Hi David,
I use a 30x wide angle eyepiece 95% of the time. I have a 25/75 zoom but prefer the field of view and brightness from the 30x. When zooming in with the 25/75 the field of view shrinks and darkens quite a bit. Most of my birding was moorland stuff before moving to the coast and the extra field of view was very useful when scanning around for distant birds.
Cheers.
Ok, that explains your feeling at 70x...
As you increase magnification the depth of field decrease proportionally. If you add very big distances, the limitations increase since atmospheric conditions become even more limiting.
I use frequently >120x to read nasal saddles codes at >220m until +350m - I even read flamingo colour rings at 500m but only on optimal atmospheric conditions - and I don't expect to get the same image quality as at 100m...
At 70x what you see at 300m is less, and specially with less image quality, than what you see at 35x at 150m...
During the summer, during the hotter hours, usually there is no gain on using high mags - that's the reason why I do my cr-birding during the early hours or late on the day!
There are no miracles but for birding at great distances you would gain using a X95 with the 1,7x extender - just don't expect the same image quality as at 30x at 100m...3

And yes, high mags at close distances, specially using binoviewers or >80º AFOV single eps, is another dimension or birding!...:king:
High mags with 70º AFOV, as with the Harpia or Swaro X95 is close but not the same...3
