Magnified AF Errors of the SAFOX IX than the SAFOX VIII !?

Further to my last test to confirm the significant and consistent Front Focusing of the K-r/SAFOX IX under Yellow Light, I decided to check further about the focusing in/accuracy of the SAFOX IX when compared with the latest SAFOX VIII used in the K-x, side-by-side and head-to-head, at the same time, under identical testing conditions, with the same lens (at the same focal) and at the same aperture.

The test was carried out with PMAF (Phase-Matching AF) and CDAF (Contrast-Detection AF) under LiveView mode for both the K-r and the K-x and the amount of Back-Fronting or Front Focusing, if any, is observed. The same test methodology and a similar setup was used, which has been briefed here before. The following illustrations are included for the current test setup and camera settings etc:-



The lens used is a DA 16-45 fixed at 35mm and a f/4 aperture.

The results are tabulated results as follows:-

Camera / AF Method	Result (Click to Enlarge; EXIF preserved.)	Lens Distance Scale	Remark:
K-r / PMAF			Obvious Back Focusing
K-r / CDAF (LiveView)			Accurate Focus
K-x / PMAF			Slight Back Focusing
K-x / CDAF (LiveView)			Accurate Focus

As it can be seen from the above, it is easy to note that back focusing is obvious when PMAF is used for the K-r but with CDAF in LV mode, the AF is dead accurate. The difference in the measured distances is quite significant, also. However, the most annoying thing is that whilst K-x do show similar back focusing tendency under the same testing conditions, the order of magnitude and the impact is comparatively less and the final result is considerably more acceptable, as the error is less.

Also, I recall last time when the 43 Limited was used, the K-r front focusing more than the K-x under "yellow" condition. Now the K-r just back focusing more than the K-x in this test with another lens. So?

The safe conclusion that can be drawn again is that the AF errors of the SAFOX IX system is clearly (far) larger than that of the SAFOX VIII, at least if it is to be compared to the one used in the K-x. It seems that any AF error, no matter what it is and what caused it, is magnified with the SAFOX IX! Damn! >:-[


Last Test:-

SAFOX IX Tungsten/Yellow Light Front Focus Issue Fully Investigated

Sigma HSM is Incompatible with SAFOX IX (of K-5 and K-r)?

Roland Mabo notes at DPR that for the comment from another DPR poster who visited the Photokina Pentax booth that his Bigmas behaved weirdly on a K-5 for the AF. So, is the Sigma HSM just incompatible with the new Pentax SAFOX IX AF system? Does the SAFOX IX uses some completely new algorithms so that the old Sigma in-lens firmware (it's just software afterall) just won't work anymore?

It's not surprised that the compatibility from 3rd party manufacturer is not ensured as they are just not the original manufacturer. Nowadays, even the compatibility between the older and new products from the same original manufacturer cannot be guaranteed sometimes, what do we expect from the 3rd parties? Nevertheless, Sigma in the past did provide some free firmware updates to their products, e.g., their lenses and flashes, to make them work with new bodies from different manufacturers. Let's see if they will do it again this time.

It will not be surprised for Pentax has updated his software, as I believe that the hardware of the SAFOX IX and SAFOX VIII is more or less the same but yet Pentax claims that there is performance improvement. Furthermore, new firmware may work better for the new "DC" AF motor for the DA 18-135 lens, possibly, as this lens is just working in a completely different principle, primitively.

Update: Well, the original tester actually responded in the thread that he found AF problem with his Bigmas on K-7, just, not K-5! :-o So, it seems that it is just an old compatibility problem/performance issue that has not yet been resolved!

SAFOX IX Tungsten/Yellow Light Front Focus Issue Fully Investigated

Background

Since K-r and K-5 have been marketed, many Pentax users have been complaining about the obvious Front Focus (FF) issue resulted when using these cameras, when they were shooting at lower light and more so under tungsten light source, actually. A recent report here.

