I have 4 Ais lenses, and the 105/1.8 doesn't feel any more stiffer to focus than what I think is the norm.
by comparison, the 180/2.8 is much stiffer, and the 24/2 is much looser(but this one needs a service as it also squeaks when focused).
It feels similar to the 50/1.2(which is also the Ais model).
My 105 does however feel about 20% more stiff in focusing from infinity to close(ie. in this specific direction!) than it does from focusing from close to infinity.
So there is a problem(which doesn't really feel like a problem, more of a note!)
As for IQ. very nice.
I don't have the 105/2.5 as others do for comparison, but compared to the 105/2.8 VR .. at f2.8 the Ais lens is sharper and more contrasty.
I find f/1.8 acceptable, and it's the kind of lens that many 'elderly' females may describe as 'complementary' rendering.
There's not enough difference at f/2 of any noteworthiness, but at f/2.8 you would see a large enough difference in contrastiness/sharpness.
I use it on a D800E and (occasionally) on the D300, but it should be noted that on both those cameras I have thirdparty focusing screens fitted.
On the D800, I have a focusingscreen S type, which gives a darkened image in the vf on slower lenses.
This is one of my primary concerns, as even with an f/2.8 lens, the vf is darkened enough to make it notable.
With the 105/1.8 fitted, the view is usably bright, so focusing is made easier(note: not easy! .. but easier .. especially at close distances)
By comparison, the 105VR is much darker on the my D800. Of course this makes accurate focusing a little more difficult for me.
So if any of my comments appear biased, or to be waxing lyrically, it's only because of the way my D800 is setup.
On the D300(with a katzeye focusing screen), because of the screen type, there is no difference in the way either lens renders through to the vf.
Weight wise, I feel the 105VR and 105/1.8 are about on par. The 105VR feels a lot bigger tho(as it is physically bigger).
It feels both wider and longer, even tho it's really only longer.
The diameter of the two lenses are really about the same(at the focusing collar), but the 105/1.8 becomes slimmer at the lens hood, and has a recessed aperture control.
So, as a comparison to the 105VR, the feeling of handling of the 105/1.8 is that it feels a lot smaller than the 105VR.
I don't have overly fat fingers, or large hands, but access to the aperture ring is easy and natural.
My take on this lens(now that I have it):
I'd recommend to myself that this lens is worth it, so get one.
* as means for comparison tho, I have the 50/1.2 Ais lens too and at the prices they go for, I'd not recommend to myself to get this lens again. Not that it's a bad lens, It's just not as nice as I thought it was going to be. At the price we pay for our stuff here in Aus .. I'd have been better off spending a few hundred more and getting a Sigma 50Art instead.
The 105/1.8 doesn't give me that kind'a feeling tho.
My next step is to organise a CPU for it (from BR of course). But this will have to wait until I can find a way to remove a damaged screw first.
