D70 focusing screen replacement

Inspired by posts by Joseph Wisniewski (<a

href="http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=008onY">here</a>

and <a

href="http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=008r74">here</a>),

and by the big nasty scratch I put in my screen trying to clean it, I

decided to try replacing the focusing screen in my D70. I'm pretty

pleased with the results, and would like to add a couple of comments

and suggestions to what has already been said.

 

<p>To remove the screen, take a cheap miniature slotted screwdriver

and grind or file a notch across the tip to fit over the wire bail.

That will keep it from slipping off. If I'd done that at first, I

wouldn't have had to replace mine at all.

 

<p>I chose a "J" screen from an N8008. It has a microprism area but no

split-image, which is how I like it. I note in passing that the edges

of the split-image area on a K3 screen stick up enough that they will

probably press against the LCD screen, which may not be a good thing.

 

<p>I cut my screen to 0.800" x 1.000", give or take about 3/1000 plus

half an inch slop in my cheap calipers. Anyway, it fit fine. By my

measurements, the center of the viewfinder is about 0.335" down from

the top, 0.465" from the bottom of the screen, where "top" means the

edge near the focal plane and "bottom" the edge near the lens mount.

(Incidentally, that's backwards optically, but matches the way you

hold the screen when you're putting it in.) Note that you'll only take

a couple of hundredths off the bottom of the screen.

 

<p>I started by putting a piece of transparent packing tape over both

sides of the screen. That way I didn't have to be very careful

handling it. I used an X-Acto knife to trim the tape away from the

edges of the screen, then measured and cut one edge at a time. If you

fully finish each edge before going on to the next, you always have a

good reference edge at the other side to measure against.

 

<p>I cut each edge roughly with an X-Acto razor saw, which is a

miniature saw with a rigid blade designed for model making. I finished

the edges on hobby sanding film--fine sandpaper with a plastic base.

Try to be as exact as you can finishing the sides, as it turns out to

be really annoying if the screen is off-center horizontally. (Luckily,

I'd figured on screwing up once, so I had two screens and got it right

the second time.)

 

<p>I don't know if it's possible to get the screen perfectly centered

vertically on the first try. I was able to trim it a little more on

sanding film until it centered up right. If the center ends up low,

you'll have to take some off the "bottom" (optical top) of the screen.

Then when you drop the screen into the camera, you'll have to turn the

whole thing upside-down and tilt it so that the screen slides forward

before clipping down the bail. The bail is tight enough that the

screen won't slide around after that, though I don't know what time

and vibration will do to it.

 

<p>The screen I used works quite well. Focus by eyeball matches up

with automatic focus and the electronic rangefinder with no

discernable difference.

What is the sense of all this? Are you too embarrassed to get a new screen from Nikon? Is there anyone foolish enough to follow your lead?

<i>What is the sense of all this? Are you too embarrassed to get a new screen from Nikon? Is there anyone foolish enough to follow your lead?</i>

<p>

gee, miss the point much? if nikon sold a D70 screen with focus aids, then we could run out and get one. since they don't, something like this can be useful for the times where critical focus is not visible on the existing screen.

Andy, I get the point precisely. Please step to the head of the line. Next!

I've installed a K screen in my F4, it makes focusing so much easier to me. I will probably try this suggestion for my D100, testing of the autofocus shows several positions where the autofocus indicates correct focus. A manual focus screen will only indicate one position. Great idea! Of course you will lose the focus pointers, but if you manually focus no great loss.

/ignore Edward Ingold

 

"Of course you will lose the focus pointers, but if you manually focus no great loss."

 

Dunno about the D100, but on the D70 the LCD with the focus point brackets is seperate from the focusing screen, so you don't lose those

How do you make sure the critical surface of the 8008 screen lies precisely on the focus

plane? Or, is the bottom surface simply flat and rests naturally? Isn't there a frame, and

isn't the screen positioned by the upper frame edge?

 

Also, how does the microprism work in the otherwise dim finder environment of a D70?

Can you focus f5.6 lenses at all? How does it work in low light?

 

I assume autofocus and metering are completely unaffected, as well as all the other finder

LCD functions, yes?

 

I wish Nikon would give use screens with split images for digital, I really like a split image

in low light with a fast lens.

Hmm...

 

I read those two links and it sounds like the D100 (what I have) is even more straight

forward. I wonder if something like and EM screen would work, IIRC, they are a simple

rectangle with no tabs, etc., Plus, EM screens can be had pretty cheaply these days.

 

Does anyone know the X & Y dimension of the D100 screen? I wonder if the D100 has the

offset center issue like the D70? I believe the D100 prism is glass, and I know from side-

by-side that the D100 finder is easier on the eyes.

 

This is a pretty cool idea.

the autofocus is under the mirror and is unaffected. the metering is in the finder so could be affected, would be nice to get more data on that. However with 1/3 stop adjustments and a histogram display, I see no reason to worry about that.

<i>How do you make sure the critical surface of the 8008 screen lies precisely on the focus plane? Or, is the bottom surface simply flat and rests naturally? Isn't there a frame, and isn't the screen positioned by the upper frame edge?</i>

 

<p>The critical surface is the top surface, where the image forms. This is spaced below the LCD screen by a shim in the form of a rectangular metal frame, maybe 5/1000" thick. The top surface bears directly on the shim. That's why the thickness of the split-image patch on the K3 screen worries me. It could keep the screen from seating correctly, or put pressure on the LCD screen, if it touches.

 

<p><i>Also, how does the microprism work in the otherwise dim finder environment of a D70? Can you focus f5.6 lenses at all? How does it work in low light?</i>

 

<p>Early impression is that it works very well. I was just playing with my 70-300 f/4-5.6 ED in a dimly-lit room and had no serious trouble focusing in light where the D70 needed focus-assist.

 

<p><i>I assume autofocus and metering are completely unaffected, as well as all the other finder LCD functions, yes?</i>

 

<p>Haven't taken a close look at exposure yet. If it's off, it's not <i>way</i> off.

Dan, as has been mentioned, all Nikon screens index against the focusing side, so thickness isn't a problem.

 

It's actually a procedure outlined in Nikon service manuals, to check the focusing accuracy of AF cameras by replacing the matte screen with a split image screen.