a FF sensor. C'est la vie.
In any case, I'm not asking whether the field of view changes after the operation. I fully understand that all that the modification does is remove the vignetting that would be seen with a FF sensor. This, however, presumably increases the *usable* field of view - which is what I and I'm guessing most people really care about. What I am asking concerns whether the lens gives a *usable* field of view with a FF sensor that is greater than the *usable* field with an APS-C sensor. I ask this in part because B&H says of this lens "equivalent to an 90-375mm f/4.0 lens upon 35mm SLR cameras".