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08-08-2013, 07:02 PM   #1
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K5-II +/- exposures have large errors, in AEB mode >>

>> K5-II +/- exposures have large errors, in AEB mode >>

Long exposures appear to have large errors, using AEB mode.
Also, even for the same starting point, two different photo
sets, can have actual +/- exposures that are different.
Strange but true.

Some examples for my Pentax K5 II with FW v1.04 follow.
The values are for a fixed aperture and ISO setting.

Ex1, Theoretical plus Actual exposure:
0EV = 1.0, 1.0
-1EV = 0.5, 0.8 (error=+60%)
+1EV = 2.0, 3.0 (error=+50%)
-2EV = 0.25, 0.30 (error=+20%)
+2EV = 4.0, 5.0 (error=+25%)

Ex2, Theoretical plus Actual exposure:
0EV = 1.0, 1.0
-1EV = 0.5, 0.8 (error=+60%)
+1EV = 2.0, 3.0 (error=+50%)
-2EV = 0.25, 0.40 (error=+60%)
+2EV = 4.0, 6.0 (error=+50%)

Ex3, Theoretical plus Actual exposure:
0EV = 2.0, 2.0
-1EV = 1.0, 0.8 (error=-20%)
+1EV = 4.0, 2.5 (error=-38%)
-2EV = 0.5, 0.4 (error=-20%)
+2EV = 8.0, 6.0 (error=-25%)

Ex4, Theoretical plus Actual exposure:
0EV = 1.0, 1.0
-1EV = 0.5, 0.6 (error=+20%)
+1EV = 2.0, 2.5 (error=+25%)
-2EV = 0.25, 0.25 (error= 0%)
+2EV = 4.0, 4.0 (error= 0%)

Ex5, Theoretical plus Actual exposure:
0EV = 1/400, 1/400
-1EV = 1/800, 1/800 (error=0%)
+1EV = 1/200, 1/200 (error=0%)
-2EV = 1/1600, 1/1600 (error=0%)
+2EV = 1/100, 1/100 (error=0%)

Ex6, Theoretical plus Actual exposure:
0EV = 1/400, 1/400
-2EV = 1/1600, 1/1600 (error=0%)
+2EV = 1/100, 1/100 (error=0%)
-4EV = 1/6400, 1/6400 (error=0%)
+4EV = 1/25, 1/25 (error=0%)

Any comments?
Thanks in advance

08-08-2013, 08:43 PM   #2
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Pictures with EXIF?

Metering mode?

Test parameters?
08-08-2013, 10:05 PM   #3
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I heard from direct Pentax source, speaking on condition of anonymity that there's an incurable bug in Safox X that defaults AE lock with corrupted readings to AF lock. Pentax will need to create brand new build of that Safox version and major firmware overhaul will have to be done. There's a saying :"If it works, don't fix it". Safox IX+ apparently worked very well and tweaking it due to complaints of some "pro photographers" in Pentax customer base led to a major problem.
08-08-2013, 10:42 PM   #4
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Hi,

>> Extra EXIF data >>
F/8
ISO 200
White Balance = Manual
Metering Mode = Matrix
Exposure Programme = Aperture Priority
Exposure Mode = AutoBracket

>> Other camera settings that might be useful >>
File Format = JPEG
JPEG Pixels = 16M
JPEG Quality = 4 stars
White Balance = Daylight
Focus = AF.S
Meter Operating Time = 10sec
AE-L with AF Locked = Off
Link AE to AF Point = Off
Auto EV Compensation = Off
One-Push Bracketing = On
WB Adjustable Range = Auto Adjustment

>> Images >>
The shots are mainly sunsets at the beach, so light is changing over time (to varying degrees).

Cheers

08-09-2013, 01:05 AM   #5
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QuoteOriginally posted by atarget Quote
I heard from direct Pentax source, speaking on condition of anonymity that there's an incurable bug in Safox X that defaults AE lock with corrupted readings to AF lock. Pentax will need to create brand new build of that Safox version and major firmware overhaul will have to be done. There's a saying :"If it works, don't fix it". Safox IX+ apparently worked very well and tweaking it due to complaints of some "pro photographers" in Pentax customer base led to a major problem.
Hahaha
08-09-2013, 02:32 AM   #6
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QuoteOriginally posted by fs999 Quote
Hahaha
08-09-2013, 02:46 AM - 1 Like   #7
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Hi All,

The Pentax K5 II AEB mode could have been implemented using one of the following methods:
(1) taking a snapshot of the exposure at shot number 1, and using this to calculate all subsequent bracketed shots.
(2) recalculating the exposure at the start of each bracketed shot.
Also, I have read about various cameras being more or less sensitive to extraneous light entering through the eyepiece.

