|
Forum: Digital Processing, Software, and Printing
02-16-2016, 09:03 AM
|
| |
Hi,
I created camera color profiles with an X-Rite ColorChecker for all Pentax cameras I own(ed) and am happy to share them with you :cool:
There are profiles for the K-5, K-5 II and K-3. They come in two varieties:
- created with the standard X-Rite software that comes with the Colorchecker (marked "X-Rite")
- created with DCamProf, a free new camera profiling software developed by Anders Torger
You can find more information about DCamProf here: DCamProf. It's command-line only and not easy for beginners, but IMO the results are fantastic.
The killer feature of DCamProf is the so-called "neutral tone reproduction operator" it uses for the embedded tone curve: More Info
All profiles can be found here:
{Dead Link Removed 6-26-2017}
Enjoy!
|
|
Forum: Pentax SLR Lens Discussion
01-18-2016, 02:33 AM
|
| |
This takes pixel peeping to a new level of madness: "Look at those vast resolution differences @800%"
(SCNR ;))
|
|
Forum: Pentax SLR Lens Discussion
12-21-2015, 08:32 AM
|
| |
The obvious answer is the current dedicated Pentax lens for portraits, the DA*55/1.4
Better bokeh than the 70/2.4 IMO, sharper than the 77/1.8 and less aberrations at the same aperture. However, the 77/1.8 might have a tad smoother bokeh, but both are outstanding in this respect; the DA 55/1.4 bokeh is a bit nervous at f/1.4, but from f/1.8 on it is very smooth.
|
|
Forum: Pentax SLR Lens Discussion
01-07-2015, 03:14 AM
|
| |
I recently bought a Sigma 17-70 C and took lots of pictures with my K-5 II to decide whether I received a good copy that is worth keeping. The good news is that the lens delivered very nice image quality, AF was always spot on at all focal lenghts (I took my test shots at 17, 21, 31 and 70mm) and there was no sign of decentering or other optical or mechanical problems. However, I discovered a compatibility problem with Pentax’s Shake Reduction (SR) function that, much to my regret, left me no choice but to return this otherwise nice lens. Please read on...
The Problem:
It took me a while to figure this out - I first noticed that some shots at 17 and 21mm were not sharp. I first suspected optical problems, but further tests proved that the lens is generally very sharp there as well. If there, the unsharpness looked like it was caused by camera shake. What I failed to understand was how it was possible to have so much blurred pictures at 17 and 21mm while none taken at 31 and 70mm, even shot with the same shutter speed, showed any sign of it. Weird…
To provoke the issue I took a series of pictures at shutter speeds where SR really matters, e.g. 1/13 or 1/10 seconds at 17mm. Result: About 9 out of 10 images showed camera shake, some of them quite pronounced.
It looked like this (100% crop): http://i.imgur.com/m5CoJ03.jpg
Now it’s getting interesting! A cross-test with my DA 18-135 (@18) and DA 15 (also at 1/13 or 1/10 seconds) showed the opposite behaviour: 9 out of 10 images were pin-sharp, only 1 showed slight signs of camera shake. Back to the 17-70, this time with SR deactivated: Only about 5 out of 10 images were blurred, and to a lesser extent than with SR activated. This led me to the conclusion that somehow SR is actually making things worse at short focal lengths. But why is SR malfunctioning here? To find out, I took a closer look at the metadata of the images created by the lens.
To function correctly, Pentax’s SR needs to know the actual focal length of the lens. Reason: the longer the focal length, the bigger the countermovement of the sensor needs to be for a given amount of camera shake. Please note we’re dealing with two values here:
1. The “normal” focal length information that can be read with almost any image editor from the EXIF data.
2. The focal length used for the SR mechanism (this is found in the so-called “manufacturer notes” metadata).
Most of the time 1. and 2. will be identical, but a different value in 2. is needed e.g. for lenses with internal focusing whose actual focal length changes with focus distance. The SR mechanism always uses the 2. value.
Now the problem: The “normal” focal length information is transmitted by the 17-70 to the camera without issues, but the “SR focal length” is plain wrong at the short end. This can clearly be seen in the metadata, where “focal length” is always correct but “SR focal length” is wrong at shorter focal lengths (I tested 17 and 21mm; from 31mm upwards it seemed OK). See for yourself the metadata of three shots at 17 or 21 mm: http://imgur.com/a/EFjUt
While “normal” focal length is correctly reported as 17mm or 21mm for all, “SR focal length” can be any value from 31mm to 70mm(!). This obviously leads to a malfunctioning of the SR mechanism, which overcorrects the camera shake and thus blurs the image.
At longer focal lengths (31mm and above) both focal length values are identical in the metadata and SR seems to work correctly.
My guess is that Sigma forgot to ensure that this value is transmitted correctly. You have to remember that they do not officially licence the K-mount and rely on reverse-engeneering the communication protocols between lens and camera. It’s easy to forget a seemingly harmless value in the manufacturer notes. However, in this case it causes real damage and makes SR useless at shorter focal lengths. Even worse, it actually amplifies the camera shake (SA - Shake Amplification :eek:) and leaves the user no option but to disable SR at these focal lengths.
