Changing D800E focusing screen. An exercise in futility.

Started Mar 24, 2013 | Discussions thread
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Rich42 Senior Member • Posts: 1,528
Changing D800E focusing screen. An exercise in futility.
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Changing the D800E focusing screen. An exercise in futility.

I have lots of AIS and AI manual focus lenses and I would love to have a ground glass screen with a split image central area surrounded by a micro prism collar just like in my film cameras to focus these lenses. Yes, I use the D800E "electronic rangefinder" function, but it's hard to compose or follow action and still look off-screen at the green arrows and the dot. (It would be much better if, at focus, the screen would light up or the focus area indicator would light up in addition to the green dot)

Some have criticized screens made for DSLRs for not being able to truly show the appearance of out-of-focus areas so that Bokeh could be properly evaluated. The reality is that DSLR screens are optimized for brightness, given that light is siphoned off for autofocusing. This is done by using extremely fine micro prisms rather than a true abrasion pattern or "ground glass" focusing surface. The micro prisms limit the ability to show blur to about what a f/2.8-f/4 would produce, even when using a larger aperture lens. True ground glass focusing surfaces give a much better indication of the image at all apertures from sharp focus to maximum blur. The image "pops" at "in-focus" much better than happens on the D800/E screen.

To be sure, it is not possible to really evaluate the OOF image on a "35 mm" SLR (or DSLR). The image is just too small. The ability to stop down and compare wide-open focusing to that at the taking aperture is just a rough idea of the effect. It really takes a medium format image or 4x5 to really see the image for such purposes.

I've read about others who have replaced the D800 screen with one that has a central split-image rangefinder feature. Some of the specialty manufacturers who make screens for Nikon cameras have announced that they have no plans for a D800/E screen due to technical reasons. (they haven't explained exactly what that problem is)

The only after-market screen available seems to be a Bresson brand which can be found on eBay for about $32-35. Some have said it works well, others have complained about the appearance of the image in the "ground glass" portion of the screen. Some have said the image goes out of focus in the split image central portion when not at the point of sharpest focus. (The image in the central rangefinder spot of film cameras is always in focus. It's split when out of focus and the 2 halves line up when in focus.)

I've wondered whether the Nikon K3 screen would work. It's a classic ground glass screen with central split image rangefinder, surrounded by a microprism collar. It also has an area outside the microprism collar where the screen is finer (brighter) than the rest of the screen. The entire screen can be used for critical manual focusing.

(Nikon also has made a K2 screen which is identical to the K3, except that the ground glass portion is a little more coarse. This makes for a slightly dimmer screen but one on which the difference between in-focus and out-of-focus is easier to determine - the image "pops" more.)

I ordered a Bresson screen for $32 and scored on a used K3 on eBay for $25.

The used K3 came in a brand new-looking package and inner plastic case which also contained a speaclized plastic tweezer. The screen appeared pristine-new. Appearance aside, it can't be used in the D800/E. It's a couple of millimeters shorter and a fraction of a millimeter less than the width of the D800 screen. It's the same thickness. That was the beginning of the frustration, because if it had fit, I would have been home free, despite reports of some interference with exposure metering caused by the central focusing spot, which the exposure system apparently sees as a black hole.

The Bresson came in nice-looking padded case with a metal tweezer in the shipping box. The screen itself was wrapped in an adherent plastic cover, inside a folded silky yellow cloth with classy "pinked" edges inside a tiny zip-lock baggie. The case also contained a plastic tweezers and two latex finger cots inside another tiny zip-lock baggie. The finger cots are meant to be used to handle the screens. I used a Nitrile examination glove instead.

The Nikon K3 was a little jewel. It appeared perfect, Its edges were polished and smooth. It was a properly manufactured element of a precision optical system.

The Bresson screen was a different story. The edges were ragged and rough as though the plastic screen had been broken away from a parent sheet of plastic. The K3 and D800 screens have a tiny plastic tab, the edges of which are as polished as the rest of the screen. The Bresson's tab was rough.

