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Pentaprism - cleaning or replacement

Jason Hauf , May 21, 2000; 11:03 p.m.

First of all I'll say I'm a beginner...so please be patient. Recently, I was looking through the viewfinder in my camera and noticing some dust(probably got there while switching lenses). So when I removed the lens I wiped the pentaprism with a lens tissue and seem to have made things worse. There are some small circular marks on the pentaprism now. They are not very noticebale but quite annoying when looking through the viewfinder. I was wondering how much it might cost to have a new pentaprism installed or have this one cleaned up. The camera body is a Canon Rebel 2000 EOS. Thanks in advance.



Harvey Yau , May 21, 2000; 11:58 p.m.

It isn't a pentaprism you need to be worried about, it is the focusing screen. I don't think the Rebel 2000 even has a prism, from what someone has told me, it has uses mirrors to accomplish the same effect.

Again, I'm not certain about the Rebel 2000, but I do know that you can pop out the focusing screen on an Elan IIe by using a pin to prick two metal loops near the lens mount on the focusing screen. I don't know if this is even possible with the R2k, but examine yours and get back to me. I'm going to disclaim all liability to anyone who attempts the below operation on their camera and messes up. Do this at your own risk.

On the Elan IIe/50e, which is not supposed to have a removable focusing screen, you can prick the two sheet metal loops inward. By doing this, you are disengaging a pressed sheet metal retaining plate. After this comes out, very gently use a pair of tweezers to remove the screen by the edges.

You can now clean the screen in whatever way you see fit. I use compressed air on the laser etched side (never touch it! you already did when you tried to clean it...) and my microfiber cloth on the smooth side.

Never *ever* touch the mirror! Don't let the focusing screen touch the mirror either.

Focusing screens can be replaced by calling Canon's parts department. They're inexpensive.

The more expensive the camera, the easier it is to pop out and exchange focusing screens. With my EOS 3 it is as simple as manipulating a little tab on the inside. The focusing screen comes down on its own little tray. New focusing screens for this camera come with tools that you should use to pick up and remove the screens.

Good luck, let me know how you make out.

Vadim Makarov , May 22, 2000; 01:57 a.m.

You've damaged (permanently) microrelief on the socusing screen (made of soft plastic) that steers light into the viewfinder and metering system. If the marks are in the metering area, metering now may be inaccurate.

I don't know if Canon will sell you a new focusing screen separately, but it definitely can be replaced at their facility (which is also safer).

Never touch surface of the focusing screen.

Harvey Yau , May 22, 2000; 03:46 a.m.

Yeah, they do, and they're not expensive at all, especially for the R2k and the Elan IIe. Maybe someone can call up and ask them the price.

Gary Watson , May 22, 2000; 06:50 a.m.

Consider your repair costs as tuition.Short of bird droppings on your focus screen, minor dust specs will have no effect on your images;indeed, the only effect will likely be annoyance for you.Stop obsessing and start taking pictures. The view through several of my older SLRs with fixed focus screens is a bit distracting.Nearly all host little archipelagos of dust and minute crud. All work just fine, thanks.Given your current troubles, you might gain from a quick archive search on "lens cleaning."Just remember that Brillo isn't an option.

Hoyin Lee , May 22, 2000; 12:07 p.m.

Jason, it's either the reflex mirror or the underside of the focusing screen you've wiped (most likely the latter), not the pentaprism (which you'll have to crack the camera open to get access to, as far as your camera model is concerned!). Basic camera maintainence rule: don't touch the mirror and the focusing screen unless absolutely necessary; if you find dusts in the viewfinder irritating, blow them out with a blower or with canned compressed air (used with extreme care at a suitable distance). Anyway, I don't think you've done too much damage to the focusing screen. Send your camera to an authorized Canon repairer; it may only need a proper cleaning instead of a new focusing screen.

Paul Darman , May 22, 2000; 10:40 p.m.

I am not sure I agree with Vadim that the marks will affect metering.

Vadim Makarov , May 23, 2000; 05:49 a.m.

<em>I am not sure I agree with Vadim that the marks will affect metering</em> <p> Well, if I obstruct the metering circle on my EOS&nbsp;500N with a piece of paper almost touching the focusing screen, the partial meter immediately shows looong underexposure. The screen surface is made to direct light into a narrow angle covering the viewfinder lens. Damaged surface does it less efficiently, probably scattering light into a wider angle and making the viewfinder dimmer for the eye. Since the meter also reads from the screen, it may be impaired as well. I don't know for sure, though.

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