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12-09-2010, 09:53 PM   #1
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[langtitle=hi]K-x Q: Light profile varies from pic to pic[/langtitle]

Friends,

I was trying to test my 1 week old K-x for the blur problem For this, I set shutter to 1/100, and tried to take consecutive shots of metal and glass (on a ceiling fan). Since I was shooting in a room lit by a table lamp, I used the flash for all these shots. I could not find a blur problem, but the pics come out brighter and darker alternately. Have you an idea why the light profile changes from pic to pic? The only thing I can think of is amount of flash from pic to pic.

Thanks,

PS:
I noticed that both my kit lenses had usage marks in the plastic mount. Have you ever checked your lens for this? Would this be because of testing or maybe a used piece?


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12-10-2010, 10:50 AM   #2
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I think you are on the right track. The P-TTL flash system uses a low-powered pre-flash to calculate how much power to use for the photo. Even if you have fixed a certain shutter speed, aperture and ISO, a change in flash power can alter the exposure. With your test shots, you have a reflective object and a slight change in framing. Reflections can really trick the P-TTL system. A slight change in framing can move a reflection from one metering segment to another, changing the flash power calculations.

I also think that the flash will alter your results. The flash is a short-duration burst of light. It will freeze movement as if you used a very high shutter speed. I don't think it's the best way to reveal the problem.

I wouldn't worry much about lens mount wear. Think of it as saving wear on your camera's mount. After 4+ years and hundreds of lenses, here's what my old camera looked like:

12-10-2010, 11:48 AM   #3
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Thanks for the info on flash.

I agree that it is better to use ambient light to test for blur. So, we can also infer that using flash reduces blur from photographer's hands. That's handy to know.

As for the wear marks, I think they were there in the packaged lens, before I put them on.

Sorry for loading the page with so many boring pics, but it was just to show a continuing sample.
12-10-2010, 01:43 PM   #4
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QuoteOriginally posted by msharma Quote
Thanks for the info on flash.

I agree that it is better to use ambient light to test for blur. So, we can also infer that using flash reduces blur from photographer's hands. That's handy to know.

As for the wear marks, I think they were there in the packaged lens, before I put them on.

Sorry for loading the page with so many boring pics, but it was just to show a continuing sample.
What Blurr problem were you testing for?

The shake reduction system causing blurr, the mirror mechanism? or just blurr from hand holding, the SR system and mirror slap would go away because SR is off in flash moide automatically, and the flash duration is so short it stops most blurr

as for the images, it is not so much the P-TTL that gets upset by the slight framing changes, but the matrix metering, since slight framing changes alter the proportional blend of other subjects in the shot.

For any test on metering you should use a tripod to gaurantee the framing between shots, although in this case the different framing shuold not have the .7EV difference you observe,

I would agree with dave that a large part of this issue could be the state of the flash charge between shots.

12-10-2010, 02:19 PM   #5
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Yeah, I was testing the blur caused by shake reduction system. I have tested it in daylight, but not very throughly, may have to choose better subjects that don't gloss over blur.

Thanks for the info on metering. I was wondering if it is metering. I had spot metering, which I changed to one of the other two. The spot metering itself didn't help, maybe because the metered subject changed.
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