Canon Focusing Screen Ee-S

Update just for more complete info.

Having used, modded and abused many different focusing screens in life, I'll share what little I know. Some of it directly pertains to modern DSLRs and the rest is background information. Hope it's helpful.

Most modern AF DSLR (and perhaps even AF film cameras) do not generally feature focusing screens that are optimised for manual focusing mainly because I suspect most manufacturers figure users would use AF more than 90% of the time.

Here's something I shared in another discussion about focusing screens. The 'darker' part refers to rough ground focusing screens like the xx-S series.

The reason why these screens (xx-S series) are darker is because the 'ground glass' is manufactured rougher, causing light to scatter more.

Rougher surface means less light goes through = darker VF, but the upshoot of that all is that images SNAP into and out of focus a lot faster on the surface of the screen. It's just like focusing the film grain when enlarging negs. The grainier the film, the easier it was to focus the enlarger lens. I remember focusing Kodak Tech Pan was an absolute nightmare - that film was virtually 'grainless'!

In the old days of large formats, the main problem facing the togs were that it was rather difficult to compose a scene properly on the very rough ground glass screen because it was sooo dark in there that one common practise was to use linseed oil to 'fill in' the rough spaces on the screen surface, creating a much smoother, brighter screen. But the downside of that was that the finer the screen, the less depth of focus you get on the surface, making focusing more difficult, necessatiting the use of magnifiers or loupes to focus.

In the modern film SLR, it was always a toss up between rough and fine grinds, which was why some pro and even semi-pro bods like the Pentax MX, LX and OM-1/2/3/4 and Canon's own F-1 system with changeable screens had the option of rough, fine or even no ground glass (for scientific and astrophotography). IIRC, the very comprehensive MX/LX and OM systems featured something like 13 to 14 different focusing screen options.

When AF came about, manufacturers slowly traded off prism sizes to save space, weight and costs and used finer and finer screens since the logic was that togs would eventually use only AF, hence, no need to use the ground glass to focus. That's why accurate manual focusing on any modern DSLR is such a pain on the standard factory supplied screens!

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As for modern split-image screens, or microprism screens (where available), most cameras still meter off the screen, and that means it will likely necessitate a compensation when you change out screens from the factory supplied screens which do not feature any central focusing aids.

It does not matter who manufacturers the central focusing aid screens or how cheap or expensive they are - you still will get metering errors (sometimes variable) unless you compensate or set an appropriate Cfn. I sometimes get metering errors even when I use the Canon made split-image screen in my 1 series cam with appropriate compensation.

Some lower end bodies like the XXX and some XX - D series bodies will loose the LED lit AF points because the AF points are etched directly onto the factory screen itself. Some bodies use a different plane to carry the AF points so AF points will always be visible no matter what screens are used, even those with central focusing aids like split-image, cross-split image and microprisms.

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Brightening treatments (Opbrite, Beatties Intenscreen etc) use special surface treatments and/or modified grinds that allow more light through. In the case of a finer grind, or even the special coatings, allowing more light trough usually results in lower contrast.

This was the same situation in the old days when comparing the smaller but more contrasty VF coverage of Nikon's FMs and FEs as compared the virtually 100% but brighter and less contrasty VF view on Olympus' OM 1s and 2s.

In modern DSLRs, it is a toss-up whether a brighter screen will actually be beneficial in manual focusing, because if you're using the ground glass portion to focus, a brighter screen will always mean it's finer and transmits more light = lower contrast = less in and out of focus 'SNAP'.

In old medium format cameras, some users may remember the notoriously dark AND difficult to compose and focus Hasselblad screens, till they changed it to something similar to what Minolta made.

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Minolta made fairly major headways in screen technology in the way they gound their ground glass portions, and this resulted in finer, brighter escreens. IIRC, they used lasers to grind their screens as opposed to more coinventional physical contact abrasive blasting/finishing. Hoada, an after-market focusing screen brand uses refurbished and cut Minolta screens, but I am not sure if this is still the case. How many old, mint condition Minolta screens can there be floating around the world?

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Canon, with the renewed and improved F-1n professional body IMO made the most headway where screen technology was concerned with the variable angle split-image screens. Without going too in-depth into their focusing and metering system (it's a chapter all by itself), the new F-1n split-image focusing screens could be used with fast lenses (2.8 or larger) or slow lenses up to 5.6 without the split-image part darkening, a common occurance with most split-image screens when slower lenses are used, even up till this day.

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Please remember that I'm recalling that off the bat; please forgive me if I messed up some parts or missed out something.

Also, at the end of the day, with different lenses, needs and shooting conditions, it's hard-pressed to use just one screen for all needs. Something somewhere will be compromised, and that's why so many different screens are manufactured. It's a shame that only 3 screens are available for models in the XX-D series and 5D series.

BTW speaking of 5D series cams, I've been told that the old Nikon K screens used in the FM/FE/FM2/FE2 series film cameras fits the 5D perfectly. I am not sure if the fit is the same for the 5D2.

If you have access to laser CAD/CAM cutting systems, grab a whole bunch of original, high-quality old focusing screens off ebay and start experimenting! Most of them come fairly cheaply.

As mentioned earlier in this thread, if misalignment occurs (VF looks sharp but photos turn up front or back-focused, it simply means that the focusing surface of the screen is very slightly closer to or further away from the precise plane of the sensor, and that's where you need to shim. Canon's lower end cameras like the D30, D60, 10D, 20D and I suspect 30D all need shims of different thickness to align their focusing screens. The good part is these shims are really cheap - I bought a whole range of different thicknesses from Canon when I was fooling around with my 10D's VF system for anout US$1 each.

Hope this info helps a little.

CHEERS and HAPPY EASTER!
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