In fact, this "Yellow Light FF Symptom" was with Pentax users for long since Pentax made their first DSLR, the *ist D. But I did find that the problem was not as severe as before since Pentax had made the K-m and with the two successive models of the K-7 and K-x, too. But rather unfortunately, with the K-r, it seems that this issue strikes again and more of those adverse reports arose, which was also confirmed shortly after a few days use of my new K-r! :-(

So, I decided to do yet another controlled experiment, to compare the old SAFOX VII of my MZ-S, the SAFOX VIII (latest version) of my K-x and the SAFOX IX (first version) of the K-r:-



Test Methodology

1. The focus target is as below. It comprises of a stair case of 3 flat surfaces. The centre one is the main target, which has a good contrasty pattern, and is used for the AF, with the central single focus point of the cameras, in AF-S mode.



2. Each of the camera body is then mounted on a sturdy tripod. The light source is changed between Yellow and White, photos are taken and then where the final focus arrives in the final image per picture is observed. The lens focus/distance scale for the final focus measure is also recorded, for each picture.

3. The shutter release button is re-pressed for a few times until there is no re-focusing/hunting and that the camera believes firmly that its decided AF focus is correct.

4. Other testing notes and conditions: FA 43/1.9 Limited in Av mode at f/2.0, ISO 200, SR off, AF Single, Central AF point, AWB, latest firmware in K-r and last latest firmware in K-x.

The Results

Camera	Recorded Image	Lens' Distance
MZ-S / White Light Source	N/A
MZ-S / Yellow Light Source	N/A
K-x / White Light
K-x / Yellow Light
K-r (AF Fine Adj Off) / White Light
K-r (AF Fine Adj Off) / Yellow Light
K-r (AF Fine Adj On, at Max. Value of -10) / White Light
K-r (AF Fine Adj On, at Max. Value of -10) / Yellow Light

Observations and Conclusions

1. Both K-x and K-r (*without* focus adjust) are fairly accurate with white light source.

2. Under yellow light source, the K-x focus shifts forward and too with the K-r. But the span of the shift of the K-x is considerably less than that of the K-r. As a result, the K-x' picture is still somehow acceptable even it is front focused. On the other hand, the K-r picture under yellow light is totally out of focus for the target owing to the serious front focusing. This is verified from the lens' focus scale readings in the above the four respective pictures, too.

3. With focus adjust at -10 for the K-r, now it focuses more correctly under yellow light, but then it then causes obvious back focusing in white light. Again, the span between white and yellow light is large, although it is not as large as when the focus adjust is off.

4. The MZ-S / SAFOX VII is affected least by the yellow light with minimal effect. By looking at the focus scale, it matches well with the best focus pictures under white light for the K-x and K-r.

Afterall, how does that ten years old SAFOX VII still outperform both the last version of SAFOX VIII and now the latest SAFOX of IX (but which is now the worst!)? How come Pentax yet once again has sucked quality from the SAFOX IX, which they had already improved it to avoid the problem somehow with the latest revision of the SAFOX VIII?? :-o

And since I purchased the K-r to upgrade but not downgrade, its more serious yellow light FF symptom than the K-x really upset me. And this is for sure a big disappointment - I did not expect the K-r could be and should be worse than the K-x! >:-[

Remedials, then?

1. Use the LiveView to focus, the LV CDAF is not affected by the yellow light, last time I checked and verified. But with LV, of course it has its problem and limitations, such as no OVF could be used and the prolonged shutter lag (the shutter will be fired twice before a picture is taken).

2. Manually change the focus adjust setting each time for Yellow or White light source (do remember to set the memory function for the last accessed menu item to avoid more troubles if you do this! And do remember to check frequently to avoid "user error"!!).

But of course, the pre-requisite for you for doing this is that you must first have an accurate K-r in AF which requires no -ve focus adjust by default in the very beginning, just like mine. Otherwise, you will never be able to enter the required amount of (the -ve) correction if you have already used up some of the quota, just in case - which could happen with the "excellent" QC of Pentax nowadays.


Read Also:-

How AF Errors Can Decrease *Effective* Resolution?

Mysterious Firmware Revision Publication Changes for the K-r (and New K-5 Firmware Released)

Since the launch of K-r and K-5, it has been widely reported that this latest SAFOX IX/+ AF system of Pentax is really problematic in AF accuracy under indoor environments and particularly with tungsten lighting.

It is even found that the AF accuracy of the K-5 deteriorates sharply for a moderate lighting level at EV8 (which is not really quite dark actually) as measurbated by someone. As for the K-r, previously Pentax mysteriously withdrew the new 1.01 firmware from their Japanese global support page, which was not by accident, but intentionally.

