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03-26-2009, 08:34 PM   #1
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K-m viewfinder shows patterned dots

Got my K-m from prodigital2000@ebay this week. The camera is brand new in box. I checked the shutter actuation is around 200.
When I mount the kit lens and tried to take some samples, I found the viewfinder was generally good. But when I shot at the lamp, the viewfinder show patterned dots in the whole screen, especially zoomed in with tele focal length. I switch to another lens, the same prob. Then I tried dust remove function and took a picture of white paper. There was no dust alerted, though.

Now I think the dots should come from the optics in viewfinder not the ccd and lens. Does anyone encounter the similar problems or have any suggestion? If this is a defect, I may return this and get a exchange in 14 days. I check a canon 400d from my friend and it's clear all the time (including shot at the lamp).

Thanks,
Ping


Last edited by duping812; 03-26-2009 at 08:52 PM.
03-26-2009, 09:11 PM   #2
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is it red dots?
could just be the focus point indicators....
03-26-2009, 09:14 PM   #3
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k-m doesn't have focus indicators...

maybe it's dust?
03-26-2009, 09:15 PM   #4
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I hope so
but they are in gray. you can not even notice them when point to general objects. they only show up when shoot very bright objects, like lamp or light.

03-26-2009, 09:18 PM   #5
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how do the photos look?
03-26-2009, 09:22 PM   #6
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QuoteOriginally posted by Stratman Quote
how do the photos look?
the photos looks fine. Attached is shot at a white paper for dust alert test.
https://www.pentaxforums.com/gallery/index.php?n=10901
03-26-2009, 09:27 PM   #7
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just could be dust in the focus screen..(or mirror)
tried blowing it off w/ a blower...?

doubt it's in the sensor if you can see it in the finder..
03-26-2009, 09:50 PM   #8
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It's not unusual to get dust on the focusing screen (above the mirror) in any SLR. You can try using an air blower (like the rocket air blower), but don't worry about it.

03-26-2009, 10:27 PM   #9
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I think he/she is referring to microlenses, wich become a bit visible with slower (darker) lens (or when zooming in with kit lens, as he stated - the lens becomes F5.6).
https://www.pentaxforums.com/forums/pentax-beginners-corner-q/33510-laser-mat...reen-150x.html

This isn't anything to worry about. If you had plain ground glass, like in older cameras, you'd even get random black dots (grain) instead of this "pattern" when using slower (darker) lens. Like in here:
http://farm1.static.flickr.com/26/94003473_ec7dcdb956_o.jpg

I think Canon has a plain'er matter focusing screen (no lenses), this makes it more smoother but darker (wich also forces it to be a bit smaller, so it dosnt get too dark). Lenses help avoid random scattering of the light (as plain matte does), and directs it to the viewer.
03-26-2009, 11:07 PM   #10
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You said "patterned"; does that mean they're arranged regularly, like they were put there on purpose? How many are there?

The matte focusing screen in my K200D will show a faint fingerprint-like ridge pattern in certain light, but that doesn't sound like the same thing you're seeing.
03-27-2009, 12:22 AM   #11
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Normal

These are the moire pattern of the matte focusing screen and you'll see them under some circumstances. Nothing to worry about :-)

QuoteOriginally posted by duping812 Quote
Got my K-m from prodigital2000@ebay this week. The camera is brand new in box. I checked the shutter actuation is around 200.
When I mount the kit lens and tried to take some samples, I found the viewfinder was generally good. But when I shot at the lamp, the viewfinder show patterned dots in the whole screen, especially zoomed in with tele focal length. I switch to another lens, the same prob. Then I tried dust remove function and took a picture of white paper. There was no dust alerted, though.

Now I think the dots should come from the optics in viewfinder not the ccd and lens. Does anyone encounter the similar problems or have any suggestion? If this is a defect, I may return this and get a exchange in 14 days. I check a canon 400d from my friend and it's clear all the time (including shot at the lamp).

Thanks,
Ping
03-27-2009, 11:19 AM   #12
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Thanks for all you guys' reply. Sorry I do not have any experience of slr before, now I know this "patterned dots or ridges" on focus screen are intentionaly made to deliver better optical images. And I forgot to mention the canon 400d uses a macro lens which might have larger aperture compared to k-m's kit lens, which could allievate the patterns.

Here I find some good information on the focus screen, some of the picture show clearly the patterns.
Translated version of http://www.xitek.com/info/showarticle.php?id=1065

Last edited by duping812; 03-27-2009 at 11:27 AM.
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