So I assumed that method (2) might have been used, and that the camera might be sensitive to light entering through the eyepiece.
I tested this assumption, and found both to be true.

I noticed that slight variations in light behind the eyepiece, had a noticeable change on the calculated exposure value for each bracketed shot.
Shining a light near the eyepiece, had a dramatic effect on the calculated exposure value for each bracketed shot.

Making a black shade for the eyepiece, was enough to get consistent exposures (at least for a few initial tests).

So that's one possible explanation for my previous test results.

Cheers
08-09-2013, 04:09 AM   #8
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That's why the camera comes with a nifty little viewfinder cover that attaches via rails.

08-09-2013, 04:56 AM   #9
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Alternatively, leave the rubber eye piece connected, and use the universal solution to everything - gaffer tape !!
Cheers
08-09-2013, 07:36 AM   #10
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Hi

In my personal opinion, these are minor nitty gritties. (Personal Opinion only, absolutely no intention of flaming or offending). I did not buy Nikon D800 / 5D Mark III. I bought a mid-range xemi-pro DSLR and for minor light correction I can use Lightroom.

I bought a camera with HIGHEST Dynamic range amongst APSc sensor cameras with dust / moisture proofing. The weight is just about right, It fits my hand - As Jim Carrey would say "Like a glove".

It has a remote control (IR), The digital leveling (from 7D).

The best - Entire range of legacy glass to most modern glass available to choose from. (Most people don't go beyond 5 lenses who buy a DSLR except really really lens savvy people).

So all the maths / physics which can be counted as short comings of this camera well, are part of the package.

Cheers!
08-09-2013, 09:35 AM   #11
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QuoteOriginally posted by Deedee Quote
Hi



It has a remote control (IR)



Cheers!
Amazon.com: IR Wireless Remote Control for PENTAX Q, PENTAX DSLR (645D, K-m, K-r, K-x, K-01, K-5, K-7, K10D, K20D, K100D, K110D, K200D, K2000) *ist (D, DL, DL2, DS, DS2) + Premium MagicFiber Microfiber Cleaning Cloth: Camera & Photo

And the "w/t" button will AF

Also it has my all-time favorite feature: CIF
You just need to calibrate it with each manual lens you have ( K-5 can memorize up to 20 lenses)
In order to do it just use "fine af adjustment" function. Activate AF-S, blur the image in OVF little bit then push shutter release all the way and start slowly turning focus ring on your manual lens. After pic is taken, check for sharpness. If it's tack sharp - you're good. If it's blurred, do not change position of focusing ring
and switch to manual focusing then to LV then hit "info button" until you get 10x mag. Now you're using more accurate, contrast detection focusing. If the subject that was "in focus" when pic was taken sharpens up while focusing ring is turned counter clockwise, move fine adj. cursor to - say - "minus five". If it sharpens up with clockwise turn, give it "plus five", Repeat the process. I had to give my Rokinon 85mm f/1.4 "minus ten" but now it's working like a charm. My other Rokinon : 35mm f/1.4 strangely didn't need any fine tuning and CIF worked here right on $ .
08-09-2013, 09:40 AM   #12
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QuoteOriginally posted by cosmo1957 Quote
Hi, >> Extra EXIF data >> F/8 ISO 200 White Balance = Manual Metering Mode = Matrix Exposure Programme = Aperture Priority Exposure Mode = AutoBracket
When I asked the question I was expecting it to be spot metering which could change enough between exposures to cause that. Try the same test with the cover on the viewfinder, it might be as simple as on the slow exposures you backed away from the camera to wait, and on the fast ones you did not have time. Try that to at least eliminate extra light through the viewfinder as a possible problem.

I have k-5 and use AEB a lot with no issues as you describe.
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