Pentax Germany even admitted before that the K-r has the front focusing issue under lower/tungsten light and committed that a new K-r firmware would be released. However, a month has elapsed now and we only see today a new version of the K-5 firmware is released at the Pentax.jp English global support page:-

http://www.pentax.jp/english/support/digital/k-5_s.html

"Changes to V1.03

• Improved the accuracy of auto focus in low-intensity light condition.
• Improved stability for general performance."

I hope Pentax can really make it this time but not just made a wild claim but users still find that it doesn't work at all, e.g., their SAFOX + system *should* work under tungsten lighting. And, as a K-r user, I hope even more for them to update the K-r firmware soonest IF their new software algorithms could really cure the problem!

As for mysterious K-r disappearance case, after weeks, the K-r 1.01 firmware has been re-uploaded and re-published at the Pentax global support page again. I quickly downloaded it and re-installed the "latest" in my K-r to see if there is any hidden improvement. What I first did was to check about the actual and exact firmware version. Below is what I learnt with the PhotoME:-

Original shipped K-r firmware:

Last mysteriously withdrawn K-r firmware:

Latest re-uploaded K-r firmware:

So, Pentax guys at their HQs actually put a previous version of the firmware for the K-r but not a newer one, which is just very head scratching plus disappointing afterall! >:-( I have made a quick check about the indoor AF accuracy with the "latest" firmware 1.01.20.08, though. See the pair of test shots below:-


(AF Fine Adjustment Disabled)

Centre Crop:


(AF Fine Adjustment Enabled and at the Maximum Value of -10)

Centre Crop:

Lens used is a DA 16-45 at 45mm and f/4, focused at an object at about 1m away, the DoF is not that shallow actually. Central AF point was used, AF-Single mode; No re-composition of the frame.

Still, as you can see, the problem is the same and it is persistent. The camera Front Focused in indoor tungsten environment. An adjustment value of -10 will make it (as usually) and a sharp picture could be obtained.


Related:-

Two Yet Unresolved Major Issues of the K-5

Magnified AF Errors of the SAFOX IX than the SAFOX VIII !?

SAFOX IX Tungsten/Yellow Light Front Focus Issue Fully Investigated

Ten Reasons for Thinking Twice before Decided on a K-5..

K-r AF Point (Mode) Selection Firmware Bug

Pentax Germany Admitted the SAFOX IX Front Focusing Problem

http://forums.dpreview.com/forums/readflat.asp?forum=1036&thread=37582888

See the Google translation of the formal reply, as below:-

"Dear .....,

Thank you for your inquiry.

The focus problem you describe is well known. We are currently working flat out on a software-side solution to the problem. Once an update is available for this issue, we will publish it on our website. We ask you to be patient.

We hope to have been helpful with our response.

Please do not hesitate to contact us again with any questions.

Sincerely,
M. ....

Pentax Camera Support Team"

So, two weeks have passed and could Pentax HQs/Hoya really put out a *software* solution to a very possibly *hardware* issue that caused by a latent design defect (as a result of cutting corners too much!)? I really doubt much about it! >:-o


Related:-

Magnified AF Errors of the SAFOX IX than the SAFOX VIII !?

SAFOX IX Tungsten/Yellow Light Front Focus Issue Fully Investigated

A Deeper Technical Investigation into K-r's Front Focusing Issue under Tungsten (Part 2)

This Post is Continued from the Last Part.

After all those tests and measurements and with much hope in resolving the problem, I quickly acquired an IR block/stop/cut filter to see IF the problem could be eliminated:-



The filter is essential a glass filter with heat reflective coating on it. As such, it is also known as hot mirror, besides calling it a IR blocking filter. (More product brochures can be found here for the B+W and here for the Heliopan.)

A typical wavelength response on the light spectrum is as follows:-



It can be observed that such a filter does reflect red or green light when viewed from a large angle of incidence. In contrast, when it is viewed near perpendicularly, it is clear. Hence, these filters should not be used for wider lenses for an Angle of View greater than 60 degrees, i.e., at about 35mm 135 film equivalent. Theoretically, it has virtually no light loss for visible light and thus the EV drop should be zero and it is negligible.

