Your finding makes it clear (no pun intended) that the Optibrite from Katzeye is more friendly for MF.
.....
Actually, I'm finding it the other way around, but with a caveat.
The Katzeye I have has the two focus aides in the split prism and the microprism collar around that.
The microprism collar is quite large through the D300, which I guess is due to the smaller overall size of the screen itself relative to the size of the microprism etching.
In this instance, my guesstimate is that the microprism circle covers roughly 1/3rd of the size of the whole screen, so that if the subject is within the 1/3rd area of the vf near the centre, then it will be in range of the microprism area.
But, the D800's S-type screen is usually more accurate if I'm manually focusing from only the matter areas(that is not using the focusing aides of the Katzeye's screen)
So if the subject is in the periphery, where you can't use the centralised focus aides of the katzeye screen, I find that the S-Type is more accurate.
All this assumes fast lenses too tho. 50 @ f/1.2, 105 @2 f/1.8, 24 @ f/2.
The 24/2 is where the accuracy difference is blurred a bit tho..
I assume that it could be due to both the f/2 aperture and the shorter focal length(which probably means deeper DOF, and hence more forgiving allowance of errors).
The 105/1.8 is the harder of the above lenses to focus, and of course the the differences between an Fx and Dx FOV also come into play.
The test target I used was a test pattern I found on the internet with stars and stripes printed on a white sheet.
I had to change distances to try to overcome any undue softness the lens may have at it's periphery too. So for the D300 I set the focus target at the periphery of the frame, and IIRC at just a very slightly longer distance(less than about 1m) whereas with the D800, I set the same target at about the 2/3rds range in the viewfinder area(ie. not right at the very edge).
My assumption here was that if the lens is less acute in it's drawing at the very edge, it'd have skewed the result a bit in favour of the D300 no matter the screen used!
While I did end up taking some images, my primary concern was on the liveview images, once I focused via the respective viewfinders.
My hit rate with the D800 setup was 'more often than not' .. in that reviewing the D800 liveview image, if I tried to tweak the image to a more focused one, it would tend to blur out of focus instead .. so I assume that focus was hit via the vf.
I do remember that the D300 usually could do with a slightly better focus point with a slight tweak more often that not, but that focus was still more than good enough tho for an image.
(the 105/1.8 has a hazy rendering wide open(up to f/2) for this area of the scene. The focus tweak was minimal, but to my eyes on the D300's Lv screen it seemed that I could do a little better.
Using the focus aides on the katzeye screen, all MF attempts were 100% spot on all the time if I allowed myself a second or so to process the scene.
In give and take situations, where only a split second is offered to get the shot(eg. a kid momentarily stopping for a photo, but with the impatience to get back to the game!
) my hit rate with the D300 was impacted a little, even tho it has the focus aids. I usually get it, but I still need multiple exposures to be sure to get one image at an acceptable level.
If I had the funds .. I would have jumped at the opportunity to acquire the Katzeye operations.
They certainly do have great products.
