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09-28-2010, 02:15 PM   #1
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My Brand New KX - Problem?

I just got a brand new Kx....

Why is the Shutter speed changing when I switch from viewfinder to LV in AV mode?
Is this normal?

Here is an example:
I just took these two pictures in AV mode on a tripod.
The ONLY thing I did different between the two is switch from LV (first picture) to viewfinder (second picture)
The camera took it upon itself to change the shutter speed.

I can't figure out why this is happening.





09-28-2010, 02:18 PM   #2
Ole
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When you remove your eye from the viewfinder, light may enter and affect the meter. Pentax usually includes a viewfinder cover with their cameras. I cannot speak for the K-x, though.

And I don't know if that's the cause, either, because I would have expected the LV photo to be darker not brighter in that case.
09-28-2010, 02:34 PM   #3
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Does it consistently repeat itself, or just with this scene? The reason I ask is that what you have presented has a fairly large dynamic range, and the metering could be adjusting based on even a slight movement (though the photos above do look to be at the same fixed position). Does it occur with different scenes, and with a subject that has less contrast? Also, can auto ISO be enabled in AV mode? The one thing that stands out to me as possibly throwing the metering off is the shine on the remote around the number pad - it is properly exposed in the bottom photo while everything else is under, while in the top photo it is slightly over exposed. Ole's thought is also a good possibility - I don't have an exif reader, what were the shutter speeds?

Edit: I see the exposures are relatively long - metering systems do have a tougher time getting an accurate reading when they receive less light - that does generally start when you get past the 1/10th of a second mark (moreso at 1/2 or more). Once you are down to those levels it starts to become more of a guess, which I think might be happening here. Though the top photo is close, even it could use a 1/3 stop more light (the top half of the remote it still under exposed and I don't think the highlights would be blown at a 1/2 second exposure in this case). The bottom line though here is that the scene is very far from optimal conditions for most metering systems to get a consistently accurate exposure.

Last edited by pxpaulx; 09-28-2010 at 02:41 PM.
09-28-2010, 02:40 PM   #4
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It consistently repeat itself in any situation.

09-28-2010, 02:44 PM   #5
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QuoteOriginally posted by Braciola Quote
It consistently repeat itself in any situation.
That might be more of a problem then! Did you read my edit above? Do you have examples with a brighter scene where the meter should have an easier job of achieving proper exposure? A few more examples of at least a well lit room, or outdoor shots would help us to see if it a result of the poor lighting, or the camera itself!
09-28-2010, 04:25 PM   #6
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QuoteOriginally posted by Ole Quote
When you remove your eye from the viewfinder, light may enter and affect the meter. Pentax usually includes a viewfinder cover with their cameras. I cannot speak for the K-x, though.

And I don't know if that's the cause, either, because I would have expected the LV photo to be darker not brighter in that case.

Actually this may well be the cause - don't forget in LV the mirror is flipped up so any light entering the rear eyepiece wouldn't have any effect -

Whereas on the regular optical viewfinder shot -
if I may hazard a guess -
since the K-x was mounted on a tripod -
after viewing, the photographer stepped back away from the camera to take the shot -
therefore removing the eye from the rear optical viewfinder -
allowing in extraneous light -
hence the darker exposure
as the K-x metering "thought" there was more light than the actual scene through the lens?

Perhaps to confirm - could cover the eye piece when taking the viewfinder shot - eg: cover with a piece of thick paper or cardboard, or put a towel over the camera body?
09-29-2010, 12:33 AM   #7
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Thanks guys, but I get the same results in any lighting, and with me eye on or off the viewfinder.
09-29-2010, 01:40 AM   #8
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QuoteOriginally posted by Braciola Quote
Thanks guys, but I get the same results in any lighting, and with me eye on or off the viewfinder.
Totally normal. In "normal" (non-LV) modes the camera is using the 16 segment metering sensor (which is located in the prism house). In LV the camera is using the imaging sensor for metering and each pixel can be considered a separate segment. No wonder that info from 12 million segments is much more accurate than from 16 segments, thus the camera can evaluate the scene better in LV.

09-29-2010, 04:27 AM   #9
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QuoteOriginally posted by simico Quote
Totally normal. In "normal" (non-LV) modes the camera is using the 16 segment metering sensor (which is located in the prism house). In LV the camera is using the imaging sensor for metering and each pixel can be considered a separate segment. No wonder that info from 12 million segments is much more accurate than from 16 segments, thus the camera can evaluate the scene better in LV.
In all of the time I've been a member of this site, this is the first time I see the most logical and obviously correct answer to this.

But are you sure?
09-29-2010, 12:43 PM   #10
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Thanks guys,

As I suspected, there is something wrong with the camera.

I'm also getting help from the guys over at Steve's Digicams forum.

One forum member who owns the same camera tried this out with his.
Here is the results he got....

"I just ran a quick check and I'm sorry to say that my Kx behaved as it should. No changes in A/S combination between VF and LV, no matter where I point the camera to or what lighting condition it is."

Thankfully, I can still return the camera and exchange it for a new one.
09-30-2010, 01:37 AM   #11
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As simico mentioned it's most probably normal. It has to do with the light metering you have chosen. ( multi-segment, center weighted or spot).

Don't worry
09-30-2010, 08:44 AM   #12
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I just tried on my k-x. There is definitely a difference in behaviour. On the VF, if I have a scene where the reading stays constant when I move the camera around a little, the LV reading would fluctuate when I do the same. That said, the reading is exactly the same though, LV of VF. (EDITED BELOW)

*edit* I tried another scene and seems like the reading does change between LV and VF. LV metering results in a darker image. I guess it depends on the scene and that your K-x isn't really defective. (or maybe both our K-xes are! )
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