My focus screen experiences have been:
first attempt for a better alternative on the D70s, a cheap .. and definitely nasty! .. ebay product.
While $30 wasn't a huge hit to my pocket, it certainly wasn't worth that amount(other than if one ever needed replacement).
moral to that story is if you want a better focusing screen(ie. experience) avoid the cheap ebay products. If you have somehow managed to damage the focus screen and simply need a replacement at $30 they're ok.
My next experience was with the Katzeye with optibright fro my D300.
In hindsight I should have also purchased one for the D70s, only because(with hindsight) it's too late now as they no longer exist. The hope being that an enterprising person may take up such a challenge one day.
In a word, the Katzeye with optibright on the D300 was, for all intents and purposes, perfect.
It's easy to focus at the periphery using just the matte even with such lenses as the 50/1.2(wide open) and even the dingy dark old 500/8.
A small amount of darkening is apparent with the 500/8, and any other smaller than f/5.6 lens(ie. lenses with teleconverters, etc).
My other lens that pertains to this point is an old Tamron 300/2.8 for which I have both a 2x and 1.4x T/C and can confirm that is still bright enough to use easily and still coarse enough to focus accurately too.
My katzeye had both microprism and split prism focus aides. I was a bit weary of Katzeye's marketing about their unique split prism design, in that black out is delayed till very late in the small aperture range .. but my fear was unfounded.
Where the relevance to the Tamron lens comes into it, is that it's my only lens that I can test at small apertures(eg. f/11 or f/16) and still get a shallow DOF to test both focus accuracy and split prism blackout.
Blackout begins to appear at about f/16 on the Tamron lens with both T/Cs attached(ie. at 840mm and f/16 and close range focus)
Even in such conditions, while the vf is significantly darker due to f/16, and the split prism is only slightly blacking out .. focus with the split prism is still easily achieved on good subject matter.
I couldn't give an accurate assessment of the brightness difference between the stock D300 screen and the katzeye with optibright, but the katzeye is most certainly brighter to begin with .. maybe 0.3 to 0.7Ev(possibly more) AND more accurate to focus faster lenses.
Manual focus has never let me down, other than for my inability as a practitioner. That is, with a stable camera and static subject matter, I can hit focus 99.99% of the time with the D300 + Katzeye.
In give and take situations where fast focus is required(of a manual lens) it's most certainly my inability that misses the shot.
My third experience with another focus screen is as Sten, with the S Type from focusingscreen.com for my D800E.
Accuracy is superb.
As above in terms of capability in ideal conditions and situations. I can hit focus easily due to the coarse nature of the screen.
Only problem is the darkness through the vf.
Once again .. one word .. massive!(darkness).
With fast f/2 or faster lenses it's not a huge problem. in fact, barely a problem. But with an f/2.8 lens of any type ... 300mm or 24mm! .. the vf is darkened enough to notice it.
Add an f/4.5 lens and it's almost a pain in low light.
Add a 500/8 and it's murderous(the darkness through the vf) .. except in very bright light.
While the stock D800 is brighter than a stock D300, with the aforementioned screens fitted now, the D800 is now a few Ev darker at f/2.8 than is the D300 + katzeye(optibright version).
So much so that the D800+S-Type with a 24-70/2.8 mounted and zoomed in to 70mm is about as dark as the D300+Katzeye with the 500/8. Both setups pointed at a blank pale wall/screen to replicate the same lighting for each focal length.
if I switch the lens/camera combos(ie. D800 with 500/8 and D300 with 24-70/2.
it's like having one eye closed(obviously the D800 eye) where by comparison to the D300 eye, a blank white PC screen is a very very dark grey and the D300 is bright enough for anyone to consider white.
The method used for the above comparison is to hold the two camera/lens combinations at each eye at the same time, in a sort of binocular manner.
Both pointed to the same PC screen, with a blank white page.
The same method used with no lens mounted on either camera produces near identical brightness levels.
For accuracy in observation, the D800 vf is significantly larger by comparison to the D300, and with the two respective screens fitted, (D800 + S-Type) and D300 + Katzeye) there are colour balance differences too. S-Type is more red cast and Katzeye is more green cast.
I can't remember there being any colour cast to either of the stock screens, and it's fiddly to replace and check this without a direct comparion.
Next time I catch up with anyone with either a D300 or D800, I will try to remember to check for this colour cast difference.
If I can work out an accurate method to capture this with consistent and accurate exposure levels to indicate the differences, I'll reply once again with those results.
But needless to say that S-Type screen at f/2.8 is approximately 3Ev darker.
You don't see this at f/2, it may well be darker than even a stock screen with an f/2 lens but it's not a noticeable. Neither is it a notable difference compared to the katzeye.
One last point, if you can bear with me.
Even tho I have commented that this S-Type screen from focusingscreen.com produces a darker vf, focusing is still somehow possible even in very dark conditions.
The other day when out with some friends, I had the opportunity to have one final play in the dark, and the thought of manually focusing the D800 in the dark crossed my mind for no obvious reason.
I mounted the Sigma 50/1.4 I have(old model) as the other thought was for how well AF would work.
AF in this dark situation was out of the question.
Couldn't give an accurate estimate of an Ev level, other than barely anything other than a well lit ferris wheel was visible through the vf. Seeing in this dark was easy enough with the eye, but not so much through the camera .. nor Lv mode(it was all noise or too dark too). You could make out shapes via Lv mode, but the noise levels with the increased gain of the Lv system made focusing on anything impossible.
YET! somehow I still managed to focus accurately in this darkness ... manually. And not only once(by luck) but consistently once I got my eye in.
Out of 4 frames, the first attempt was missed(frontwards).
Once I got my eye in(to the light conditions), the next 3 shots were all focused. At 50mm with an acceptably sharp lens(not the sharpest at f/1.4) in almost total darkness.
So on one hand the S-Type sounds like a major liability, yet even with that obvious liability it still allows accurate focus.
I've never experienced either AF issues, nor metering issues with either focus screen fitted.