By the way, you can also see the weird SR behaviour in action during Live View: The image seems somewhat “jerky” and panning movements look really strange at the short end. If you zoom beyond 28mm or so the behaviour goes back to normal.
I strongly suspect this is a general issue with all copies of this lens and probably affects all Pentax camera bodies with SR. Unfortunately, all the images I found on the web from other Pentax users of this lens had most of their metadata stripped (Adobe products regularly do this) and no longer contained the manufacturer notes which show the “SR focal length” value. So to confirm the issue it would be great if owners of the lens could test their copy in the 17-21mm range to find out if this issue applies to all copies of the lens (and to all cameras). You can check the “SR focal length” value (both for JPG and Raw files) with programs like PhotoMe, or just upload them somewhere and I can check for you. Thanks!
Possible Solutions/Workarounds:
For now, the only option is to deactivate SR at shorter focal lengths because it does not reduce but actually amplifies camera shake. This won’t cause motion blur at shorter shutter speeds like 1/100 or above (where you wouldn’t need SR anyway :hmm:), but at speeds where SR matters it will actually work against you...
The Next Steps:
I guess the only party that can truly solve this problem is Sigma. Hopefully it is fixable with a firmware update of the lens. But I fear this will probably be regarded as a minor issue (I disagree!) that only applies to their least important supported camera mount.
As soon as others confirm the problem with their copies of the lens, I will notify my local Sigma representatives (Sigma Germany) of this issue and point them to this thread, and I encourage you to do the same in your part of the world. Maybe then we’ll have a chance that Sigma HQ takes notice of this problem and will try to fix it.
I will update this thread if I receive any news from Sigma regarding this problem.
Please note that I cannot do any further tests with this lens as I returned my copy to the seller. I will happily buy a copy again as soon as Sigma resolves this problem, because otherwise I really liked the lens.
-----------------
UPDATE:
Believe it or not, Sigma has already addressed this issue and published a firmware update that is supposed to fix the SR misbehavior. Kudos to Sigma for this quick reaction and for caring about their customers!
Further Information: https://www.pentaxforums.com/articles/pentax-related-news/sigma-addresses-17-...ion-issue.html
|
|
Forum: Pentax SLR Lens Discussion
01-23-2015, 02:07 PM
|
| |
Good news!
Today I received a notification from Sigma Germany that Sigma HQ acknowledged the problem and has already provided a fix:.
 Quote: 2015.01.23
Dear SIGMA 17-70mm F2.8-4 DC MACRO HSM | Contemporary PENTAX Users - Firmware Update of the Lens
Thank you for purchasing and using our products.
We have found that the SIGMA 17-70mm F2.8-4 DC MACRO HSM | Contemporary PENTAX does not function properly when the image stabilizing system on the camera body is used.
For those who own the lens, we are going to provide the firmware update free of charge.
Please note that all lenses shipped from our factory from now on will have the latest firmware.
We appreciate your continued support for our company and products.
[Product]
SIGMA 17-70mm F2.8-4 DC MACRO HSM | Contemporary PENTAX
[Phenomenon]
When the image stabilizing system on the camera body is used, the degree of image blur becomes bigger.
For further information, please contact your nearest authorized subsidiary / distributor of SIGMA.
For those who own the SIGMA USB DOCK, it is possible to update the firmware through SIGMA Optimization Pro 1.2. Source: https://www.sigma-photo.co.jp/english/new/new_topic.php?id=491
I must say I'm surprised how well Sigma has handled this issue - I didn't expect a solution so fast (and was worrying if it would be forthcoming at all...)! Many thanks to the diligent people at Sigma!:)
|
|
Forum: Pentax SLR Lens Discussion
01-09-2014, 01:37 AM
|
| |
There are different kinds of decentering which need different tools to detect.
One kind is that the lens elements are parallel but not lined up exactly at their center.
The other kind is that one or more elements are at an angle (i.e. tilted), which leads to a tilted focal plane and the typical one-sided unsharpness. Your lens clearly(!) suffers from the tilt problem. If I were you I wouldn't hestitate to send the lens back with some pictures that demonstrate the one-sided unsharpness and point out the possible tilt problem in your accompanying letter. No lenses are perfect, but if the asymmetric sharpness distribution can even be detected on such scaled-down images this is simply unacceptable, especially for a premium-priced prime lens.
|
|
Forum: Pentax SLR Lens Discussion
01-08-2014, 02:15 AM
|
| |
I don't think it's related to the hoods. The reason for the difference is probably due to how spherical abberation is corrected at large apertures. The Sigma seemingly has slightly under-corrected spherical abberation, which leads to smoother bokeh (and smoother specular highlights without outlining), but as a side-effect suffers from a certain haziness and lower contrast wide open. The DA*55, in contrast, seemingly has slightly over-corrected spherical abberation at large apertures, which eliminates the haziness but leads to more nervous bokeh due to the light distribution in the circles of confusion. This leads to more nervous bokeh and can e.g. be seen in the specular highlights, which are brighter at the outside than at the center. This is the price we have to pay for the excellent sharpness and contrast already at f/1.4 ;). Used rightly, however, the somewhat weird f/1.4 bokeh can even support a surreal, impressionistic effect with a suitable background. I've seen several examples here on PF where people have used this bokeh characteristic to great effect. But in other instances, it may only looks harsh:rolleyes:
Fortunately, the bokeh is already much smoother at f/1.8, so it's no big deal IMO.
