Thanks useful information: 
I was blind and now I can see!
Most people dont' realise it, but you can change the viewfinder screen(normally called the focusing matte screen in your camera. I think there are a few cameras that don't have changeable focusing matte screens though. (an internet search will answer that question, if you're unsure).
Q; Why would I change the focusing matte screen in my camera?
A: because!
Actually because is actually the correct answer! There are many6 reasons why you'd want to change your focusing screen. They can be brighter, better for manually focusing with various visual aides.
Focusing screen.com has the best site with visual representations as to what, how, and why(a third party matte screen helps).
THIS webpage has the most comprehensive info and visual comparisons as to what each focusing aid does and how it works. I've been used to the split prism in Nikon's SLR's from way back, and the micro prism to a lesser degree. The biggest dissapointment I found when I first started using a DSLR about 4-5years ago. I didn't realise they don't come with focusing aids through the VF!
I'm only going to discuss and display the images I took when I recently cleaned out my focusing screen a few months back. Reactions thread twigged my memory about this the past few days, and these images have been sitting idle on my PC since.. got to get my moneys worth out of them before they get deleted in a few months!
First of all, what is a focusing matte(screen) and why do you need it. Look it up in you're Funk and Wagnell's or believe what I say(possibly at your peril).
As I understand it: they're an etched in-between screen overlay that assists the SLR operator in acquiring focus through the vf. They're position is between the lens and the prism(or pentamirror) that directs the image through the lens to your eye. They don't actually make any difference to the image formed on the sensor(or film) not in the same optical path. So with that they only aid you in focusing/seeing the image you want to capture. They don't help the camera(to capture a better pic) one iota!
So if you were to change yours, then it's for reasons such as 'failing eyesight' more consistent manual focusing(if you do that) and so forth. It's not like a CPL which can alter how an image will be exposed.
Where is the focusing matte screen?
Inside the mirror box area of your camera and below the prism area. It's 'easily' removable(on cameras that allow you to do so) and is like a window to the prism area, acting like a barrier. It stops dust and specks getting onto the prism box, but I've found I get specks and hairs in there on the odd occasion. When that happens it's time to pull it out, blow out any crud and give the matte screen a quick clean too.
The matte screen is the opaque looking window below the lens contacts.
I give the mirror box area a quick blow out with canned air before I remove the matte screen.
These images are not how I normally do it though!! These are the single handed versions of how to do it, as it's hard to operate another camera and hold the camera upright at the same time. Normally I hold the camera up in the air to allow any large particles to drop out as they're being blown on with the canned air straw.
***Note if you use caned air, never shake the can before use. Propellant discharges lay a white-ish residue. Easily cleaned off, but more work to do later***
How is the matte screen held in place?
... a retaining clip around the perimeter on Nikon DSLR's. Note that it;s flat apart from one small raised bump, which is located conveniently at the front to assist in unclipping it from it's locked position. On Nikon cameras, the clip is almost impossible to see directly due to the foam sponge that runs along the leading edge of the mirror stopping/resting area. That foam sponge must never be damaged, as (I think) it acts a a vibration dampener for the mirror as it swings up and stops against it.
You do have to rest on it and compress it a little as you release the retaining clip.
**Note the two small screws near the sponge. They can be removed apparently to give a clear path to the retaining clip. I can't remove them, and I do have enough tools to do that, but I found them to be too tightly locked and risked stripping the cross heads. Easier to leave them and do it the normal way. Those screws hold the sponge in place.
lever the retaining clip upwards and it swivels up and out of the way to remove the matte screen.
*note: sometimes the retaining clip comes out of it's dedicated spot, and completely out of the camera. No problem. it's easily located back into it's position to swivel up and down. notice the splayed ends. These ends are located into small holes at the back of the matte screen recess*
This is the matte screen assembly, with the retaining clip removed. On Nikon cameras there may be a very fine spacer. I've read others reports that their camera didn't have a spacer fitted(??.. I don't know if this is true or not).
If this(or more) spacers need to be placed back into the assembly they go in first. They're supposedly spacing washers to maintain the optical path to certain specs.
Makes sense to me as manufacturing tolerances need to be factored into somehow.
Both my cameras(D300 and D70s) have only one each. I put them back as I found them.
Always try to keep the matte screen clean as you can. Try not to touch it. although you can handle it with care by holding it in your fingertips at the very edges of the screen without damage. Apparently oils in your skin can mark the screen. I guess if that happens, a solvent can clean it.
If I have to handle it all over, I wrap it in a PecPad. I do this to clean it too, rubbing it carefully between my fingers. After that, I'll blow it off with a burst of canned air again.
some side notes:
Apologies for some of the images being either dark/blurry/not particularly interesting in an arty sense. Next time I'll add some HDR/ToneMapping/copper toning effects via Nik software's Color Efex Pro
I have to leave this one here for the moment. I'll tend to the kids for a while and coem back after lunch. Doing the laundry too as we speak
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. No biggie! There is a mark and it's annoying, but no big deal.. I'm wanting a new screen anyhow. I just hope the standard screens are not too expensive if I ever want to revert again(for the purpose of selling the D300 only).
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Originally Posted by Papou
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