Now, that's the most important part which we are looking for - the Results! Of course all tests were carried out under the same pure tungsten environment (at the same time). This time I only tested at 35mm of the focal, which was found to have a more dominant effect for the problem than the tele-side:-

Condition	Record of the Focus Scale for where AF was Measured	Result Image (Central 100% Crop)	Result Image (Large and Uncropped)
Without IR Cut Filter, Optical PMAF		View	Download
With IR Cut Filter, Optical PMAF		View	Download
With IR Cut Filter, Live View CDAF		View	Download
Without IR Cut Filter, Focus Adjust at -10 (Max.), PMAF		View	Download
With IR Cut Filter, Focus Adjust at -10 (Max.), PMAF		View	Download

Well, once again, the best focus was achieved with Live View. With the help of the IR block filter, the front focusing symptom has been relieved somehow, but only partially! :-( Now that the focusing error seems to be halved in this case and indeed it even did slightly better than making Focus Adjust at a full span backwards at -10 as allowed. Most possible focus correction was achieved with the use of IR cut filter together with a Focus Adjust at -10 - but it was still NOT there for exactly where the Live View could reach! :-o

To explain the half-failure (and half-success anyway!) of this IR cutting remedial, there are at least two possibilities:-

1. The IR block filter is not strong enough to reject all the harmful IR lights from tungsten and the SAFOX IX is just too sensitive to those;

2. The harmful IR light or near-IR lights are out of the flat rejection band of the filter such that the filtering is not as effective as desired. As such, some improvement can be seen but yet the problem is not totally eliminated!

No matter how, at the end of the day, Pentax must be blamed for the in-born latent defect and that complete design fault of the SAFOX IX system that they created. In fact, this fault is a very serious one and is unforgivable for the large amount of focusing error that is produced! >:-[

Nevertheless, I am still feeling somehow good to find out and know about the truth and then to report in details here for what I've discovered. It is a tragedy for all we K-r and actually all Pentax users after all as it is seen that Pentax created an inferior AF system like this. I do hope that it should *never* happen again in the Pentaxland, for any new Pentax body to come!

N.B. Last time I used an entry level Canon 550D (for a complete month), it never had this kind of front focusing problem under tungsten and the AF had been dead accurate! >:-(


Related:-

Pentax UK and Pentax Germany Admitted K-r Tungsten Front Focusing Issue (But there is No Solution, as Both Clearly Told)

Still Annoying K-5 and K-r Old Issues, Users are Pissed Off!

SAFOX IX Tungsten/Yellow Light Front Focus Issue Fully Investigated

Mega Poll: Current Pentax DSLR Body Selection Dilemmas!

Since the launches of the K-r and the K-5, I have seen daily at various Pentax forums over the net that Pentaxians have puzzled much about their purchase of a new Pentax DSLR amongst the four models which are currently available for selection, at least for this transitional period. In fact, I haven't seen such a big chaos since Pentax marketed their first DSLR! Some of the biggest dilemmas include K-r Vs K-7 as the price is so close or K-r Vs K-5 as the price difference is so big and so on.. Well, the decisions are always tough! :-o :-[

How to Vote?

If you have to choose between two (i.e., a typical X or Y question) amongst four models, it simply means 6 combinations (i.e., 4 x 3 / 2). Amongst all these 6 combinations, choose the utmost dilemma(s) you would face and then make the decision for voting. Please don't vote in a dilemma that you would never face, e.g., if you are not interested in neither the K-x nor the K-7, then you should not vote in that particular sub-poll.

Okay, here we go and let's go! :-D

1. K-x Vs K-7 (Latest Prices at Amazon are $499.88 w/ DAL 18-55 Vs $1016.83 w/ DA 18-55 WR):

What to be Puzzled About: 12M Sony Vs 14M Samsung Sensor, High ISO Noise Performance difference, different Colour Response and Taste, Lack of Weather Sealing or Not, ex-Entry Level body Vs Mid-level ex-Flagship, Control Interface and Operation differences, Metal body Vs Plastic, Support Cable Switch or Not, Smaller/Lighter or Larger/Heavier Body, SAFOX VIII Vs SAFOX VIII+, 100 Colours Vs 2 Colours, Forced Dark Frame Subtraction for Long Exposure (>30s) or Not, 4.7 fps Vs 5.2 fps, Use of AA Batteries Vs Proprietary Li-ion and so on..

