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Yesterday I was photographing an event and had to change a lot between lenses (50mm and 18-55mm). Surprise, surprise, today when I looked on the viewfinder I saw a little piece of fabric and a little black dot.

I cleaned with a brush and blower (click for example): the lenses, the eye piece, the base of the pentaprism (which is that pink line in the figure below), and even the mirror. After the "cleaning" I looked again and the viewfinder was even dirtier, now with small translucent fragments, and the original dust still there.

I'm sure the dust is over the "focussing screen" (according to the pink line in the figure), because I observed the mirror and it's clean and I took a photo and it's also clear of dust. How can I effectively clean that base of the pentaprism? I even tried using the corner of a paper sheet and scrub it but without success.

Any ideas? Get a better blower?

dslr-inside

P.S: I have a Nikon 3100.

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    \$\begingroup\$ Note that the D3100 has a pentamirror, not a pentaprism. Check out this nifty disassembly video which shows both. Unlike a prism, which is a chunk of glass, it's actually possible for dust to get inside the little box with the mirrors, and that may be the case here. The edits we've made to the title make sense each step-to-step, but since I noticed this, I think maybe we should go back to something more like the original. (Or maybe leave it open — "How to clean dust from inside my camera's viewfinder?") \$\endgroup\$
    – mattdm
    Commented Jul 1, 2015 at 14:46

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I would say don't bother. It won't appear on your photographs and will only bother you if you focus on it (pardon the pun).

if it is really bad then give it a puff with a rocket blower, if that fails then send it to a proper repair shop otherwise I feel you're in danger of causing damage.

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  • \$\begingroup\$ +1 for rocket blower. In my experience, blowers with brushes are usually a menace, not a help. \$\endgroup\$
    – RedGrittyBrick
    Commented Feb 27, 2013 at 23:22
  • \$\begingroup\$ I agree with brushes, blowing fine but keep bristles out of the housing :o) \$\endgroup\$
    – Tony
    Commented Feb 28, 2013 at 12:42
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Most SLR's have removable/replaceable focusing screens, and I gather the D3100 is no exception. There are instructions here for removing and cleaning your focusing screen. Be aware the the screens are usually plastic and quite fragile. On the other hand, if you really screw it up, a new one won't set you back all that much.

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  • \$\begingroup\$ I don't think I have the courage to do so :P I prefer more "passive" approaches, without touching or messing with parts of the camera \$\endgroup\$
    – dialex
    Commented Feb 26, 2013 at 18:57
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    \$\begingroup\$ It's not like you're opening something that you're not supposed to open. The camera is designed such that the user can swap in different screens. Removing the screen and doing a gentle cleaning would definitely be better than trying to slip a piece of paper between the screen and the prism! I can understand being uncomfortable, though, and if that's the case you should consider taking the camera to your local camera store for some professional cleaning help. \$\endgroup\$
    – Caleb
    Commented Feb 26, 2013 at 19:02
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First, try something like a Giotto Rocket blower. They shoot a very powerful air stream. Hold the body with the lens mount facing down so anything you knock loose, falls out.

I just bought a K screen for my F3 from KEH. BGN grade, because $7 was more to my liking than $17. It had a noticeable spot on the lower (contoured) surface, the one you're not supposed to mess with. I decided to try warm DISTILLED water with a drop of dish soap in it. I used a syringe with a plastic tip to apply it to the spot with one hand while I held the screen tilted, so the water would run off with the other hand. Rinsed with DW and it almost came off. I did another pass and scrubbed very lightly with a Qtip and rinsed again. Used a hair dryer on LOW to speed the drying. Spot completely gone!

Nikon screens are 2 layer, I discovered. So some of my water got trapped between the layers. About 5 minutes of hair dryer, held a foot away, on LOW, evaporated it.

Good luck with yours!

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This screen also known as a "ground glass screen" (though it's not always made of glass) has a very fine etched pattern on one side of it to facilitate the way it scatters light. Cleaning the side of it with this surface is not practical as it's likely to both deposit small particles into this etched surface and possibly damage the etched surface (think those beer glasses or vases that appear permanently frosted, if you run a coin over them you leave a mark permanently).

The dust on it is more likely to be on the "bottom" surface (mirror side) than the top surface (pentaprism/pentamirror side) and I believe this is the etched side unfortunately.

Blow it with a blower, make sure you don't introduce too much more dust in there in the process (do it in a relatively dust-free room). Don't blow with your mouth as that contains particles.

If the blower doesn't help you could put up with it, or take it to a shop. Some people here have reported success cleaning it by removing it and running it under warm water - without touching or scrubbing the surface.

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I also have the 3100 and have recently had the same problem. If you take off the lens and look at the edge of the screen, you'll see a rectangular wire that holds it in. Just push it free from the clip it's tucked under at the front and the screen will fall right out. Be careful: the focusing screen scratches really easily and then your view will always look like there's a hair in it. Also, under the screen is a black rectangular spacer. It falls out quite easily, so be careful not to lose it.

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