Why don't modern DSLRs have split-screen or microprism areas?

I appreciate that most lenses these days are auto-focus, but there are a good number of high quality manual focus specimens out there (including some from Canon themselves - such as the TS-E lenses). So, why is it that split focusing screens are available only as 3rd-party accessories?; and why have Canon arranged it so that if we use these things, we're likely to find that the metering system stops working properly?

Anyone who's used a split-screen or microprism on an old 35mm SLR will know how quick and easy they make manual focusing - it seems odd that it's so hard to get this facility on a modern DSLR - or am I just too old-fashioned?

It's mostly because the AF system steals a LOT of the light coming in through the lens. The reflex mirror only partially reflects the image up into the viewfinder. The rest of the light goes downward to the AF sensors. Split prisms require a lot of light to work and steal a lot of light themselves too. Given that most of the light is already robbed, this makes the viewfinders too dark for general use, making split prisms only suitable with specialty lenses that are faster (i.e. F/2.8 or faster). Canon is not going to use a default screen that will NOT work well with many of their EF lens lineup.

Also, modern viewfinder sizes are painfully small compared to their manual focus predecessors, making the split prism centre themselves a lot smaller, and therefore, much harder to use.

Canon's priority is to make the viewfinders as bright as possible with the little amount of light that is left over.

Canon does make split focus screens. I'm know they make one for the 1Ds Mark III and other bodies as well. www.google.com/url?sa=​t&source=web&cd=1&sqi=​2&ved=0CBYQFjAA&url=ht​tp%3A%2F%2Fwww.learn.u​sa.canon.com%2Fapp%2Fp​dfs%2Fquickguides%2FCD​LC_FocusingScreens_Qui​ckGuide.pdf&rct=j&q=ca​non%201ds%20mark%20III​%20split%20screen%20fo​cusing%20screens&ei=QO​RnTr6FHKTXiALKtJmUDQ&u​sg=AFQjCNEpa0e1bpA6D0W​zGlha-bTEVLV6fQ&cad=rja

Take Care,
Cheers, Patrick

picturecrazy wrote in post #13066009
It's mostly because the AF system steals a LOT of the light coming in through the lens. The reflex mirror only partially reflects the image up into the viewfinder. The rest of the light goes downward to the AF sensors. Split prisms require a lot of light to work and steal a lot of light themselves too. Given that most of the light is already robbed, this makes the viewfinders too dark for general use, making split prisms only suitable with specialty lenses that are faster (i.e. F/2.8 or faster). Canon is not going to use a default screen that will NOT work well with many of their EF lens lineup.

Also, modern viewfinder sizes are painfully small compared to their manual focus predecessors, making the split prism centre themselves a lot smaller, and therefore, much harder to use.

Canon's priority is to make the viewfinders as bright as possible with the little amount of light that is left over.

Thanks for the insight. I knew the AF stole some light, but hadn't realised it was so much as to compromise the operation of a prism on the focusing screen.

I agree on the viewfinder size issue - I picked up an old OM-1 recently and was bowled over at the size of image in the finder (and the brightness now I think of it). Beautiful - if only my 5dii was that good.

This thread is very Illuminating, if you'll pardon the pun. I love everything about digital over film, EXCEPT for the lack of a decent manual focus screen (on my 7D). I guess I was spoiled by my now ancient FTb, which despite its simplicity was a joy to look through.

It is not that much light that goes away for the AF.
Seems to be 40% for the AF and 60% for the viewfinder with the EOS 5D classic.

I am working to get a 100% silver mirror into a EOS 5D, that will bring me some two thirds of an f-stop more light into the viewfinder.
The mirror is inside the camera at the moment, but only with tape. I need to test the EE-S focussing screen calibration, and have to shave the mirror frame (for the use with some manual lenses). And after that I suppose I will glue the mirror.

But it would be great, to have the split screen option, without paying high prices for it.
Will try this way to make a cheap split / microprism screen for my 5D.

Why not just use live view with the zoom on for manual focus (runs and hides from the incoming projectiles flung by the purists).

I do occasionally miss the elegance of focusing my old AE-1 Program. Bringing a vertical line together in those two semicircles in the center of the viewfinder was pretty solid in its simplicity.

Keyan wrote in post #13069702
Why not just use live view with the zoom on for manual focus ...

Liveview operation is much to slow for photographing my moving child with a fast lens.
Furthermore I do only have a 1000D as liveview camera, but like my two 5D much more.
With the optimized viewfinder I could see the hole image at once, and could focus my f/1.2 lenses wherever I want.
And such without problems with th sun shining on my back.

picturecrazy wrote in post #13066009
It's mostly because the AF system steals a LOT of the light coming in through the lens. The reflex mirror only partially reflects the image up into the viewfinder. The rest of the light goes downward to the AF sensors. Split prisms require a lot of light to work and steal a lot of light themselves too. Given that most of the light is already robbed, this makes the viewfinders too dark for general use, making split prisms only suitable with specialty lenses that are faster (i.e. F/2.8 or faster). Canon is not going to use a default screen that will NOT work well with many of their EF lens lineup.

Also, modern viewfinder sizes are painfully small compared to their manual focus predecessors, making the split prism centre themselves a lot smaller, and therefore, much harder to use.

Canon's priority is to make the viewfinders as bright as possible with the little amount of light that is left over.

I am not sure how split prism focusing screens relates to your reply, and I believe that there is now some confusion on the part of the OP.

TeamSpeed wrote in post #13070871
I am not sure how split prism focusing screens relates to your reply, and I believe that there is now some confusion on the part of the OP.

I think your statement is the most confusing one in this thread?? He asked why modern dslrs don't have split prisms by default. I told them it all requires lots of light and good size to be effective. Installing a split prism will darken the viewfinder. Canon's priority is to make the viewfinder as bright as possible to work well with ALL EF lenses. Hence, no split prisms by default in modern dslrs. How does that not have anything to do with the original question? The OP's response was "thanks for the insight". What part of that says the OP is confused? You're the one who has ME confused??

Split prism and microprism focusing aids require a lot of light to work with. Even with the older cameras with bright viewfinders if you stopped your lens down with the DOF prevue button pressed, one side of the little "prism" would go dark. Some longer lenses with a maximum aperture of f5.6 or smaller would cause that to happen without the DOF prevue button pressed.

With one side of the split image focusing aid or one side of each microprism going dark, the "aid" could not be used and focus had to be judged on the screen itself.

The current generation of first time DSLR purchasers, dependent on autofocus, could not deal with darkening microprism "grid" or split image with half of it going dark.

TeamSpeed wrote in post #13070871
I am not sure how split prism focusing screens relates to your reply, and I believe that there is now some confusion on the part of the OP.

No - not too confused really!! I've learnt that the AF steals about 40% of the light going to the viewfinder and that means that split-screen focusing aids don't work too well with slower lenses. That's probably a good reason why Canon has ditched them - except as an option on the 1D line.

It's also true though that the finders on modern DSLRs are small compared to those on old 35mm SLRs - I can only assume that Canon (and other manufacturers) believe that we don't need such luxury in the age of AF - which is a shame If anyone has an OM-1 hanging around - go take a look in the finder. It's quite an experience if you've been using an xxxD/Rebel or xxD - or even an xD.

New to the dslr scene, I'm a bit surprised how often I've taken my lens off AF for better tweaking. Boy, do I miss the ol' split screen daze.

They have split screen, with Magic Lantern in LiveView

(digital split screen, not optical)