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10-10-2012, 08:13 AM   #1
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K-5 possible problem or just stupidity?

I was shooting some lanscape panaramas on the weekend. I set my camera on F18 but every time I pull the trigger it changes to F14 or something else. Is there a reason why it would do back. This meant that I had to change it back to F18 and sometimes that means I'd nudge the camera on the tripod.

Any help will be aprecaited.

10-10-2012, 08:39 AM   #2
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QuoteOriginally posted by lightningthief Quote
I was shooting some lanscape panaramas on the weekend. I set my camera on F18 but every time I pull the trigger it changes to F14 or something else. Is there a reason why it would do back. This meant that I had to change it back to F18 and sometimes that means I'd nudge the camera on the tripod.

Any help will be aprecaited.
If you panning, you should try to use M mode to avoid any metering changes by the camera.
10-10-2012, 08:43 AM   #3
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You probably have exposure bracketing on -- its taking an overexposed image, next it would take a normal exposure and after that, an underexposed image.
10-10-2012, 08:53 AM   #4
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I was snapping in "M" ... having done the metering and focussing, I also swiched auto focus off - so that the lens doesnt hunt and the focus stays constant.
The panorama bit is irrelavant - it's more the fact that it takes the photo on the required setting (F18) and then it switches to a different F-stop after pulling the trigger. I would expect the f-stops to stay the same until I change it. Cant wrap my brain around it.

10-10-2012, 09:01 AM   #5
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QuoteOriginally posted by lightningthief Quote
I was snapping in "M" ...
You can shoot in bracketing mode and M mode -- they aren't mutually exclusive
10-10-2012, 10:57 AM   #6
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I've also experienced a similar problem but using AE-L which, when using any mode other than Tav, can see a change in exposure from shot to shot.

I've advised Pentax of the problem having sent them sample images but they seem unconcerned and depite chasing them through the UK agent, I've had no acknowledgement whatsoever.

I've received various comments through tis forum about my usage of AE-L whilst performing panoramic sequences but none that will accept that the K5 has a intermittent faulty AE-L under certain conditions.
10-10-2012, 12:03 PM   #7
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I don't know if this falls into the same area but I'll throw it in.

I've noticed while taking bracketed shots, when I go to adjust either the number of shots or the amount of exposure, the shutter speed and aperture also change respectively. I need to manually reset them after.
10-10-2012, 04:01 PM   #8
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QuoteOriginally posted by lightningthief Quote
This meant that I had to change it back to F18 and sometimes that means I'd nudge the camera on the tripod.
Maybe the camera is doing you a favour. Why would you use f18? Do you like soft images?

10-12-2012, 08:11 AM   #9
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QuoteOriginally posted by rawr Quote
Maybe the camera is doing you a favour. Why would you use f18? Do you like soft images?
I was shooting a landscape - do you use f2.8?
10-12-2012, 09:08 AM   #10
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QuoteOriginally posted by lightningthief Quote
do you use f2.8?
Sure, if the distance and the DOF work ought OK, and I am happy with the sharpness of my lens at that aperture.

You need to check out the concept of diffraction is all I was suggesting...

This image from Lenstip, for example, shows how at f18 an otherwise very sharp lens like the DA 35 f2.4 is unable to deliver great resolution anymore, due to diffraction limiting. When using this lens, to get good DOF and maximise sharpness, probably f5.6 or f8 would have been a much better choice, for example.

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It's also quite true that your camera may really have been trying to rescue your image from a poor aperture choice. If you had your Program Line setting set to 'MTF Priority' (p 102 of the K-5 manual), when you use a Pentax lens the camera will indeed attempt to choose an aperture value to deliver the maximum resolution for your lens. The camera may be aware that f18 would not deliver optimal sharpness with the lens you were using.
10-14-2012, 11:00 AM   #11
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Page 114 in the manual. In some situations you can have set the aperture but it can change with other adjustments. Hyper manual, essentially you set the exposure with a button, then any adjustments up on one dial will move the other down. Not sure if this is happening, but worth a check.
10-16-2012, 08:36 AM   #12
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After I updated the firmware to 1.3 it works like new :-)
10-18-2012, 04:18 AM   #13
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QuoteOriginally posted by rawr Quote
Sure, if the distance and the DOF work ought OK, and I am happy with the sharpness of my lens at that aperture.

You need to check out the concept of diffraction is all I was suggesting...

This image from Lenstip, for example, shows how at f18 an otherwise very sharp lens like the DA 35 f2.4 is unable to deliver great resolution anymore, due to diffraction limiting. When using this lens, to get good DOF and maximise sharpness, probably f5.6 or f8 would have been a much better choice, for example.

Attachment 143202

It's also quite true that your camera may really have been trying to rescue your image from a poor aperture choice. If you had your Program Line setting set to 'MTF Priority' (p 102 of the K-5 manual), when you use a Pentax lens the camera will indeed attempt to choose an aperture value to deliver the maximum resolution for your lens. The camera may be aware that f18 would not deliver optimal sharpness with the lens you were using.
Thanks for your input... I was merely calculating hyperfocal distance. I do use F10 - F18 in lanscapes. You cannot always use your lens' sweetspot if you want the correct DOF in landscape photography, expecially is you have forground interest which you'd like to keep in focus whilst keeping the rest sharp.
So please check out the concept of hyperfocal distance :-)
10-18-2012, 05:18 AM   #14
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This has gone off the original query: why does the camera change the exposure in manual? Has bracketing been eliminated? The upgrade in firmware could have reset the bracketing.

Increasing aperture will increase DOF but when it is too high (f18 is high) diffraction kills the gain of extra DOF. It does become universally soft. Photography is management of compromises.
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