K-x or K-7 Now?
	K-x
	K-7
pollcode.com free polls

2. K-x Vs K-r (Latest Prices at Amazon are $499.88 w/ DAL 18-55 Vs $829.15 w/ DAL 18-55):

What to be Puzzled About: Extra (software expanded) ISO of 25600 (a non-issue to me, frankly), Essentially the Same Sensor, New Li-ion Power with Optional AA Adaptor, Red-Dot Indication for AF Points and Selection, Different Style in Appearance (mainly the cameras' top/head), New Entry Level Vs ex-Entry Level, Slightly Smaller/Lighter or Larger/Heavier Body, 20 Body Colours Vs 10, 5 Grip Colours Vs 12 and so on..

K-x or K-r Now?
	K-x
	K-r
pollcode.com free polls

3. K-r Vs K-7 (Latest Prices at Amazon are $829.15 w/ DAL 18-55 Vs $1016.83 w/ DA 18-55 WR):

What to be Puzzled About: 12M Sony Vs 14M Samsung Sensor, High ISO Noise Performance difference, different Colour Response and Taste, Weather Sealing or Not, New Entry Level Vs Mid-level ex-Flagship, Control and Interface, Plastic Vs Metal body, Support Cable Switch or Not, Smaller/Lighter or Larger/Heavier Body, SAFOX IX Vs SAFOX VIII+, 100 Colours Vs ONE (i.e., in Black Only), No Forced Dark Frame Subtraction for Long Exposure (>30s) or Not, 6 fps Vs 5.2 fps, Support of AA Batteries (with Optional Adaptor) Vs Proprietary Li-ion and so on..

K-r or K-7 Now?
	K-r
	K-7
pollcode.com free polls

4. K-r Vs K-5 (Latest Prices at Amazon are $829.15 w/ DAL 18-55 Vs $1749.95 w/ DA 18-55 WR):

What to be Puzzled About: Sony 12M or 16M Sensor, No Weather Sealing or Not, New Entry-Level Vs New Mid-level Flagship, Control Interface and Operation Differences, Plastic Vs Metal body, No Support of Cable Switch or Not, Smaller/Lighter or Larger/Heavier Body, SAFOX IX Vs SAFOX IX+, 120 Colours Vs ONE, 6 fps Vs 7 fps, Support of AA Batteries with Optional Adaptor or Not, HD Vs Full HD Videos (all in Motion JPEG anyway), and so on..

K-r or K-5 Now?
	K-r
	K-5
pollcode.com free polls

5. K-5 Vs K-7 (Latest Prices at Amazon are $1749.95 w/ DA 18-55 WR Vs $1016.83 w/ DA 18-55 WR):

What to be Puzzled About: Sony 16M Vs Samsung 14M Sensor, High ISO Noise Performance difference, different Colour Response and Taste, New Flagship Vs ex-Flagship, Essentially the Same Body Chassis and Frame, Super Slow CDAF Vs Quite Fast CDAF, Full HD Vs HD Videos, SAFOX IX+ Vs SAFOX VIII+, Black Colour Only Vs Black or Silver, No Forced Dark Frame Subtraction for Long Exposure (>30s) Vs Forced, 5.2 fps Vs 7 fps, practically faster Continuous AF on Continuous Frame Mode and so on..

K-5 or K-7 Now?
	K-5
	K-7
pollcode.com free polls

6. K-5 Vs K-x (Latest Prices at Amazon are $1749.95 w/ DA 18-55 WR Vs $499.88 w/ DAL 18-55:

What to be Puzzled About: After so many technical comparisons above, I just don't even list out any of those between the two this time. We should know there is one very obvious and important difference here, i.e., the price! The K-x kit is only 28% something of the cost of a K-5 one, both with a 18-55 lens. If you just want a new Pentax DSLR body c/w a standard kit zoom, should you get the cheapest or the dearest? :-o

K-5 or K-x Now?
	K-5
	K-x
pollcode.com free polls

Okay, it's Your Take Now! I shall come back to do some analyses and quick summaries a few days after. :-)

A Deeper Technical Investigation into K-r's Front Focusing Issue under Tungsten (Part 1)

I started a more systematic approach to investigate the tungsten front focus problem of the K-r and see what's wrong with the design of that SAFOX IX AF system that is used.