The D800 (as the D700) is known as a camera for which the focusing screen is not intended to be replaced by the camera owner. Replacement is a "custom" process recommended done only by Nikon or an authorized repair shop. By contrast, Nikon "pro" cameras have owner-replaceable screens and the procedure is very easy to do. I was worried about being able to successfully release the D800 screen, get it out, replace it and lock the replacement back in place. There are no instructions from Nikon on this. The few descriptions online are confusing, such as this one: http://www.focusingscreen.com/work/d800en.htm .

It took me 2 days to figure out how to release the D800E screen, and I scratched it with the metal tweezer, whose real use I still don't know. There's a trick to it. Once you know the trick, it's ridiculously simple. No tools are required. In fact they hopelessly complicate the task and increase the risk of damage. It takes no more than a few seconds to do the whole job. Here's how:

The screen is held in place by a thin wire underneath that runs around under the perimeter, is hinged at the back and locks under a little plastic tab at the center front. Above the screen sit one or more very thin brass shims like thin picture frames around the edge of the screen, between it and the electronic display screen above which itself is fixed in palce under the fixed pentaprsim.

Reach in the upside down camera with your thumb covered with an exam glove or finger cot, hook your thumbnail over the wire which has a very small "hump" at the front edge of the screen just to the left of the center locking tab, push upward toward the pentaprism and toward the back of the camera, in the plane of the screen. The wire will release from under the plastic locking tab. It may stay in place against the underside of the screen. Coax it away from the screen and it will hinge downward.

The screen will either drop down and rest in the cradle of the wire or may need a little coaxing. The shim(s) may also drop down. Carefully remove the screen with your fingers or a plastic tweezer. Put the replacement screen in. If the shim(s) have dropped down to rest in the wire cradle, slightly reposition the camera to make them fall "up" against the underside of the display screen, put the new screen in and press the wire back in place with your thumb. It will click under its locking tab.

The screen has a little orienting tab along the front edge. It goes to the left of the locking tab, exactly where the wire has its little "grab" hump. That orients the screen to have its focusing surface (including the microprisms) up against the display screen.

After the first (terrifying) time, it can be done with your eyes closed

Looking through the Bresson screen is the final frustration. Ugh! First, no part of the major screen area allows focusing the image or judging the OOF image. The image in this area just looks more or less smeared, depending on focus. No part of it has anything to recommend. The central split image is useable, but just barely. I tried it with lenses from 20 mm to 200 mm. All worked and I confirmed that with very, very patient examination that vertical details lined up, I got accurate focus in the resulting file.

But it was not easy. The central circle is too small. Worse, the image is defocused in a very disconcerting way before it comes into focus by aligning vertical detail. It was nothing like my experiences with my film cameras. Also, the split in the rangefinder is horizontal. This means that only vertical lines can be used for focusing. (or the camera has to be rotated at least 45° to focus on horizontal lines - a very awkward thing to do in studio, and especially when shooting fast in the field. It's amazing how often scenes seem to have nothing but horizontal detail!)

All my previous film cameras (and the K3 screen) have the rangefinder split oriented at 45°, making it easy to focus on vertical or horizontal detail.

The final frustration is that the microprism collar around the central rangefinder area does not function at all as I am used to such a micro prism doing. In all my fim cameras the image "shatters" in the micro prism collar when out of focus, then "pops" into clarity when in focus. In the Bresson screen, the image is uncomfortably out of focus in the microprisms when it is actually not focused (like happens in the rangefinder area) and is split, top from bottom, just like in the split image rangefinder. It becomes less blurred (but not sharp) as the image is focused and top and bottom merge, left to right. The whole effect, in concert with what is simultaneously happening in the rangefinder area, is confusing, irritating and distracting.

In short, the Bresson screen is a mess on the D800/E. Using it is like looking through someone else's prescription bifocal glasses. Things are blurred, "broken," distorted, confusing and headache-inducing.

I tried for several days to get used to this screen and gave up. The original screen is back in the camera (with a tiny scratch mark (*sigh*) on one edge and I am breathing a sigh of (optical) relief.

If only someone would make a K3 type screen that actually fits the D800/E. I have a wacky idea to try to graft tiny extensions to its length so that it will seat in the D800. The Bresson screen is useless for anything but as a donor for such grafts. Stay tuned . . .

Rich

Nikon D700 Nikon D800 Nikon D800E
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