By the way, the "onion-ring" look of the Sigma's specular highlights is caused by imperfectly polished aspherical element(s).
|
|
Forum: Pentax K-5 & K-5 II
10-07-2013, 02:29 AM
|
| |
Hi,
after some testing with the K-5II and indirect (i.e. tilted) flash I have made some interesting observations that I'd like to share. Plus, I've also got a theory about the cause of the overexposure problems.
For a long time I've used a flash with only an "A" setting and only recently bought a P-TTL flash (the Metz 58 AF-2). Before investing in this flash for my K-5II I contacted Metz (who are renowned for their great customer service) for any news on the notorious indirect flash overexposure problem that has plagued the K-5 and K-5II (at least with early firmware). The Metz technician who answered my inquiry confirmed the misbehaviour of the K-5 but told me that the K-5II (with latest firmware) behaves very differently and tends to slightly underexpose with indirect flash (compared to direct flash). Furthermore, he claimed that the exposure behaviour of genuine Pentax flashes is exactly the same.
Here are my observations for Metz 58 AF-2 and K-5II, both of which are running on the latest firmware, by the way (4.1 and 1.06, respectively)
My first pictures with the new flash and 2 lenses (DFA 100/2.8 Macro WR and DA 18-135) completely confirmed the tendency of slight underexposure described by the Metz technician - with indirect flash the camera tends to underexpose about 1/3 to 2/3 stops (compared to direct flash). What is more, it seems to do so pretty consistently, so by dialling in +1/3 to +2/3 flash exposure compensation for indirect flash the results are good. Problem solved, I thought.
That is until I used I tried the flash with my DA*55/1.4. There it behaves differently and still can suffer from overexposure. Why can? I've found that it depends on the subject you're photographing. For subjects without very bright parts, the exposures are OK (very little difference between direct and indirect flash). The trouble starts if there are larger bright areas (e.g. white walls) in your picture. Then I usually got about +2/3 stops overexposure with indirect flash (compared to direct).
After some more testing I have a theory what's causing the problem: The pre-flash exposure measurement. To be more specific, a mismatch between the strength of the pre-flash and the light sensors used to measure the reflected light (and thus calculate the flash exposure). The light sensors probably have a certain working range, e.g. they can record the measured luminosity range on a 0 to 100 range.
When using direct flash, this limited range is not problematic because the possible range of reflectivity given a specific pre-flash can be known pretty well in advance, so pre-flash exposure and measurement can be well matched in advance.
The problem with indirect flash is that there are great unknowns about the probable reflectivity range. It can be
(1) similar to direct flash (when flash is bounced on a white ceiling that is not far away) or
(2) much lower (when flash is bounced off something darker and further away).
In the latter case, a too weak pre-flash might not be strong enough to get useful reflectivity data (i.e. the sensors might just get data between, say, 0 and 1). My guess is that the camera thus uses a much stronger pre-flash when the flash reflector is tilted to avoid running into the "too little data" problem in the case of (2). However, it can now run into the opposite problem, the "100" ceiling, if the conditions are like (1). So, even if light with the strength of 130 hits the sensor, it only sees "100". Thus, it underestimates the reflected light (because the data from some of the sensors may be clipped) and thus overestimates the needed flash power, leading to overexposure.
The theory of different pre-flash strength for tilted and non-tilted flash head might explain why the overexposure problem has always already been present by just tilting the flash head slightly so that the camera thinks it's using indirect flash while in reality it's more like direct flash.
So, my guess is that the overexposure is a mixture of hardware limitation of the flash system shared by K-5 and K-5II (sensitivity range of light sensors) and a not very intelligent use of pre-flash strength.
A further guess is that Pentax has partly addressed this problem in the latest firmware for the K-5II so that pre-flash strength and measurement are better matched. However, it still doesn't seem to be matched perfectly to the speed of the lens. A f/1.4 lens lets in 4 times as much light from the pre-flash as a f/2.8 lens and thus can seemingly still run into the upper limit of the light sensors.
To sum up, the tilt flash overexposure seems to be fixed at least for lenses 2.8 or slower, at least when using genuine indirect flash (and not slightly tilted direct flash). Faster lenses might still suffer from overexposure in certain conditions, but the amount seems to be a lot smaller than the +1 to +2 range reported from K-5 and early firmware K-5II.
I hope that Pentax addresses this remaining problem, then we'd (finally!) have a flash exposure system that can be called "reliable".
Clarification: I presume that the pre-flash is of course measured with the lens at wide open aperture (and not the set aperture), hence the different amount of light that enters through a very fast vs. a slow lens. The overexposure issue with DA*55 was regardless of the used aperture (I tried f/2 through f/5.6) (and also regardless of ISO or zoom reflector settings, by the way).
|