To begin with, I tested the camera in a dark room, selected an object with a flat surface on which there was clear contrasty patterns, and then projected pure Red light (using the spotbeam projector of an external dedicated Pentax flashgun) and Green light (using the built-in AF assist light) onto the target and did the AF. The results were: NO problem for both, the AF was fairly accurate!

I then tried the Blue light. But since I could not find a pure Blue light source for projection. I used pure 6000K White light source and then put on a 80A (Blue) filter and did the same test. Again, the AF had been *accurate*! :-o

As such, I re-thought again.. What lights actually a tungsten bulb contains? It is Yellow light, which should be somewhere between the Red and Green for the wavelength in the visible light spectrum.

But however, since the above investigations shown that it is not the problem with neither Red nor Green and thus it is safely derived that Yellow light should cause no problem neither. So, actually what is the real *source* of problem? Could it be the Infrared? Which was just invisible, as tungsten does also emit very strong Infrared, as a heat source more than a light source actually.

Some time later, I picked out my old Pentax F35-70 AF lens, which has two Infrared focusing marks on the distance scale. I then tried to shoot under a *pure* tungsten environment that was actually fairly bright, at 260 Lux:-



The camera was set up like this and the shoot target is also shown below:-


(Firmware in Camera is the Latest, i.e. V1.11; Focus Fine Adjustment was Disabled.)



Below are the test results obtained:-

AF Method and Focal	Record of the Focus Scale for where AF was Measured	Result Image (Central 100% Crop)	Result Image (Large and Uncropped)
@ 35mm, Optical Phase-matching AF		View	Download
@ 35mm, Live View Contrast-detection AF		View	Download
@ 70mm, Optical Phase-matching AF		View	Download
@ 70mm, Live View Contrast-detection AF		View	Download

After all, what do you observe above? Indeed, Live View CDAF always measured correct focuses, whilst front focusing *had to* be resulted with PMAF under tungsten. Now, as seen from the above, it is confirmed that amount of errors and the shifts in distances from the correct focus points are very close to the indicated derivation with the IR marks from the central focus mark for normal (visible) light. This holds true for both 35mm and 70mm respectively! That's say if we shoot Infrared film with our Pentax K-r cameras, then the results *should* be mostly correct! :-o

It should be further noted that the effect and amount of error is lower for tele than wide angle, i.e., the magnitude of the distance error is larger as focal length becomes shorter. Indeed, this is what shown on the Infrared marks on the above lens, already.

But since that all Pentax DSLRs are 1.5X cropped with the APS-C sized sensors inside, a shorter focal length is always used for the same Angle of View. As such, the effect of this error is magnified! >:-(

Now, I just could never imagine that after twenty something years, the Infrared marks of my old lens have been useful again, but they are used in another way, i.e., instead of to put the focus to a closer distance, the lens should be manual focus to a farther distance! :-o

After all these, it seems that the main cause of the problem is about the existence of Infrared light in the shooting environment, which is received by the AF module and ultimately onto the sensor and then the whole focus measurement is flawed! The fact is that the those SAFOX IX Pentax DSLRs had to focus on IR instead of visible light when IR is existent and they are rather too sensitive to it! Really damn it! >:-(

In fact, the old AOC Pentax engineers knew about the adverse effect of the Infrared light to the AF system when the original SAFOX (I and II) was designed and created, see this diagram (Credit: Bojidar's Pentax K-mount Page):-



Where the component #5 in the above is just the Infrared Filter!

I am 100% sure that neither my SFX (the first Pentax mass-production AFSLR) nor my MZ-S (which is the second last Pentax 135 film SLR) that uses the older SAFOXes did suffer from this tungsten front focusing issue. There was no nightmare of this issue not until I acquired my *ist D, the first Pentax DSLR, back to January 2004!

So, am I going to resolve this tedious and super annoying problem, which is simply a latent design flaw and defect of the K-r (and many of the Pentax DSLRs) created by Pentax? We shall see in the next/coming part of my report.

Continued on the Next Part.


Previous Related:-

Pentax UK and Pentax Germany Admitted K-r Tungsten Front Focusing Issue (But there is No Solution, as Both Clearly Told)

SAFOX IX Tungsten/Yellow Light Front Focus Issue Fully Investigated