K20D Exposure Inaccuracy and Inconsistency

As we all know, the DPR review of the K20D has been out.

Whilst as usual, typical DPR review does not measurbate AF speed, AF accuracy, system time lag and exposure accuracy which IMO are the most important performance aspects for a DSLR, the sample photo gallery of the review does give us some hints, on the exposure accuracy of the Pentax DSLR system, with their current "flagship":-

http://www.dpreview.com/gallery/pentaxk20d_samples/

By doing some simple and basic statistical anlaysis, we can actually get much more useful information than what DPR have already told us:-

1. There are 12 samples out of the total 36 did not require exposure compensation. So, the hit rate is only 1/3, or 33.3%;

2. For the rest of the 24 samples (2/3 of he total samples) that required manual exposure compensation, 16, i.e., 16/36 or 44.4%, had +ve exposure compensation applied (so as to avoid underexposure);

3. Whereas for the other 8, i.e., 8/36 or 22.2%, -ve exposure compensation was made (so as to avoid overexposure);

4. The mean (average) value for the +ve compensation is +0.59EV with a standard deviation of +/- 0.21EV. The mostly applied (mode) compensation value is +0.7EV ;

5. The mean value for the -ve compensation is -0.55EV with a standard deviation of +/-0.17EV. The mostly applied compensation value is -0.7EV;

Well, as I always emphasize, we need to compare other results from the same (gang of) measurbator(s) for those measurbation reports published at the measurbation sites, so as to make things meaningful and for fair comparison as well so that we could interpret the results sensibly. By using the same methodology above, here we can get a summary of the results for the K20D, 450D (Canon), D300 (Nikon), A350 (Sony) and E-420 (Olympus), which are all the latest current DSLRs as most recently reviewed by the DPR. I tabulate them as follows:-

Camera (DPR Sample Gallery Link):	Pentax K20D	Canon 450D	Nikon D300	Sony A350	Olympus E-420
Number of Samples	36	36	36	36	40
Correct Exposure Rate	33.3%	44.4%	75%	80.6%	80%
Underexposure Rate	44.4%	2.8%	5.6%	2.8%	2.5%
Underexposure Compensation Amount (Mode)	+0.7EV	+0.7EV (one sample only)	+0.3EV and +0.7EV (two only)	+0.3EV (one only)	+0.3EV (one only)
Underexposure Compensation Amount (Mean)	+0.59EV	+0.7EV (one only)	+0.5EV	+0.3EV (one only)	+0.3EV (one only)
Underexposure Compensation (Standard Deviation to Mean)	+/-0.21EV	0EV (of course)	+/-0.2EV	0EV (of course)	0EV (of course)
Overexposure Rate	22.2%	52.8%	19.4%	16.7%	17.5%
Overexposure Compensation Amount (Mode)	-0.7EV	-0.7EV	-0.7EV	-0.7EV	-0.3EV
Overexposure Compensation Amount (Mean)	-0.55EV	-0.6EV	-0.59EV	-0.73EV	-0.36EV
Overexposure Compensation (Standard Deviation to Mean)	+/-0.17EV	+/-0.27EV	+/-0.18EV	+/-0.24EV	+/-0.14EV

Remark for Above: Green colour means the Best; Red colour means the Worst.


So, here comes the further analysis and observations for the above:-

1. The most unreliable DSLR in the exposure accuracy department is the Pentax K20D;

2. The King of Underexposure belongs to the Pentax! The K20D underexposes pictures in an unbelievable large percentage of 44.4%, which is very far more than the underexposure failure rate of all other DSLRs under test, which are all able to keep a very low percentage of underexposure;

3. The amount of underexposure for the Pentax is in a great amount of 0.7EV, also, in addition to the huge number of underexposed shots recorded (as they could be if not compensated);

4. The King of Overexposure belongs to the 450D, which has also an unbelieveable high rate of 52.8% (!?) of overexposure recorded (as they could be if not compensated). Whilst many Pentax fanboys always talked about the overexposure issue of the entry level Canon DSLRs just in order to defend the infamous underexposure problem of the Pentax DSLRs, I actually found that kind of defences is silly and pointless. Does a tends-to-overexpose-most 450D would turn a tends-to-underexpose-most K20D into a correctly exposing DSLR with their unsubstantiated argument? This stupidity just recalls my memory of my primary school classmates who told my teachers about the wrong acts of other classmates when they were caught of doing something wrong! ;-)

5. Surprisingly, the most reliable exposure system and DSLR outthere is the Olympus E-420. Despite the larger number of sample photos posted in the gallery. It nearly didn't underexpose any photos nor the amount of underexposure is significant (0.3EV only and for one sample only, out of 40). It did not overexpose more also, most of the time only a -0.3EV compensation is required (for those 7 overposed shots (as it could have been), there are 6 out of 40 applied -0.3EV only). I am really impressed. Well Done, Olympus!

6. In fact, the exposure system of Sony and Nikon are also very good to good. It is just that the Olympus is so excellent that they cannot be the best in this Shootout.

Ironically, the above shootout comparison breaks the myth of "Pentax DSLRs preserve highlights best" (Really?) as particular Pentaxians have been insisting on and strongly believe like the Gospel! The K20D is obviously not preserving highlight well neither, which just comes in second after the Canon 450D, for the risk of burning highlights. But do bear in mind that the K20D has also a super great tendency of underexposure (which no others will), which simply implies it is just a very inferior exposure system with very poor consistency afterall!

I know that some people would think or just to argue that the sample size is just "too small" (as always, when the test results are not so favourable to *them*. But how many samples are those guys need? There are 4 x 36 + 40 sample photos plus at least five officially provided bodies with various different lenses tested already). Or, those brand-blinded fan boys are consistently accusing that the reviewer(s) of DPR are being biased or even they don't know how to use the Pentax DSLRs (really funny! In fact the DPR crew are the real camera experts! They are just professional gear heads with far more technial knowledge about cameras than any Average Joe - they earn a living by testing cameras afterall!).

Anyway, I know that those people would still not be convinced but would start to bash Phil Askey and his employees. SO, I would point you to an expert Pentax user who is so official (and maybe too official! ;-)) and authoritative for you to believe. Inspect all the EXIF data of the sample photos in the following links:-

http://nedbunnell.blogspot.com/2008/06/17-70-test.html

http://nedbunnell.blogspot.com/2008/06/35mm-macro-photos-at-9000-ft.html

See, think and judge yourself. I won't explain and talk furthermore (as I have no more to say)!

In fact, the wonky metering and exposure system of Pentax DSLRs has been one of the biggest annoyances to many Pentaxians (as who have encountered the problem and reported or complained about it for years). The users have been simply wasting too much time in fiddling around with the exposure compensation values, just hoping to get the best exposure but in the end either photo opportunities were missed or just not-so-ideal exposures were resulted.

If Pentax still do not improve their system which is just with such a low hit rate and has great underexposure tendency but yet actually does not preserve highlights well neither, I really doubt how they could compete (or simply just to survive).

I think technically there must be something wrong inside their metering/exposure system in their DSLRs (and/or digital lenses) which only Pentax themselves would know (for why their this metering/exposure system is inferior). But anyway I still hope that they can improve and will improve, in the near future, and in the coming next models (although I have been rather disappointed and desperate for long already).

Read Also:- Underexposure Tendency of K10D and K100D